Application of Several Variable-Valve-Timing Concepts to an LHR Engine

Abstract

An analytical study was made of advantages provided by electronically controlled hydraulically activated valves when applied to a low heat rejection engine with and without exhaust heat recovery devices. The valves, which could be designed to operate with variable timings and variable rates of opening and closing, would allow the use of certain sophisticated valve strategies not possible with conventional systems. Three individual investigations were carried out. The first concerned the optimization of the timing and rate of valve opening at several speeds and loads, to obtain maximum volumetric efficiency and lowest BSFC. A second investigated early intake valve closing (IVC before BDC), coupled with increased boost, a concept that had been suggested previously in the literature. The present results showed much lower benefits than those predicted by the earlier study. The final study addressed the use of an organic Rankine cycle bottomer (ORCB) to extract energy from the exhaust stream and directing the ORCB output power to the engine air compressor shaft rather than to the engine output shaft. At rated engine conditions, when not employing a power turbine, this concept was found to produce higher BSFC compared to the more standard configuration where the ORBC was directly coupled to the engine shaft. When a power turbine was used between the engine and the ORCB, nearly the same BSFC was achieved with the two configurations.