A Comparative Study on Influence of EIVC and LIVC on Fuel Economy of A TGDI Engine Part III: Experiments on Engine Fuel Consumption, Combustion, and EGR Tolerance

The present paper is Part III of an investigation on the influences of the late intake valve closing (LIVC) and the early intake valve closing (EIVC) on the engine fuel consumptions at different loads and speeds. The investigation was conducted with two 1.5L turbo-charged gasoline direct injection (TGDI) engines, one with a low-lift intake cam (the Miller engine) and the other with a high-lift intake cam (the Atkinson engine). This paper focuses on the influence of the intake-valve-closing timing on the fuel economy with and without exhaust gas recirculation (EGR). It was found that the Miller engine had a lower friction than the Atkinson engine; however, the impact of the difference in engine frictions on the fuel economy was mainly for low-speed operations. Across the engine speed range, the Miller engine had longer combustion durations than the Atkinson engine as a result of the impact of EIVC on the cylinder charge motion. The Miller engine also had a lower EGR tolerance in comparison to the Atkinson engine, which limits the EGR benefits in the Miller engine. Overall, the Miller engine showed a better fuel economy at low engine speeds, and the Atkinson engine performed better at medium and high engine speeds.