SI 엔진에서 흡기밸브 개폐시기 변화와 배기스로틀이 잔류가스율과 배기가스 변화에 미치는 영향

Abstract

In -cylinder residual gas fraction(RGF) affects engine performance and emission characteristics. With RGF, the flame speed and maximum combustion temperature are decreased, which are deeply related with combustion stability particularly at idle and NOx emission at relatively high load, respectively. In this work, in-cylinder RGF was measured in a 2.0L Variable Valve Timing (VVT) SI engine for various intake valve timing, torque conditions. A Gas Chromatography (GC) and a high-speed solenoid valve were used for the sampling and measurement of CO2 concentration. Increased valve-overlap resulted in an increased RGF and a decreased torque. At each operating conditions, RGF could be increased by applying the exhaust throttle. Those phenomena were liked to the back flow and pressure difference generated difference between intake and exhaust pressure during the valve overlap period.