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An overview of hydrogen as a vehicle fuel
H. Fayaz
a,b,
n
, R. Saidur
a,b
, N. Razali
a
, F.S. Anuar
a,b
, A.R. Saleman
a,b
, M.R. Islam
b
a
Department of Mechanical Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia
b
Centre of Research UMPEDAC, Level 4, Engineering Tower, Faculty of Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia
article info
Article history:
Received 24 December 2010
Received in revised form
1 June 2012
Accepted 4 June 2012
Available online 31 July 2012
Keywords:
Hydrogen
Vehicle fuel
Engine
Emissions
Combustion
abstract
As hydrogen fuel cell vehicles move from manifestation to commercialization, the users expect safe,
convenient and customer-friendly fuelling. Hydrogen quality affects fuel cell stack performance and
lifetime, as well as other factors such as valve operation. In this paper, previous researcher’s development
on hydrogen as a possible major fuel of the future has been studied thoroughly. Hydrogen is one of the
energy carriers which can replace fossil fuel and can be used as fuel in an internal combustion engines and
as a fuel cell in vehicles. To use hydrogen as a fuel of internal combustion engine, engine design should be
considered for avoiding abnormal combustion. As a result it can improve engine efficiency, power output
and reduce NO
x
emissions. The emission of fuel cell is low as compared to conventional vehicles but as
penalty, fuel cell vehicles need additional space and weight to install the battery and storage tank, thus
increases it production cost. The production of hydrogen can be ‘carbon-free’ only if it is generated by
employing genuinely carbon-free renewable energy sources. The acceptability of hydrogen technology
depends on the knowledge and awareness of the hydrogen benefits towards environment and human life.
Recent study shows that people still do not have the sufficient information of hydrogen.
&2012 Elsevier Ltd. All rights reserved.
Contents
1. Introduction .....................................................................................................5512
2. Hydrogen as a fuel in internal combustion engines ......................................................................5512
2.1. Engine concept . ............................................................................................5512
2.2. Combustive properties of hydrogen . . ..........................................................................5513
2.2.1. Flammability limit .................................................................................. 5513
2.2.2. Minimum ignition energy ............................................................................ 5514
2.2.3. Small quenching distance ............................................................................ 5514
2.2.4. High autoIgnition temperature. . . .................................................................... 5514
2.2.5. High flame speed, high diffusivity and low density ........................................................ 5514
2.3. Abnormal combustion .......................................................................................5514
2.3.1. Pre ignition . . ...................................................................................... 5514
2.3.2. Backfire........................................................................................... 5515
2.3.3. Knock ............................................................................................ 5515
2.3.4. Avoiding abnormal combustion ........................................................................ 5516
2.4. Engine components .........................................................................................5516
2.4.1. Spark plugs . . ...................................................................................... 5516
2.4.2. Injection systems ................................................................................... 5516
2.4.3. Hot spots . . . ...................................................................................... 5516
2.4.4. Piston rings and crevice volumes . . .................................................................... 5517
2.4.5. Lubrication . . ...................................................................................... 5517
2.4.6. Crankcase ventilation . . . ............................................................................. 5517
2.4.7. Compression ratio .................................................................................. 5517
2.4.8. In-cylinder turbulence . . ............................................................................. 5517
2.4.9. Materials.......................................................................................... 5517
Contents lists available at SciVerse ScienceDirect
journal homepage: www.elsevier.com/locate/rser
Renewable and Sustainable Energy Reviews
1364-0321/$ - see front matter &2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.rser.2012.06.012
n
Corresponding author at: Department of Mechanical Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia. Tel.: þ601 72654023; fax: þ603 79675317.
E-mail addresses: katperfayaz@gmail.com, fayaz_me@yahoo.com (H. Fayaz).
Renewable and Sustainable Energy Reviews 16 (2012) 5511–5528
2.5. Thermal efficiency ..........................................................................................5517
2.5.1. Thermodynamic analysis ............................................................................. 5517
2.6. Emission production ........................................................................................5518
2.7. Power output . .............................................................................................5519
2.8. Emissions and cost..........................................................................................5519
2.9. Hydrogen production plant ...................................................................................5520
2.10. Public acceptability of hydrogen fuelling station ..................................................................5521
2.11. Life cycle of hydrogen . . . ....................................................................................5522
3. Hydrogen production..............................................................................................5524
3.1. Natural gas to Hydrogen . ....................................................................................5524
3.2. Coal gasification ............................................................................................5525
3.3. Electrolysis . . . .............................................................................................5525
3.4. Biomass gasification.........................................................................................5526
3.5. Photolytic processes.........................................................................................5526
3.5.1. Photobiological water splitting . . . ..................................................................... 5526
3.5.2. Photoelectrochemical water splitting ................................................................... 5526
4. Conclusion ......................................................................................................5526
Acknowledement . . ...............................................................................................5526
References ......................................................................................................5527
1. Introduction
The main sources at present, to satisfy world’s energy demand,
are mainly fossil fuels, which are going to be depleted very fast.
Fossil fuel resources are now clearly run through and their prices
have become unstable presently. That is due to, first, influential
economic acceleration mostly in China and India and, second, by
economic recession. In pursuit of energy security, the challenges of
controlling prices and the uncertain reserves are strong incen-
tives [1]. Significant environmental and societal problems, such as
global warming and local pollution are directly associated with
excessive usage of fossil fuels. Such problems strongly stimulate the
research, development and demonstrations of clean energy
resources, energy carriers, and in the case of transportation and
power trains. In recent study, hydrogen is one of the energy carriers
that can replace fossil fuels, but further research is needed to expose
itsadvantagesanddisadvantagesbefore this alternative fuel can be
commercialised. Hydrogen is the cleanest fuel having a heating
value three times higher than petroleum. However, being man-
made fuel the hydrogen is not natural source of energy, therefore, it
involves production cost, which is responsible for it is three times
more cost than petroleum products. There are still problems in the
realization of the renewed hydrogen from water, but the market
supply and the cost of hydrogen do not constitute the bottleneck of
hydrogen vehicles today although the hydrogen used presently may
not be renewed. But, hydrogen’s excellent characters, studying the
availability of H
2
in internal combustion (IC) engines, and investi-
gating the performance of hydrogen fuelled engines, become one of
the utmost important research directions for researchers. That is
why in this study, we are going to review previous developments
and studies that have been done by other researchers on hydrogen
as a possible major fuel of the future, used as in an internal
combustion engines and as a fuel cell in vehicles. The aim of
this study is to review hydrogen as a fuel for internal combus-
tion engines for the vehicle propulsion in terms of advantages,
disadvantages and fundamentals of hydrogen engines. Whereas
for vehicle fuel cells the study focuses on performances, cost,
infrastructure, type of storage and type of productions in hydrogen
[13].
2. Hydrogen as a fuel in internal combustion engines
In the following sub-sections several aspects that are related to
the use of hydrogen as a fuel in internal combustion engine will
be discussed further [4]. The discussion includes properties of
combustive hydrogen, abnormal combustion in hydrogen engine,
engine components, thermal efficiency, emission production,
power output, emissions and cost, hydrogen production plant,
people acceptability of hydrogen fuelling station and life cycle of
hydrogen [5,6].
2.1. Engine concept
Hydrogen can be used in SI engine by three methods [7]:
(i) By manifold induction
Cold hydrogen is introduced through a valve controlled
passage into the manifold.
(ii) By direct introduction of hydrogen into the cylinder
Hydrogen is stored in the liquid form, in a cryogenic cylinder.
A pump sends this liquid through a small heat exchanger
where it is converted into cold hydrogen gas. The metering of
hydrogen is also done in this unit. The cold hydrogen helps to
prevent pre-ignition and also reduces NO
x
formation.
The arrangement of liquid hydrogen storage and details of
hydrogen induction into the SI engine cylinder can be seen in
Figs. 1 and 2, respectively [8,9].
(iii) By supplementing gasoline
Hydrogen can also be used as an add-on fuel to gasoline in SI
engine. In this system, hydrogen is inducted along with
gasoline, compressed and ignited by a spark.
Fig. 1. Liquid hydrogen storage and gaseous hydrogen injection [7].
H. Fayaz et al. / Renewable and Sustainable Energy Reviews 16 (2012) 5511–55285512
2.2. Combustive properties of hydrogen
A brief summary of previous literatures are reviewed and
discussed based on fundamentals of hydrogen combustion,
flammability, ignition energy and octane number. Details of these
characteristics to hydrogen engines based on recent studies as
well as on-going efforts in the development of H
2
ICEs and H
2
ICE
vehicles will be discussed later [11].
Some properties of hydrogen are listed in Table 1 in compar-
ison with iso-octane and methane, which are representing as the
natural gas and gasoline, respectively [12].Table 2 shows the
mixture properties of hydrogen–air when operated at lean and
stoichiometric mixture in comparison with iso-octane–air and
methane–air at stoichiometric mixture [13].
2.2.1. Flammability limit
Flammability limit gives the proportion of combustible gases
in a mixture; between these limits, this mixture is flammable.
From Table 1 it is seen that the flammability of hydrogen in air
(mixture) is at 4–75% which gives hydrogen wide range of
flammability as compared to other fuels [14]. It is clear that 4%
of hydrogen in air is still flammable but non-coherently and burns
incompletely. The 4% value relates to configuration of one
particular experiment. Therefore, the limit may vary being below
4% or above, (depending on condition), in real-world situations.
For safety considerations this limit is important where it is less
important for engine combustion [15]. Wide ranges of mixture of
hydrogen permit extremely lean or rich mixture that combust
with air. This makes the hydrogen engine operate at lean mixture
resulting in greater fuel economy and more complete combustion
reaction [16]. Final combustion temperature will also generally
lower due to lower laminar burning velocity as can be seen in
Table 2.The burning velocity for hydrogen engine that operates at
lean mixture is rapidly lowered as compared to hydrogen engine
that runs on stoichiometric mixture which is 12 cm/s (at
j
¼0.25)
and 290 cm/s (at
j
¼1). This absolutely will reduce amount of
pollutants such as NO
x
[17].
Fig. 2. Hydrogen induction in spark-ignition engine [10].
Table 1
Hydrogen properties compared with methane and iso-octane properties. Data
given at 300 K and 1 atm, taken from [12].
Property Hydrogen Methane Iso-octane
Molecular weight (g/mol) 2.016 16.043 114.236
Density (kg/m3) 0.08 0.65 692
Mass diffusivity in air (cm
2
/s) 0.61 0.16 0.07
Minimum ignition energy (mJ) 0.02 0.28 0.28
Minimum quenching distance (mm) 0.64 2.03 3.5
Flammability limits in air (vol%) 4.75 5-15 1.1–6
Flammability limits (
l
)10–0.14 2–0.6 1.51–0.26
Flammability limits (
c
)0.1–7.1 0.5–1.67 0.66–3.85
Lower heating value (MJ/kg) 120 50 44.3
Auto-ignition temperature in air (K) 858 723 550
Flame velocity (ms
1
) 1.85 0.38 0.37–0.43
Higher heating value (MJ/kg) 142 55.5 47.8
Stoichiometric air-to-fuel ratio (kg/kg) 34.2 17.1 15
Stoichiometric air-to-fuel ratio
(kmol/kmol)
2.387 9.547 59.666
Table 2
Mixture properties of hydrogen–air, methane–air, and iso-octane–air. Data given
at 300 K and 1 atm (with the exception of the laminar burning velocity, given at
360 K and 1 atm) [12].
Property H
2
–air H
2
–air CH
4
–air C
8
H
18
–air
l
¼1
l
¼4
l
¼1
l
¼1
j
¼1
j
¼0.25
j
¼1
j
¼1
Volume fraction fuel (%) 29.5 9.5 9.5 1.65
Mixture density (kg/m
3
) 0.85 1.068 1.123 1.229
Kinematic viscosity (mm
2
/s) 21.6 17.4 16 15.2
Auto-ignition temperature (K) 858 4858 813 690
Adiabatic flame temperature (K) 2390 1061 2226 2276
Thermal conductivity
(10
2
W/mK)
4.97 3.17 2.42 2.36
Thermal diffusivity (mm
2
/s) 42.1 26.8 20.1 18.3
Ratio of specific heats 1.401 1.4 1.354 1.389
Speed of sound (m/s) 408.6 364.3 353.9 334
Air-to-fuel ratio (kg/kg) 34.2 136.6 17.1 15.1
Mole ratio before/after
combustion
0.86 0.95 1.01 1.07
Laminar burning velocity,
360 K (cm/s)
290 12 48 45
Gravimetric energy content
(kJ/kg)
3758 959 3028 3013
Volumetric energy content
(kJ/m
3
)
3189 1024 3041 3704
H. Fayaz et al. / Renewable and Sustainable Energy Reviews 16 (2012) 5511–5528 5513
2.2.2. Minimum ignition energy
Minimum ignition energy is the minimum amount of energy
required to ignite a combustible vapour or gas mixture. At
atmospheric conditions, the minimum ignition energy of a
hydrogen–air mixture is an order of magnitude lower than for
the mixtures of iso-octane–air and methane–air. For hydrogen
concentrations of 22–26% only 0.017 MJ is obtained. Normally,
capacitive spark discharge is used to measure minimum ignition
energy, and thus is dependent on the spark gap [12].The values
quoted in Table 1 are for a 0.5 mm gap. The minimum ignition
energy can increase about 0.05 MJ and more or less constant for
hydrogen concentrations between 10% and 50% when using a gap
of 2 mm. The benefits for having minimum ignition energy
to enable hydrogen engine to ignite lean mixture and ensure
prompt ignition [18]. But having minimum ignition energy will
increase possibility for hydrogen air mixture in the combustion
chamber to be ignited by any other source (hot spot) rather than
spark plug [13].
2.2.3. Small quenching distance
As compared to gasoline and other fuels, hydrogen has small
quenching distance. In Table 1 the quenching distance for hydro-
gen is about 0.64 mm compare to methane which is 2.03 mm and
Iso-octane 3.5 mm. This parameter measures how close hydrogen
flames can travel closer to the cylinder wall before they extin-
guish. The smaller the distance, more difficult to quench the flame
and this will increase the tendency for backfire. Experimentally,
from the relation between minimum ignitions energy and the
spark gap size quenching distance can be derived or can be
measured directly [12].
2.2.4. High autoIgnition temperature
Referring to Table 1, taken from [18] hydrogen has relatively
high auto-ignition temperature as compared to methane and iso-
octane which is 858 K. This high auto-ignition is important
parameter to determine engine compression ratio, since during
compression, the temperature rise is pertained to the compres-
sion ratio when considering Otto cycle [19] as shown in the
Eq. (1) below.
T
2
¼T
1
r
c

k1
ð1Þ
From this equation it can be seen that compression ratio is
dependent on T
2
which is temperature during compression. This
T
2
is limited by auto-ignition temperature to prevent fuel air
mixture to auto ignite before the spark, given from spark plug.
Higher auto-ignition temperature will increase T
2
and simulta-
neously increase compression ratio. As relating to thermal effi-
ciency of the system, higher compression ratio is important [20].
2.2.5. High flame speed, high diffusivity and low density
At stoichiometric ratios, hydrogen acquires high flame speed
as shown in Table 1, which is about 1.85 ms
1
compared to
methane and iso-octane which is 0.38 ms
1
and 0.37–0.43 ms
1
,
respectively. Having high flame speed, hydrogen engines can
more be similar to the thermodynamically ideal engine cycle.
However, the flame velocity goes to decreases significantly at
leaner mixture, [18]. Hydrogen also possesses remarkably high
diffusivity, which is its capability to disperse in air more than
methane and iso-octane. This shows that hydrogen can form
uniform mixture of fuel and air, and if hydrogen leaks, it will
disperse rapidly and leaking hydrogen is not a pollutant to the
environment. Low density of hydrogen will result in two pro-
blems of IC engine. Large volume needs to store more hydrogen to
provide sufficient driving range and reduce power output due to
low energy density [21].
2.3. Abnormal combustion
The main problem to use hydrogen as a fuel in internal
combustion engine, is to control the undesired combustion
phenomena due to low ignition energy, wide flammability range
and rapid combustion speed of hydrogen that causes mixture of
hydrogen and air to combust easily [22]. In this section the main
abnormal combustion in hydrogen engine which are pre-ignition,
backfire, and knock in terms of cause and method to avoid will be
discussed.
2.3.1. Pre ignition
Pre-ignition is one of the undesired combustion that needs to
be avoided in hydrogen engine. During the engine compression
stroke, these abnormal combustion events occur inside the
combustion chamber, with actual start of combustion prior to
spark timing [23]. Pre-ignition event will advance the start of
combustion and produce an increased chemical heat-release rate.
In turn, the increased heat-release rate results in a rapid pressure
rise, higher peak cylinder pressure, acoustic oscillations and
higher heat rejection that leads to rise in-cylinder surface tem-
perature. The start of combustion can further be advanced by
latter effect, which in turn can be led to runaway effect, and will
cause the engine failure if unchecked [24]. It is observed from
Fig. 3, that as the stoichiometric condition (
j
¼1) is approached
from the lean side (
j
o1), the minimum ignition energy for
hydrogen is a strongly decreasing function of the equivalence
ratio with the minimum at
j
E1 This trend shows that it is
extremely difficult to operate an H
2
ICE at or near the stoichio-
metric condition in the absence of frequent pre-ignition events.
Therefore, the maximum
j
and, consequently, peak power output
can be limited by the pre-ignition limit for practical application.
Stockhausen et al. [25] report a pre-ignition limit of
j
E0.6 for a
4-cylinder 2.0-lengine at an engine speed of 5000 rpm. Although
the pre-ignition limit is engine specific, the consistent trends with
variations in engine properties and operational conditions have
been found: the pre-ignition limited
j
decreasemonotonically
with increased compression ratio (CR) [25,26] and increase
mixture temperature [25]. An effect on engine speed has also
been shown [26] but due to the coupled effect of residual mass
fraction the trend is more complicated.
From above description, it is clearly seen that pre-ignition
limit will border on the peak power output of hydrogen engine
and this will decrease the performance of H
2
ICE powered vehicle
in comparison to its gasoline equivalent [27]. Therefore, deter-
mining the mechanism of pre-ignition, practical operational
limits, and control strategies has been a primary focus of many
research studies. Unfortunately, there are still no guaranteed
Fig. 3. Minimum ignition energies of (K) hydrogen–air, () methane–air and (m)
heptane–air mixture in relation to at atmospheric pressure [18].
H. Fayaz et al. / Renewable and Sustainable Energy Reviews 16 (2012) 5511–55285514
preventive steps, but identification of pre-ignition source has
provided the necessary minimizing steps.
Source of pre-ignition;
Hot spark plugs or spark plug electrodes.
Hot exhaust valves or other hot spots in the combustion
chamber.
Residual gas or remaining hot oil particles from previous
combustion events.
Combustion in crevice volumes [18].
As the minimum ignition energy is dependent on the equiva-
lence ratio, the pre-ignition becomes more pronounced when the
hydrogen–air mixture approach stoichiometric levels. At increased
engine speed and load, operating conditions will also be prone to
the occurrence of pre-ignition due to higher gas and components
temperature [12].
Several steps have been taken to minimize the source of pre-
ignition which are [12]:
Proper design of spark plug.
Ignition system design with low residual charge.
Specific design of crankcase ventilation.
Sodium-filled exhaust valve [19].
Optimized design of the engine cooling passage to avoid
hot spot.
With the use of hydrogen direct injection systems.
Variable valve timing for effective scavenging of exhaust
residuals [18].
Kondo et al. [18] used an ignition system specification,
designed to prevent residual energy and a water-cooled spark
plug. From the test conducted, variance of equivalence ratio based
on advanced control strategies is shown in Table 3.
2.3.2. Backfire
Backfire is one of the main problems to run a hydrogen fuelled
engine. Backfire or flashback is the uncontrolled combustion of
fresh hydrogen–air mixture during the intake stroke in the
combustion chamber and/or the intake manifold. The fresh
hydrogen–air mixture is aspirated into the combustion chamber
with the opening of the intake valves. Backfiring is caused when
combustion chamber hot sopts, hot residue gas or remaining
charge in the ignition system ignite the fresh charge as hydrogen
has low ignition temperature [28]. This abnormal combustion
occurs due to the same concept of pre-ignition. The difference is
the timing at which the anomaly occurs. In pre-ignition, the
uncontrolled combustion happens during compression stroke
when the intake and exhaust valves close before spark plug fires
in cylinder [22,27], while backfire occurs during intake stroke
when the intake valve is opened. The backfire initiates from the
pre-ignition during the compression stroke, and then proceeds to
the ignition of the intake mixture [29].
Effect of backfire resulting in combustion and pressure rise in the
intake manifold, is clearly audible as well as can also damage or
destroy the intake system. When mixture approaches stoichiometry,
the occurrence of backfire is more likely due to the low ignition
energy, and when using PFI-H
2
ICE, as the hydrogen is injected before
theintakevalveopens,tomixwithairintheintakemanifoldbefore
entering combustion chamber. While in DI-H
2
ICE,theoccurrenceof
backfire can be neglected as hydrogen injection starts after the intake
valve closes difference with external mixture formation concept [12].
Recently, many works have been carried out on optimizing the
intake design and injection strategies to avoid backfiring. Conse-
quently, the measures those help in avoiding pre-ignition also
reduce the risk of backfiring. Some of the strategies that are used
to avoid backfiring:
Injection strategies that allow pure air to flow into the
combustion chamber to cool potential hot spots before aspir-
ating the fuel-air mixture.
The possibility of backfiring mainly depends on the concentra-
tions of H
2
residual at intake ports in a manifold injection
H
2
ICE, and the leaner the concentration of the residual, the
lower the possibility of the backfire.
Optimization of the fuel-injection strategy in combination
with variable valve timing for both intake and exhaust valves
allow operation of a port injected hydrogen engine at stoichio-
metric mixtures over the entire speed range.
2.3.3. Knock
Knock, or spark knock [24] is defined as auto-ignition of the
hydrogen–air end-gas ahead of the flame front that has originates
from the spark. This follows a rapid release of the remaining energy
generating high-amplitude pressure waves, mostly referred to as
engine knock. Engine damage can be caused by the amplitude of the
pressure waves of heavy engine knock due to increased mechanical
and thermal stress [1]. The knocking tendency of an engine is
dependent on the engine design along with the fuel-air mixture
properties. The high auto-ignition temperature, finite ignition delay
and the high flame velocity of hydrogen mean that knock, as defined
is less likely for hydrogen relative to gasoline, and hence the higher
research octane number (RON) for hydrogen (RON4120) in com-
parison with gasoline [18].
Following are the effects of knock to engine operation [25]:
Increased heat transfer to the cylinder wall.
Excessively high cylinder pressure and temperature levels and
increased emissions.
Undesirable engine performance and the potential damage to
engine components.
It is critically important not only to avoid knocking but also to
know the limiting conditions for its incidence under any set of
operating and designing conditions. Effective means for extending
knock-free operation need to be developed. Several tests have
been done to understand knock behaviour and detection in
hydrogen engine. From [30] knock is influenced by parameters
including the engine compression ratio, the type of fuel, ignition
timing, and the fuel-air-dilution mixture. Several results are
drawn based upon the observation and analysis in this work:
It is rational to say that hydrogen knock can be treated similar
to gasoline knock for practical engine applications. As a result,
gasoline knock detection and potential engine control techni-
ques can be extended for use with hydrogen without signifi-
cant changes.
The combustion knocks level probability distributions for both
hydrogen and gasoline changes as the knock level increases.
The skewness of the distribution reduces as the overall knock
level increases.
Table 3
Effect of advance control strategies to the equivalence ratio limit to the pre-
ignition occurrence [18].
Equivalence ratio Advance control strategies
j
E0.35 Without any advanced control
j
E0.6 Elimination of residual energy in the ignition system
j
E0.8 With addition of the water-cooled spark plug
H. Fayaz et al. / Renewable and Sustainable Energy Reviews 16 (2012) 5511–5528 5515
Changes required from gasoline combustion knock detection
and control would result primarily from hydrogen’s sensitivity
to engine operating conditions including the engines compres-
sion ratio, stoichiometry, dilution levels, ignition timing and
the differences in operating conditions for a hydrogen engine
to obtain optimal performance.
Fig. 4 [26] shows the effect of compression ratio and equiva-
lence ratio on the engine power, at optimum spark timing for best
torque and 25 rps engine speed. The figure shows that the high
useful compression ratio (HUCR), which gives the highest power,
occurred at the compression ratio (CR) of 11:1. With further
increase in compression ratio, the engine power decreases due to
unstable combustion [23,31]. However, the loss of combustion
control, which is pre-ignition, limits the maximum power output
of a hydrogen engine. As referred to Fig. 4, it is observed that
operating at lean or rich mixtures tends to decrease the engine
power for all compression ratios. Air-to-fuel ratios rich of stoi-
chiometric decrease engine power due to decreasing combustion
efficiency. Air-to-fuel ratios lean of stoichiometric decrease
engine power due to a reduction in the volumetric lower heating
value of the intake mixture, despite increasing combustion
efficiency. Fig. 5 [26] show the effect of engine speed on the
engine power, at optimum spark timing for best torque and
HUCR. It is clearly seen that as the engine power increases engine
speed increases [32].
2.3.4. Avoiding abnormal combustion
It is an effective measure to limit maximum fuel-to-air
equivalence ratio to avoid abnormal combustion in hydrogen
operation. By operation, employing a lean-burn strategy, the
excess air in lean operation acts as an inert gas and reduces
combustion temperature effectively and components tempera-
tures consequently. Although lean operation is very effective, it
does limit the power output of hydrogen engine. Using thermal
dilution technique, pre-ignition conditions can also be curbed,
such as water injection or exhaust gas recirculation (EGR).
A portion of the exhaust gases is re-circulated back into the
intake manifold by EGR system. It helps to reduce the tem-
perature of hot spots by introducing the exhaust gases, hence
reducing the possibility of pre-ignition. Additionally, peak
combustion temperature is reduced by recirculation of exhaust
gases, which also reduces NO
x
emissions. Typically, a 25% to
30% recirculation of exhaust gases is effective in elimination of
back fire [34].
Injection of water is the other technique for thermally diluting
the fuel mixture. Injecting water into the hydrogen stream prior
to mixing with air has produced better results than injecting
it into the hydrogen–air mixture within the in-take manifold.
A potential problem of mixing of water with oil exists with this type
of system, so care must be taken ensuring that seals do not leak.
2.4. Engine components
Some features of engines designed for or converted to hydro-
gen operation, will be discussed in this section. As discussed in
the previous section, the occurrence of combustion anomalies, or
more particularly, the desire to prevent it, has led to most of the
countermeasures, which were put forwarded in the early work on
H
2
ICEs [35].
2.4.1. Spark plugs
To avoid spark plug electrode temperature that exceeds the
auto-ignition limit and causing backfire, cold-rated spark plugs
are recommended [36]. This cold spark plug can be used since
there are no carbon deposits to burn off. Since spark plugs with
platinum electrodes can be catalyst to hydrogen oxidation, there-
fore these are to be avoided.
2.4.2. Injection systems
In hydrogen engine, there are two types of injection systems,
which can be used, one is port fuel injection (PFI) and other is
direct injection (DI). In PFI-H
2
ICE, time injection is a prerequisite
as what has already been discussed previously that the main
problem in PFI-H
2
ICE is to avoid backfire. Therefore, PFI needs the
programming of the injection timing such that an air cooling
period is created in the initial phase of the intake stroke, and the
end of injection is such that all hydrogen is inducted, leaving no
hydrogen in the manifold when the intake valve closes. The
advantage of using PFI system is the pressure tank for injector,
which is lower as compared to DI system.
In DI-H
2
ICE, hydrogen is injected directly into the combustion
chamber during compression stroke. Hydrogen injection at com-
pression stroke prevents knock and gives an increase in thermal
efficiency and maximum output power [37].
2.4.3. Hot spots
Minimizing the hot spot in combustion chamber of hydrogen
engine is important to avoid abnormal combustion which is the
major problem in burning hydrogen well because it will reduce
power output and engine efficiency. Hot spot can act like ignition
source as hydrogen needs minimum ignition energy to be ignited.
There are several steps to minimize hot spots in combustion
Fig. 4. Typical variations in spark timing for optimum efficiency and avoidance of
knock for lean mixture operation with hydrogen [33].
Fig. 5. Typical variations in indicated power output and efficiency with changes in
compression ratio when using optimum spark timing for borderline knock [33].
H. Fayaz et al. / Renewable and Sustainable Energy Reviews 16 (2012) 5511–55285516
chamber as few are given as following [12,38]:
Using cooled exhaust valve; multi-valve engine leads to
further bringing the temperature of exhaust valve down.
Additional engine coolant passages around valves and other
area with high thermal loads.
Adequate scavenging to decrease residual gas temperature.
2.4.4. Piston rings and crevice volumes
Previously, many experiments [12] have been conducted to
eliminate all hot spots (e.g., careful cleaning of the engine,
enhanced oil control or even, scavenging of the residual gases,
cold spark plugs, cooled exhaust valves, etc.), where, backfire and
uncontrolled spark-induced ignition still occurred. On the other
hand, hydrogen engines have been demonstrated, run on stoi-
chiometric mixture without any occurrence of backfire, by careful
selection of crevice volumes and piston rings, without any need
for timed injection or cooled exhaust valve. Therefore, it needs
careful selection of piston rings and crevice volumes in order to
prevent hydrogen flame from propagating into the top land [39].
2.4.5. Lubrication
Lubrication is an important aspect that needs to be considered
when switching over to hydrogen as fuel in internal combustion
engine. During engine operation, blow will always occur due to
the rapid pressure rise and the low density of hydrogen gas. The
exhaust gases, entering crankcase can condense, when there is no
provision of proper ventilation. Water mixing into the crankcase
oil (lubrication oil) reduces its lubrication ability and as a result,
there occurs a higher degree of engine wear [12]. Measurement of
the composition of the gases in the crankcase at Ghent University
[40] showed a very high percentage of hydrogen arising from
blow by. The investigation of the lubricating oil is carried out and
is compared to that of the unused oil. The oil properties severely
changed with a strong decrease in the lubricating qualities [41].
Engine lubrication oil having compatibility with increased
water concentration in the crankcase, has to be chosen. Engine
specific oil, which is developed for hydrogen engines, is probably
the best solution but currently is not available [42].
2.4.6. Crankcase ventilation
Using hydrogen as a fuel for spark-ignited internal combustion
engines, especial attention has to be given to the crankcase
ventilation as compared to gasoline engines. Carbon based depos-
its from the engine’s lubricating oil, in the combustion chamber,
on the top of the piston, in the ring grooves, and in the cylinder’s
squish areas are potential hot spots waiting to happen. Blow by
effect can cause unburned hydrogen entering the crankcase and
at certain concentration, hydrogen can combust in the crankcase
due to lower energy ignition and wide flammability limits.
Hydrogen should be prevented from accumulating through ven-
tilation [12,43].
2.4.7. Compression ratio
It is the similar choice of the optimal compression ratio to that
for any fuel; for increasing engine efficiency it should be chosen
as high as possible, with the limit given by increased heat losses
or the occurrence of abnormal combustion (in the case of
hydrogen, primarily surface ignition). The choice may be depen-
dent on the application, as the optimum compression ratio for
highest engine efficiency might be different from the optimum
compression ratio for highest power output. Compression ratios
used in H
2
ICEs range from 7.5:1 to 14.5:1 [12,44].
2.4.8. In-cylinder turbulence
Low turbulence combustion chamber can be used due to high
flame speeds of hydrogen. Low radial and tangential velocity
components can be reduced by the use of disk-shaped combus-
tion chamber (flat piston and chamber ceiling) can help produce
and does not amplify inlet swirl during compression. This will be
beneficial for engine efficiency by increase in the volumetric
efficiency and decrease heat loses [42]. The overall trends are
such that turbulence increases auto-ignition delay times and
accordingly the ignition length and pressure further contribute
to this delay [45].
2.4.9. Materials
Hydrogen effects on the mechanical properties of iron as
embrittlement, such as decrease in true stress of fracture and
ductility [46].
Types of hydrogen embrittlement of steels [12]:
As concentrations of hydrogen occur on surface, the hydrogen
reaction embrittlement is arisen, resulting in chemical
reaction.
Environmental embrittlement: in the atmosphere containing
hydrogen, there happens adsorption of molecular hydrogen on
the surface and its absorption within the lattice after dissocia-
tion into atomic form.
It happens in the absence of hydrogenated atmosphere and
due to the hydrogen that enters the lattice during processing
or fabrication of steel.
Brass and copper alloys, aluminium and aluminium alloys, and
copper beryllium are the materials which can be used for the
applications of hydrogen. Nickel and high-nickel alloys, titanium
and titanium alloys are very sensitive to hydrogen embrittlement.
In the case of steel, for hydrogen embrittlement sensitivity, it
depends on the exact chemical composition, heat or mechanical
treatment, microstructure, impurities and strength [41].
2.5. Thermal efficiency
The theoretical thermodynamic efficiency of an Otto cycle
engine is based on the compression ratio of the engine as shown
in Eq. (2)
Z
th
¼11
r
c

g
1
ð2Þ
The higher compression ratio r
c
and/or the specific heat ratio
g
,
indicated the thermodynamic efficiency of the engine. Hydrogen
(
g
¼1.4) has much simpler molecular structure than gasoline and
therefore its specific–heat ratio is higher than that of gasoline
(
g
¼1.1). As a result, theoretically, hydrogen engine can have higher
thermal efficiency compared to gasoline engine [44].ThehighRON
and low-flammability limit of hydrogen provides the necessary
elements to attain high thermal efficiencies in an internal combus-
tion engine [18]. In DI-H2ICE, hydrogen injection at later stage of
compression stroke can achieve the thermal efficiency higher than
38.9% and the brake mean effective pressure 0.95 MPa [37].
2.5.1. Thermodynamic analysis
Using test data from different operating modes, the engine
efficiencies and the losses of the working cycle can be calculated.
Fig. 6 shows the efficiencies and losses for gasoline and hydrogen
operation with both port injection and direct injection. The data
for all fuels were collected on a single-cylinder research engine at
an engine speed of 2000 RPM and indicated mean effective
H. Fayaz et al. / Renewable and Sustainable Energy Reviews 16 (2012) 5511–5528 5517
pressures of 2 bar and 6 bar. Table 4 shows summary of the
analysis [47].
Comparative combustion characteristics of gasoline and hydro-
gen fuel, in internal combustion engine have been done [48].
The ability of elucidating the potential performance and efficiency
of a hydrogen fuelled ICE compared to a gasoline fuelled ICE was
achieved in the analysis of the comparative combustion character-
istics of hydrogen and gasoline fuelled internal combustion engine.
It was noted that the hydrogen fuelled ICE had a higher thermal
efficiency of approximately 6.42% due to the reasons as; less heat
rejection during the exhaust stroke, less blow down during the
exhaust stroke, combustion taking place closer to TDC and combus-
tion taking place in an closer to isochoric environment. Thus, it was
closer to an actual Otto cycle [49]. An important conclusion is that
improvement in H
2
ICE efficiencies will require strategies to mini-
mize heat transfer losses to the cylinder walls as higher combustion
temperatures and shorter quenching distance associated with
hydrogen combustion are believed to cause the greater convective
heat transfer to the cylinder walls [42] Table 5.
2.6. Emission production
Because of the reasons that hydrogen can be produced form
any kind of energy source and it is combusted without emitting
carbon dioxide or soot, it is considered as an ideal alternative fuel
to conventional hydrocarbon fuels [50]. The only potential emis-
sions are the nitrogen oxides (NO
x
) as pollutants from hydrogen
combustion, hence it becomes crucial to minimize the (NO
x
)
emissions from the combustion of hydrogen. Eqs. (3) and (4)
show the exhaust gas emission from hydrogen which is water and
NO
x
[38].
2H
2
þO
2
¼2H
2
Oð3Þ
H
2
þO
2
þN
2
¼H
2
OþN
2
þNO
x
ð4Þ
The formation of nitrogen oxides occurs, because the higher
temperatures are generated within the combustion chamber
Table 4
Result analysis of losses compared to the theoretical engine cycle at load 2bar IMEP.
Efficiency/losses Cause
AT 2 bar IMEP
Efficiency of the ideal engine in
gasoline operation is lower
than in H
2
Compression ratio and AF ratio higher
in H
2
due to lean operation
Incomplete combustion losses Due to extremely lean condition in H
2
operation
Actual combustion lossesin gasoline
around 3% lower than H
2
Due to the lean combustion in H
2
Wall heat losses in H
2
operation
higher than gasoline
Higher pressure levels in H
2
operation
resulting from unthrottled operation
Wall heat losses in H
2
DI are higher
than PFI.
Due to higher in-cylinder charge
motion
Gas exchange losses in H
2
operation
are only fraction compared to
gasoline
Since the engine is operated
unthrottled
Overall indicated thermal efficiency for H
2
PFI is higher than gasoline & H
2
DI
Fig. 6. Analysis of losses compared to the theoretical engine cycle; gasoline versus hydrogen (PFI and DI), at two loads [12].
Table 5
Result analysis of losses compared to the theoretical engine cycle at load 6 bar IMEP.
Efficiency/losses Cause
AT 6 bar IMEP
Efficiency of the ideal engine in
gasoline operation is lower
than in H
2
Compression ratio and AF ratio higher
in H
2
due to lean operation
PFI lower than DI due to the air
displacement effect
Incomplete combustion losses in
gasoline is more than 1%, H
2
PFI &
H
2
DI less than 0.5%
Very complete combustion in H
2
due
to the fast flame speed & small
quenching distance
Actual combustion lossesin
gasoline around 2% and H
2
is lower
H
2
: unthrottled & lean mixture, the
combustion still faster than gasoline
Wall heat losses in H
2
operation
higher than gasoline
Due to higher flames speeds and the
smaller quenching distance
Wall heat losses in H
2
DI operation
higher than H
2
PFI operation
Due to higher level of in-cylinder
charge motion and turbulence caused
by DI event.
Gas exchange losses in H
2
operation
are lower compared to gasoline
Due to engine operated unthrottled.
Overall indicated thermal efficiency for H
2
more than 2.5% both with DI and
PFI compare to gasoline.
H. Fayaz et al. / Renewable and Sustainable Energy Reviews 16 (2012) 5511–55285518
during combustion. These higher temperatures cause some of the
nitrogen and oxygen to combine, present in the air [51]. The
technique of rich-lean combustion or staged combustion is used
to reduce NO
x
formation in continuous combustion burners such
as gas turbines and boilers [52]. Where, water injection in the
compression ignition engine helps to control combustion tem-
perature and pressure. Hence, it is beneficial in controlling
unwanted emissions. Many researchers have demonstrated the
effect with conventional hydrocarbon fuels [53].
The amount of NO
x
formed depends on;
The air/fuel ratio.
The engine compression ratio.
The engine speed.
The ignition timing.
Thermal dilution is utilized or not [54].
2.7. Power output
Volumetric efficiency, fuel energy density and pre-ignition
primarily determine the H
2
ICE peak power output. The volu-
metric efficiency has been proved to be the limiting factor for
determining the peak power output for most of the practical
applications. The displacement of intake air by the large volume
of hydrogen in the intake mixture is the reason for PFI-H
2
ICEs to
inherently fusser from volumetric efficiency. For example, about
30% of hydrogen is possessed by mixture of hydrogen and air by
volume, whereas a 2% gasoline is possessed by stoichiometric
mixture of fully vaporized gasoline and air by volume. The higher
energy content of hydrogen partially offsets the corresponding
power density loss. The stoichiometric heat of combustion per
standard kg of air is 3.37 MJ and 2.83 MJ for hydrogen and
gasoline, respectively. It follow that approximately 83% is the
maximum power density of a pre-mixed or PFI-H
2
CE, relative to
the power density of the gasoline operated identical engine [18].
For applications where peak power output is limited by pre-
ignition, H
2
ICE power densities, relative to gasoline operation, can
significantly be below 83%. For direct injection systems, which
mix the fuel with the air after the intake valve closes (and thus
the combustion chamber has 100% air), the maximum output of
the engine can be approximately 15% higher than that for gasoline
engines. Therefore, depending on how the fuel is metered, the
maximum output for a hydrogen engine can be either 15% higher
or 15% less than that of gasoline if a stoichiometric air/fuel ratio is
used [55].
However, at a stoichiometric air/fuel ratio, the combustion
temperature is very high and as a result it will form a large
amount of nitrogen oxides (NO
x
), which is a criteria pollutant.
Since one of the reasons for using hydrogen is low exhaust
emissions, therefore hydrogen engines are not normally designed
to run at a stoichiometric air/fuel ratio. At this air/fuel ratio, the
formation of NO
x
is reduced to near zero. Unfortunately, this also
reduces the power out-put. To make up the power loss, hydrogen
engines are usually larger than gasoline engines, and/or are
equipped with turbochargers or superchargers [47].
2.8. Emissions and cost
In future, main goal of development of energy is to get the best
efficiency with the affordable cost. In order to achieve this goal,
there are a few things, which should be considered. In terms of
vehicles the production cost, the fuel cost, and the environmental
impacts should be considered [38]. In the previous study, a
comparison between conventional, hybrid, electric or battery,
hybrid fuel cell and battery and fuel cell vehicle has been
investigated in terms of fuel cost, production cost and air pollu-
tion emission [47,56].
From the first study, it summarizes that Tables 6 and 7,the(13)
represent types of considerations, and it is as:(1) electricity is
produced from renewable energy sources including nuclear
energy; (2) 50% of the electricity is produced from renewable
energy sources and 50% from natural gas with an efficiency of
40%; (3) all electricity is produced from natural gas with an
efficiency of 40% [57]. According to those results, hybrid and
electric cars are competitive if nuclear and renewable energies
account for about 50% of the energy to generate electricity. If
fossil fuels (natural gas) are used for more than 50% of the energy
to generate electricity, the hybrid car has significant advantages
over the other three [58]. The fuel cell shows quite low efficiency
due to the production of hydrogen generated high air pollution
and also greenhouse gases emission that reduce its efficiency. The
air pollution is analysed using the curb weight of the vehicle and
that increases the fuel cell air pollution emission [38,56].
In other study the comparison is made between internal
combustion engines (ICE), Fuel cell vehicle (FCEV), battery vehicle
(BEV), and Fuel Cell & battery Hybrid vehicle (FCHEV). This study
considers the cost of power train of the vehicle and also the fuel
costs. It is estimated in terms of optimistic, pessimistic and
Table 6
Normalized and environmental indicators for four types of car [56].
Car Normalized indicators General indicator Normalized general indicator
Car Range Fuel cost Greenhouse gas emission Air pollution emission
1
a
Conventional 1 0.581 0.307 0.108 0.126 0.00243 0.0651
Hybrid 0.733 1 0.528 0.174 0.205 0.0138 0.37
Electric 0.212 0.177 1 1 1 0.0374 1
Fuel cell 0.154 0.382 0.532 0.163 0.247 0.00126 0.0336
2
Conventional 1 0.581 0.307 0.336 0.436 0.0261 0.176
Hybrid 0.733 1 0.528 0.541 0.708 0.148 1
Electric 0.216 0.177 1 1 1 0.0374 0.252
Fuel cell 0.154 0.382 0.532 0.488 0.807 0.0123 0.0832
3
Conventional 1 0.581 0.307 0.599 0.628 0.067 0.197
Hybrid 0.733 1 0.528 0.911 0.967 0.341 0.341
Electric 0.212 0.177 1 1 0.824 0.0308 0.0908
Fuel cell 0.154 0.382 0.532 0.794 1 0.0248 0.0728
H. Fayaz et al. / Renewable and Sustainable Energy Reviews 16 (2012) 5511–5528 5519
average cost of the estimated power train costs and fuels in year
2030 [59]. From the study results, it shows that if the cost
predictions for fuel cell, battery, hydrogen and electricity are
correct, then for this scenario both the FCHEV and BEV options are
the cheapest by 2030 in terms of lifecycle costs. The results also
show that by 2030 the FCEV costs will have approached
parity with the internal combustion engine costs as per
Tables 8 and 9 [60].
In term of capital cost, in 2010 FCEV and BEV and FCHEV are
far more costly than conventional ICE power trains. But in year
2030 capital cost could drop significantly, with the FCHEV is the
lowest followed by BEV and FCEV. In terms of fuel cost per miles,
electric vehicles achieve the highest miles per GJ than hydrogen
and gasoline vehicles. In 2030, BEVs and FCHEVs are relatively
insensitive to fuel (electricity) cost changes, whereas FCEVs and
ICEs exhibit marked sensitivity to hydrogen and gasoline costs,
respectively. This is partly due to the differing power train
efficiencies and lastly the total lifecycle costs over 100,000 miles.
FCHEVs appear to be slightly cheaper than BEVs but exhibit a
wider overall sensitivity to combine (capital and running) costs.
Both ICEs and FCEVs have much greater lifecycle costs than
FCHEVs and BEVs, around 1.75 times higher [56,60].
It is the source of electricity on which economics and environ-
mental impact associated with use of an electric car are dependent
substantially. It will be advantageous for electric car to the hybrid
vehicle, if electricity comes from renewable energy sources. It will
be competitive for electric cars only if the electricity is generated
on-board, when the electricity comes from fossil fuels. The initial
cost for fuel cell and battery is higher compared to conventional but
throughout the year of 2030 the price of both battery and also fuel
cell is almost competitive with internal combustion engine, it is the
impact of the improvement and availability increases throughout
the year [56,60].
The summary of fuel cost and emissions is shown in Table 7.
From table we can see that the most efficient and less emission
car is the hybrid car. Hydrogen generates high cost in terms of
production cost but it generates the lowest air pollution emis-
sions and high in greenhouse gases compared to electric and
hybrid vehicle [56,60]Tables 10 and 11.
2.9. Hydrogen production plant
The main challenge to develop hydrogen fuel cell vehicle is the
infrastructure. In recent study in china the main technologies of
producing hydrogen are natural gas steam reforming (NGSR), coal
gasification, and water electrolysis. As for storage is concerned
there are three ways in which it can be stored as; hydrogen gas,
liquid hydrogen and hydride [61]. The development is considering
the situations of resources, environment, energy supply and
technical economy in China [41,62]. The problem is studied in
view of ‘‘time’’ and ‘‘space’’. In terms of time, Coal dominates the
energy structure in China; the infrastructure should change with
the energy structure. Coal generates more CO emissions but
produces low hydrogen. But the change of energy will reduce
the usage of coal hence the usage and production of hydrogen via
other primary source will increases. The technology progress will
change the hydrogen infrastructure. In terms of space, the
hydrogen infrastructure will probably be different in different
region in China. In different region, the electricity is generated
using different methods [63].
From Fig. 7, it is seen that plans 5 and 6 show the highest
energy efficiency and plans 9 and 10 show the lowest energy
efficiency. The conclusion for production is arranged from the
best to the worst is coal gasification, NGSR, methanol reforming
on-board and water electrolysis. And as for the storing and
transporting methods, the ranking is done as hydrogen gas by
Table 10
Summary of production cost, fuel cost, and emissions [56,60].
Production
average cost
in 2030 (RM)
Fuel
costs
(G/J)
Greenhouse gas
emissions
(kg/100 km)
Air pollution
emission
(kg/100 km)
Gasoline 2,465 28.5 21.4 0.0600
Hydrogen 10,530 35 15.2 0.0342
Electric or
Battery
7,865 36 12.0 0.0448
Hybrid 5,665 – 13.3 0.0370
Table 7
Greenhouse gas and air pollution emissions related to the fuel utilization stage
and total environmental impact for different types of cars [56].
Car type Fuel utilization stage General indicator
GHG emissions
per 100 km of
vehicle travel
(kg per
100 km)
AP emissions
per 100 km of
vehicle travel
(kg per
100 km)
GHG emissions
per 100 km of
vehicle travel
a
(kg per
100 km)
AP emissions
per 100 km
of vehicle
travel (kg
per 100 km)
Conventional 19.9 0.0564 21.4 0.06
Hybrid 11.6 0.0328 13.3 0.037
1
b
Electric 0.343 0.00131 2.31 0.00756
Fuel cell 10.2 0.0129 14.2 0.0306
2
Electric 5.21 0.0199 7.18 0.0262
Fuel cell 10.6 0.0147 14.7 0.0324
3
Electric 10.1 0.0385 12 0.0448
Fuel cell 11.1 0.0165 15.2 0.0342
Table 8
Summary of the capital cost input data [60].
2010 2030
optimistic
2030
pessimistic
2030
average
Power train cost
20 kW fuel cell 10,000 700 1,500 1,100
80 kW fuel cell 43,700 4900 10,030 7,465
6 kW h battery pack 6,000 1200 1,800 1,500
25 kW h battery
pack
25,000 5000 7,500 6,250
Electric motor and
controller
1,700 1200 2,030 1,615
Hydrogen storage 2,000 900 2,000 1,450
Conventional (ICE) 2,200 2400 2,530 2,465
Total cost
ICE 2,200 2400 2,530 2,465
FCEV 47,400 7000 14,060 10,530
BEV 26,700 6200 9,530 7,865
FCHEV 19,700 4000 7,330 5,665
Table 9
Summary of the running cost input data [60].
Fuel cost 2010
(GJ)
2030
Optimistic
(G/J)
2030
Pessimistic
(G/J)
2030
Average
(G/J)
Miles
(G/J)
Typical units
Gasoline 12.7 19 38 28.5 253 40 mpg
Hydrogen 42 14 56 35 506 72 miles/kg
Electric 36 27 45 36 1013 3.6 mileskW/h
H. Fayaz et al. / Renewable and Sustainable Energy Reviews 16 (2012) 5511–55285520
pipeline, hydrogen gas by cylinder, liquid hydrogen, and Hydride
[6,63].
In terms of pollutant emission from the plant operation can be
concluded as per Fig. 8. The ranking of four methods of producing
hydrogen in environmental performance is NGSR, methanol
reforming on-board, coal gasification, and water electrolysis.
And as for the rank of four methods of storing and transporting
hydrogen in environmental performance is, hydrogen gas by
pipeline, hydrogen gas by cylinder, liquid hydrogen, and
hydride [63].
In Fig. 9 the ranking of four methods of producing hydrogen in
economic performance is: methanol reforming on-board, coal
gasification, NGSR, and water electrolysis. The four methods of
storing and transporting hydrogen in economic performance
are ranked as hydrogen gas by cylinder, liquid hydrogen, and
hydrogen gas by pipeline, and hydride [59]. Plan 10 is more
advantageous than Plan 9 in economic performance because
valley electricity is much cheaper than industrial electricity,
although this will cause more equipment of water electrolysis
to be needed in Plan 10 than that in Plan 9 owing to shorter work-
hour in Plan 10 [64].
Overall the best plant in terms of energy performance is the
plant that uses the combination of coal gasification and pipeline
with total efficiency 30%. From the environmental aspect, perfor-
mance is the combination of the usage NGSR and pipeline emitted
the lowest emission of dangerous gas pollutant and regarding
economic aspect, performance is the usage of methanol reforming
on-board, gives the lowest cost [66].
2.10. Public acceptability of hydrogen fuelling station
In development of hydrogen, the public acceptability and
behaviour towards hydrogen fuelling station should also be
considered. In previous study, a survey was conducted regarding
hydrogen fuel stations and safety at three locations, which are in
Back Yard, Greater Stavanger and London [67]. From the survey,
it shows that most of people in Greater Stavanger support the
fuelling station, whereas for London, it shows that people need
more information about hydrogen but still has high percentage of
people who support hydrogen fuelling station as compared to
people who are opposed and indifferent to hydrogen fuelling
stations [17,68].
The main point that helps people to accept hydrogen is the
knowledge and awareness of hydrogen; that can be seen in
Fig. 10. Most of the people in London need more information
Table 11
Summary of hydrogen plan [63,65].
Plan
no
Production system Transportation subsystem Refueling
subsystem
Utilization subsystem Efficiency, environmental & ecoomic
performance
1 Central factory: NGSR Hydrogen gas cylinder by
truck
Hydrogen gas
cylinder
Hydrogen gas
Low emission of air pollutant
2 Central factory: NGSR Hydrogen gas by pipeline Hydrogen gas tank Hydrogen gas
Low emission of air pollutant
3 Central factory: NGSR Liquid hydrogen tank by
truck
Liquid hydrogen
tank
Liquid hydrogen
Low emission of air pollutant
4 Central factory: NGSR Hydride cylinder by truck Hydride cylinder Hydride
Low emission of air pollutant
5 Central factory: coal Gasification Hydrogen gas by truck Hydrogen gas
cylinder
Hydrogen gas
High energy efficiency
3rd lowest emission of air pollutant
2nd lowest cost
6 Central factory: coal Gasification Hydrogen gas by pipeline Hydrogen gas tank Hydrogen gas
High energy efficiency
3rd lowest emission of air pollutant
2nd lowest in costs
7 Central factory: coal Gasification Liquid hydrogen tank by
truck
Liquid hydrogen
tank
Liquid hydrogen
3rd lowest emission of air pollutant
2nd lowest in costs
8 Central factory: coal Gasification Hydride cylinder by truck Hydride cylinder Hydride
3rd lowest emission of air pollutant
2nd lowest in costs
9 Refueling stations: water electrolysis
(industrial electricity)
Hydrogen gas tank Hydrogen gas
Low energy efficiency
Has high concentration of air pollutant
emission
10 Refueling stations: water electrolysis
(Valley electricity)
Hydrogen gas tank Hydrogen gas
Low energy efficiency
Has high concentration of air pollutant
emission
The highest cost
11 Central factory: methanol synthesis
via natural gas
Methanol tank by truck Methanol tank Methanol Reforming on
board
2nd lowest emission of air pollutant
The lowest costs in term of material
Fig. 7. The total energy efficiency in percentage [63].
H. Fayaz et al. / Renewable and Sustainable Energy Reviews 16 (2012) 5511–5528 5521
regarding hydrogen, whereas for Greater Stavanger and Back
Yard, they already have the knowledge about hydrogen and give
high percentage of support. As for London the percentage may be
changed if they know more about hydrogen [69]. These conclu-
sions are supported by another study done by a survey that had
been conducted before and after that people experienced with the
hydrogen vehicle. Another part of the study is done by looking at
peoples’ response towards how far they would travel for hydro-
gen fuelling station? It also shows a positive feedback from
people. In terms of fuelling station location people who live
nearby the station give quite high support towards the hydrogen
station implementations [70,71].
Overall, the media should play an important role in order to give
the information regarding hydrogen in terms of environmental
aspect, technological progress and regional success. This factor
may contribute to the acceptability of hydrogen vehicles people
[72]. In the development of hydrogen technology, safety measure-
ment should also be considered, even though the society does not
take it into their main consideration. Accidents may occur and will
affect people judgments towards hydrogen vehicle [68,71].
Another study shows that in order to develop hydrogen
technology, we should consider the usage of electricity needed
for hydrogen production, to make sure that the hydrogen fuel can
be competitive to other fuel options. Either than that, based on
fuel price in certain country, hydrogen can compete with gasoline
price under conditions of electricity price and fuel taxes. And
lastly the storage of hydrogen is the main technical issue for
hydrogen production, and the best solution maybe by developing
inexpensive hydrogen storage tanks [71,73].
2.11. Life cycle of hydrogen
Life cycle is a process of a product or a service from its
extraction of natural sources to its disposal. In previous study
the life cycle of hydrogen is assessed through comparison, by
comparing life cycle of gasoline from crude oil, hydrogen from
natural gas and two types of renewable energies, which are solar
and wind energies. Fig. 11 shows the life cycle process for crude
oil and natural gas whereas,
Fig. 12 shows the renewable energy life cycle to produce
hydrogen [74]. From Fig. 11, the extraction from natural sources
is fossil fuels. These then are transport to reforming plant by using
pipeline. Reforming is the production process of gasoline and
hydrogen from fossil fuels. This process produces gasoline and
hydrogen, both fuels are then transported or distributed to
fuelling station by using tank trucks, but as for hydrogen it needs
Fig. 9. The constitution of hydrogen cost (Yuan RMB/kg H
2
)[63].
Fig. 10. People respond towards hydrogen vehicle [68].
Fig. 8. The standard indexes of classified environment effect [63].
H. Fayaz et al. / Renewable and Sustainable Energy Reviews 16 (2012) 5511–55285522
additional pressure to be stored in tank, hence adding some
additional energy and also material for the tanks. The final stage
is the usage by the consumers and the emission of both fuels
[74,75]. As for renewable energy in Fig. 12, its natural sources are
wind and solar. Both solar and wind energies generate electricity
via photovoltaic element and wind turbine, respectively.
The electricity is transported directly to fuelling station to
produce hydrogen using chemical reactions (electrolysis). The
hydrogen produced then is compressed before it can be stored.
And the final stage is same as fossil fuels, the utilization or the
usage of the consumables [74,76].
Fig. 13 shows that the energy consumption, to produce gaso-
line, is less compared to hydrogen via natural gas team reforming.
Whereas for renewable energy, wind energy uses low energy
consumption to produce hydrogen and the solar is the less
efficient due to the energy consumption needed to produce
hydrogen fuels [62].Fig. 14 shows that hydrogen and gasoline
produce almost the same amount of Carbon Dioxide. The hydro-
gen emits high volume of CO
2
during the production process.
As for gasoline, the high emission comes from the fuel utilization.
For renewable energies both show low emission of CO
2
, but the
lowest is from wind energy [74].
The gasoline production from crude oil has better efficiency
compared to production of hydrogen using natural gas from all of
above methods in producing fuels. The emission of both, hydro-
gen fuel from natural gas and gasoline from crude oil show no
significant difference, both has high emissions of greenhouse
gases compared to renewable energy source [62]. The high
emission comes from the production process. In terms of cost to
produce hydrogen via natural gas is about five times less than the
cost to produce hydrogen via wind energy, due to the construc-
tion materials of the technology, but it can be reduced if further
study is done in terms of reducing the material used in the
construction of the wind turbine and also the improvement in
terms of electricity generated by the turbine [7476].
Overall, the advantages, disadvantages and improvements of
hydrogen in internal combustion engine are tabulated in Table 12.
Fig. 12. Production of hydrogen from renewable energy [74].
Fig. 11. Production of gasoline and hydrogen from fossil fuel [74].
Fig. 13. Energy consumption by type of process [74].
H. Fayaz et al. / Renewable and Sustainable Energy Reviews 16 (2012) 5511–5528 5523
3. Hydrogen production
There are many ways to generate hydrogen as an energy
carrier and the sources are so abundant in this world. The biggest
part of today’s 500 billion cubic meters hydrogen sold worldwide
is generated from fossil sources (natural gas, oil), or is obtained as
by-product-hydrogen in chemical processes [77]. There are many
processes of chemical processes for fuel cell vehicles such as small
reformer, steam reforming and partial oxidation; gasification.
Besides those on-board hydrogen productions, hydrogen can also
be produced by electrolysis. There are many types of electrolysis
such as alkaline water electrolysis, Proton-Exchange-Membrane
(PEM), water electrolysis and High Temperature Electrolysis [78].
Other than water electrolysis, the hydrogen can also be produced
by biomass gasification, which is also one of the renewable
resources. Different types of hydrogen productions have their
own source and it varies in terms of system applications as well.
The best method to produce hydrogen is the one which has
simplest process, easily to get the main sources, low cost and
environmentally safe [6].
3.1. Natural gas to Hydrogen
Natural gas is considered as a fossil fuel since it is formed from
tiny sea animal and plants that died 200 to 400 million years ago.
Raw natural gas consists of many different gases with the main
gas is methane that is mixed with heavier hydrocarbon and
carbon dioxide. Steam reforming is the process to convert natural
gas to hydrogen. In high temperature steam, the hydrogen atoms
separate from the carbons atoms in methane (CH
4
). The reactions
are reversible in nature, first is an endothermic reaction, which is
the reaction that consumes heat to produce synthetic gases as H
2
and CO. During the reaction process, the methane reacts with
steam at 750 1C to 800 1C with the pressure 3 bar to 25 bar [79].
The second reaction which, known as a water gas shift reaction, is
exothermic that mildly produces heat. This process occurs in two
stages, consisting of a high temperature shift (HTS) at 350 1C and
a low temperature shift (LTS) at 190–210 1C[79]. The chemical
equations to produce hydrogen by natural gas reforming are
shown as following [80,81]:
CH
4
þH
2
OðsteamÞ-3H
2
þCO ð5Þ
Table 12
Positive features, limitations and improving the operational of hydrogen for engine application [29].
Positive features of hydrogen for engine application Limitation associated with hydrogen engine
applications
Improving the operational features of SI hydrogen
engines
Less cyclic variationsThis leads to a reduction in
emissions, improved efficiency, and quieter and
smoother operation.
Engines fuelled with H
2
suffer from reduced power
output, due mainly to the very low heating value of H
2
on volume basis.
Employ lean mixtures with wide-open throttle. (To
apply optimal variable partial throttling at extremely
lean mixtures to effect better engine performance)
H
2
engines are more amenable to high-speed engine
operation mainly due to the associated fast burning
rates.
The mass of the intake air is reduced for any engine size
because of the relatively high stoichiometric H
2
to air
ratio.
Uniquely compatible and specially designed
turbochargers need to be used for hydrogen engine
applications.
Moderately high compression ratio operation is
possible with lean mixtures of H
2
in air, which
permits higher efficiencies and increased power
output
There are serious potential operational problems
associated with the uncontrolled pre-ignition and
backfiring into the intake manifold of H
2
engines.
Higher compression ratios can be applied
satisfactorily to increase the power output and
efficiency, because of the relatively fast burning
characteristics of the very lean H
2
–air mixtures.
The reaction rates of H
2
are sensitive to the presence
of a wide range of catalysts. This feature helps to
improve its combustion and the treatment of its
exhaust emissions.
The high burning rates of H
2
produce high pressures
and temperatures during combustion in engines when
operating near stoichiometric mixtures. This may lead
to high NO
x
emissions.
Carefully controlled cooling of EGR can be applied for
knock avoidance and control. For lean mixture
operation with H
2
suitably heated exhaust gas
recirculation can be used.
The thermodynamic and heat transfer characteristics
of H
2
tend to produce high compression
temperatures that contribute to improvements in
engine efficiency and lean mixture operation.
Hydrogen engine operation may be associated with
increased noise and vibrations due mainly to the high
rates of pressure rise resulting from fast burning.
Time injection of PFI or DI need to be optimized for
injection duration, timing and pressure. This is
important especially for the avoidance of pre-ignition
and backfiring. Provision of some water injection
when needed can be also made
H
2
high burning rates make the H
2
fuelled engine
performance less sensitive to changes to the shape
of the combustion chamber, level of turbulence and
the intake charge swirling effect.
Great care is needed to avoid materials compatibility
problems with hydrogen applications in engines.
Optimum spark ignition characteristics in terms
energy, spark plug gap size and material, plug
geometry, electrical insulation etc. need to be
employed.
The gas is highly diffusive and buoyant which make
fuel leaks disperse quickly, reducing the fire and
explosion hazards associated with H
2
engine
operation.
Hydrogen requires a very low ignition energy, which
leads to uncontrolled pre-ignition problems.
Further improvement in performance can be obtained
by having the design features of the combustion
chamber and its surfaces suitably optimized for H
2
operation.
There is an increased potential for undesirable
corrosion and lubricating oil contamination due to
exhaust water vapour condensation.
Variable valve timing needs to be incorporated and
optimized to effect higher volumetric efficiency and
better control of EGR.
Fig. 14. Greenhouse gases emitted by type of hydrogen production [74].
H. Fayaz et al. / Renewable and Sustainable Energy Reviews 16 (2012) 5511–55285524
COþH
2
OðsteamÞ-CO
2
þH
2
ð6Þ
Nowadays, the majority of hydrogen produced worldwide is
accomplished by steam methane reforming. The efficiency of
steam reforming process is about 65–75% among the highest of
current commercially available products [79]. Natural gas is the
best method to produce hydrogen as it is convenient, easy to
handle, and high hydrogen-to-carbon ratio. Fig. 15 shows one of
the hydrogen applications as reforming the natural gas. The
hydrogen can be used in fuel cell in order to generate electricity.
3.2. Coal gasification
Through coal gasification with the addition of carbon capture
technology, high volume stream of hydrogen can be produced. In
gasification process, the mixing of pulverized coal with an
oxidant, heated to about 1800 1C have a very hot synthesis
(syngas). The syngas consists of hydrogen, carbon monoxide,
carbon dioxide, other gases and particle. To remove the other
gases and particle, the syngas is cooled and cleaning process is
proceeded.
During the cleaning of syngas, any particulate such as mercury,
sulphur, trace contaminants and foreign matter are removed.
Then, the syngas reacts with steam by a process called water gas
shift reaction to produce more hydrogen and carbon dioxide as
final product as in Fig. 16. The hydrogen then can be used as a
vehicle fuel or to generate electricity for other purposes such as
power plant and industry. Meanwhile, as carbon dioxide has also
been produced at the end, a technology is needed to decrease or
at least sustain the amount of carbon dioxide emissions in the
atmosphere. Nowadays, carbon dioxide emissions can be reduced
near to zero when applying carbon capture storage and seques-
trations technologies [82,83]. By increasing the efficiency of
operation in the gasification process, the pollutants can also be
reduced significantly.
Carbon capture and storage concept is used for capturing and
storing the carbon dioxide permanently that has been produced
from coal gasification or any other industrial activity [84]. The
carbon is stored naturally in the earth’s terrestrial biosphere (in
forests, soil, and plants) and ocean reservoirs (via the ocean
carbon cycle), from which it is cyclically released and absorbed
[82]. The percentage of carbon dioxide emissions to atmosphere
can be reduced is about 90% by implementing the concept of
carbon capture and storage in pulverized coal plant.
3.3. Electrolysis
Fossil fuel energy sources such as natural gas, coal and
petroleum are not sustainable as these are depleting and there
are severe damages to the environment because of the activities
to produce hydrogen. In order to make a global sustainability and
stability, renewable energy such as electrolysis and biomass
gasification needs to be commercialized, and replaces the use of
fossil fuel significantly [85].
To operate the electrolysis process, the electricity needed, can
be generated either from fossil fuels or renewable energy such as
solar power. In water electrolysis process, the hydrogen produced
is clean, with high purity and is as simple as using electricity,
generated by fossil fuels. Besides using electricity as the source,
the hydrogen can also be produced by photo catalytic water
splitting. This technology is still in experimental stage due to low
efficiency and high cost [86]. At present, only about 5% of
hydrogen in the world is produced by water electrolysis [87].
Currently, the best solution to the high cost of electrolysis
process is by using sustainable sources such as solar, wind and or
nuclear. In this paper, renewable energy as the source for
electrolysis will be discussed. There are many types of electrolysis
such as alkaline water electrolysis, polymer electrolyte membrane
(PEM) electrolysis, solid oxide electrolysis, and photo-electrolysis
[87,88]. The difference among the electrolysis systems is the
source of power to conduct the electrolysis, the constructions,
conversion efficiency, and availability in industries.
Alkaline water electrolysis is one of the easiest methods for
hydrogen production because of its simple construction. A basic
water electrolysis unit consists of an anode, a cathode, power
supply and an electrolyte [88]. The molecules of water (H
2
O) can
be split to form pure hydrogen and oxygen by using electricity.
However, when the electricity used, is generated by burning fossil
fuels, the pollutant emissions cannot be avoided. But producing
hydrogen by using renewable energy source, the efficiency is
around 68% [89]. For application in transportation sector, the
electrolyzers, used in the electrolysis process, can be reduced in
size to suit the fuel cell vehicles that give an important advantage
in the development of FCV market.
Table 13 shows the different electrolysers that can be used to
produce hydrogen gas. The different electrolytes are used in
Fig. 16. Coal gasification process [82].
Fig. 15. Hydrogen from natural gas for fuel cell application [81].
H. Fayaz et al. / Renewable and Sustainable Energy Reviews 16 (2012) 5511–5528 5525
electrolysis and the efficiency in producing the hydrogen. Besides
that, the maturity or the level of acceptance in the current
market also varies. The PEM electrolyser has the highest efficiency
of 65–85% and can be one of the replacement to the existing
alkaline electrolyser. Photoelectrolysis technology which uses
solar power as its main source needs more research and devel-
opment in future to have high efficiency [90].
3.4. Biomass gasification
Biomass can be a fuel source, derived from plant and animal
wastes. From biomass, the natural gas (methane) can be obtained.
Actually, methane can be obtained naturally as the waste; organic
matter decays. Landfills are the places, where methane can be
collected. The methane gas is used for heating and producing
electricity.
Biomass gasification is one of the most mature technologies to
produce syn-gas. This technology is however very expensive due
to high energy requirements and inherent energy losses in
biomass gasification. Biomass gasification means incomplete
combustion of biomass that produces combustible gases consist-
ing of carbon monoxide (CO), hydrogen (H
2
) and methane (CH
4
).
The mixture of combustible gases is also known as producer gas.
Producer gas can be used to run both combustion engines either
compression or spark ignition. The production of producer gas is
called gasification. Gasification is partial combustion of biomass
and is reacted in gasifier at 1000 1C[91].
The gasification process occurs in a gasifier involving four pro-
cesses; (a) drying the fuel (b) pyrolysis (c) combustion (d) reduction
[91]. Sometimes, the processes are overlapping but the processes can
still be classified, happening at different zones and temperatures,
based on the different chemical and thermal reactions.
3.5. Photolytic processes
Photolytic processes use light energy to split water into
hydrogen and oxygen. Currently in the very early stages of
research, these processes offer long-term potential for sustainable
hydrogen production with low environmental impact. Two pro-
cesses to produce hydrogen are used in photolytic processes,
namely, photobiological water splitting and photoelectrochemical
water splitting.
3.5.1. Photobiological water splitting
In this process, sunlight and specialized microorganisms are
sources for hydrogen production, such as green and cyanobac-
teria. Hydrogen is produced as by-product by these microorgan-
isms as a by-product of their natural metabolic process, just as
plants produce oxygen during photosynthesis. Photobiological
water splitting is a long-term technology. At present, for efficient
and commercial hydrogen production, the microbes split water
very slow, which is to be used. There are many ways under
research by scientists to modify the microorganisms and to
identify other naturally occurring microbes, which can produce
hydrogen at higher rates. Photobiological water splitting offers
long-term potential for sustainable hydrogen production with
low environmental impacts, even though it is in the very early
stages of research [92].
3.5.2. Photoelectrochemical water splitting
Sunlight and specialized semiconductors called photoelectro-
chemical materials are used to produce hydrogen, in this process.
In the photoelectrochemical (PEC) system, light is directly used to
dissociate water molecules into hydrogen and oxygen by the
semiconductor. Different semiconductor materials work at parti-
cular wavelengths of light and energies.
Research focuses on finding semiconductors with the correct
energies to split water that are also stable when in contact with
water. Photoelectrochemical water splitting offers long-term
potential for sustainable hydrogen production with low environ-
mental impacts, even though it is in very early stages of research [93].
4. Conclusion
The crucial outcomes of this study are summarized below:
Hydrogen in internal combustion engines has many advan-
tages in terms of combustive properties but it needs detailed
consideration of engine design to avoid abnormal combustion,
which is the major problem in hydrogen engine. This, as a
result can improve engine efficiency, power output and reduce
NO
x
emissions.
In fuel cell vehicles, the hydrogen purity can affect the
performance of the fuel cell vehicles. This impurity comes
from the poisoning of the sulphur during production process.
From the environmental aspects, the emission of fuel cell is
low as compared to conventional vehicles but as penalty, fuel
cell vehicles need additional space and weight to install the
battery and storage tank, thus increases it production cost.
The cost and also the efficiency of the hydrogen plant depend
on the electricity tariff and the sources for producing hydro-
gen. If the location is near with its natural resources, it will
help in reducing its cost, so for the development of hydrogen
plant, location with its sources should be considered.
The acceptability of hydrogen technology by people is through
the knowledge and also the awareness of the hydrogen
benefits towards environment and human life. Recent study
shows that people still do not have the information of hydro-
gen. Media role in introducing hydrogen technology to citizens
is crucial in order to get support of people in development of
hydrogen technology.
There are many ways to generate hydrogen as an energy
carrier and the sources are in abundance. Mainly it is produced
from fossil fuels and as by-product hydrogen in chemical
processes. Different types of hydrogen productions have their
own source and it varies in terms of system applications
as well.
The best method to produce hydrogen is the one which has
simplest process, easily to get the main sources, low cost and
environmentally safe.
The study in the production methods, vehicle performance,
plant performance, infrastructure availability, emissions and
air pollution is needed, before the hydrogen fuel and vehicles
can be commercialized and compete with other type of fuels.
Acknowledement
The authors would like to acknowledge the Ministry of Higher
Education of Malaysia and The University of Malaya, Kuala
Table 13
Efficiency comparison among different types of electrolyser [88].
Technology Efficiency (%) Maturity
Alkaline electrolyser 59–70 Commercial
PEM electrolyser 65–82 Near term
Solid oxide electrolysis cells 40–60 mediate term
Photo electrolysis 2–12 long term
H. Fayaz et al. / Renewable and Sustainable Energy Reviews 16 (2012) 5511–55285526
Lumpur, Malaysia for the financial support under UM.C/HIR/
MOHE/ENG/15 (D000015-16001).
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... In a hydrogen internal combustion engine, it is necessary to use cold rated spark plugs so that spark plug electrode temperature avoids exceeding the auto-ignition limit and causing backfires. At the same time, it is not advisable to use spark plugs with platinum electrodes, since platinum is a catalyst for the oxidation of hydrogen [10,18,45,46]. It is also necessary to use grounding or a properly designed ignition system to avoid uncontrolled ignition due to residual ignition energy [9]. ...
... As in other combustion engines, this parameter is optimized for highest efficiency. In the case of hydrogen-fueled combustion engines, the compression ratio may have higher values than for gasoline engines (depending on the application and engine design, it ranges from 7.5:1 to 14.5:1) [10,15,45,46,49]. ...
... Based on the BMW Hydrogen 7 (bi-fuel), a BMW Hydrogen 7 Mono-Fuel demonstration vehicle was developed, which runs on hydrogen only [9,15,52,55]. Another similarly known vehicle is the five-seater Ford P200 sedan, presented in 2001 with a two-liter engine equipped with highly optimized hydrogen port injection, powered by 250 bar compressed hydrogen from two carbon-fiber reinforced aluminum tanks [10,15,46]. Three years later, Ford fully engineered a demonstration fleet of 30 E-450 shuttle buses [9,56]. ...
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... This process is green and safe since it does not emit hazardous gases to the environment [52,53]. Besides, hydrogen produced through electrolysis is clean and has high purity [54,55]. The electrolysis process is irreversible and hydrogen can be directly collected at cathode without mixing with other gaseous products. ...
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... Interestingly, the authors also discuss the cost-benefit analysis of H 2 use and suggest that labour costs are an issue [18]. Certainly, as H 2 is developed more for other industries, such as a transport energy source [19], the cost and delivery of H 2 is likely to become cheaper. ...
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Chapter
This chapter surveys lean combustion techniques in internal combustion (IC) engines. The chapter begins by providing a brief review of the fundamentals of theoretical combustion and ideal combustion emissions. Next, the effects of lean combustion in conventional and advanced spark-ignited IC engines are explored, including the effect of stratification and fueling with hydrogen. Strategies used to extend the lean limit of operation are also presented along with experimental results demonstrating the different strategy's efficacy. Lastly, conventional and advanced compression-ignition engines are discussed including homogeneous-charge compression-ignition engines.
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reviews of various alternative energy for use in agriculture
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The current development of fuel cell scooters has been reviewed in this paper. Fuel cell scooters, by nature, have zero emissions, and they have the potential to replace current petroleum-propelled engine scooters. First, the fundamentals of fuel cells, including the critical technologies pertaining to fuel cell engines and hydrogen storage, were introduced. Then, the technical feasibility of fuel cell scooters was discussed in parallel with the hydrogen infrastructure model. The accomplishments of fuel cell scooters in Taiwan were presented. Moreover, the contribution of replacing petrol scooters by hydrogen fuel cell scooters to reduction in greenhouse gas (GHG) emission and energy conservation was evaluated. Furthermore, industrial competition with regard to the development of fuel cell scooters was discussed on the basis of a strengths, weaknesses, opportunities, and threats (SWOT) analysis. In conclusion, with mature fuel cell technology together with solid foundation of the scooter industry, Taiwan offers conditions that were conducive for the development of fuel cell scooters. Its social and technical capability will be proved on account of the leading demonstrations of fuel cell scooters in the world. If it can develop a successful business model, Taiwan could enjoy the advantages of tapping the huge global market for zero-emission scooters.
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The effect of variable water injection timing on performance and emission characteristics of hydrogen fueled compression ignition (HFCI) engine has been investigated and the results are presented in this paper. In this study, water is injected from 20°BTDC to 20°ATDC with injection duration of 20°CA and 40°CA. Hydrogen is injected at the intake port with fixed injection timing from 0°CA to 40°CA and constant flow rate of 5 LPM. The results indicate that water injection timing of 20°ATDC and duration of 20°CA has shown better engine performance due to increased gross indicated work and indicated thermal efficiency. It has also demonstrated that the lowest NOx concentrations for engine speed greater than 2500 RPM and lower EGT throughout entire speed range. Water injection timing of 20°BTDC and duration of 40°CA has shown the highest heat release rate and the longest ignition delay. Water injection timing of 0°CA and duration of 40°CA indicated that the highest O2 and SO2 emissions throughout entire speed range. It is observed that water injection technique appears to be promising method to enhance the performance and emissions quality of HFCI engine effectively.
Article
In this study, the effect of hydrogen addition to DME/CH4 dual-fuel RCCI (Reactivity Controlled Compression Ignition) engine is investigated using three dimensional calculations coupled with chemical kinetics. A new reduced DME (Dimethyl Ether) oxidation mechanism is proposed in this study. With the addition of H2, the ignition time is advanced and the peak cylinder pressure is increased. The addition of hydrogen has a greater effect on the beginning stage of combustion than the later stages of combustion. The CH4 emission is reduced with the addition of H2. However, as the flame does not propagate throughout the charge, the CH4 emission is still high. The CO emission is reduced and most of the remaining CO is produced by the combustion of the premixed CH4. With the addition of hydrogen, NO emission is increased. The simulation shows that the final NOx emissions are significantly determined by the injection strategy and quantity of the pilot fuel during dual fuel operation conditions.
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This paper shows the results of the tests carried out in a naturally aspirated vehicle spark ignition engine fueled with different hydrogen and methane blends. The percentage of hydrogen tested was up to 50% by volume in methane. The tests were carried out in a wide range of speeds with the original ignition timing of the engine. Also, lean equivalence ratios were proved. Just the fuel injection map was modified for each fuel blend and equivalence ratio tested. In this paper, the results of thermal efficiency and pollutant emissions achieved at full load have been compared with the corresponding gasoline test results. The best balance between thermal efficiency and pollutant emissions was observed with the 30% hydrogen and 70% methane fuel blend.