International Journal of Automobile Engineering Research & Development (IJAuERD) ISSN 2277-4785 Vol. 3, Issue 1, Mar 2013, 35-46 TJPRC Pvt. Ltd. AN EXPERIMENTAL INVESTIGATION OF EFFECT OF COOLED EXHAUST GAS RE-CIRCULATION (EGR) FOR NOX REDUCTION IN SINGLE CYLINDER CI ENGINE USING BIODIESEL BLENDS APARNA V. KULKARNI 1, SACHIN L. BORSE 2 & MAHESH P.JOSHI 3 1 Lecturer, Sidhhant College of Engineering, Pune, India 2 Professor, Rajarshi Shahu College of Engineering, Pune, India 3 I/C HOD, Marathwada Mitra Mandal s Polytechnic, Pune, India ABSTRACT The world is confronted with the twin crises of fossil fuel depletion and environmental degradation. Thus biomass derived fuels are preferred as alternative fuels for IC engines due to its abundant availability, environmental friendly and renewable nature. Many research studies have reported that exhaust from biodiesel fuel has higher NOx emission than operated with diesel fuel. The aim of the present investigation is to reduce NOx emission by using an effective after gas treatment technique like cooled Exhaust Gas Recirculation (EGR) as it enables lower flame temperature and oxygen concentration in combustion chamber. In the present work, experiments are conducted on 5.2 KW(7 HP) single cylinder, four stroke, water cooled, direct injection, naturally aspirated diesel engine fitted with short loop, cooled EGR system. Diesel, biodiesel and their blends were used as fuel for conducting experiments. Based on this study, it can be concluded that BD20 CSOME with 12% cooled EGR rate produced 27% less NOx emission without any significant engine performance-emission penalties. Hence it is recommended to use BD 20 CSOME as substitute fuel with 12% cooled EGR rate for optimum performance-emission characteristics. KEYWORDS: Biomass, Exhaust Gas Recirculation, Emission INTRODUCTION ASTM D6751 definition of biodiesel states that biodiesel is composed of mono-alkyl esters of long chain fatty acids, oxygenated fuel derived from plant oils or animal fats.[1] Many alternative fuels are identified and tested successfully in the existing engine with and without engine modification. However, research is still continuing in this field to find the best alternative fuel for the existing petro fuel. Bio-fuels have the potential to meet their growing energy demand in sustainable manner. Bio diesel is produced from plants, algae and animal fats. These have almost similar energy density, cetane number, heat of vaporization and stoichiometric air fuel ratio compared to mineral diesel fuel. Bio diesel has almost eliminates lifecycle of CO2 emissions. It has high cetane number which is a measure of fuel s ignition quality. The high cetane number of biodiesel contributes to easy starting and low idle noise. Use of biodiesel can extend life of CI Engine because it is more lubricating and energy secure source than petroleum diesel fuel. Not only this, biodiesel has reduced emissions of carbon dioxide, carbon monoxide and hydrocarbons. Using pure biodiesel fuel in diesel engine sustains various problems like poor fuel atomization, piston ring sticking, injector choking and lubricating dilution. These problems are because of high viscosity, low volatility and low calorific value. Hence transesterification and blending of biodiesel is done to reduce viscosity and improving other performances. However, biodiesel minimizes CO, HC, and CO 2 to large extent but increases NOx and PM because of presence of more O 2 molecules. Owing to this, bio-diesel with NO x
36 Aparna V. Kulkarni, Sachin L. Borse & Mahesh P. Joshi emission reduction techniques in CI Engine will not only solve energy crises but also bring vital revolution in CI Engine development. S.Kent Hoekman., Curtis Robbins. et al.,[8] conducted a review on biodiesel NOx effects and present theories. Also, the scope and challenges being faced in this area of research are clearly described. Agrawal D., Agrawal A. K. et al.,[4] investigated that rice bran oil (RBO) biodiesel blended with diesel produces less HC, CO, UHC, and PM. However, it was found that higher NOx emission. EGR as effective technique to reduce NOx was used with diesel-rbo blends. However, 20% RBO biodiesel with 15% EGR was found to be optimum operating condition which improves thermal efficiency and reduces exhaust emission and BSEC. Other emission such as HC, CO, also found to be decreased at this optimum operating condition. M.K.Duraisamy, T.Balusamy and T. Senthilkumar et al.,[9] conducted a performance evaluation and emission characteristics of a diesel engine using jatropha methyl ester and reported that 15% EGR rate is found to be optimum, which improves the performance while reducing emission specially NOx and smoke. Rajan K. and Senthilkumar K. R. et al.,[6] compared there research with conventional diesel fuel, it was found that NOx was reduced about 25% at 20% BD of SFME and 15% EGR. The reason stated was due to less oxygen available in exhaust gas which reduces flame temperature in a combustion chamber. Total UBHC and CO emissions were decreased by 5% and 10% for BD20 of SFME biodiesel blends respectively compared to diesel fuel. Also, smoke emission was observed as increases due to incomplete combustion. However, engine operated with high rate of EGR at high load found to reduce 25% NOx with penalty of reduction in thermal efficiency, and increase in smoke, CO, and UBHC were observed as compared to diesel. MATERIALS AND METHODS Cotton Seed Oil Methyl Ester India is the fifth largest cotton producing country in the world today, the first-four being the U.S, china, Russia and Brazil. Our country produces about 8% of the world cotton. Cotton is a tropical plant. Cottonseed oil is a vegetable oil extracted from the seeds of the cotton. After being freed from the linters, the seeds are shelled and then crushed and pressed or treated with solvents to obtain the crude cotton seed oil. Cotton seed oil is one of the most widely available oils and it is relatively inexpensive. Table 1: Properties of Fuel Studied Transesterification Biodiesel is made through a chemical process called transeterification whereby the glycerin is separated from the fat or vegetable oil as shown in Fig. 1 & 2 below [8].
An Experimental Investigation of Effect of Cooled Exhaust GAS Re-Circulation (EGR) 37 for Nox Reduction in Single Cylinder CI Engine Using Biodiesel Blends Figure 1: Chemical Equation of Transesterification Process Figure 2: The Flow Chat of the Cotton Seed Oil Methyl Ester (CSOME) Production Process Exhaust Gas Recirculation Exhaust gas recirculation (EGR) is effective technique to reduce nitrogen oxides (NOx) from diesel engines because it lowers the flame temperature and the oxygen concentration of the working fluid in the combustion chamber. However, as NOx reduces, particulate matter (PM) increases, resulting from the lowered oxygen concentration. Recirculating part of the exhaust gas helps in reducing NOx, but appreciable particulate emission are observed at high loads, hence there is a trade-off between NOx and smoke emission. To get maximum benefit from this trade-off, a particulate trap may be used to reduce the amount of unburnt particulates in EGR, which in turn reduce the particulate emission also. The EGR rate was calculated based on mass flow rate (volumetric basis) % EGR *100
38 Aparna V. Kulkarni, Sachin L. Borse & Mahesh P. Joshi However, mass of re-circulated exhaust gas was calculated based on difference in manometer column for consecutive revolution (position) of EGR valve. For respective EGR valve position decrease in difference in manometer column was observed compared to (without EGR) total intake charge suction. This decrease in column is nothing but mass of exhaust gas re-circulated during respective valve position. Therefore, this value of mass of exhaust gas re-circulated was determined. Experimental Set-up and Methodology The engine selected for conducting tests is Kirloskar TV1, four-stroke, single-cylinder, water-cooled, naturally aspirated, DI (open chamber), diesel engine. Eddy current dynamometer has been used for loading the engine. The engine was operated at a rated constant speed @ 1500 rev/min. Moreover, all tests were conducted and parameters were measured under steady state operation. Figure 3: Pictorial View of EGR Set-Up 1. Exhausts gas calorimeter, 2. Exhaust gas re-circulated M.S. piping with control valve No. 1, 3. Moisture absorber fitted after EGR cooler, 4. An orifice and opening, 5. EGR valve No. 2, 6. Particulate filter, 7. Joint to suction manifold.
An Experimental Investigation of Effect of Cooled Exhaust GAS Re-Circulation (EGR) 39 for Nox Reduction in Single Cylinder CI Engine Using Biodiesel Blends Figure 4: Schematic of Engine Set-Up Fitted with Cooled EGR System A short partially cooled EGR system was fabricated as per requirements and used in the set-up.to gain significant EGR effects, several components like EGR cooler, moisture absorber, orifice meter, particulate filter, etc. were fitted as shown in Figs. 3 and 4. Engine was loaded from zero to full load in step of 20%. At these loadings fuel consumptions, air consumption, various emissions, in-cylinder peak pressure, and exhaust gas temperature were measured. In addition, EGR rate was varied and controlled with the help of manually operated gate valve. RESULTS AND DISCUSSIONS Effect of Varying EGR Rate on 100% CSOME Biodiesel Performance Parameter --Brake Thermal Efficiency (BTE) The increase in performance and NOx emission with 100% CSOME biodiesel at optimized parameters has appealed to control the NOx emission. The use of varying EGR rate for NOx reduction has brought some significant results. As seen in Fig. 5, EGR rate of 12% was found to be optimum. This may be because, with rise in EGR rate from 7% to 25% there was considerable decrease in NO (30-60%) as well as thermal efficiency from 3% to 40% at full load. At 12% EGR rate, % decrease in BTE was 7. This was marginal drop in thermal efficiency, compared to 10% increase in thermal efficiency during engine optimizing parameters. Also, at this rate NO reduction was significant. Figure 5: Effect of Various EGR Rate on Brake Thermal Efficiency with 100% CSOME
40 Aparna V. Kulkarni, Sachin L. Borse & Mahesh P. Joshi Performance Parameter -- Brake Specific Fuel Consumption (BSFC) The rise in fuel consumptions 8% was observed for BD 100 at 12% EGR rate. Beyond, 12% EGR rate may reduce NO values promisingly, but with more penalties of decrease in BTE and rise in BSFC (~ 20 to 40%). From Fig.6, it was found that, rise in BSFC was higher upto 41% for EGR rate at 25% compared to 0 % EGR. This may be stated due to replacement of fresh oxygen molecules from suction with diluents called emission. Which may lead to rich fuel-air mixture and responsible to cause higher HC & CO emission. Figure 6: Effect of Various EGR Rate on Brake Specific Fuel Consumption with 100% CSOME Performance Parameter -- Exhaust Gas Temperature (EGT) Figure 7 reveals the profile of exhaust gas temperature. As expected EGT increase with increase in load or power. However, temperature of exhaust gas was observed to be lower in case EGR operated engine. The possible reason for this temperature reduction may be stated as relatively lower availability of oxygen molecule and higher specific heat of intake diluents. The lower EGT with EGR rate signifies reduction of NOx emission. Figure 7: Effect of Various EGR rate on Exhaust gas Temperature with 100% CSOME Emission Parameter The NO emission reduced with increase in EGR rate as cited in Fig.8, EGR rate @ 12% was found to be optimum with NOx emission reduction of 43.3% at full load & 28.7% at part load. Further increase in EGR rate will go on reducing NO but this rate is limited by rise in HC, CO, BSFC, and fall in BTE as seen & discussed in Figs.5-10.
An Experimental Investigation of Effect of Cooled Exhaust GAS Re-Circulation (EGR) 41 for Nox Reduction in Single Cylinder CI Engine Using Biodiesel Blends The recycled exhaust gas acting as diluents for fresh air not only reduces fresh oxygen molecules but also increases specific heat of intake mixture. Owing to this lowers peak combustion temperature and oxidation of nitrogen reactions. At lower load (0 to 25%), higher EGR rate (20-25%) can be applied to reduce NO emission upto 45% with very little penalties and at higher load (80-100%) lower EGR rate (7-12%) was found to be prominent for NO emission reduction from 31% to 43.28% with marginal penalties. At maximum EGR rate of 25%, and full load, NO emission was reduced to 57.71% which is 25% higher than optimum EGR rate @ 12% we determined with very much serious scarifies to other parameters like HC, CO, BTE, and BSFC etc. Figure 8: Effect of Various EGR Rate on NOx Emission of 100 % CSOME The effects of EGR on HC and CO emission was as shown in Fig. 9 and 10 respectively. CI Engines operate with lower HC & CO emission using diesel fuel. The HC and CO emission was found to be increased with increase in EGR rate and load. Reason may be attributed to lower oxygen present for combustion. This lower excess oxygen resulted in rich air- fuel mixture at different locations inside the combustion chamber resulting higher HC emission. Also, owing to lack of oxygen; in-complete combustions were resulted to rise in CO emission. At full load application and 12% EGR rate it was found that 14% rise in HC and CO emission. Figure 9: Effect of Various EGR Rate on HC Emission with 100% CSOME
42 Aparna V. Kulkarni, Sachin L. Borse & Mahesh P. Joshi Figure 10: Effect of Various EGR Rate on CO Emissions with 100% CSOME Effect of Optimized EGR Rate (12%) on Varying Fuel Brake Thermal Efficiency The brake thermal efficiency with diesel fuel was higher compared to BD100 & BD 20 at all load operation. Without EGR operation BTE at full load with diesel, BD20 and BD100 was 28.8%, 28.0% and 25.9% respectively. However, at 12% EGR and full load operation BTE with diesel, BD20 and BD100 was 26.3, 24.5, and 22.2 respectively. The maximum BTE was reduced with diesel @ 12% EGR rate was 9% in Fig 1 1. Thus, compared to BD20 and BD100 more BTE was decreased. Also, with BD20 and BD100 7% BTE was observed lower at full load and 12% EGR rate. In concerned with EGR & BTE, 12% EGR rate with BD20 fuel finds suitable option. Figure 11: Effect of Optimized EGR Rate (12%) on BTE for Diesel, BD20 & 100% CSOME NO Emission The NO emission reduction 43.2% was highest for CSOME 100% at optimized EGR rate and full load operation. Also, more NO reduction was seen for BD100%, BD20 & diesel respectively. The higher oxygenated
An Experimental Investigation of Effect of Cooled Exhaust GAS Re-Circulation (EGR) 43 for Nox Reduction in Single Cylinder CI Engine Using Biodiesel Blends molecules responsible for more NO formation were reduced by EGR. Notable point can be maintained that, EGR at 12% with BD20 brings promising result negating some penalties. The NO reduction at full load was observed to be 27% with BD20. Also, at full load and 12% EGR rate, NO reduction with diesel was found to be 22%. NO values so obtained with 12% EGR with biodiesel, BD20 and diesel was 478, 496, 463 ppm respectively. Figure 12: Effect of Optimized EGR Rate (12%) on NOx Emission for Diesel, BD20 & 100% CSOME HC and CO Emission The effect of optimized EGR rate (12%) and biodiesel on HC and CO emission was as shown in Fig. 13 and 14. HC and CO emission was increased with increase in load. Due to lowers excess oxygen available for combustion, results in increase in rich air-fuel mixture at some zones in combustion chamber. Thus, HC and CO emissions were increased.the HC and CO emission was 89 ppm and 0.45% vol. respectively at full load and 12% EGR rate with BD 100 biodiesel as in Fig.13 and 14. Also, HC and CO emission with BD20 (78 ppm and 0.37 % vol.) was lowest compared with BD100 fuel at same operations of EGR and load. However, BD20 showed significant reduction of NO (27%) at full load with least penalties of HC and CO of ~5 % and ~ 10% respectively. Figure 13: Effect of Optimized EGR Rate (12%) on HC Emission for Diesel, BD20 & 100% CSOME
44 Aparna V. Kulkarni, Sachin L. Borse & Mahesh P. Joshi Figure 14: Effect of Optimized EGR Rate (12%) on CO Emission for Diesel, BD20 & 100% CSOME The HC and CO emission was increased for BD 100 as seen in Fig. 13 and 14 compared to diesel and BD20. Further, rise in CO emission @ 12% EGR rate was 13%, 10% and 6% with 100% biodiesel, BD20 and diesel respectively. CONCLUSIONS Based on the exhaustive tests conducted on engine using CSOME, following conclusions are drawn:- It was found that the properties of cotton seed oil methyl esters (CSOME) biodiesel were closer to the specifications of biodiesel given in ASTM standard D6751-06. Engine could be run without any difficulty using cotton seed oil methyl esters (CSOME) and their blends for present diesel engines without any modification. Effect of cooled EGR with BD100 biodiesel was studied with 7%, 9%, 12%, 20% and 25% rate of EGR. However, 12% EGR rate gave best results (43% NO reduction, 14% rise in HC, CO and 7% decrease in BTE at full load). Influence of optimized cooled EGR rate on diesel, BD20 and biodiesel was comparatively studied. It was observed, that for biodiesel, NOx emission reduction ~ 43% was at higher rate compared to ~ 22% for diesel and 27% BD20% at 12% EGR rate on full load condition. Hence it is recommended to use BD 20 CSOME as substitute fuel with 12% cooled EGR rate for optimum performance-emission characteristics. Future Scope Though many advantages of EGR still there are some limitations which can be resolved by further modification in future. In future long term assessment of engine durability and effect on lubricating oil of bio-diesel fueled engine with EGR need to be examined. Another field of research is development of sophisticated EGR valve which could response to dynamic mode of engine operation. Extensive tests can be conducted by varying EGR rate with step of 0.5%.
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