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

For realizing a super-leanburn SI engine with a very-high compression ratio, it is necessary to design a new fuel which could have low ignitability at a low temperature for antiknocking, but high ignitability at a high temperature for some contribution to stable combustion. C₂H₆ has a very-long ignition delay time at a low temperature, close to that of CH₄, but a short ignition delay time at a high temperature, close to that of gasoline. C₂H₆ also has a laminar burning velocity about 1.2 times higher than that of gasoline. C₂H₆ addition to gasoline could be a good example of fuel design to improve both combustion stability and antiknocking property. In the present study, the antiknocking effect of adding CH₄, C₂H₆, or C₃H₈ with the RON of 120, 115, or 112, respectively, to a regular-gasoline surrogate fuel with the RON of 90.8 has been investigated in an SI engine with a stoichiometric mixture. With the energy fraction of the gaseous fuel of less than 0.35, knocking limit CA50 is advanced further in the order of C₂H₆ addition > C₃H₈ addition > CH₄ addition, which is conflict with the order of RON of CH₄ > C₂H₆ > C₃H₈. The effect is dependent on not the RON of the gaseous fuel, but the rate of OH consumption by the gaseous fuel. The effect of adding each gaseous fuel to a premium-gasoline surrogate fuel with the RON of 100.2 has been also investigated. The effect is not dependent on the cool-flame reactions of the liquid fuel.