Improvement in Performance of the Blowdown Supercharged HCCI Gasoline Engine by Increasing Compression Ratio

The objective of this study is to extend the HCCI operational range while maintaining high thermal efficiency of a HCCI engine using the blowdown supercharge (BDSC) system. Two different compression ratios of 11.7 and 14.1 were tested by replacing the piston. The effect of compression ratio on both the HCCI operational range and thermal efficiency were investigated. The experimental results showed that the HCCI operational limit and the fuel consumption at the low load operation were successfully improved by increasing compression ratio. On the other hand, high load operational limit was hardly affected by compression ratio. Also, it was found that the BDSC-HCCI engine with higher compression ratio improves thermal efficiency of the whole HCCI operation range.