Modeling In-Cylinder Water Injection in a 2-Stroke Internal Combustion Engine

摘要

In this study, we apply Computational Fluid Dynamics (CFD) models in investigating the effect of injecting water into the combustion chamber of a 2-stroke Internal Combustion Engine (ICE). Using the commercial code. Star-CD, 3-D models for a port scavenging, in-cylinder feel-injection; 2-Stroke engine is developed. The adapted engine's effective compression ratio (CR), crank Revolution per Minute (RPM) and fuel type are 8.5, 2000 rpm and Heptane (C7H16) respectively. Two types of water mixing techniques are investigated: homogenous pre-mixing with the reactants, and direct injection around the walls of the combustion chamber. The engine's pressure, temperature, and pollutant mass fraction are estimated as a function of crank angle and injected water to fuel mass ratio, for both mixing techniques. The calculated indicated work (area under P-V diagrams) is used to estimate other engine performance indicated parameters. Results showed that although the homogenous mixing of water has an effect of reducing the combustion temperature and resulting NO_x emissions, the pressure exerted on the piston is greatly diminished by this technique. However, when water vapor is injected around the chamber walls, the resulting reduction in temperature and NO_x emissions has a minimum effect on the engine's P-V diagram. This is as a result of a water vapor blanket formed around the combustion zone, by the injected water vapor, which cools down the cylinder's wall with a minimum influence on the combustion process. Further analysis showed that the water injection technique could increase the power/torque per engine size and hence, increase energy efficiency. Ultimately, the study presents the advantages of using water injection for enhancing fuel efficiency and reducing pollutant emissions.