Low-load expander deactivation studies for a light-duty single-shaft piston-compounded engine

Abstract

A single-shaft, piston-compounded engine has shown great potential for improvements in efficiency over current state-of-the-art light-duty engines through the use of an efficient second expansion process to more fully recover energy still present in the exhaust gasses. This process inherently works well at mid to high loads where the displacement ratio of the piston expander can be maximized and fully utilized, but the positive-displacement nature of piston compounding creates a liability in efficiency and exhaust gas temperature at low loads. This study examined the trade-offs in efficiency, exhaust temperature, and engine design for various methods of mitigating the low-load deficiencies of the piston-compounded design. An optimum solution was identified, and these results were then used to guide the design of an experimental piston-compounded engine.