THE STUDY OF EGR EFFECT ON DIESEL ENGINE PERFORMANCE AND EMISSION - A REVIEW Srinath Pai 1, Amriya Tasneem H.R. 2, Shivaraju N 3 & Dr. Sreeprakash B 4 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 CO 2 emission, which is believed to be the main cause for global warming. The main disadvantage of diesel engine is it emits nitrogen oxides (NO X ) 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 NO X. 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. NOx is comprised of nitric oxide (NO) and nitrogen dioxide (NO 2 ) where both are considered to be dangerous for human as well as environmental health. NO 2 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 NO 2 and NO in diesel engine exhaust is quite small, but NO gets oxidized quickly by reacting with oxygen present in air forming NO 2. 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 NO x 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. 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(co 2 ), water vapor(h 2 O), nitrogen(n 2 ), oxygen(o 2 ), 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. 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 1
shown in figure 2, where it helps to attenuate the formation of NO X 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 tradeoff 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. 2
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 (NO X ) 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. 3
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 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 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 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 4
decrease and thus the formation of NOx is decreased. Opacity of the exhaust gas increases as the rate of EGR is increased. 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 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 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, O 2 is available in sufficient quantity but at high loads, O 2 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 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 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 5
and 0.3050 kg/kw-hr respectively. For higher level of EGR 20%, specific fuel consumption increased for diesel. Figure 15. Variation of NO emissions with EGR rate 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. 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 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. [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 Automotive Engineering and Technologies, Vol. 2, Issue 1, pp. 1 9, 2013. [2] MUKESH Rameshbhai Zala, Optimization of EGR Rate on multi cylinders 4-stroke diesel engine International Journal of Engineering Research & Technology (IJERT) Vol. 1 Issue 4, June - 2012 ISSN: 2278-0181. 6
[3] AVINASH KUMAR AGRAWAL, SHRAWAN KUMAR SHAILENDRA SINHA and MRITUNJAY KUMAR SHUKLA Effect of EGR on the exhaust gas temperature and exhaust opacity in compression ignition engines Sadhana Vol. 29, Part 3, June 2004, pp. 275 284. http://www.ias.ac.in/sadhana/pdf2004jun/pe1131.pdf [4] Hussain. J, Palaniradja. K, Alagumurthi.N, Manimaran.R, Effect of Exhaust Gas Recirculation (EGR) on Performance and Emission of a Compression Ignition Engine with Staged Combustion (Insertion of Unburned Hydrocarbon) International Journal of Energy Engineering 2012, 2(6): 285-292 DOI: 10.5923 / j.ijee.20120206.03. [5] V.Manieniyan and S.Sivaprakasam, Experimental Analysis of Exhaust Gas Recirculation on DI Diesel Engine Operating with Biodiesel International Journal of Engineering and Technology (IJET) Volume 3 No. 2, February, 2013. [6] 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 International Journal of Advanced Engineering Technology. IJAET/Vol.II/ Issue II/April- June, 2011/202-208, E-ISSN 0976-3945. 7