Fuel Design Concept to Improve Both Combustion Stability and Antiknocking Property Focusing on Ethane

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. In the present study, the antiknocking effect of adding methane with the RON of 120, ethane with the RON of 108, or propane with the RON of 112 to a regular gasoline surrogate fuel with the RON of 90.8 has been investigated. Adding each gaseous fuel by less than 0.4 in heat fraction advances knocking limit in the descending order of SI timing advance of ethane, methane, and propane, and in the descending order of CA 50 advance of ethane, propane, and methane. Adding methane extends combustion duration slightly, but adding ethane or propane shortens it considerably. Shortening combustion duration has a negative effect on advancing knocking limit SI timing. The effect on advancing knocking limit CA 50 is dependent on not the RON’s of the gaseous fuels, but the rates of OH removal by the gaseous fuels. The antiknocking effect of adding each gaseous fuel to a premium gasoline surrogate fuel with the RON of 100.2 has been also investigated. The effect on advancing knocking limit CA50 is not dependent on whether the liquid fuels have cool-flame reactions or don’t.