The stable combustion of the air-diluted lean gasoline mixture was achieved with dimethyl ether(DME) direct injection in a 4 stroke single cylinder gasoline engine. Results show that the DME direct injection at 1 500 r/min and a fixed fuel low heating value in a cycle can stabilize combustion

accelerate initial flame propagation speed

shorten combustion duration and expand the upper limit of excess air coefficient(λ) in the lean burn conditions. The combination of lean burn and DME direct injection can improve engine's fuel economy under lean burn conditions. Compared to the stoichiometric mixture

the indicated specific fuel consumption can be decreased by up to 11.7%. The optimum combustion phases under different λ can be realized by changing the spark timing and the DME-to-gasoline ratio

meanwhile

the optimum heat release center will be advanced with the increase of λ.