Direct cylinder water injection to reduce knock using low pressure injectors in a spark ignition system

A theoretical and experimental investigation of the effect of water injection on end-gas properties in a constant volume cylinder was conducted. The results of the investigation were used to understand end-gas properties and their effect on knock creation and suppression. An in-cylinder, low-pressure, direct water injection method was applied to suppress knock. Water's very high latent heat of vaporization (hfg) and cost were the reasons for using water as a coolant to reduce the temperature of the unburned mixture end-gas zone. The investigation was based on a two-zone model. The first zone is the burned product mixture, and the second zone is the unburned reactant mixture. The first law of thermodynamics, chemical equilibrium principles, and conservation of mass equations were applied to derive the reactant temperature, mixture pressure, product temperature, and product production rate before and after water injection. A computer model was developed to apply these equations to a cylindrical, constant volume chamber using direct cylinder water injection as a method to suppress knock in the end-gas zone. The numerical results were then used to optimize the experiment hardware, setup and process.; A Design Of Experiment (DOE) technique was utilized using the computer model results to screen for factors effects. The results show that compression ratio, and injected water amount have a significant effect on the end-gas properties. The air fuel ratio (A/F) has minimal effect on end-gas temperature, but a significant effect on product temperature. This study has shown that water injection in the end gas has the potential of upgrading spark ignition engine performance to match the compression ignition engine without knock, running a compression ratio up to 15:1, while also lowering product temperature.