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Effects of water injection to the fuel and air mixture on equilibrium gas composition in combustion products and selected parameters of the theoretical Otto cycle.

The aim of the water injection into the air or air/fuel mixture is to cool a mixture for reducing the gas temperature level during combustion for reducing knock. Fundamentally, water injection in the spark-ignition (SI) engine helps in controlling the temperature and pressure of combustion process. Intake air humidification by means of spraying water in liquid phase significantly reduces the temperature of intake air mainly because of the high value of latent heat of vaporisation. In compression stroke a decrease in the initial temperature and adiabatic index and an increase in the specific heat capacity of working medium resulting from increased water content, lowered the in-cylinder temperature and pressure. In the paper will be given the methodology for determining the equilibrium combustion product composition in expansion stroke resulting from the combustion of fuel CαHβOγNδ in humidified air. In the case of gasoline as a fuel, an exemplary calculations and analyzes will be made to investigate the impact of water injection on the composition of combustion products and selected parameters of the theoretical Otto cycle (temperature, pressure, power and thermal efficiency) for different possible water-fuel mass ratios.Two water injection systems will be analyzed: to the inlet manifold and directly to the cylinder in compression stroke
Topic: Combustion processes in SI and CI engines
Author: Andrzej Sucheta