Access Type

Open Access Dissertation

Date of Award

January 2014

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Mechanical Engineering

First Advisor

Ming-Chia Lai

Abstract

In order to increase engine efficiency as well as to reduce emission, optimizing combustion is always the challenge in research and product development. Gasoline direct injection (GDI) engines have been popularized due to its higher power density, fuel efficiency, and the possibility for advanced engine technologies over conventional port-fuel-injection (PFI) gasoline engines. However, many issues are heavily investigated, such as air-fuel mixing preparation, fuel wall-wetting, higher HC and PM emissions, catalytic convertor efficiency, knocking, and pre-ignition. Besides, advanced technologies represent higher production cost.

Because of the limited resource of petroleum-based fuels, ethanol is deemed as the alternative fuel for gasoline due to its availability, renewability, and fuel properties. It is also known for its lower energy content (LHV ~ 27 MJ/kg) that the fuel economy would decrease if such a fuel is used. Besides that, lower HC, CO, NOX, and PM emissions may be achieved with the presence of ethanol in fuel. The present study is focused on visualizing GDI combustion with different fuels (E0 and E85) along with engine-out emission measurement specially focusing on PM emission. Different engine operation conditions are taken into consideration to study the effects on engine performance in terms of engine start-up, combustion quality and variation, and engine-out emission. High speed imaging techniques are used for visualizing the combustion process, and high speed emission measurement devices are used for engine-out emission study. PM emission is the primary focus in the current study on emissions with the assistance of in-cylinder visualization to identify the location of diffusion flame where the soot is formed. CFD modeling is also implemented to analyze the air-fuel mixture preparation as well as the combustion process.

The results indicate that the combustion process may not be ideal under certain operating conditions. By various image processing techniques, it is found that the flame kernel development could be either too slow or too heterogeneous. Fuel wall impingement is also found that pool fire is in inevitable in some cases that HC, CO, and PM emissions are high. Injection timing, ignition timing, and air-fuel ratio are the three primary factors that need to be carefully controlled for engine calibration in order to achieve higher efficiency and lower emissions. Some advanced technologies, e.g. one-valve deactivation, may not be ideal at certain speed and load. The use of alternative fuel could reduce PM emission in mass, but the particle number could sometimes be higher than using E0. The CFD simulation also validates the similar results found from the experiments.

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