Combustion, performance and exhaust emission characterizations of a diesel engine operating with a ternary blend (alcohol-biodiesel-diesel fuel)

Abstract

Interest in alternative and clean energy has increased in order to meet increasing energy need and control over air pollution. In this context, studies on renewable alternative fuels such as biodiesel and alcohols for diesel engines continue intensively. However, pure biodiesel cannot be used alone in diesel engines due to its high density and viscosity. Therefore, in order to improve the density and viscosity of the biodiesel blend, alcohols are used as a fuel additive. The objective of this study is to evaluate the effect of the biodiesel and various alcohols additions to petroleum-based diesel fuel (DF) on combustion, performance and emissions of a single-cylinder diesel engine at different engine loads. In preparing the fuel blends used in the experiments, 20% cottonseed biodiesel was first mixed with DF and coded as B20. The mixture ratio was set at 20% biodiesel: 10% butanol, 10% ethanol, or 10% methanol and coded as B20Bu10, B20E10, and B20M10, respectively.Our results showed that ignition delay (ID) of the biodiesel and alcohol blends was longer than that of DF because of their low cetane numbers. The values of maximum cylinder pressure (CPmax), maximum pressure rise (Rmax), and maximum heat release rate (HRRmax) of B20 and their locations were very close to the DF at all the loads. However, due to the low cetane number of the alcohols and the rapid combustion of the fuel accumulated in the combustion chamber during the long ignition delay, the CPmax, HRRmax and Rmax values of the alcohol blends were higher than those of B20 and DF for all the engine loads. This difference was more apparent at the high engine loads. Since the heating values of the biodiesel and alcohols were lower than those of DF, the B20 and alcohol blends had higher brake specific fuel consumption (BSFC) values. The brake thermal efficiency (BTE) values of all the fuels used in the experiments were very close to each other, followed a similar trend and reached their maximum at 0.27 MPa. The B20 and alcohol blends led to a slight increase in nitrogen oxide (NOx) and hydrocarbons (HC) emissions while reducing smoke and carbon monoxide (CO) emissions. With the addition of the alcohols, a significant reduction in smoke emissions was observed at all the engine loads due to the high oxygen content and low C/H of the alcohols.