Experimental Study On Spray Combustion And Emission Characteristics Of Gasoline Compression Ignition Engine Fueled With Gasoline-Hydrogenated Catalytic Biodiesel Blends

Diesel engines are widely preferred as a prime mover in the automotive sector(low to medium speed heavy duty)or off-road applications due to their lean operation and higher brake thermal efficiency.However,the conventional diesel engines suffered to unresolved nitric oxides-particulate matter trade-off issues.Moreover,the fast rate of depletion of fossil fuel resources and stringent emission regulations forced the researchers to develop alternative strategies to address the nitrogen oxide-particulate matter trade-off issue and to establish the sustainable fuel sources for internal combustion engines.In this regard,low-temperature combustion(LTC)is one of the promising advanced in-cylinder combustion strategies for reducing both nitrogen oxide and particulate matter emissions simultaneously.Some of the low-temperature combustion modes are homogeneous charge compression ignition(HCCI),premixed charge compression ignition(PCCI),reactivity controlled compression ignition(RCCI)and gasoline compression ignition(GCI).GCI mode is one of the low-temperature combustion strategies using gasoline instead of diesel fuel and it is better than the other low-temperature combustion modes in terms of ignition controllability.However,difficulty in ignition at low loads and maximum pressure rise rate during high load extension is the main problem in commercializing this engine.To solve these problems hydrogenated catalytic biodiesel(HCB)blended with gasoline in different proportions and its combustion and emission characteristics are investigated.Initially,the spray liquid length,ignition and combustion characteristics for hydrogenated catalytic biodiesel and gasoline/HCB blends have been researched in a constant volume combustion chamber under different ambient conditions and compared with the diesel results.Then the combustion and emission characteristics of different gasoline/HCB blends are tested in a heavy-duty diesel engine at different loads in a single injection mode with different start of injection timings and in a double injection mode with different pilot injection ratio and injection timings.The main research work and results are as follows:For this study,a new fuel named hydrogenated catalytic biodiesel prepared through hydrodeoxygenation process.The spray liquid length,ignition delay and flame lift-off length of HCB fuel under reactive conditions are tested simultaneously in the constant volume combustion chamber and compared with those of the diesel fuel.The spray liquid length of HCB is shorter than that of diesel fuel,which indicates that HCB has better atomization and less chance for occurrence of wall-impingement.While a shorter ignition delay and lift-off length of HCB reveals that it cannot be applied in blends with large proportion due to knocking combustion and more soot emission.The gasoline/HCB blends are tested in the constant volume combustion chamber for the fundamental study and to find the appropriate blends aimed for GCI engines.The results show that the ignition delay and flame lift-off length decreases with an increasing proportion of HCB in the blends,while it is vice-versa for spray liquid length.The ignition delay of gasoline/HCB blends is longer than the diesel fuel,and there is a certain gap for fuel and air mixing between the flame lift-off length and spray liquid length,which is better to form the high-quality mixtures and reduces the soot generation.The soot generation characteristics were quantitatively measured by diffused back-ground illumination extinction method.The soot generation is lower for the blended fuels than the pure diesel due to the longer flame lift-off length which makes the better fuel-air mixing.The soot production of G50H50 is close to that of diesel fuel,and it is even higher than that of diesel under high temperature and oxygen concentration.The blend ratio of HCB with gasoline should be less than 50% from soot formation.Then the combustion and emission characteristics of different gasoline/HCB blends(G80H20,G70H30 and G60H40)are researched in a heavy-duty diesel engine under different engine loads,injection timing and injection modes.Stable combustion is achieved by using all the tested gasoline/HCB blends without using any combustion assistance and increasing intake temperature.From the combustion and emission results of different fuel blends,G70H30 blends may be a good choice for further being applied in GCI combustion mode.Double injection strategy is prosed to control the maximum pressure rise rate and retarded combustion phasing in a GCI engine during single injection mode and to find the optimal injection conditions for this tested fuel.Increasing pilot injection ratio(20-40%)advances the combustion phasing and increases the maximum pressure rise rate,nitric oxides,and hydrocarbon emissions,while it reduces the particle emission.Late pilot injection from-60 to-40 deg.CA a TDC reduces the CO and HC emissions,while it increases the particle emissions.