Research and Development of Self-Contained Water Injection Systems

Abstract

Reducing fuel consumption and thus CO2 emissions is one of the most urgent tasks of current research in the field of internal combustion engines. Water Injection has proven its benefits to increase power or optimize fuel consumption of passenger cars. This technology enables knock mitigation to either increase the engine power output or raise the compression ratio and efficiency while enabling λ = 1 operation in the complete engine map to meet future emission targets. Current systems have limited container capacity. It is necessary to refill the water tank regularly. This also means that we cannot get the benefits of an engine with a higher compression ratio. For this reason, the self-contained system was investigated. This article is a methodology for finding the right design of a self-contained water injection system, but also a vehicle test that proves the function.

Full text

Int. J. Environ. Res. Public Health 2021, 18, 5392. https://doi.org/10.3390/ijerph18105392 www.mdpi.com/journal/ijerph
Article
Research and Development of Self-Contained Water
Injection Systems
Jiri Bazala 1,2, Guillaume Hébert 1, Oliver Fischer 3, Jürgen Nothbaum 3, Matthias Thewes 4, Tobias Voßhall 4,
Peter Diehl 5 and Pavel Kučera 2,*
1 Hanon Systems Autopal Services s.r.o., 687 25 Hluk, Czech Republic;
jbazala@hanonsystems.com or Jiri.Bazala@vut.cz (J.B.); ghebert4@hanonsystems.com (G.H.)
2 Institute of Automotive Engineering, Brno University of Technology, Technická 2896/2,
616 69 Brno, Czech Republic
3 Hanon Systems Deutschland GmbH, 50170 Kerpen, Germany; ofische3@hanonsystems.com (O.F.);
jnothbau@hanonsystems.com (J.N.)
4 FEV Europe GmbH, 52074 Aachen, Germany; Thewes@fev.com (M.T.); vosshall@fev.com (T.V.)
5 Consultant, 50667 Köln, Germany; pdiehl@posteo.de
* Correspondence: kucera@fme.vutbr.cz; Tel.: +420-541-142-274
Abstract: Reducing fuel consumption and thus CO2 emissions is one of the most urgent tasks of
current research in the field of internal combustion engines. Water Injection has proven its benefits
to increase power or optimize fuel consumption of passenger cars. This technology enables knock
mitigation to either increase the engine power output or raise the compression ratio and efficiency
while enabling λ = 1 operation in the complete engine map to meet future emission targets. Current
systems have limited container capacity. It is necessary to refill the water tank regularly. This also
means that we cannot get the benefits of an engine with a higher compression ratio. For this reason,
the self-contained system was investigated. This article is a methodology for finding the right de-
sign of a self-contained water injection system, but also a vehicle test that proves the function.
Keywords: water injection; compression ratio; self-contained tank; EGR; exhaust condensate
1. Introduction
The need to further reduce fossil fuel consumption in the context of current and fu-
ture global CO2 emission limits requires intensive search for new solutions for automotive
engines. For reciprocating internal combustion engines, the mass of CO2 emitted into the
atmosphere is a function of their fuel consumption. Therefore, research into internal com-
bustion engines is currently focused both on reducing the passive resistances of all mech-
anisms and on improving the efficiency of their thermodynamic cycles. As for the second
option, the most promising solution is to lower the in-cylinder temperature and ensure
stoichiometric combustion throughout the engine operating map. The maximum operat-
ing conditions of gasoline internal combustion engines are, in general, restricted by the
temperature limit of engine components and knocking conditions. Knocking is sharp
sound effects caused by premature combustion of part of the com-pressed air-fuel mixture
in the cylinder. This phenomenon is destructive for engine itself and it is mainly caused
by high temperature of combustion mixture. Knocking is con-trolled by engine manage-
ment by fuel enrichment. With modern turbocharged gasoline engines, the maximum ac-
ceptable exhaust gas temperature is limited by the thermal material resistance of the tur-
bine. To protect critical components, fuel enrichment (λ < 1) has been used under these
conditions. The high vaporization enthalpy of the gasoline enables a significant reduction
of the exhaust gas temperature without putting additional thermal load on the cooling
system [1].
Citation:
Bazala, J.; Hébert, G.;
Fischer, O.; Nothbaum, J.; Thewes,
M.; Voßhall, T.; Diehl, P.; Kučera, P.
Research and Devel
opment of Self-
Contained Water Injection Systems
.
Int. J. Environ. Res. Public Health
2021,
18
, 5392. https://doi.org/10.3390/
ijerph18105392
Academic Editor:
Michal Puškár
Received:
14 April 2021
Accepted:
11 May 2021
Published:
18 May 2021
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Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
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Attribution (CC BY) license
(http://creativecommons.org/licenses
/by/4.0/).

Int. J. Environ. Res. Public Health 2021, 18, 5392 2 of 12
Nowadays, mixture enrichment is undesired along with the expected extension of
regulations in future legislation, which may also include restrictions on Fuel Consump-
tion/CO2 emissions. The new emission regulation will require stoichiometric operation (λ
= 1) under all engine operating conditions. Consequently, a different medium with a high
vaporization enthalpy is required. Based on the patent of Pierre Hugon in 1865 [2], Water
Injection (WI) into the combustion chamber of a gasoline engine can also be used to control
the temperature of engine components.
Water Injection can be used either for:
• Engine performance improvement or
• Improved fuel consumption
For improved performance, the injection of water into the cylinder lowers the gas
temperature, mitigating knocking and allowing a higher load at λ = 1. As shown in Figure
1 below, this increases power/torque characteristics.
Figure 1. Performance/Torque improvement using water injection [3].
As far as fuel consumption (FC) improvement is concerned, using WI on a down-
sized, turbocharged gasoline engine allows improved combustion phasing and knock mit-
igation at an increased Compression Ratio (CR) while avoiding fuel enrichment. This will
allow stoichiometric operation throughout the entire engine map. Current engine devel-
opments seem to concentrate on the effect of “Performance Improvement”, but it can be
expected that the development of engines for the mid 2020′s will shift focus to improving
fuel consumption [4–9]. What both strategies have in common is the use of vaporization
enthalpy of a liquid. Injecting Water for vaporization offers an improved cooling effect
compared to fuel by a factor of more than 5. It must be mentioned that the “Water Injec-
tion”—Technology is only one option of FC improvement through mixture dilution. It
competes with Exhaust Gas Recirculation (EGR) in some modes for the same purpose
(Figure 2). It has been demonstrated that at medium load a 40–50% Water-to-Fuel Ratio
(WFR) with Port Water Injection (PWI) has the same effect as an EGR-rate of 10% [10].

Int. J. Environ. Res. Public Health 2021, 18, 5392 3 of 12
Figure 2. Summarizes the respective effects of EGR and Water Injection.
However, WI does have benefits when compared to EGR, especially better controlla-
bility as this is not a closed-loop as with EGR, the timing of injection is not linked to other
parameters such as turbo charger backpressure, limited inertia (PWI timing not linked to
engine operation) and combustion delay (as present with EGR). Additionally, it does not
deteriorate combustion stability significantly. The combustion delay linked to EGR dilu-
tion and the necessary adaption of the recirculated gas mass flow to the maximum turbo-
charger characteristics are typically two limiting parameters of the maximum acceptable
EGR rate.
2. Motivation
As Figure 3 shows, WI has significant effect on fuel consumption. It is without doubt
that Fuel Consumption is even lower with a higher compression ratio. Unfortunately, cur-
rent WI systems in series production are not able to use this maximum possible benefit to
their advantage. If the water injection liquid were drained from the tank and the combus-
tion mixture were not cooled through water evaporation, fuel consumption would signif-
icantly increase, as evaporation of fuel would take place instead of evaporation of water.
To ensure the system has a sufficient amount of water injection liquid, a self-contained
tank is necessary.
Figure 3. Fuel consumption benefits of EGR and WI for various drive cycles.

Int. J. Environ. Res. Public Health 2021, 18, 5392 4 of 12
Competing on-Board Water Sources
There are limited sources of liquid that can be contained without human refill. These
are:
• Harvesting air humidity from ambient (e.g., by A/C condensate)
• Surface Water (e.g., rain water collected from vehicle body)
• Exhaust Gas Condensate
The first two variants are highly dependent upon weather ambient conditions with
sufficiently high humidity levels or driver habits (A/C operation is undesirable). Conse-
quently, an adequate supply of water cannot be ensured. On the contrary, the condensa-
tion of water vapour formed during gasoline combustion is a reliable source of water. The
temperature and humidity levels have only a minor contribution to the full amount of
water being present in the exhaust gas. Almost all water in exhaust comes from a com-
bustion reaction from carbohydrates and oxygen from air, not from humidity in air. This
can be seen in Equation (1) where ideal combustion is described.
818 + 12.5(2 + 3.762)→ 82 + 92 + 472,
(1)
The formula above can calculate that 1 kg of fuel on the left side of the formula is 1.4
kg of water vapour on the right side which can be harvested as liquid for WI.
3. WAHASY Efficiency
The fact that water vapour (WC) is present in exhaust is already known. In order to
harvest water from exhaust, it is necessary to condensate water vapour to water liquid.
The exhaust pressure at tailpipe is around 1 bar and it is common knowledge that water
molar concentration is 14%. Therefore, the partial water vapour pressure can be deter-
mined according to Dalton’s law which is 0.14 bar. The water vapour partial pressure
specifies dew point, below which the water vapour condensates as shown in Figure 4,
based on the data in [11]. At a pressure of 0.14 bar, the saturation temperature is 53 °C (see
Figure 4).
Figure 4. Water saturation pressure.
In order to achieve a “closed-loop”-operation (e.g., on-board generation of water us-
ing exhaust gas) a system called WAHASY (WAter HArvesting SYstem) has been devel-
oped. Its primary target is to provide enough water in liquid state to match the required
amount as needed for intended engine operation. This amount is given by Equation (2),
where WFR stands for “Water to Fuel Ratio” (e.g., the volume of liquid water injected)

Int. J. Environ. Res. Public Health 2021, 18, 5392 5 of 12
compared to the volume of fuel and the WAHASY efficiency is the total efficiency of the
system (e.g., the amount of water which can effectively be used for the water injection). In
an ideally dimensioned system, this efficiency also matches the amount of water being
condensed divided by the total amount of water present in the exhaust gas.

 = =
ℎ
(2)
Initial investigation in the past showed a wide array of water consumption figures
when applying Water Injection, depending on test procedures and/or driving habits (see
Figure 5).
Figure 5. Water Consumption for Various Test Conditions [12].
Figure 5 shows that the required Water-to-fuel ratio (WFR)—even if it is able to raise
up to 20%—is mostly under 10% in the tested drive cycles. This leads to a required
WAHASY-efficiency of around 8% (up to 15% is considered for the most extreme “Real
Drive” (RDE) profile). The efficiency of the WAHASY system is comprised of water con-
densation efficiency and the separation efficiency of small droplets from the exhaust
stream.
4. Results
4.1. GT-Suite 1D Model
To determine the right WAHASY size, a GT-Suite model was developed and verified
by engine testing. GT Suite is the industry-leading simulation tool with capabilities and
libraries aimed at a wide variety of applications in automotive technology. Criteria of the
decision matrix were:
• Limit system complexity
• Increase package compactness
• Maximize thermal performance
• Minimize heat dissipated through the LT coolant loop
• Minimize costs
A two-stage cooling design was selected as the best design (initial HT HEX followed
by a second LT HEX) to condensate water vapour. A third device (“Harvester”) is in-
tended to separate the condensate droplets from the exhaust gas flow. The GT-Suite 1D
Tool was chosen to model behaviour measured on a real vehicle (see Figure 6). See the
maximum available water content in exhaust gases below.

Int. J. Environ. Res. Public Health 2021, 18, 5392 6 of 12
Figure 6. Data from the vehicle test.
The data above will serve as inputs to the GT model (Figure 7), especially the inlet
temperature and mass flow of exhaust. As mentioned above, the system has two coolant
loops. High temperature (HT) and low temperature (LT). The high-temperature loop has
two parallel coolers with a temperature of 90 °C. The low-temperature cooler is connected
to a low-temperature radiator cooled by ambient air. The cooler thermal properties were
taken from real calorimeter measurements (Figure 8).
Figure 7. GT model of HAWASY system.

Int. J. Environ. Res. Public Health 2021, 18, 5392 7 of 12
Figure 8. Thermal data of heat exchangers used for 1D simulation.
To check proper function of the GT Suite model, an engine test was established (Fig-
ure 9), using the same engine as FEV their vehicle test (Figure 6). For repeatability reasons,
stationary points from WLTC driving cycle measurements were selected. For M07 point
the engine settings was 2700 rpm and torque 100 Nm which represents 31.4 g/s as exhaust
mass flow. Exhaust gas temperature was monitored on the downstream and upstream of
each cooler. Measured results data was used for comparison with the GT Suite model
(Figure 10).
Figure 9. Engine test stand.
Figure 10 shows the three temperatures EGT1, EGT2 and EGT3 from the test. All of
these sensors have a twin value from GT Suite. EGT1 is at the inlet temperature to the HT
coolers, EGT2 temperature is inlet temperature to the LT cooler. EGT3 is the main

Int. J. Environ. Res. Public Health 2021, 18, 5392 8 of 12
temperature from the output of the LT cooler. It is obvious that this temperature is safely
under the Dew point (53 °C) of water vapour in the exhaust calculated above.
Figure 10. Comparison of exhaust temperatures between experiment and simulation.
The 1D model was verified by experiment and can be used for WAHASY modelling
and finding its suitable parameters. Figure 5 shows that WAHASY with an efficiency of
only 15% in worst conditions is necessary. Hypothetically, if applied to the WLTC cycle,
only 300 mL of water is necessary to harvest. This would be enough to operate the
WAHASY system and also to replenish the tank condensate. This is also the reason why
the WAHASY is focused only on low load modes where lower back pressure losses in
exhaust and better efficiency of condensate harvester are expected. Only 693 mL of water
is available for the first 1000 s of WLTC cycles. By applying our GT-Suite model, it was
found that just two coolers (one HT and one LT) are enough (Design—J). Figure 11 shows
that up to the first 1000 s, both variants have similar efficiency. If the exhaust gas has more
energy than our 1 + 1 design is able to cool, it will be automatically bypassed by the ex-
haust valve outside the WAHASY unit.
Figure 11. Comparison of different WAHASY designs.

Int. J. Environ. Res. Public Health 2021, 18, 5392 9 of 12
4.2. Harvester Separator Unit
As explained above, the efficiency of water vapour cooling under the dew point is
only the first phase of total efficiency. The second phase concerns collecting the conden-
sate droplets and separating them in the tank. For the unit to be developed, it was neces-
sary to measure the size and distribution of droplets in the exhaust. An experiment was
therefore carried out where photos were taken, through which droplet size and distribu-
tion could be measured indirectly (Figure 12).
Figure 12. Condensate droplets size measuring.
The mode of measured diameters was determined as 0.47 mm and the minimal di-
ameter as 0.3 mm. In the CFD simulation, the diameter was set to uniform for all droplets
with its value of 0.25 mm to overcome possible inaccuracy of measurements and simulate
worse scenario. The CFD model analyses droplets movement by DPM (Discrete phase
model) settings in Fluent (Figure 13). In DPM settings the interaction with continuous
phase was enabled and the injection of water droplets was subjected to inlet surface. The
diameter of droplets was assumed to be uniform with a value of 0.25 mm and mass flow
rate of the droplets was set to 3.8 g/s, mass flow of total (water droplets and exhausts gas)
was set to 47.9 g/s. This point comes from 88 s of the WLTC cycle considered aver-age
value.
Figure 13. CFD Simulation of flow in harvester unit.

Int. J. Environ. Res. Public Health 2021, 18, 5392 10 of 12
The calculation of harvester efficiency was determined as follows. If the water drop-
lets touch the inside wall of the harvester, they are then considered “caught”. After calcu-
lation, the results of efficiency are at 95%.
4.3. Vehicle Experiment
After system simulation, a vehicle prototype was built to measure the actual effi-
ciency of the WAHASY system. To simulate similar conditions, 88 s point of the WLTC
cycle was simulated by driving at constant speed at 3rd gear and 3500 rpm to have iden-
tical inputs as during simulation. The results recorded in the graph (Figure 14) show that
the run achieved an efficiency 90%.
Figure 14. Vehicle test and vehicle test results.
5. Conclusions
The scope of the WAHASY project was to demonstrate the possibility of an autono-
mous, self-contained system, able to condensate and harvest sufficient amounts of water
to allow a “maintenance-free” and “user-independent” water injection strategy.
WAHASY, a water condensation & harvesting system, was developed and subse-
quently proven through engine and vehicle testing. It has been demonstrated that suffi-
cient water can be condensed and harvested. Analytical methods and simulation models
have been worked up and a vehicle has been modified with the on-board WAHASY
(FEV’s Audi TT-S WI Demonstrator Vehicle).
In the nearest future, additional tests allow extensive research of condensate. The
comparison of the required condensation efficiency with the actual efficiency of this “first
generation” WAHASY sample revealed the possibility to significantly reduce the size of
the system without restricting its potential. Simplifying and downsizing the overall de-
sign will sup-port applications with different engine and exhaust system packages and
lay-outs.
Tail pipe emissions have not been investigated during the initial study and will re-
quire further attention. As demonstrated in another study, WI has a positive impact of
NOx emissions but may create some increase of unburned HC [13]. This is especially a
problem during the first 30 to 50 s after cold start, before the three-way catalyst achieves
its light-off temperature. Another study [14] has indicated that a partial wash-out of un-
burned HC can be achieved through water condensation. As water is not injected during
cold start but WAHASY may be used, this could enable an emission advantage when us-
ing the unit.

Int. J. Environ. Res. Public Health 2021, 18, 5392 11 of 12
Also, anti-freezing techniques must be investigated to make the system reliable in all
weather conditions. Nevertheless, currently existing solutions for other fluids (e.g., as
urea injecting) may be re-used if necessary.
Finally, self-contained water harvesting enables the option of wide-spreading on wa-
ter injection as a future fuel consumption improvement technology without creating dif-
ficulties for final customers to accept. The possible positive global impacts of water injec-
tion applications on the environment and public health can also be documented by the
following facts. Figure 3 shows that a gasoline engine with water injection can save more
than 3% of fuel consumption. According to EUROPEAN VEHICLE MARKET STATIS-
TICS, Pocketbook 2020/21 [15], 16.6 million new passenger cars were registered in the Eu-
ropean Union in 2019, of which 60% with gasoline engines. If average emissions of 127 g
CO2/km are considered, the application of water injection could save 531,495 ton of CO2
emission per year for new cars.
Author Contributions: Conceptualization, J.B. and G.H.; methodology, J.B.; software, J.B.; valida-
tion, M.T., T.V. and P.D.; formal analysis, O.F. and J.N.; writing—original draft preparation, J.B.;
writing—review and editing, P.K.; supervision, G.H. All authors have read and agreed to the pub-
lished version of the manuscript.
Funding: The authors gratefully acknowledge funding from the Specific research on BUT FSI-S-20-
6267.
Institutional Review Board Statement: Not Appliable.
Informed Consent Statement: Not Appliable.
Data Availability Statement: Not Appliable.
Acknowledgments: The authors thank to Brno University of Technology for support and Open Ac-
cess Fund at BUT
Conflicts of Interest: The authors declare no conflicts of interest.
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