Abstract
To realize a super-leanburn SI engine with a very-high compression ratio, it is required to design a new fuel which could have low ignitability at a low temperature for antiknocking, but high ignitability at a high temperature for stable combustion. Ethane shows a long ignition delay time at a low temperature close to that of methane, but a short ignition delay time at a high temperature close to that of gasoline, as well as having a higher laminar burning velocity than those of methane and gasoline. In the present study, the antiknocking effect of adding methane with the RON of 120 or ethane with the RON of 108 to a regular gasoline surrogate fuel with the RON of 90.8 has been investigated. Adding methane or ethane by 35 % or 25 % in heat fraction, respectively, shows the same knock limit SI timing as that of a premium gasoline surrogate fuel with the RON of 100.2. In the relationship between the heat fraction of the gaseous fuel and the advance of knock limit CA50, the effect of adding ethane is 1.9 times larger than that of adding methane. The effect of adding the gaseous fuel is dependent not on the RON of the gaseous fuel, but on the OH consuming rate of the gaseous fuel. The effect of adding methane or ethane to the premium gasoline surrogate fuel has been also investigated. The effect of adding ethane is 1.7 times larger than that of adding methane. The effect of adding the gaseous fuel is not dependent on whether the liquid fuel has cool-flame reactions or not.
