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International Journal of Research in Science And Technology http://www.ijrst.com
(IJRST) 2014, Vol. No. 4, Issue No. III, Jul-Sep ISSN: 2249-0604
71
INTERNATIONAL JOURNAL OF RESEARCH IN SCIENCE AND TECHNOLOGY
STUDY OF FUEL INJECTION PRESSURE AND
INJECTION TIMING EFFECT ON A DIESEL ENGINE
PERFORMANCE AND EMISSION
Srinath Pai
1
, Dr. Abdul Sharief
2
, Dr. Shiva Kumar
3
, Dr. Ramachandra C.G
4
& Dr. Sreeprakash B
5
1
Research scholar, Department of M.E, SSE, Mukka, Mangalore-575021, Karnataka, India
2
Professor and Principal, P.A.College of Engineering, Mangalore-574153, Karnataka, India
3
Associate Professor, Dept of M.E & Manufg, MIT, Manipal-576104, Karnataka, India
4
Professor and HOD of M.E, SIT, Valachil, Mangalore-574 143, Karnataka, India
5
Professor and Principal, SSE, Mukka, Mangalore-575 021, Karnataka, India
ABSTRACT
Diesel engine combustion quality is based on the formation of fuel-air mixture. Enormous efforts have
made to reduce the harmful diesel engine emissions. High engine noise, Particulate matter (PM) and NOx
production are the results of improper combustion process and considered as the major constraints. The
performance and emission characteristics of diesel engines depend on many parameters. Precise control
over the fuel injection process is one of the most important factors and plays a very important role in
combustion to increase the engine performance with minimal exhaust emission. The injection system must
satisfy high pressure capability, injection pressure control, flexible timing control, and injection rate
control. The purpose of this study is to find the performance and exhaust emission of diesel engines by
implementing the combination of various high injection pressures and variable injection timings. Present
paper is concentrated towords optimization of the best combination of high pressure injection with suitable
injection timing in a diesel engine fueled with pure diesel, to reduce the emission and fuel consumption
with increased engine power.
Keywords: Diesel Engine, Performance, Emission control, Injection pressure, Injection timing;
INTRODUCTION
In the last few decades of global scenario, internal combustion engines utilisation numbers in
automoblie tranportation and stationary sector, increased tremendously with an unavoidable
spectre of environmental deterioration. Combustion of fuels has led to widespread release of
pollutants such as CO, UBHC, NO
X
, PM and many other harmful compounds in the environment,
resulting in deterioration of air quality with health effects.
NOx is the main component in the formation of photochemical smog, while PM emissions
causes increased cardiovascular mortality rates, impaired lung development in children, and a host
of other health impacts. Result of this, emission control regulatory bodies have legislated
substantial reductions in PM and NOx emissions from diesel engines, which made great
difficulties for the diesel engine manufacturers to provide a quite efficient engine to satisfy the
consumers. PM, NOx production and engine noise are purely depends on the combustion process
[9]. Therefore precise control over the fuel injection, spray atomization and fuel-air mixing is
essential in making improvements to the combustion process. Injection pressure with right
injection timing will play an important role in combustion process, which influences the
performance, noise and exhaust emission of diesel engine. High injection pressure contributes
International Journal of Research in Science And Technology http://www.ijrst.com
(IJRST) 2014, Vol. No. 4, Issue No. III, Jul-Sep ISSN: 2249-0604
72
INTERNATIONAL JOURNAL OF RESEARCH IN SCIENCE AND TECHNOLOGY
reduced sized fuel droplet with very fine atomization and improved combustion, resulting in
reduction of smoke emission [3, 8]. Low injection pressure is required to reduce noise at idling
and in the very low load range. Proper injector opening pressure and injection timing a substantial
improvement in the performance and emissions can be obtained [4].
G.R. Kannan et al [1], varied the injection pressure and timing, and found that the combined
effect of higher injection pressure of 280 bar and an advanced injection timing of 25.5°BTDC had
substantial improvement in the brake thermal efficiency, cylinder gas pressure and heat release
rate with decrease in nitric oxide and smoke emission. Kiplimo et al. [2], found that reduced NO
emissions and increased UBHC, smoke and CO emissions were obtained when the injection
timing was advanced, meanwhile smoke, UBHC and CO were low with Higher injection pressure.
Murari Mohon Roy [3], found that shortest ignition delay and minimal emissions were lower at
high Injection pressures (60–80 MPa). K. M. Mrityunjayaswamy et al [4], found that, with the
proper injector opening pressure and injection timing (200 bar and 30°BTDC) a substantial
improvement in the performance and emissions can be obtained. N.Venkateswara Rao et al [5],
concluded that, injection timing advance and increase in injector opening pressure will reduce
exhaust emissions from an engine with biodiesel operation. Venkatraman et al [6], stated that, the
combined increase of compression ratio, injection timing and injection pressure increases the BTE
and reduces BSFC. Meyyappan Venkatesan [7], found through experiments that, CNG - JOME
can be used as fuel with better performance for higher pressure and advanced injection timing.
Srinath Pai et al [8,9], suggested that; an increase in injection pressure will improve the
combustion, which in turn improves the performance parameters and emission reduction they also
observed that, smoke opacity gets reduced with increase in injection pressure for all loads.
A. Effect of injection prresure on diesel engine performance
The engine performance, power output, fuel economy and emissions are greatly depends on
combustion processes. At the end of compression stroke, fuel is injected in to the combustion
chamber and atomize into very fine droplets. These droplets vaporize due to heat transfer from the
compressed air and also from an air-fuel mixture. Continued heat transfer from hot air to the fuel
yields the temperature to reach a value higher than its self- ignition temperature and makes the
fuel to ignite spontaneously. By atomizing the fuel into very fine droplets, it increases the surface
area of the fuel droplets resulting in better mixing and subsequent combustion. Atomization is
done by forcing the fuel through a small orifice under high pressure. For low fuel injection
pressure, fuel particle diameters and ignition delay period during the combustion will increase,
results in increased pressure and the decrease in engine performance.
Increase in the injection pressure leads to reduce the fuel particle diameter, the mixing of fuel
and air becomes better during ignition period. The fuel injection pressure in a standard diesel
engine is in the range of 200 to 1700 atm depending on the engine size and type of combustion
system employed [10]. The fuel penetration distance become longer and the mixture formation of
the fuel and air was improved when the combustion duration became shorter as the injection
pressure became higher. The effects of high injection pressure benefits are;
Improved fuel atomization producing finer fuel droplets.
The smaller fuel droplets evaporate at a faster rate resulting in rapid fuel-air mixing.
Shorter injection duration.
With shorter injection duration injection timing may be retarded.
International Journal of Research in Science And Technology http://www.ijrst.com
(IJRST) 2014, Vol. No. 4, Issue No. III, Jul-Sep ISSN: 2249-0604
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Fuel may be injected closer to TDC in hotter air giving shorter ignition delay, resulting in
emission control.
Higher spray penetration and better air utilization.
The high injection pressure effect on PM-NOx trade off is shown on Figure1. The width of
band on the shown Figure1 relates to the contribution of the particulate emissions. As the injection
pressure increases the PM-NOx trade-off curve moves closer to origin indicating reduction both in
the PM and NOx.
Figure 1. Effect of high injection pressure on PM-NOx trad-off for a DI diesel engine.
B. Diesel Timing importance
According to literature review rightist timing results in lowering emissions of nitrogen oxides
(NOx) [2,3]. Lower timing is best for NOx levels, increase in carbon monoxide; hydrocarbon
levels and brake specific fuel consumption. In addition to this lowered timing decreases cylinder
pressure and reduces peak flame temperature (since the fuel is injected once the piston has past
TDC and is already on its way back down the cylinder in the power stroke).
Literatures also suggest that advancing the timing results in increased cylinder pressures and
higher peak flame temperatures which leads to a more complete burn of the fuel injected and the
effect on emissions is significant [1, 4 - 7]. In the mean while, the NOx level increases drastically
past just a few degrees of advance, while hydrocarbons increase and carbon monoxide decreases.
Brake specific fuel consumption drops off quickly as.well.
International Journal of Research in Science And Technology http://www.ijrst.com
(IJRST) 2014, Vol. No. 4, Issue No. III, Jul-Sep ISSN: 2249-0604
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INTERNATIONAL JOURNAL OF RESEARCH IN SCIENCE AND TECHNOLOGY
.
Figure 2. Effect of injection timing on emissions.
It is clear from Figure 2, that results were favoring the proper ignition timing should be
managed to obtain the fuel economy with minimum emissions.
EXPERIMENTAL SET UP AND TEST PROCEDURE
Experiments were carried on a Kirloskar make TV1 model single cylinder, four stroke, water
cooled 7 hp (5.2 kW) capacity diesel engine coupled to an eddy current dynamometer for loading
purpose. The engine is provided with temperature sensors for the measurement of jacket water,
calorimeter water, and calorimeter exhaust gas inlet and outlet temperature and also provided with
pressure sensors for the measurement of combustion gas pressure and fuel injection pressure. An
encoder is fixed and used for crank angle record.
The engine specifications are given below. To measure the air flow rate, an orifice tank is
used. The pressure difference between the inside of the cylinder during suction and atmosphere is
measured by a manometer fitted to the tank. By noting the difference in water level in the two
limbs of manometer the air flow rate can be calculated. The rate of fuel consumption is measured
by recording the time taken for consumption of 10 cc of fuel using a graduated burette.The engine
is directly coupled to an eddy current dynamometer. The dynamometer has the capacity to absorb
the maximum power that can be produced by the engine at all normal speeds. The brake power
produced by the engine is measured by the dynamometer. The engine specification is shown in
Table-1.
Table I. Engine Specificaton.
Engine Type
Kirloskar Make (TV1Model)
Number of cylinders
1
Number of strokes
4
Rated power
5.2KW (7 HP) @1500RPM
Cylinder diameter
87.5mm
International Journal of Research in Science And Technology http://www.ijrst.com
(IJRST) 2014, Vol. No. 4, Issue No. III, Jul-Sep ISSN: 2249-0604
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INTERNATIONAL JOURNAL OF RESEARCH IN SCIENCE AND TECHNOLOGY
Stroke length
110mm
Compression ratio
17.5:1
Cubic Capacity
661cc
Dynamometer
Eddy current type
Load Measurement
Strain gauge load cell
Speed Measurement
Rotary encoder
Temperature Indicator
Digital, PT-100 type temperature
sensor
Fuel Injection Pressure
Measurement
Piezo Sensor, range 5000 Psi
Table II. Nomenclature.
BTDC: Before top dead center
BTE: Brake thermal efficiency, (%)
BSFC : Brake specific fuel consumption, (g/kWh)
PM : Particulate matter
CO: Carbon monoxide
CO
2
: Carbon dioxide
NOx : Nitrogen oxides
The experiment is carried out on a single cylinder, four stroke diesel engine with pure diesel.
The experiment is carried out for the combination of injection pressures (180 bar, 190 bar, 200
bar, 210 bar and 220 bar), and injection timings (15.5°, 20.5°, 23° and 25.5°BTDC) at
compression ratio 17.5:1, with a constant speed of 1500 rpm for 0% to 100% load.
Initially the injection timing of the engine was set to 23° BTDC (as set by the manufacturer).
For this injection timing, the injection pressure was varied from 180 bar to 220 bar in steps of 10
bar and performance, emissions and combustion characteristics were recorded from 0% to 100%
load in steps of 25% with a constant speed of 1500 rpm. The experiment was repeated for different
injection timings of 15.5°, 20.5°and 25.5°BTDC. Cooling of the engine was carried out by
circulating water through the jackets of the engine block and the cylinder head. The injection
pressure was varied by changing the spring tension of the injector and the timing was varied by
varying the shim thickness at the connection point between the pump and the engine. Reducing the
shim thickness by 0.3 mm advances the injection timing by 2.5° crank angle. The results obtained
were compared.
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Figure 3. View of test rig.
RESULTS AND DISCUSSIONS
The results obtained from the experiments are represented in form of charts and are discussed
as follows
A. Performance Parameters
Figure 4. Brake thermal efficiency Vs Injection timing for various injection pressures.
The comparison of brake thermal efficiencies for different injection pressures and timings are
shown in Figure 4. For all the injection pressures and timings used the brake thermal efficiency
increases with increasing load. Maximum brake thermal efficiency of 36.5% was observed at an
injection pressure of 220 bar and an injection timing of 25.5° BTDC at 100% load condition. The
increase in brake thermal efficiency is due to proper combustion as a result of better atomization
owing to the increase in the injection pressure. When injection pressure is increased, the fuel
particle diameters will become small and also proper injection timing leads to improved and better
mixing of fuel to air during ignition period, hence engine performance will increase. It is observed
from Figure 4 that, for the combination of increasing injection pressure with improved injection
International Journal of Research in Science And Technology http://www.ijrst.com
(IJRST) 2014, Vol. No. 4, Issue No. III, Jul-Sep ISSN: 2249-0604
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INTERNATIONAL JOURNAL OF RESEARCH IN SCIENCE AND TECHNOLOGY
timings, the brake thermal efficiency starts increasing. It leads to improvement in engine
performance.
Figure 5. Total fuel consumption Vs Injection timing for various injection pressures.
It is noticed that the brake thermal efficiency was improved with injection pressure along with
injection timing. It was found to be the best at injection pressure 220 bar and 25.5° BTDC due to
better combustion. The fuel injection pressure and Injection timing affects the Total Fuel
Consumption performance of an engine as shown in Figure 5. The variation of Total fuel
consumption for diesel at different injection pressures and timings is observed in Figure 5. The
Total Fuel Consumption decreases with increasing load, irrespective of injection pressure and
increasing timing. The lowest Total Fuel Consumption of 0.18 kg/hr was noted for an injection
pressure of 180 bar and injection timing of 25.5° BTDC at 100% load condition. The reduction in
Total Fuel Consumption was due to the increase in injection pressure which leads to proper
mixing of fuel and air. Impact of fuel injection pressure shows that the highest Total Fuel
Consumption took place at 220 bar at injection timing 15.5° BTDC, and injection pressure and the
least Total Fuel Consumption at 180 bar at injection timing 25.5° BTDC.
C. Emission parameters
Figure 6, shows the variation of NOx emissions with different injection pressures and injection
timings for full load conditions. NOx emissions were lower for 180 bar injection pressure at
injection timing 15.5º BTDC in comparison with all injection pressures and injection timings. It is
also noted that, as the injection pressure increases with proper timing, NOx increases for all loads
till 200 bar, since the formation of NOx is very sensitive to temperature, which is responsible for
thermal NOx formation.
NOx concentration increases monotonically with increase in engine load except for the lowest
load. In case of engines, with less injection pressure, more fuel is injected at high engine loads,
leading to improper atomization and penetration, which results in higher temperature of the
burning gas. NOx concentration is drastically increased after 200 bar and recorded to be highest at
220 bar at injection timing 23.5º BTDC due higher injection pressure leading to higher
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combustion temperature. When pressure is more and injection time is retarded NOx is found to be
low. This may be due to retarded injection timing might reduced and compensated the high
combustion temperature, which would be obtained due to high pressurized fuel injection into the
engine cylinder. Result obtained may be smaller fuel particles, better penetration and atomization
hence best combustion would have been obtained and reduced the NOx formation.
Figure 6. NOx Vs Injection timing for various injection pressures.
Figure 7. Smoke Opacity Vs Injection timing for various injection pressures.
From Figure 7 it is observed that, smoke opacity gets reduced with increase in injection
pressure and retarded injection timing for all loads. In general, retarding injection timing reduces
NOx emissions from the diesel engine because it decreases the combustion temperature as well as
the residence time of the high-temperature-burned gas inside the cylinder. On the other hand,
advanced injection timing, an earlier crank angle achieves high pressure and, hence, higher
combustion temperature results in high NOx emissions. It is also clear that, at the lower injection
pressure results in higher smoke emissions than high injection pressure. At lower injection
pressure, the atomization process will be poor. This resulted in bigger droplets and hence bigger
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kernel. Therefore, at lower injection pressure, higher smoke emissions were formed due to bigger
droplet. However, at a higher injection pressure of 220 bar, it was observed that lower smoke
emissions were formed due to small size fuel droplets, better air-fuel mixing and complete
combustion. Injection pressure 220 bar provided 57% reduction of smoke opacity when compared
with the standard engine fueled with 180 bars. This is probably because of the smaller drop size of
the injected fuel and proper timing results in better atomization of fuel and sprays propagation
leading to improved and complete combustion.
CONCLUSIONS
It is clear from the experimental investigations results that, for a diesel fueled engine, an
increase in the injection pressure with proper injection timing will significantly increases the
engine performance with drastic reduction in emission. Higher injection pressures and appropriate
injection timing also shows a cut down in specific fuel consumption with the smooth engine
operation. It is strongly recommended to study the impact of ultra high injection pressure with
proper injection timing for improvening the performance and emissions of a diesel engine fueled
with biodiesel blends, with a hope to obtain better results for higher percentage blends, so as to
help the socity by reducing the harmful emissions and depleting diesel problem.
Finally, it is concluded that the information obtained from this investigation is useful in the
analysis of injection pressure impact in increasing the performance of diesel engines along with
their emission control to meet current and future government regulations.
REFERENCES
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(IJRST) 2014, Vol. No. 4, Issue No. III, Jul-Sep ISSN: 2249-0604
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INTERNATIONAL JOURNAL OF RESEARCH IN SCIENCE AND TECHNOLOGY
[8] Srinath Pai, Abdul Sharief, Shiva Kumar and Shree Prakash B., “ A Study on Increased Fuel
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