Study on combustion and emissions reduction characteristics of butanol blended biodiesel fuel in a compression ignition engine

Abstract

In this dissertation, the effect of biodiesel-butanol blended fuel on spray development, combustion performance, and exhaust emission characteristics in a compression ignition (CI) engine was experimentally investigated under various operating conditions, such as injection strategy, engine speed, and engine load. The butanol blending ratio was restricted to 30% by weight ratio, and the results were compared with those of conventional diesel fuel (ultra-low-sulfur diesel (ULSD)). In order to investigate the macroscopic spray characteristics, a spray visualization experiment was performed under conditions similar to those present when fuel is injected into the cylinder. The results indicated that the macroscopic spray characteristics, such as spray tip penetration and spray cone angle, were similar regardless of test fuel used. Therefore, biodiesel-butanol blended fuel can be applied directly to test engines fueled with biodiesel. The ignition delay increased with the butanol blending ratio, because butanol fuel causes the deterioration of the cetane number. In particular, in the case of Bu30 fuel, the combustion stability was worse in the condition of retarded injection timing, high engine speed, and low engine load. However, the combustion stability was improved by applying multiple-injection strategies. The fuel consumption of biodiesel-butanol blended fuels decreased when the butanol blending ratio was increased, because butanol fuel compensate for the low lower heating value (LHV). In particular, the brake specific fuel consumption (BSFC) was decreased by applying multiple-injection strategies to all tested conditions. The brake specific carbon monoxide (BS-CO) and brake specific unburned hydrocarbon (BS-HC) emissions of biodiesel-butanol fuel were slightly decreased compared to those of ULSD fuel by increasing the butanol blending ratio. In addition, the biodiesel and biodiesel-butanol blended fuels showed lower values of BS-CO and BS-HC emissions than ULSD fuel under most of test conditions. In the same trend as combustion stability, the BS-CO and BS-HC emissions were increased in the condition of late injection timing, high engine speed, and low engine load. In the case of biodiesel-butanol blended fuels, the brake specific nitrogen oxide (BS-NOx) emission trends differed depending on the operating conditions, such as engine speed and engine load, compared to those of ULSD fuels. However, the brake specific soot (BS-Soot) emissions of biodiesel and biodieselbutanol blended fuels reduced to almost zero level; thus, they decreased remarkably compared to those of ULSD fuel.