Bai, Yibo; (2023) Combustion and Emission Characteristics of Oxygenated Fuels from Pyrolysis of Renewable Feedstocks in a Gasoline Direct Injection Engine. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The tremendous increase in the worldwide consumption of fossil fuels in the last decades has led to several environmental issues, for example, greenhouse gas (GHG) emissions and deteriorating air quality. It is urgent, therefore, to find alternative and sustainable fuel sources for society and industry. Lignocellulosic biomass is the most abundant renewable source of carbon, with the potential to support the sustainable production of renewable biofuels. This study focused on experimentally investigating the effect of utilising a range of fuel molecules from pyrolysis of lignocellulosic biomass, with different chemical compositions and properties, as fuel blending components on combustion and emissions in a spark-ignition engine. In this work, a modern gasoline direct injection (GDI) engine (BMW B48) was utilised to test various molecules, which were representative products of biomass pyrolysis, at different fuel injection timings and air/fuel ratios. Initially, a group of short-chain oxygenated molecules, including acetic acid, hydroxyacetone, and propylene glycol, were tested at two different conditions with different IMEP, injection timings and λ values. Subsequently, engine experiments were undertaken on oxygenated aromatics and furans from biomass pyrolysis at 4 bar IMEP, with four different operating conditions achieved by varying the injection timing and λ value to simulate the homogeneous and stratified modes of modern GDI engines. The major of the molecules investigated saw stable engine operation at a variety of conditions, with the exception of anisole, 1,2-dimethoxybenzene and 2,5-dimethylfuran at the stratified condition. A significant influence of the physical properties of the oxygenated fuel molecules on the engine combustion characteristics was observed, especially at the late injection timing. For example, the significantly higher viscosity of propylene glycol compared to ethanol resulted in later heat release and a longer combustion duration at the semi-stratified condition. Effects of the oxygenated fuel molecule structure on the engine-out emissions were also observed. For example, the methoxyl functional group on anisole, guaiacol, and 1,2-dimethoxybenzene contributed to the formation of particulate matter at the homogeneous lean condition. At the stratified condition, molecules such as guaiacol and 1,2-dimethoxybenzene with more than one oxygenated functional group reduced CO emissions. Furthermore, the addition of a second methyl group to 2-methylfuran to form 2.5-dimethylfuran reduced NOx emissions through reduced rates of heat release.

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