Studies on The Performance, Combustion & Emission Characteristics of A Multicylinder Si Engine Fueled with lpg Along with Varying Steam Induction Rates

Abstract

Vehicle and fuel technologies have undergone important developments in the last 30 years. The volatility of oil prices and increasing concerns about the environment has influenced researchers to look in to possible alternatives to petroleum based fuels. Efforts are on to improve the combustion efficiency of the engines operating with conventional fuels. The various alternative fuels for spark ignition (SI) engines on which research is going on at present includes alcohols, liquefied petroleum gas (LPG), natural gas etc. Ethanol enriched gasoline blends are increasingly being used in SI engines due to the renewable nature of ethanol as well as increased governmental regulatory mandates. Ethanol can be produced from natural products or waste materials, compared with gasoline which is produced from non-renewable natural sources. In addition, ethanol shows good antiknock characteristics. Gaseous fuels are promising alternative fuels due to their economical costs, high octane numbers, higher heating values and lower polluting exhaust emissions. From the point of view of reduction of exhaust emissions such as unburnt hydrocarbon (HC) and carbon monoxide (CO), liquefied petroleum gas (LPG) is a useful alternative fuel for SI engines. Due to its higher octane value, LPG fuel can be used under the higher compression ratios. Combustion of LPG results in greater emissions of the oxides of nitrogen (NOX) than that for gasoline, the values reaching more than double at some operating conditions. Injection of water into the intake manifold has been found to be an effective way to reduce NOX emission in SI, CI and LPG engines. The present study deals with experimental investigations on the effect of steam induction with the intake air while using LPG as fuel on engine performance, combustion and emissions in a modified multi-cylinder SI engine. The engine operating parameters of speed, throttle opening positions and static ignition timings are varied. To compare the results of the above experiments, an ethanol enriched gasoline blend is optimized as a baseline fuel based on engine performance, combustion and emissions. The experimental setup consists of a stationary, fourstroke, four cylinder, multipoint port fuel injection (MPFI) engine of 44 kW capacity at 6000 rpm, which is connected to an eddy current dynamometer for loading. A piezo-electric pressure transducer is used for recording the cylinder pressure. The setup has a stand-alone panel box consisting of air box, fuel tank, manometer, fuel measuring unit, differential pressure transmitters for air and fuel flow measurements, process indicator and engine indicator. An AVL Digas 444 five gas Exhaust gas analyzer is used to measure the NOX (ppm), CO (%vol.), CO2 (%vol.) and HC (ppm) emissions in the exhaust. Initially experiments are conducted to study the performance, combustion and emission characteristics of the test engine fueled with ethanol enriched gasoline blends viz: E5, E10, E15 and E20 (on volume basis, and E5 means 5% ethanol and 95% gasoline) to optimize a baseline fuel. In the next part tests are conducted on the engine modified to run with injection of LPG as fuel and the combustion, performance and emission characteristics are evaluated. Separate four gas injectors are installed in the inlet manifold near the inlet port of each cylinder for injecting LPG. The gas injectors are operated by solenoid valves driven by 12V DC power supply. A separate gas ECU has been used for driving the solenoid valves. Experiments are conducted at wide open throttle (WOT) and part throttle conditions with varying loads in the engine speed range of 2000 rpm to 4500 rpm. Tests with ethanol enriched gasoline are conducted at the pre-set static ignition timing of 5 degree before top dead center (bTDC). The LPG performance and emissions are evaluated at various static ignition timings of 3, 4, 5 and 6 deg. bDTC. In the last part of the investigations, the engine tests are conducted with LPG along with steam induction. The waste heat from the exhaust gas has been used to generate steam from deionized water. Steam to LPG flow rates of 10, 15, 20 and 25% (on mass basis) are used. The steam is mixed with the intake air in the intake manifold of the engine. Results of the experiments have shown that among the various ethanol enriched blends, the blend of 20% ethanol was the most suitable one from the engine performance and CO & HC emissions points of view. At WOT operations the effect of ethanol blending on coefficient of variation of IMEP is to reduce it by an average of 2% with E15 fuel blend when compared to gasoline fuel operation over the entire speed range. All the ethanol-gasoline blends exhibit better cyclic variation pattern compared to gasoline at WOT operation. The engine performance has improved with the addition of ethanol, increasing the thermal efficiency and reducing the brakespecific energy consumption. A significant reduction in the HC emission was observed as a result of leaning effect and additional fuel oxygen caused by the ethanol addition. CO emission is reduced by addition of ethanol to gasoline. All engine exhaust emissions were lower at 3500-4000 rpm at various throttle valve opening condition except NOX which has shown an increasing trend with ethanol blended fuel. Hence it can be concluded that blending ethanol up to 20% to gasoline will reduce the cycle-by-cycle combustion variations and emissions though a marginal increase in NOX emissions results. The findings of the experiments with LPG suggest that higher thermal efficiency and therefore improved fuel economy can be obtained from SI engines running on LPG as against gasoline at the pre-set static ignition timing of 5 deg. bTDC. Also the exhaust emissions of CO, HC have reduced considerably. But the emissions of NOX have increased significantly at higher engine speeds. The CO emission has reduced from an average value of 5 % to about 1.3 % and corresponding change in HC noticed was from 350 ppm to 22 ppm when LPG was used instead of gasoline at pre-set static ignition timing. The NOX emission with LPG was almost double when compared to that with gasoline at higher engine speeds. When engine runs with LPG, better performance has been observed when static ignition timing is advanced to 6 deg. bTDC. Advancing the static ignition timing has also resulted in reduced CO and HC emissions. But the advanced ignition timing shows a further increase in NOX emissions. Retarding the ignition timing achieves lesser NOX emissions at higher engine speeds. Steam induction is one of the methods to reduce NOX emissions. Steam induction will reduce the peak temperature of the engine cylinder so that NOX formation will be reduced. The experimental results showed that steam induction worked as a cooling means for the fuel-air charge and slowing the burning rates, resulting in reduction of the peak combustion temperature. It is found that NOX emissions have reduced significantly by 20 - 45% over the entire operating range when compared to LPG operation. No considerable changes in CO and HC emissions are observed. Hence use of LPG with advanced ignition timing of 6deg. bTDC with steam induction up to 25% steam to fuel mass ratio at higher engine speeds and up to 10% steam to fuel massratio at lower engine speeds can be used from the point of view of improved engine performance and reduced exhaust emissions. When comparing the performance and emissions of ethanol enriched gasoline and LPG with steam induction, it is noted that, comparatively E20 blends performs better that LPG alone. With steam induction the performance with LPG deteriorates. The brake thermal efficiency of 15% steam with LPG at wide open throttle condition and 3500 rpm is lower by 3.5% when compared to E20. CO reduces with LPG when compared to E20. But a slight increment is noted when steam is inducted. NOX emissions are higher for both E20 and LPG when compared to gasoline. However, with the induction of steam along with LPG, the NOX can be substantially brought down. At 3500 rpm and wide open throttle condition, the NOX emissions of E20 and 15% steam with LPG are similar. But at 4500 rpm, NOX emission is higher by 580 ppm. From the experimental investigations it can be concluded that use of ethanol enriched blends in unmodified engine is an alternative for the use of gasoline as a sole fuel. However with the current option of LPG as alternative fuel to SI engines, it can be used along with steam induction as a means to considerably reduce NOX emissions, with marginal reduction in engine performance