Abstract
The effect of exhaust gas recirculation (EGR) on combustion characteristics and thermal efficiency has been investigated in homogeneous charge compression ignition (HCCI) engines using diesel engines with single- and multi-cylinder having compression ratios of 17.8 and 18.2 respectively. These HCCI engines were operated by natural gas premixed with a small amount of dimethyl ether (DME) as an ignition source. In the present study, the effect of EGR was focused on improvement in the brake thermal efficiency. It is noticed that the brake thermal efficiency higher than 4% was achieved by the high EGR ratio of 0.5 compared with the case without EGR, and almost equal improvements due to EGR are obtained in both single- and multi-cylinder engines. It is found that an increase in brake thermal efficiency due to EGR is based on the improvement in combustion efficiency mainly resulting from a significant reduction in the unburned hydrocarbon emission.
