Kim, Dongsu; (2022) Investigating Sustainable Fuel Effects on Mixing and Combustion through Design and Development of a Gasoline Direct Injection Optically Accessible Engine. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Due to ever-growing sustainability issues, more demanding exhaust emission regulations are imposed on internal combustion engines. There is growing introduction of full electrification but, as there are practical issues regarding the full electrification, internal combustion engines are proven to be still useful and often coupled with electric motors. It is, therefore, vital to establish detailed understandings of in-cylinder combustion processes so that the release of greenhouse gas and production of pollutant emissions can be reduced and minimised. Therefore, novel fuels, such as second-generation biofuels, are thoroughly studied to explore possible use as future fuels for hybrid gasoline direct injection powertrains which are derived from sustainable feedstock and provide efficient energy release. For this project, a novel optical engine was designed that facilitate easy access to the piston and rapid cleaning of the piston crown window. A state-of-the-art gasoline direct injection engine was selected for hybrid applications. The initial design of the optical engine was modified to resolve the slackness in the extended timing chains. As the optical engine adopted the Bowditch system and only number 1 cylinder operated, various auxiliary components were also designed and developed to accommodate optical systems and oil circulation, and consider the change in the crankshaft balancing and volume of the air intake. Furthermore, an external fuel supply system was designed to enable a use of different fuels, while minimising a risk of damaging or contaminating the conventional fuel supply lines, by allowing easy cleaning processes. To quantitatively compare the difference in both spray and combustion images between various fuels, MATLAB codes were developed to process the captured images from a high-speed camera. Seven fuels were tested namely gasoline, ethanol, acetic acid, anisole, guaiacol, 2-MF and 2-MTHF; one a reference fossil fuel, one a first-generation biofuel and five second-generation biofuels, respectively. Three different injection timings were applied to simulate stratified, quasi-homogeneous and homogeneous states at low and high injection pressures for combustion studies, with only the injection pressure varied for the constant injection timing at the stratified spray studies. In general, injection pressure did not have a significant effect on soot formation, with exception for anisole, with injection timing found to be the dominant factor. Ethanol showed a similar spray development pattern to that of gasoline but displayed narrower sprays around the injector tip and became wider towards the spark plug. Acetic acid showed an indistinctive spray pattern and all six sprays merged together to form a cloud of fuel. Anisole showed wider sprays than gasoline and ethanol, but exhibited a similar penetration rate. Guaiacol exhibited similar spray characteristics to that of acetic acid, in that it formed a fuel cloud rather than maintaining distinct fuel sprays. Both 2-MF and 2-MTHF showed wide sprays.

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