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The performance and emission of spark ignition engines are optimized using combustion characteristics. The flame characteristics such as flame kernel growth rate, flame speed, flame development angle, rapid burning angle, over all burning angle and drift velocity influence the combustion process of SI engines. In this direction, experiments were conducted to measure flame kernel growth rate in AVL research spark ignition engine using AVL VISIO FEM instrument. The flame kernel growth rate measured at different engine speeds and spark timing. The measured flame kernel growth rate for gasoline fuel was in the range of 4 to 6 m/s. It was observed from the results that flame kernel growth rate is the highest at MBT spark timing. The effects of flame kernel growth rate on performance and emission characteristics were analyzed in detail. Brake thermal efficiency increases with the increase of flame growth rate. CO emission is good agreement with the kernel growth rate.

Biodiesel can be used as a supplementary fuel in diesel engines and it will be implemented in automotive fleets and power genset diesel engines in near future in our country. There is lot of studies available in literatures on use of biodiesel blends in unmodified diesel engines. However, it is reported NOx emission and SFC increases with the blends in the engine. It is the major problems for use of biodiesel blends in unmodified or in-use engine. The motivation of the study is to enhance performance and emission characteristics of a diesel engine for use of biodiesel by modifying fuel quality. The studies were carried out in a single cylinder, constant speed diesel engine with rated power of 7.4 kW. The percentage of karanja biodiesel in diesel was kept as constant (B20) throughout the study where as percentage of Diethyl Ether (DEE) was varied from 5% and 10% (by volume) in the biodiesel blend. The smoke opacity (%) decreased significantly for all loads.

Use of water diesel emulsions in diesel engines reduces simultaneously smoke and NOx emissions. However the ignition delay increases and there is a rise in the HC and CO levels as well. In this work hydrogen peroxide was added to water diesel emulsion and tested in a diesel engine. Initially the engine was run with water diesel emulsion (water to diesel ratio of 0.4:1). The water diesel emulsion with a H2O2/diesel ratio of 0.05 was used. The single cylinder diesel engine was tested at the rated speed of 1500 rpm. Brake thermal efficiency increased with hydrogen peroxide from 32.6% to 33.5% as compared to the plain emulsion at full load. These values are even better than neat diesel operation. CO and HC levels decreased significantly with the addition of H2O2. HC with the neat diesel engine at full load was 50 ppm. It rose to 75 ppm with water diesel emulsion and was controlled to 50 ppm when H2O2 was used. This is due to the strong oxidizing nature of H2O2.