Experimental analysis of the volumetric and thermal efficiency performance of a novel direct piezo-acting cvvt mechanism

Abstract

In this study, a specifically designed direct-acting continuously variable valve timing mechanism was used to determine speed optimised valve timings for best volumetric efficiency of an engine. This mechanism basically consists of a piezo stack and a hydraulic magnifier integrated into it. To avoid effects of excessive vibrations on the piezo-stack, the engine was operated in a non-combustion mode. An electric motor was used to power the engine. Some system limitations of the hydraulic magnifier and the piezo-stack were the main challenges to a non-stop operation. A valve lift of approximately 4 mm, obtained with maximum applicable voltage of 600V to the piezo-stack, was referred to for comparison instead of the 7.6 mm original value. Tests were conducted for 30 inlet valve timing combinations at four different engine speeds from 1500 to 3000 rpm with 500 rpm increments. Timing pairs for the best VE were determined. They yielded 11.5% to 19.4% better volumetric efficiencies at 4mm lift than those obtained with the original valve timing of the cold engine. We also predicted 5-11.5% overall efficiency improvement, depending on engine type and operating conditions. Despite some practical challenges, better VE values have been obtained for a specific engine at varied speeds.