Performance Enhancement Of Petrol Engines At High Engine Speeds Using Variable Intake And Exhaust Valves Duration

Abstract

The study was conducted in order to investigate the influence of different engine valve duration on engine brake power (BP), brake specific fuel consumption (Bsfc), and brake thermal efficiency (BTE). In this study, eight different valve durations were considered and compared with the engine of fixed valve duration. Intake valve opening time (IVO) and exhaust valve closing time (EVC) are taken 10^o crank angle (CA) before top dead center (bTDC) and 5^o CA after top dead center (aTDC) respectively, these are the same valve timings as the fixed-timing engine. Different valve opening duration depends on changing the intake valve closing time (IVC) and the exhaust valve opening timing (EVO). The IVO duration changes from 200^o to 250^o CA, while the EVO duration is from 210^o to 240^o CA. Whenever both valves (intake and exhaust) opening duration increased, the engine performance in terms of BP, Bsfc, and BTE are improved significantly particularly at high engine speeds. After analyzing the data by using simulation software, the best valve opening duration was selected according to the engine each speed. For 2000, 3000, and 4000rpm, the best intake and exhaust opening duration is 225^o and 240^o CA respectively, whereas at 5000 and 6000rpm were 250^o and 240^o CA respectively is the best duration, when compared to the fixed-timing engine. At 6000rpm, at the best intake and exhaust opening duration (250^o and 240^o CA), the brake power is 70.7kW, while at the fixed-timing engine, the brake power is 42.6kW, a significant increase of about 66%. The Bsfc at the same condition are equal to 0.29 and 0.325kg/kW.h respectively, so around 11% of the reduction ratio is achieved. Lastly, the BTE at same valves duration are equal to 27.2 and 24.6% respectively, an increase of about 11% when compared to the fixed-timing engine.