Combustion and regulated/unregulated emissions of a direct injection spark ignition engine fueled with C3-C5 alcohol/gasoline surrogate blends

Abstract

Abstract C3-C5 alcohols have gradually drawn more attentions as gasoline alternative fuels. In this paper, an experimental study based on the toluene reference fuel (TRF) was conducted to investigate the combustion and emissions of C3-C5 alcohol/TRF blends in a gasoline direct injection (GDI) engine. The research octane number (RON) of alcohol/TRF blends were kept at 95. Two sets of comparative experiments were performed at constant volume fraction of alcohols and oxygen contents of the mixtures, respectively. The results of ethanol/TRF and gasoline were served as a reference. It can be found that the maximum brake torque/knock-limited spark timing (MBT/KLST) of ethanol/TRF and n-propanol/TRF blends were advanced by 2∼3oCA at 6 bar and 6∼7oCA at 8 bar, comparing with those of n-butanol/TRF and n-pentanol/TRF mixtures. Under the same blending ratio, n-butanol/TRF exhibited the shortest flame development duration and rapid combustion duration along with highest indicated thermal efficiency. With the increase of carbon chain length, the emissions including CO, THC, alkanes, ethylene and propylene, acetylene and aromatics show a trend to drop first and then increase. N-butanol/TRF and n-pentanol/TRF featured lower aldehyde emissions but higher NOx emissions. For blends with the same oxygen content, n-propanol/TRF had the highest indicated thermal efficiency (ITE). Ethanol/TRF and n-propanol/TRF had lower CO emissions but higher NOx emissions. With the increase of alcohol carbon chain length, the alkene, acetaldehyde and acrolein emissions decreased firstly and then increased. Under present operation conditions, the addition of C3-C5 alcohols in gasoline reduced more PM emissions than ethanol did. From the standpoint of combustion and emissions in this gasoline direct injection engine, n-propanol and n-butanol were more suitable candidates as gasoline alternative fuels.