Performance and Emission Characteristics of a Miller Cycle Engine

Abstract

In this study, intake and exhaust cams were designed to perform the late intake valve closing (LIVC) Miller cycle operation (MA and MB cycles) using spline functions in a single-cylinder, four-stroke, spark-ignition (SI) engine. A special camshaft was manufactured and adapted to the engine to adjust valve opening and closing timings. The experiments were conducted at two different Miller cycle operation and the results were compared with Otto cycle. The tests were conducted between 1700-3200 rpm engine speed range at wide open throttle (WOT). In the experiments, the variation of brake torque, power output, specific fuel consumption (SFC), thermal efficiency, HC, CO, NOx emissions and exhaust gas temperature versus engine speed were investigated. More power output was obtained with Otto cycle than Miller cycles for all engine speeds. Brake torque and engine power decreased by 5.24%, and 1.17% respectively with MA cycle compared to Otto cycle at 2600 rpm engine speed. Thermal efficiency increased by 1.29%, while the SFC decreased 2.08 % with Otto cycle in comparison with MA cycle at maximum brake torque speed. HC and CO emissions increased by 6.48% and 11.66%, respectively with MA cycle compared to Otto cycle at the same operation condition. NOx emissions decreased up to 7.79% with MA cycle compared to Otto cycle due to the lower exhaust gas temperature at maximum brake torque engine speed of 2600 rpm.