An experimental assessment on semi-low temperature combustion using waste oil biodiesel/C3-C5 alcohol blends in a diesel engine

Biodiesel fuel properties should be improved in order to be able to use such alternative fuels at high mixing ratios in diesel engines. Higher alcohols such as propanol (C3), n-butanol (C4) and 1-pentanol (C5) are competitive alternative fuels for diesel engines due to their liquid nature, high oxygen contents, high cetane number (CN), lower latent heat of evaporation (LHE) and their production from renewable biomass. Oxygen-containing fuels that can be used in diesel engines reduce the combustion chamber temperature and harmful emissions. At this point, the addition of higher alcohols to biodiesel also has the potential to improve both low temperature combustion and fuel properties. The purpose of this work is to investigate the fuel properties of binary blends of waste oil methyl ester (WB) and the higher alcohols of C3, C4 and C5, and their effects on engine characteristics to achieve semi-low temperature combustion (S-LTC) and obtain lower regulated emissions in comparison to WB. Three different test fuel blends were prepared by volume: 80%WB-20%C3, 80%WB-20%C4, and 80%WB-20%C5. In order to determine engine performance and exhaust emissions, tests were performed at four engine loads (0, 3, 6, 9 kW) with a constant engine speed (1800 rpm). According to engine performance and exhaust emissions results, the addition of C3, C4 and C5 to WB had the effect of increasing brake specific fuel consumption (BSFC) and exhaust gas temperatures (EGT), while the brake thermal efficiency (BTE) decreased. The overall WB-C3/C4/C5 blends lean combustion of the diesel engine provided low carbon monoxide (CO) and oxides of nitrogen (NOx) emissions compared to WB, alone. Use of binary blends as S-LTC providers in diesel engines offer the benefits of ultra-low NOx and CO emissions but suffers from a lowered energy efficiency and higher hydrocarbon (HC) emission due to the high oxygen and volatility of higher alcohols. It can be concluded that C3, C4 and C5 are capable of reducing harmful emissions, however, this is accomplished at the expense of lower engine performance characteristics.