Date of Award

2020

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering-Engineering Mechanics (PhD)

Administrative Home Department

Department of Mechanical Engineering-Engineering Mechanics

Advisor 1

Jeffrey Naber

Committee Member 1

Seong - Young Lee

Committee Member 2

Jeremy Worm

Committee Member 3

Aleksandr Sergeyev

Abstract

One of the limiting factors influencing the improvement of engine efficiency in gasoline engines is engine knock. Several techniques including reduced compression ratio, cooled exhaust gas recirculation, using high premium fuels, late intake valve closing have been used to mitigate knock at different operating regimes. Water due to its higher latent heat of vaporization compared to gasoline fuel has been used to reduce the charge temperature and mitigate knock. When water is injected into the intake manifold or into the cylinder, it evaporates by exchanging energy from the surrounding mixture resulting in charge cooling. This allows the engine to be run with advanced spark timing without engine knock resulting in better engine performance. With this motive, the impact of water injection on the combustion characteristics of gasoline direct injection engine was investigated.

The research was conducted in three parts. First, an analytical model was developed using the principles of thermodynamics to determine the impact of direct water injection on the cycle efficiency. An ideal thermodynamic cycle with constant volume heat addition was considered for the analysis consisting of air, fuel and water mixture. State properties of the mixture were determined at different points in the thermodynamic cycle and efficiency was calculated. This established a baseline on the amount of water that can be injected into the cylinder and its impact on the overall cycle efficiency. This was followed by spray studies on a spray and combustion vessel that were conducted at engine conditions by varying the ambient conditions to determine the vaporization of water and water methanol sprays. This study gives a comparison of the amount of water that can be vaporized from the thermodynamic model. Experimental studies were conducted on a single cylinder engine with a compression ratio of 10.9:1. Baseline tests without water injection were run using gasoline fuel blended with 10% Ethanol (E10) (Anti-Knock Index = 87.0) injected directly into the cylinder. Impact of water injection was studied by injecting water and blends of water and methanol in the intake manifold at different water fuel ratios within controlled knock limit. Furthermore, injection mechanism was changed to direct water injection and tests were conducted at the same conditions to compare the effect of water injection mechanism on the combustion and knock performance.

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