The effect of variation in fuel composition on combustion quality in a modified-CFR engine has been studied with twelve kinds of unleaded test fuels. The modified-CFR engine at a fixed engine speed and load was mainly used under lean conditions of air-fuel ratios. The combustion quality of the fuels was evaluated by measuring three parameters, maximum temperature of combustion gas (Tmax), maximum pressure (Pmax) and flame propagation time (tImax), which represented the combustion quality.
It was found that the parameters were expressed as a f unction of excess air ratio, λ, but at fixed λ values they varied largely from fuel to fuel. The aromatic and olefinic content of the fuels correlated with Tmax over a range of λ varied, Pmax at λ=1.1 and tImax at λ=1.0. Similar results were obtained in terms of atomic hydrogen to carbon ratio of the fuels. It was estimated that an engine power increased with decreasing 50% evaporated-temperatures of the fuels.
It was concluded that the fuel of which the aromatic and olefinic content was small and the 50% evaporated-temperature was low was desired in consideration of engine power-up and NO emission control at a lean mixture such as λ=1.2.
