Influences of C5 esters addition on anti-knock and auto-ignition tendency of a gasoline surrogate fuel

The research octane numbers and auto-ignition characteristics of a toluene primary reference fuel (TPRF), when blended with three C5 esters, gamma-valerolactone (GVL), methyl butanoate (MB), and methyl crotonate (MC), were investigated on a cooperative fuel research (CFR) engine and a constant volume combustion chamber (CVCC). In fuel preparation, ethanol was used to improve the miscibility, and the total additive comprised 1/3 ethanol and 2/3 GVL/MB/MC on a molar basis. The experimental results first reveal that the addition of the three series of additives boost fuel octane rating, and their boosting effects rank as MB > GVL similar to MC when fuels are blended on a molar basis. In contrast, the auto-ignition tendency of the three series of fuel blends, when blended on the molar basis, ranks as the MC blends > the GVL blends> the MB blends. Different from the similar reactivities observed for the MC blends and the GVL blends in the RON tests, the MC blends exhibit higher auto-ignition propensity than the GVL blends, probably because the higher enthalpy of vaporization of GVL causes a more significant cooling effect. Finally, different from the literature studies that reported similar reactivities for pure MB and MC, in this study MB shows lower reactivity than MC when blending with the TPRF gasoline surrogate.