Date of Award

10-5-2017

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Mechanical, Automotive, and Materials Engineering

First Advisor

Zheng, Ming

Second Advisor

Reader, Graham

Keywords

engine efficiency, ethanol, low temperature combustion, mixing, n-butanol, reactivity

Abstract

The objective of the research reported in this dissertation was to achieve clean and efficient combustion in a compression ignition engine. Previous research and literature have indicated that the control of the in-cylinder mixture preparation and charge reactivity are critical to improve combustion performance and to reduce emission formations. This research work hence focused on the exploration of the desired fuel mixing process and charge reactivity to reduce the emissions of nitrogen oxides and smoke while maintaining the high engine efficiency. Neat n-butanol, ethanol, and ultralow sulfur diesel were used as the representative fuels to demonstrate the potential of using the significantly different physical and chemical properties to achieve the targets of combustion performance and emissions. Various fuel delivery strategies, assisted with intake boosting and EGR, were examined for the active control of charge mixing and reactivity. Extensive experiments were performed on the two compression ignition engine platforms to systematically study the effectiveness of various engine control parameters on the regulation of ignition, combustion rate, and emission formation. The insufficient mixing of the diesel injection was observed as the primary cause for the high smoke emissions with the application of exhaust gas recirculation, while the high peak pressure rise rate in the n-butanol combustion is the main constraint for the high load applications. A promising approach to tackle the emission challenge is using inert premixed fuel to substitute the direct injection fuel. The combustion with the ethanol premixed fuel demonstrated promising results in emissions and efficiency. The n-butanol combustion showed an improved control over the combustion phasing. With the knowledge obtained from the empirical analysis, the enhanced control of the incylinder charge mixing and reactivity was demonstrated in the partially premixed combustion with alcohol fuels. The combustion with n-butanol direct injection and ethanol port fuel injection was found to have low smoke emissions. The combustion with n-butanol multiple injections improved the control flexibility with different fueling strategies. The optimal combustion was demonstrated with the active management of fuel delivery, intake properties, and exhaust gas recirculation in each of the fueling strategies. The n-butanol high pressure injection was also characterized with the injection rate measurement and the optical visualization under various injection conditions. The differences between the n-butanol injection and the diesel injection were investigated. The observations potentially improve the understanding of the combustion performance with the n-butanol injections.

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