Oxidation of gasoline fuels with renewable oxygenated additives on a motored compression ignition engine

This study investigated the oxidation behavior of ethanol, 2-methylfuran (2-MF), and ethyl tert-butyl ether (ETBE) as renewable oxygenated additives in an actual gasoline and five gasoline model fuels, PRF (n-heptane/iso-octane), TRF-30T and TRF-20T (n-heptane/iso-octane/toluene), TRFD-20D (n-heptane/iso-octane/toluene/diisobutylene), and TRFDC (n-heptane/iso-octane/toluene/diisobutylene/cyclopentane). The actual gasoline and its model fuels possessed the same research octane number (RON) of 80, and the experiments were conducted on a Cooperative Fuel Research (CFR) engine at 600 rpm, an intake temperature of 493 K, and an equivalence ratio of 0.5. Experimental results show the three additives inhibit reactivity in the order of 2-MF > ethanol > ETBE. Gasoline composition also affects blends reactivity, that is, actual gasoline blends are most reactive, followed by TRFD-20D, TRFDC, TRF-30T, TRF-20T, and PRF blends. These differences indicate synergistic or antagonistic interactions between additives and gasoline components. To elucidate these interactions, a kinetic model with key components was developed and validated with experimental critical compression ratio data. Simulations revealed the reactivity inhibition of additives depends on their OH scavenging and chain termination efficiency. 2-MF irreversibly scavenges OH by forming stable adducts, effectively terminating chain reactions. ETBE produces weak C–O bond intermediates that generate HO2, which regenerates OH and sustains the chain, leading to minimal inhibition. Ethanol, with stronger C–OH bonds, forms fewer HO2 and regenerates less OH, resulting in moderate inhibition. Additionally, the coupling kinetics between the oxygenated additives and gasoline components, particularly toluene and diisobutene, affect OH concentrations in the active radical pool and thereby affects fuel reactivity.