Combustion and emission characteristics of a gasoline–dimethyl ether dual-fuel engine

An experimental investigation was performed to investigate the effect of a split-injection strategy on the combustion and exhaust emission characteristics as well as on the particle number distribution for a single-cylinder compression ignition engine with gasoline-dimethyl ether dual fuelling. The gasoline-dimethyl ether dual-fuel injection system utilized port injection for gasoline and direct injection for dimethyl ether. In the present system, premixed fuel (i.e. gasoline) was injected into the premixing chamber at an injection pressure of 3 MPa using gasoline direct injection to mix the air-gasoline mixture sufficiently. However, dimethyl ether fuel was injected at an injection pressure of 50 MPa directly into a combustion chamber in order to control the combustion phase, resulting in a change in the direct-injection timing from -20° to +2° crank angle. The experimental results show that the gasoline-dimethyl ether dual-fuel engine exhibited benefits in the indicated mean effective pressure for early-injection cases (i.e. near -10° crank angle after top dead centre). However, the indicated mean effective pressure of the gasoline-dimethyl ether dual-fuel engine deteriorated for delayed-injection cases owing to incomplete combustion. In addition, a significant reduction in the nitrogen oxide emissions was observed using gasoline-dimethyl ether dual fuel compared with those obtained using conventional dimethyl ether combustion. In particular, soot emissions are almost at zero level for all the cases. On the other hand, hydrocarbon and carbon dioxide emissions increase with an increasing portion of premixed injection fuel (i.e. gasoline) in conventional injection timing, which is near top dead centre.