Performance and Emission Characteristics of a Multi-Cylinder Si Engine on Gasoline-Lpg Dual Fuel Mode of Operation

Abstract

Population growth over the last decades has led to tremendous growth in fossil energy demand with increased industrialization and use of vehicles. The most common fuel for internal combustion engines is still made out of oil, but continuous increases in oil prices has increased interest in alternative fuels. Strict international regulations on emissions and improving the combustion efficiency, gaseous fuels found to be better alternative fuel for conventional fuel. Gaseous fuels are promising alternative fuels due to their economic costs, high octane numbers, higher heating values and lower polluting exhaust emissions. LPG, as a relatively clean fuel, is considered one of the most promising alternative automotive fuels because of its emission reduction potential and lower price than gasoline. Turbocharger plays vital role in enhancing the boost pressure of IC engines. Turbocharging the engine will improve the combustion characteristics and reduces the NOX emission. Dilution of intake charge is the one of the method to reduce NOX emission. Vaporised watermethanol induction is used to reduce the emissions from the engine. The present study deals with experimental investigations of LPG-gasoline dual fuel mode of operation on engine performance, combustion and emission characteristics with turbocharging and vaporized water-methanol induction. A stationary four stroke, four cylinders, MPFI engine capable of developing 44 kW at 6000 rpm has been modified to operate on LPG fuel. A separate gas ECU has been developed with software to operate dual fuel mode of operation. The engine operating parameters of speed, load conditions and static ignition timings are varied. A turbocharger is selected based on the exhaust mass flow energy of the engine and installed in the experimental test rig with necessary modification in the intake and exhaust manifold. The waste heat from the exhaust gas has been used to generate vapor from water-methanol mixture and induced into the intake manifold to reduce the emissions from the engine. Initially experiments are conducted to study the performance, combustion, cycle by cycle variations and emission characteristics of the test engine fueled with different percentage of LPG by mass viz: 0%, 25%, 50%, 75% and 100%. In the next part of investigation, static ignition timings are advanced from 5 deg. bTDC to 8 deg.iv bTDC and 11 deg. bTDC to analyze performance and emission characteristics. During this stage percentage of LPG and static ignition timing are optimized based on performance and emission characteristics. Experiments are conducted at full load and part loads in the engine speed range of 2000 rpm to 4500 rpm. In third stage of research, a turbocharger is installed and conducted the experiment for optimized conditions. In the last part of the investigations, the engine tests are conducted with vaporized water-methanol induction. The waste heat from the exhaust gas has been used to generate vapor from deionized water-methanol mixture. Vapor to LPG flow rates of 10, 20 and 30% (on volume basis) are used. The vapor is mixed with the intake air in the intake manifold of the engine. From experimental investigation for dual fuel mode of operation at 5 deg. bTDC it is found that with the 50% usage of LPG, increases the brake thermal efficiency and volumetric efficiency when compared to gasoline for speed range of 2000 rpm to 4000 rpm. 100% LPG will have much lower CO and HC emissions when compared to gasoline. This is a positive effect on environment. But for other LPGgasoline ratio these emissions going to increases when compared to 100% LPG but it is well below when compared to gasoline for all speeds. NOX emission is more for 100% LPG almost 4 times that of gasoline for all speed conditions. For other LPGgasoline ratio NOX emission is lower. Combustion results revealed that as the LPG percentage increases the peak pressure also increases and it is maximum for 100% LPG for all the speed. This increase in peak pressure will indicate the LPG will give better combustion properties compared to that of gasoline. Compared to peak pressure, the variation in cycle to cycle for IMEP is less for 50% LPG at higher speed conditions. 50% LPG showed better cycle by cycle fluctuations when compared to other fuel conditions. Net heart release rate shows that gasoline will give the more heat release compare to all other fuels, but 100% LPG will release the heat little earlier than gasoline. Since peak pressure is near to TDC for 100% LPG which results in NHRR to occur earlier than gasoline. Final outcome of the research is 100% LPG will have better combustion properties compared to gasoline but cyclic fluctuations are more for 100% LPG.v Results have shown that advancing the static ignition timing will increase the BP by 12 % at 11 deg. bTDC and 7% at 8 deg. bTDC for gasoline. Whereas for 100% LPG increased in BP is 5 % at 11 deg. bTDC and 2% at 8 deg. bTDC. BTE also increased for both gasoline and LPG when advancing static ignition timing because of reduction in the fuel consumption. Also advancing the ignition timing will engine will work leaner side hence reduction in the fuel consumption. From the results it is revealed that as the static ignition timing is advanced volumetric efficiency is increases for gasoline and 100% LPG. For other fuel conditions there is not much effect of static ignition timing on volumetric efficiency. CO emission will drastically reduce when static ignition timing advanced to 8 deg. bTDC after that not significant reduction in CO emission. 100% LPG shown major reduction in CO emission is obtained while advancing the static ignition timing. But advancing the Static ignition timing resulted in increased HC emission for all fuel blends. NOX emission also increases with advancing the static ignition timing for all fuel blends because of increase in the incylinder temperature. Finally after varying the static ignition timing it is found that 8 deg. bTDC with 100% LPG will resulted in better performance and emission characteristics hence these conditions are optimized for the further research work. Using turbocharger performance characteristics are improved. For 100% LPG and gasoline with turbocharger BP and BTE is increased when compared to without turbocharger. BTE obtained is maximum at 8 deg. bTDC with turbocharger for 100% LPG when compared to all other condition. Turbocharged engine fuelled with LPG has higher volumetric efficiency as compared to engine without turbocharger for all speed and load conditions. Volumetric efficiency increases for turbocharged engine because of higher intake air pressure will increase the density of air which leads to increase in the efficiency. When compared to base fuel gasoline at 5 deg. bTDC average increase in volumetric efficiency for 100% LPG with turbocharger is 13% at same condition. Emissions are greatly reduced with turbocharger with 100% LPG when compared to gasoline with turbocharger. When compared to base fuel gasoline at 5 deg. bTDC average decrease in CO emission for LPG with turbocharger is 72% at same condition. There is no much variations in HC emission when compared LPG with and without turbocharger at full load conditions. The turbocharged engine fuelled with LPG, there will be a good decrease in NOX for all load conditions. This is because turbochargervi will increase the charge density hence mixture becomes to lean in the combustion zone hence formation of NOX will reduces for all load conditions. In-cylinder pressure and net heat release rate (NHRR) also greatly improved with usage of turbocharger. Maximum of 17 bar increase in the in-cylinder pressure is obtained with usage of turbocharger. Turbocharged engine gave great improvement in cycle by cycle fluctuations when compared to naturally aspirated engine. Maximum of 84% reduction in COV of IMEP is obtained for turbocharged LPG fuel. Turbocharger will give the better combustion, performance and emission characteristics for LPG fuel. From the experimental results for deionized water-methanol induction system it is observed that as the percentage of water-methanol increases, the engine brake thermal efficiency increased for part and full load conditions. Further increase in the flow rate of water-methanol beyond 30% will reduce the brake thermal efficiency drastically. Also results show that water-methanol induction will results in reduction of brake specific energy consumption (BSEC). Water-methanol induction has good effects in decreasing NOX emission significantly. At full load condition around 30% and 40% average reduction in NOX emission are obtained for 20% and 30% watermethanol flow rate. HC and CO emissions are going to reduce slightly with watermethanol induction due to presence of more oxygen in the charge to the engine. It can be seen that use of 50% LPG is superior alternative for unmodified multi-cylinder SI engine for better engine performance and emission characteristics. The use of 100% LPG is best suited for SI engines at 8 deg. bTDC advance static ignition timing with turbocharging and 20%vaporized water-methanol induction rate to get enhanced engine performance and emission characteristics.