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Influence of the molecular structure of biofuels on combustion in a compression ignition engine

Schönborn, A.; (2009) Influence of the molecular structure of biofuels on combustion in a compression ignition engine. Doctoral thesis, University of London. Green open access

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Abstract

This thesis presents an experimental study on the influence of the molecular structure of potential biofuels on combustion in a compression ignition engine. The molecular structure of a fuel is amongst the most fundamental parameter controlling its physical and chemical characteristics, and is thus critical to the combustion process within an engine. The approach employed in this work was to study the combustion of several individual molecules in a series of experiments whilst varying a single feature of the molecular structure at a time. This yielded information about how a particular structural feature of a molecule affects the combustion process. During the course of this project, a special fuel injection system was developed, which allowed the injection of small fuel samples into the engine at high pressure. This allowed tests to be carried out on purposely synthesised fuel samples that were only obtainable in small quantities. Detailed studies on the combustion of fatty alkyl esters (commonly termed biodiesel), acetals, ethers and alcohols were conducted. The combustion chamber pressure of the engine, the energy release of combustion, the engine efficiency, the exhaust gas composition and the emission of particulate matter were measured and analysed. It was observed that in the diffusion combustion of biofuels, the emission of nitrogen oxides from the engine depend primarily on the ignition delay of the fuel, which governs the combustion stoichiometry and peak cylinder pressures and temperatures within the combustion chamber, and secondly on the adiabatic flame temperature of the biofuels. It was found that the number of double bonds present in biofuel molecules correlated with the amount of particulate mass emitted from the engine. It was further observed that oxygenated biofuels such as fatty acid alkyl esters, acetals, ethers and alcohols produced much lower levels of particulate mass from their combustion than petroleum-derived diesel fuel. The emission of particulates depended on the fuel oxygen content, as well as on the boiling point of the fuel. Combustion experiments conducted in homogeneous charge compression ignition combustion demonstrated that ethers of low molecular mass could be amongst the most-suited liquid fuel molecules for this type of combustion method.

Type:Thesis (Doctoral)
Title:Influence of the molecular structure of biofuels on combustion in a compression ignition engine
Open access status:An open access version is available from UCL Discovery
Language:English
Keywords:Acetal, biofuel, combustion, diesel, engine
UCL classification:UCL > School of BEAMS > Faculty of Engineering Science > Mechanical Engineering

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