Experimental Investigation of Improving Homogeneous Charge Induced Ignition (HCII) Combustion at Medium and High Load by Reducing Compression Ratio

This research focuses on the potential of Homogeneous Charge Induced Ignition (HCII) combustion meeting the Euro V emission standard on a heavy-duty multi-cylinder engine using a simple after-treatment system. However, in our previous studies, it was found that the gasoline ratio was limited in HCII by the over-high compression ratio (CR). In this paper, the effects of reducing CR on the performances of HCII at medium and high loads were explored by experimental methods. It was found that by reducing CR from 18:1 to 16:1 the peak in-cylinder pressure and the peak pressure rise rate were effectively reduced and the gasoline ratio range could be obviously extended. Thus, the combustion and emission characteristics of HCII at medium and high loads were noticeably improved. Soot emissions can be significantly reduced because of the increase of premixed combustion ratio. The reduction could be over 50% especially at high load and high speed conditions. However, the effects of reducing the CR on NOx, CO and THC emissions are not obvious. Then the HCII strategy was optimized through the whole operating range aiming at meeting the Euro V limitations. The optimization results showed that there was a great potential for HCII to meet the Euro V emission standard over the whole operating map only with a simple and cheap after-treatment system (diesel oxidation catalyst). The fuel consumption was also reduced with the dual fuel strategy. The results in this paper also have reference value for other dual fuel engines.