Recycled Water Injection in a Turbocharged Gasoline Engine and Detailed Effects of Water on Auto-Ignition

Abstract

In recent years, many engine manufacturers have turned to downsizing and boosting of gasoline engines in order to meet the ever more stringent fuel economy and emissions regulations. With an increase in the number of turbocharged gasoline engines, solutions are required to manage knock under a range of operating conditions. The engine is required to operate with spark retard and/or boost reduction to provide knock reduction leading to reduced fuel economy. The charge air cooler has been introduced to mitigate knock and yield a denser intake charge. However, under certain conditions, water condenses onto the charge air cooler inner surfaces, and this water can be introduced into the combustion chamber. Therefore, water ingestion may cause abnormal combustion. In addition, many researchers have advocated water injection as an approach to replace or supplement existing knock mitigation techniques. To maximize the efficiency of the water injection system for a given amount of water, a deeper understanding of the ability to capture and utilize water is required. The first part of this dissertation pursues an understanding of the condensates generated inside of the charge air cooler is discussed. To understand the ingestion of condensates into the cylinders, the hard acceleration is applied with the condensates and quantitatively correlated the amount of condensation and number of abnormal combustion behavior such as misfire and slowburn in different engine conditions. The next study is designing the condensation separator to prevent the abnormal combustion behavior due to the condensates ingestion. An approach to designing a unit to separate condensation in the flow from the charge air cooler while maintaining a low pressure drop is described. The effect of water on auto-ignition is described using modified CFR engine. Three test fuels gasoline, PRF, and TRF which have similar RON blends are used for this test at various intake pressure and amount of water conditions. The first test is done with constant intake air temperature and φ to exclude the effects of intake air cooling. For the second part of this research, the comparison of the effect of the intake air cooling and the effect of the intake air property change is made. The numerical calculations of the chemical effect of water addition with high octane number fuels and oxygenated fuels such as iso-Octane, toluene, n-Butanol, and Ethanol are presented. Using chemical reaction simulation, CHEMKIN, the simulations have been conducted on the change of hydrocarbon and oxygenated hydrocarbon oxidations process with water addition by examining ignition delay, sensitivity analysis and chemical reaction pathway analysis. At the beginning of the study, change of the ignition delay due to water addition is quantified. Then, the sensitivity analysis and the reaction pathway analysis are carried out to verify more detail of chemical effect of water on combustion process. Through the studies presented in this thesis, some of potential contributions to high efficiency gasoline engine have been obtained. By collecting the condensate, the abnormal combustion behavior such as misfire or slowburn can be prevented, and also collected water condensate can be utilized as a source of water injection system. Because detail effect of water has been shown in the studies, it is expected that the gasoline engine could achieve higher compression ratio by avoiding knock with water injection system.