Heat release modelling of a range extender scroll engine

Abstract

The proposed study aims to evaluate the feasibility of a range extender scroll engine by means of an analytical heat release rate analysis. This novel engine technology is comprising an upstream compressor and a downstream scroll expander which is mechanically connected and drives the compressor. Hence, the compression and expansion processes of the air-fuel mixture are decoupled which enables the possibility to apply higher expansion than compression ratios resulting in a scroll engine combustion process being similar to the Miller or Aktinson cycle. The scroll engine performance in terms of power output and thermal efficiency was accordingly evaluated for two compression ratios of 8.2:1 and 10.1:1 and six corresponding expansion ratios in the range of 8.2:1 to 17.8:1. It has been proven that high compression ratios are beneficial for the power output as more fuel can be introduced into the expander part. At a constant compression ratio, the power output increased for a rising expansion ratio but at the expense of a reduced power density. The evaluation revealed a peak value of 44.48kW at a compression ratio of 10.1:1 and an expansion ratio of 17.8:1. A more thorough expansion process due to the implementation of a Miller/Aktinson cycle resulted in a significantly increasing thermal efficiency for a rising ratio of expansion to compression ratio reaching a peak value