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THE STUDY OF EGR EFFECT ON DIESEL
ENGINE PERFORMANCE
AND EMISSION - A REVIEW
Srinath Pai1, Amriya Tasneem H.R.2, Shivaraju N3 & Dr. Sreeprakash B4
1, 2, 3 Department of Mechanical Engineering, Srinivas School of Engineering, Mukka, Mangalore-575021, Karnataka, India
4 Professor and Principal, Srinivas School of Engineering, Mukka, Mangalore-575 021, Karnataka, India
E-mail: srinath_pai@rediffmail.com
Abstract—Diesel engines provide high fuel efficiency hence
widely used on heavy duty transport applications. Diesel engines
even have reduction in CO2 emission, which is believed to be the
main cause for global warming. The main disadvantage of diesel
engine is it emits nitrogen oxides (NOX) and particulate matter
(PM), which are considered as the main toxic gases. These
emissions are therefore limited by the environment regulating
authorities in almost all the countries. A best way to reduce the
nitrogen oxide emissions of a diesel engine is the use of exhaust
gas recirculation (EGR). EGR is a device which recirculates a
portion of an engine's exhaust gas back into the combustion
chamber. NOx is produced when a mixture of nitrogen and
oxygen is subjected to high temperature in the combustion
chamber. This can be reduced by using EGR which helps in
maintaining the lower combustion chamber temperatures and
reduces peak combustion temperature, which in turn reduces the
formation of NOX. The aim of the present paper intends the study
on performance and emission rates of a diesel engine equipped
with EGR system and to find the EGR system importance in the
reduction of NOx as well as particulate matter (PM) emissions
with improvements in engine performance.
Keywords— Diesel Engine, Emission control, EGR, NOx,
particulate matter;
I. INTRODUCTION
Diesel engine vehicles have increased their popularity due to
its higher compression ratio, better fuel economy, higher
power with lower maintenance cost and their robustness.
These advantages have even increased the sales of diesel
engines in the global market. Diesel engines are used for bulk
movement of goods, powering stationary and mobile
equipment, and also to generate electricity more economically
than any other device in this size range. Diesel engines are
good alternative to gasoline engines because they produce
lower amount of emissions. The major constituents of diesel
exhaust includes carbon dioxide(CO2), water vapor(H2O),
nitrogen(N2), oxygen(O2), carbon monoxide(CO),
hydrocarbons(HC), oxides of nitrogen (NOx) and particulate
matter(PM). Although, NOx and PM amount present in
exhaust is smaller but they are considered as more toxic
pollutants and environmentally significant quantities. This
drawback has motivated manufacturers to take a challenge for
upgrading the technology and improving the diesel engines in
terms of emissions, power and fuel economy.
NOx is comprised of nitric oxide (NO) and nitrogen dioxide
(NO2) where both are considered to be dangerous for human
as well as environmental health. NO2 is more toxic than NO, it
affects human health directly, mainly results in photochemical
smog formation, causes acid rain and is also responsible for
some extent in the depletion of ozone layer. Even though the
ratios of NO2 and NO in diesel engine exhaust is quite small,
but NO gets oxidized quickly by reacting with oxygen present
in air forming NO2. While PM emissions causes increased
cardiovascular mortality rates, impaired lung development in
children, and a host for other health impacts.
Result of this, emission control regulatory bodies have
legislated substantial reductions in PM and NOx emissions
from diesel engines as shown in figure 1, which made great
difficulties for the diesel engine manufacturers to provide a
quite efficient engine with less emissions to satisfy the
consumers.
Figure 1. Soot and NOX emission limits by emission control regulations
In order to reduce emission levels, engine manufacturers and
various researchers have studied a number of strategies for
reducing exhaust emissions including EGR, high pressure
injection, electronically controlled injection, multiple fuel
injections, redesigning the combustion chamber and sulfur
sensitive exhaust gas after treatment etc., may be used to
reduce the exhaust emissions.
An effective means of reducing NOx emissions in diesel
engines is EGR or after treatment system. In EGR, a part of
the exhaust gas is rerouted into the combustion chamber as
2
shown in figure 2, where it helps to attenuate the formation of
NOX by reducing the local reaction temperature.
The use of EGR is suggested as a method of improving the
engine performance and reducing the emissions of diesel
engines. By increasing the intake charge temperature, EGR
could promote better combustion. Some of the unburned fuel
can be reburned with this method. The use of EGR is a
promising method for improving part load operation and
reducing the exhaust NOx emissions. However, when EGR is
used it will change the rate of combustion or the rate of
pressure rise inside the combustion chamber. There is trade-
off between NOx emission hence as the EGR rate increases,
the level of NOx go down.
Figure 2. Circuit of EGR system
The purpose of the EGR system is to precisely regulate EGR
flow under different operating conditions, and to override flow
under conditions which would compromise good engine
performance. It was found from figure 3 that adding EGR to
the air flow rate to the Diesel engine, rather than displacing
some of the inlet air, appears to be a more beneficial way of
utilizing EGR in Diesel engines. About 15% recycle will
reduce NOx emission by about 80%.
Figure 3. Effect of EGR on NOx emission.
II. REVIEWS
Number of research papers and studies has been conducted
on the utility of EGR effect on diesel engine performance and
emission. Number of reviews has been taken into
consideration below to complete the present study.
Gurumoorthy S. Hebbar and Anant Krishna Bhat [1], in their
study on “Investigations on Performance and Emissions of a
Stationary DI Diesel Engine with Different Exhaust Gas
Recirculation Temperatures” they have addressed about the
application of EGR for reduced NOx emissions from naturally
aspirated direct injection stationary diesel engine. EGR is an
attractive method to reduce combustion temperature. EGR
temperature is an important factor while admitting higher
percentage of EGR. As High temperature EGR, obtained due
to increase in loads, limits the conduct of higher EGR ratios.
Cooling of EGR can be done when higher ratios of EGR need
to be admitted. The effect EGR temperature on NOx
reductions and thermal efficiency were found to be better for
hot EGR up to about 30% EGR and thereafter EGR cooling
shows better results.
MUKESH Rameshbhai Zala [2], in his study on
“Optimization of EGR Rate on multi cylinders 4 stroke diesel
engine” they conducted an experimental study on a naturally
aspirated 4 cylinders, 4 stroke diesel engine with modification
to run with EGR. Engine performance and emission was tested
at varying EGR Rate (0- 40%) and optimum EGR Rate for the
naturally aspirated engine is found out by taking the
performance and emission readings at varying load conditions
(0-120%) and at 1500 RPM. Brake power was measured with
electric dynamometer. The evaluation of experimental data
showed that NOx emission was reduced by about 80% because
of EGR.
AVINASH KUMAR AGRAWAL, SHRAWAN KUMAR
SHAILENDRA SINHA and MRITUNJAY KUMAR
SHUKLA [3], in their study on “Effect of EGR on the exhaust
gas temperature and exhaust opacity in compression ignition
engines” they conducted an experimental study on a INDEC
Engines Ltd make two cylinder, direct injection, rated
capacity 9.3 kW at speed 1500 rpm, air-cooled diesel engine.
The objective is to investigate and demonstrate the effects of
various EGR rates on exhaust emissions from the engine. A
long route partially cooled EGR system was choosen.
Experiments were carried out by using a setup to prove the
efficiency of EGR as a technique for NOx reduction. It is seen
that the exhaust gas temperatures are reduce drastically by
employing EGR.
Hussain. J, Palaniradja. K, Alagumurthi.N, Mani-maran.R
[4], in their study on “Effect of Exhaust Gas Recirculation
(EGR) on Performance and Emission of a Compression
Ignition Engine with Staged Combustion (Insertion of
Unburned Hydrocarbon)” they conducted an experimental
study on a two cylinder 4 Stroke, 52 HP, 1500 rpm constant
speed diesel engine generator set to study the effect of EGR on
the performance and emissions of diesel engine components.
The results were shown that UHC can be reduced by 20 to
25% from this method.
3
V.Manieniyan and S.Sivaprakasam [5], in their study on
“Experimental Analysis of Exhaust Gas Recirculation on DI
Diesel Engine Operating with Biodiesel” they used EGR
technique in the diesel engine with B20 biodiesel as fuel.
Madhua oil is used to prepare the biodiesel for investigation of
a four stroke, water cooled, single cylinder, direct-injection
(DI), vertical diesel engine running at a rated power of 5.2 kW
and at a rated speed of 1500 rpm coupled to an Eddy current
dynamometer with EGR and without EGR at various level
(5%, 10%, 15%, and 20%). The result shows that NOx
emission is reduced using EGR for diesel and bio diesel.
Donepudi Jagadish, Dr.Puli Ravi Kumar, Dr.K.Madhu
Murthy [6], in their study on “Performance characteristics of a
diesel engine operated on biodiesel with exhaust gas
recirculation” conducted an experimental study on a Kirloskar
Oil Engines with naturally aspirated single cylinder 3.7 kW at
1500 rpm, water cooled diesel engine with D.C shunt
dynamometer is selected for experimentation. Modifications
are made for the original engine set up to work with option
EGR. They found that effect of EGR is to increase the fuel
consumption of the engine; EGR is the best method to reduce
the NOx emission.
III. RESULTS AND DISCUSSION
Diesel exhaust contains nitrogen oxides (NOX) and
particulate matter (PM), which are considered as main toxic
gases. One of the techniques of reducing the oxides of
nitrogen in the exhaust from the engine is to use EGR
technique. A brief review on the effect of EGR on engine
performances and exhaust emission characteristics of
compression ignition engines based on the reports of different
researchers, literatures results have taken below for discussion.
Gurumoorthy S. Hebbar and Anant Krishna Bhat [1], in their
study on “Investigations on Performance and Emissions of a
Stationary DI Diesel Engine with Different Exhaust Gas
Recirculation Temperatures” conducted an experimental study
on a Kirloskar AV1, 4 Stroke, Single Cylinder Diesel Engine
with rated power 3.7KW at 1500 RPM with data acquisition
systems (DAS) for recording engine performance parameters.
Modifications were made to cool the exhaust gas being
recirculated by using two heat exchangers. An orifice meter
was used to determine the flow rate of recirculated exhaust
gas. Percentage of exhaust gas was taken as ratio of amount of
exhaust gas recirculated to total engine exhaust gas. AVL
smoke meter was used to measure the smoke level and INDUS
gas analyzer for O2, CO, CO2, HC and NOx measurements.
Figure 4. Effect of EGR temperature on NOx, HC and smoke emission.
EGR is cooled using two heat exchangers to reduce the
temperature of EGR gas before it was mixed with fresh air. It
was possible to attain the EGR temperatures of 37, 46, 56 and
75 degree centigrade. At these temperatures values recorded
for NOx, UBHC and smoke are plotted in figure 4. At 40%
EGR, it is clear from the graph that smoke percentage tends to
decrease with increased EGR temperature. Reduced oxygen
availability and presence of exhaust gas constituents during
combustion modifies the normal combustion. Combustion
tends to be incomplete and further deteriorates as the
percentage of EGR increases. Percentage of oxygen reduces as
the inlet EGR temperature increases tending the combustion to
be incomplete emitting more HC in the exhaust. EGR reduces
the engine out NOx emission and it is clear from the plot that
NOx is temperature sensitive.
From figure 5, it is clear that, the thermal efficiency
decreases as EGR percentage increase for all cases of EGR
cooling. It is clearly observed that cooling of EGR slightly
improves the efficiency after 30% EGR. Engine torque and
brake power slightly reduces as the percentage of EGR
increases for all cases of EGR cooling. For hot EGR this is
more pronounced as more compression work is required to
compress expanding hot gas. Fuel consumption also increases
to govern the constant engine speed.
Figure 5. Effect of EGR on Thermal Efficiency for 3 Cases of EGR Cooling.
4
The lower torque and increased fuel consumption tends to
reduce the thermal efficiency. Increased temperature of EGR
reduces availability of oxygen due to increased thermal
throttling. The lack of oxygen effects mixing time and normal
combustion as well.
MUKESH Rameshbhai Zala [2], in his study on
“Optimization of EGR Rate on multi cylinders 4 stroke diesel
engine” conducted an experimental study on a naturally
aspirated 4 cylinders 4 stroke diesel engine, modified to run
with EGR.
Figure 6 shows, Engine Performance graph for variation of
fuel consumption with respect to brake power, without and
with different EGR Rates for the same engine.
For all the tested cases, fuel consumption is found to be
increased with increase in the brake power. It is clear that as
the load increases, fuel consumption increases to the
maximum at full load (15 kw) for all the trails without and
with different EGR rates. A slight increase in fuel
consumption is found due to the introduction of EGR which
reduces the availability of fresh charge. At 10% EGR rate,
average fuel consumption increases only about 1.5%. At 20%
EGR rate, average fuel consumption increases upto 4%. At
30% EGR rate, average fuel consumption is increased about
6% and at 40% EGR Rate average fuel consumption increases
to 11% than that of without EGR.
Figure 6. Effect of EGR on Brake power vs. Fuel consumption.
Figure 7 is an Engine Emission graph for variations in NOx
emission with respect to brake power, without and with
different EGR Rates for given engine. It shows that the NOx
emission has the tendency to increase with increase in brake
power for all the trials. NOx formation is a strong function of
temperature. Higher the temperature, higher is the NOx
formation. The presence of high gas temperature inside
cylinder will create a conductive ambient for reaction of
atmospheric nitrogen with oxygen. This is the major reason for
higher NOx emission at higher load range.
Figure 7. Effect of EGR on NOx emissions in DI diesel engine.
However, NOx emission reduces drastically with the
introduction of EGR. At 10% EGR rate, NOx reduction is 19-
22% depending on engine loads and the average NOx
reduction is about 20%. At 20% EGR rate, NOx reduction is
about 39-42% and average NOx reduction is about 40%. At
30% EGR rate, NOx reduction is about 58-66% and average
NOx reduction is about 62%. At 40% EGR rate, NOx
reduction is about 76-82% and average NOx reduction is
about 79%. Hence, at rated power i.e. 15 kw where NOx
emission is maximum, 40% EGR Rate would be required to
bring NOx emission within acceptable limit.
AVINASH KUMAR AGRAWAL, SHRAWAN KUMAR
SHAILENDRA SINHA and MRITUNJAY KUMAR
SHUKLA [3], in their study on “Effect of EGR on the exhaust
gas temperature and exhaust opacity in compression ignition
engines” conducted an experimental study on an INDEC
Engines Ltd make two cylinders, direct injection, rated
capacity 9.3 kW at speed 1500 rpm, and air-cooled diesel
engine.
Figure 8. BSFC vs load at constant EGR.
It is clear from figure 8 that the brake specify fuel
consumption (BSFC) is fairly independent of EGR. As load
increases, BSFC decreases rapidly.
Experimental results indicate a decrease in the exhaust
temperatures with increasing EGR, therefore it can be safely
concluded that the combustion chamber temperatures also
5
decrease and thus the formation of NOx is decreased. Opacity
of the exhaust gas increases as the rate of EGR is increased.
Figure 9. Smoke opacity in exhaust gas vs load at constant EGR.
At low loads, the rate of increase in opacity is almost the
same with increase in EGR but at higher loads and higher rates
of EGR, opacity increases rapidly, as shown in figure 9.
Experiments were carried out using the setup to prove the
efficiency of EGR as a technique for NOx reduction. It is seen
that the exhaust gas temperature reduce drastically by
employing EGR, hence NOx.
Hussain.J, Palaniradja.K, Alagumurthi.N, Mani-maran.R [4],
in their study on “Effect of Exhaust Gas Recirculation (EGR)
on Performance and Emission of a Compression Ignition
Engine with Staged Combustion (Insertion of engine generator
set was chosen to study Unburned Hydrocarbon)” 4 stroke
Diesel engine was run on different loads at 1500 rpm with
different EGR rates (from 0% to 25%) to investigate the effect
of EGR on engine performance and emissions. The
performance and emission data was analyzed and presented
graphically.
Figure 10. Brake Specific Fuel Consumption for different EGR Rates.
Figure 10 represents comparison of BSFC for all datasets
using EGR with baseline data. BSFC is lower at lower loads
for engine operated with EGR compared to without EGR.
However, at higher engine loads, BSFC with EGR is almost
similar to that of without EGR. At higher loads, amount of
fuel supplied to the cylinder is increased at higher rate and
oxygen available for combustion gets reduced. Thus, air fuel
ratio is changed and this increases the BSFC.
Figure 11. NOx for different EGR Rates.
Figure 11 shows the main benefit of EGR in reducing NOx
emissions from diesel engine. The degree of reduction in NOx
at higher loads is higher. The reasons for reduction in NOx
emissions using EGR in diesel engines are reduced oxygen
concentration and decreased flame temperatures in the
combustible mixture. At the part load, O2 is available in
sufficient quantity but at high loads, O2 reduces drastically,
therefore NOx is reduced more at higher loads compared to
part loads.
V.Manieniyan and S.Sivaprakasam [5], in their study on
“Experimental Analysis of Exhaust Gas Recirculation on DI
Diesel Engine Operating with Biodiesel” conducted
investigation on a four stroke, water cooled, single cylinder,
direct-injection (DI), vertical diesel engine running at a rated
power of 5.2 kW and at a rated speed of 1500 rpm coupled to
an Eddy current Dynamometer with EGR and without EGR at
various levels (5%, 10%, 15%, and 20%). The result shows
that NOx emission is reduced using EGR for diesel and bio
diesel.
Figure 12. Specific Fuel Consumption (Diesel) Vs Brake power.
For diesel, the variation of specific fuel consumption with
brake power was shown in figure 12. Specific fuel
consumption without EGR, under full load was found to be
0.2779 kg/kW-hr for diesel. Full load values of diesel with
5%, 10%, 15%, and 20% EGR were 0.2853, 0.2796, 0.2832
6
and 0.3050 kg/kW-hr respectively. For higher level of EGR
20%, specific fuel consumption increased for diesel.
Figure 13. Oxides of Nitrogen (Diesel) Vs Brake power
Figures 13 indicate the variation of nitrogen oxide with brake
power. NOx value was found to be 736 ppm for diesel without
EGR at full load condition. This was due to higher peak
combustion temperature inside the cylinder. With increase in
EGR level, the NOx value gets reduced. With 20% EGR, NOx
levels were 157 ppm for diesel. With increase in EGR level
NOx level was reduced. Also reduction in brake thermal
efficiency and large increase in smoke density were observed.
Donepudi Jagadish, Dr.Puli Ravi Kumar, Dr.K.Madhu
Murthy [6], in their study on “Performance characteristics of a
diesel engine operated on biodiesel with exhaust gas
recirculation” conducted an experimental study on a Kirloskar
Oil Engines make naturally aspirated single cylinder 3.7 kW at
1500 rpm, water cooled diesel engine with D.C shunt
dynamometer is selected for experimentation. Engine
modifications were made to the original engine set up to work
with option EGR.
Figure 14. BSFC with different EGR rates at Full load
BSFC variation with EGR rate at full load is shown in figure
14. With the rise in EGR rate there is a rise in specific fuel
consumption, this is severe for higher EGR rates i.e. more than
20%. The engine was made to run with EGR at the cost of
little fuel loss.
Figure 15. Variation of NO emissions with EGR rate
The quantities of NO are considerably reduced with EGR
rate. EGR rate the observed reduction of NOx emissions from
figure 15.
Comparison of literatures results proved that an increase in
the engine performance, power and satisfy emissions
regulations can be achieved by adopting the EGR to the diesel
engines. IV. CONCLUSION
It is clear from the experimental investigations that the
engine can be run without any abnormality when modified to
implement EGR in it. This is due to the fact that EGR admits
the inert gases in the chamber which have specific heat higher
than that of air so they absorb the heat of combustion and also
dilute the fresh air which increases the ignition delay and
hence reduce the heat of combustion which ultimately result in
lower exhaust gas temperature and lower NOx emission.
Exhaust gas recirculation (EGR) has been found a very
effective way to reduce NOx emission from the diesel engine.
EGR is still the most viable technique that can drastically
reduce NOx to meet the emission regulations.
ACKNOWLEDGMENT
WE ARE THANKFUL TO THE MANAGEMENT, SRINIVAS SCHOOL
OF ENGINEERING, MANGALORE, FOR THEIR SUPPORT AND
ENCOURAGEMENT.
REFERENCES
[1] Gurumoorthy S. Hebbar and Anant Krishna Bhat “
Investigations on Performance and Emissions of a
Stationary DI Diesel Engine with Different Exhaust Gas
Recirculation Temperatures” International Journal of
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1, pp. 1 – 9, 2013.
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on multi cylinders 4-stroke diesel engine‟ International
Journal of Engineering Research & Technology (IJERT)
Vol. 1 Issue 4, June - 2012 ISSN: 2278-0181.
7
[3] AVINASH KUMAR AGRAWAL, SHRAWAN KUMAR
SHAILENDRA SINHA and MRITUNJAY KUMAR
SHUKLA “Effect of EGR on the exhaust gas temperature
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http://www.ias.ac.in/sadhana/Pdf2004Jun/Pe1131.pdf
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