Vehicle and engine biodiesel investigations

Abstract

Biodiesel is an environmentally friendly alternative diesel fuel consisting of the alkyl esters of fatty acids which are expected to play a significant role in reducing overall CO2 emissions. Biodiesel is produced commercially by a chemical reaction called transesterification which is a chemical process to lower the viscosity of the vegetable oils. Since Biodiesel is an oxygenated, sulfur free fuel, it typically reduces engine out emissions except for the oxides of nitrogen (NOX). The chemical and physical properties of the fatty acids, as well as the effect of molecular structure, determine the overall properties of biodiesel fuel. Investigations into the impact of FAME properties on diesel engines are highly topical, as higher blends of biodiesel are introduced. The aim of this work is to perform a comprehensive study on the use of biodiesel fuel in production diesel engines, and its impact on emissions, performance and fuel consumption.This thesis has shown that the use of biodiesel fuel reduces the engine out emissions of CO, HC and PM (except at sub-zero temperatures), and causes a slight increase in NOX emissions and fuel consumption compared to baseline diesel fuel. However, the lower exhaust gas temperatures seen when using biodiesel blends leads to reduced catalyst conversion efficiency and an adverse effect on tailpipe emissions. The cylinder pressure and rate of heat release profiles of biodiesel blends are very similar to those of baseline diesel fuel when similar torque is demanded from the engine with relatively similar start of combustion for the main charge. Biodiesel blends show a slightly quicker rise in the rate of heat release and higher peak values compared to baseline diesel fuel. In the case of matched pedal positions, the ignition delay time decreases slightly with biodiesel use at lower engine load conditions compared to baseline diesel fuel. The sensitivity of engine performance and emissions with B25 is more pronounced for EGR rate, rail pressure, and main injection timing variations than for baseline diesel fuel. Finally, an adverse thermal impact of using biodiesel fuel on the performance of diesel oxidation catalyst was observed compared to baseline diesel however, no solid evidence of exhaust gas HC speciation effects was found.

Date of Award	1 Aug 2011
Original language	English
Awarding Institution	University of Bath
Supervisor	Gary Hawley (Supervisor) & Christopher Bannister (Supervisor)