Application of Miller cycle in a spark ignition engine and the investigation of performance and emission characteristics

In this study, intake and exhaust cams of a single-cylinder, four-stroke, spark-ignition engine were re-designed by using 5th degree classic spline method to realize Miller cycle with the method of late intake valve closing (LIVC). The produced camshaft which provides variable valve opening and closing timing was adapted to the engine. The experiments were conducted with unleaded gasoline and MTBE10 (vol. 10% MTBE and 90% unleaded gasoline blends) fuels for two different intake valve closing timing (Miller A and Miller B) and the results were compared with Otto cycle. The experiments were conducted at 1700 - 3200 rpm engine speed range at wide open throttle. In the tests, the variation of engine torque, power, specific fuel consumption, thermal efficiency, HC, CO and NOx emissions and exhaust gas temperature with engine speed were investigated. Engine torque, specific fuel consumption, thermal efficiency, HC and CO emissions deteriorated at Miller cycle conditions due to the late closing of the intake valve at low engine speeds with unleaded gasoline and MTBE10 fuels. Compared to Otto cycle, up to 50 % decrease was observed in NOx emissions due to the lower exhaust gas temperature at Miller cycle conditions with unleaded gasoline. At high engine speeds (3200 rpm), engine performance and exhaust emissions were improved at Miller cycle conditions. The torque and engine power were increased by 4.67 %, thermal efficiency was increased by 10.56 %, while the specific fuel consumption was decreased by 9.55 %, HC emissions were decreased by 9.83 %, CO emissions were decreased by 7.84 % and NOx emissions were decreased by 14,16 % with respect to Otto cycle with unleaded gasoline. Engine torque, power and thermal efficiency were decreased with MTBE10 fuel, both Otto and Miller cycle conditions. However, exhaust emissions were decreased because of the oxygen content of the MTBE fuel.