Experimental investigation of a variable compression ratio system applied to a gasoline passenger car engine

Gasoline spark-ignited internal combustion engines for passenger cars are still a major part of the worldwide market share. With legislation pushing towards a lower carbon footprint, many technological alternatives are under scrutiny. Among them, one of the most promising is a variable compression ratio (VCR). This paper aims to experimentally prove the potential of this technology when applied to a state-of-the-art 3-cylinder, direct injection, turbocharged engine fuelled with regular RON 95 gasoline. A 2-stage variable compression ratio (VCR) system was applied to a series engine: The VCR prototype engine features compression ratio stages of 9.56:1 and 12.11:1. The engine has undergone only minor modifications, remaining substantially original. Dynamometer tests with in-cylinder pressure analysis were performed. The engine was tested over an operational map up to 4000 rpm and up to 26 bar BMEP, with stoichiometric operation and original ECU calibration. A fuel consumption reduction of up to 4% was found at part-load, where combustion phasing tended to be optimum. Penalties in fuel consumption at high loads were present due to knock-limited spark-timing. Results show that an even higher compression ratio variation range would further reduce of fuel consumption in both low and high load.