Improving diesel engine efficiency at high speeds and loads through improved breathing via delayed intake valve closure timing

Abstract

Valve train flexibility enables optimization of the cylinder-manifold gas exchange process across an engine’s torque/speed operating space. This study focuses on the diesel engine fuel economy improvements possible through delayed intake valve closure timing as a means to improve volumetric efficiency at elevated engine speeds via dynamic charging. It is experimentally and analytically demonstrated that intake valve modulation can be employed at high-speed (2200 r/min) and medium-to-high load conditions (12.7 and 7.6 bar brake mean effective pressure) to increase volumetric efficiency. The resulting increase in inducted charge enables higher exhaust gas recirculation fractions without penalizing the air-to-fuel ratio. Higher exhaust gas recirculation fractions allow efficiency improving injection advances without sacrificing NOx. Fuel savings of 1.2% and 1.9% are experimentally demonstrated at 2200 r/min for 12.7 and 7.6 bar brake mean effective pressure operating conditions via this combined strategy of delayed intake valve closure, higher exhaust gas recirculation fractions, and earlier injections.