Date of Award

9-21-2018

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Mechanical, Automotive, and Materials Engineering

First Advisor

Zheng, Ming

Keywords

Chemical kinetics, Flame propagation speed, Ion current, Lean and premixed combustion, Spark ignition

Rights

CC-BY-NC-ND

Abstract

Spark ignited internal combustion engines are expected to continue to be the mainstay for the passenger cars and light duty trucks for the next few decades. It is understood that to conform to the stringent fuel efficiency legislations as well as meet the regulated exhaust emission limits, combustion technology must evolve significantly. It is imperative to develop a deeper understanding of the fundamental engine processes such as air intake, fuel-air interaction, and ignition so that avenues for incremental improvements may be explored. With this broad objective, the present study focuses on spark ignition engines in which premixed and lean (air in excess) charge of fuel and air can be burned efficiently. Studies have indicated that under these conditions, it is possible to simultaneously reduce the oxides of nitrogen (NOx), while keeping the carbon monoxide (CO) and unburned hydrocarbons (UHCs) at low levels. The in-cylinder turbulence plays a major role in the fuel-air mixture preparation. When this mixture ignites, the combustion may propagate through what is known as a premixed turbulent flame. Turbulence is beneficial since it enhances the mass burning rate. This is particularly critical in lean burn engines in which it is difficult to complete the combustion within the extremely short time scales typical of modern engines. Excess turbulence however, may lead to flame quenching. In order to investigate the conditions leading up to and the propagation of the turbulent flame itself, analytical and empirical studies are performed. Tests are conducted on a constant volume combustion chamber with optical access to provide insight into the combustion characteristics of lean mixtures subject to turbulence. Fundamental studies on premixed flame propagation are performed with a variety of fuels at different equivalence ratios with different fuels. Impacts of engine operating conditions such as air-fuel ratio, exhaust gas recirculation, engine load, fuels, and ignition strategies on the flame initiation and development are investigated in detail on a research engine test setup. Chemical simulation and computational fluid dynamics (CFD) tools are used to supplement the understanding of the results. Finally, an attempt is made to comprehensively understand the combined effects of in-cylinder flow and fuel reactivity on premixed and lean combustion.

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