The advantages of ethanol cannot be fully utilized when ethanol is mixed with gasoline in a fixed proportion. To solve this problem

a system which can inject both ethanol and gasoline directly into cylinder was developed. With this system

the effects of three different injection strategies on combustion characteristics and engine performance under lean-burn condition were experimentally conducted on a spark ignition gasoline engine. The three injection strategies were: injecting gasoline and ethanol at the same time; fixing gasoline injection timing and delaying ethanol injection timing gradually; fixing ethanol injection timing and delaying gasoline injection timing gradually. The results show that with the three injection strategies engine power output and thermal efficiency increase first and then decrease with the delay of the injection timings under lean-burn condition. When the amount of injected fuel is kept constant

the effective thermal efficiency increases remarkably with the excess air coefficient

while the equivalent fuel consumption decreases gradually. The optimal combustion is obtained at the excess air coefficient of 1.2 and with the gasoline injection timing of 180° in crank angle before the top dead center and ethanol injection timing of 300° in crank angle before the top dead center. In this case

the effective thermal efficiency peaks to 40.5%. Besides

adding ethanol into gasoline makes lean-burn combustion more stable with less cycle variation.