Effects of Variable Intake Valve Timings and Valve Lift on the Performance and Fuel Efficiency of an Internal Combustion Engine

摘要

To comply with the new Corporate Average Fuel Economy (CAFE) standards, automakers are expected to increase the average fuel economy of their vehicles to 54.5 miles per gallon from the current 24.8 miles per gallon by 2025. This research aims at proposing a feasible solution to narrow down the gap between the current and expected fuel economy of the vehicles, yet maintaining the engine’s original performance. A standard model of the KTM 510 cc single cylinder, fuel injected, internal combustion engine (IC) engine is modelled and simulated in Ricardo Wave software package to map the stock engine performance and specific fuel consumption at wide open throttle (WOT). The baseline simulation model is validated against the experimental readings with 98% accuracy. The intake valve timings (IVO, IVC), valve lift and profile, being major contributors to the wave and gas dynamics in the combustion chamber are then varied at all engine speeds to capture the amplified induction pressure wave to boost the volumetric and thermal efficiency and attain optimized engine performance. As a combined effect of varying the above parameters, the engine performance (torque and power) is boosted by an average of 6.02 percent throughout the engine’s operating speed range. The improvement in the lower speed range of 3000-4000 rpm is around 18.72% as this KTM is originally tuned for higher speed range of 5500 to 6000 rpm. The addition of variable valve lifts (VVL) to variable valve timings (VVT) further reduces brake specific fuel consumption (BSFC) at all engine speeds with an average reduction of 0.35%. The results show that the not only the performance of the engine can be boosted, but also the fuel efficiency can be increased by a precise control of VVT and VVL induction assembly.