Numerical and Experimental Study by Quasi-Dimensional Modeling of Combustion and Emissions in Variable Compression Ratio High-Speed Spark-Ignition Engine

Abstract

This work presents the development and use of a comprehensive, quasi-dimensional, two-zone combustion model aiming at predicting the combustion characteristics, performance, nitric oxide (NO), and carbon monoxide (CO) emissions of high-speed spark-ignition (SI) engine. The model is validated against pertinent data from experimental investigation conducted at the authors’ laboratory on experimental, Ricardo E6, mono-cylinder, high-speed SI engine, having the capability to operate over a wide range of compression ratios (CR) (variable compression ratio engine, VCR) and (fuel-air) equivalence ratios (EQR). In this work, a comparison between experimental and computational results is carried out for the engine fueled with gasoline, operated under various CR and EQR values at wide open throttle (WOT) position. The developed model is a two-zone one consisting of an unburned and a burned zone. It simulates the combustion process by following closely the flame front movement and development in the combustion chamber, at each instant of time, taking into account the history of pressure, temperature, and local composition. The unburned mixture turbulent entrainment into the burning zone through the flame front area is considered with its subsequent combustion. The flame front movement determines also the wetted areas and the volumes in the two zones. To determine the concentration of the chemical species equilibrium model is employed, while pertinent chemical kinetics schemes are used for computing NO and CO concentrations. The obtained pressure, mass fraction burned (MFB), mass fraction entrained (MFE), temperatures in the two zones, and NO and CO histories assist in the understanding of the complex phenomena involved, while they facilitate the interpretation of performance indices and knocking tendency. They shed light into the underlying physical and chemical mechanisms influencing the related SI engine performance and emissions attributes. The computed results are found to be in good agreement with the respective experimental ones.