Impacts of dimethyl ether enrichment and various injection strategies on combustion and emissions of direct injection gasoline engines in the lean-burn condition

As an alternative fuel, dimethyl ether (DME) improves the combustion and reduces emissions of gasoline engines. Moreover, the control of injection strategies of direct injection (DI) gasoline engines could form the preferable stratified charge, enhancing the performance characteristics, especially under lean burning conditions. Thus, the co-effects of injection strategies and DME addition on the performance of a DI gasoline engine were investigated under the lean-burn condition. Results showed that the appropriate injection ratio (IR) during the two-stage injection strategy could exhibit a higher brake thermal efficiency (BTE), a lower cyclic variation and HC emissions compared to the single injection mode. Moreover, the cyclic variation was decreased firstly then increased, the BTE and heat release rate were raised firstly then reduced with the increase of IR. Furthermore, NOx emissions were increased firstly and then decreased, HC emissions were decreased firstly and then increased and the trend of CO emission was increased constantly. In addition, the DI gasoline engine blended with DME raised BTE, shortened the combustion phase, eased cyclic variation, increased CO emission and dropped HC emissions under tested conditions. The use of DME with optimum IR could be a practical way to improve the trade-off between BTE and NOx emissions.