Quasidimensional modeling of reacting fuel sprays using detailed chemical kinetics
Date
2016
Authors
Dobos, Aron Peter, author
Kirkpatrick, Allan T., advisor
Marchese, Anthony, committee member
Gao, Xinfeng, committee member
Venayagamoorthy, Karan, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Since its invention in the late 1800s, the internal combustion engine has been indispensable to society for motive transport at all scales worldwide. Despite growing concern about the environmental damage caused by the pervasive use of these engines, no compelling alternative has yet emerged that matches the internal combustion engine's robustness, versatility, and high power-to-weight ratio. Consequently, as requirements on engine designs continue to increase to meet new emissions and efficiency standards, there is a strong need for computationally efficient and accurate predictive modeling of complex engine combustion processes. This work presents an efficient approach to direct injection engine combustion simulation that uses detailed chemical kinetics with a quasidimensional fuel spray model. Instead of a full multidimensional approach that solves continuity, momentum, energy, and chemistry equations simultaneously over a fine grid, the spatial information is greatly reduced and modeled phenomenologically. The model discretizes the fuel spray into independent parcels that entrain air from the surroundings and account for liquid fuel vaporization. Gas phase species concentrations and heat release in each parcel are calculated by detailed chemical kinetic mechanisms for the fuel under consideration. Comparisons of predicted pressure, heat release, and emissions with data from diesel engine experiments show good agreement overall, and suggest that spray combustion processes can be modeled without calibration of empirical constants at a significantly lower computational cost than with standard multidimensional tools. The new combustion model is also used to investigate spray structure and emissions trends for biodiesel fuels in a compression ignition engine. Results underscore the complex relationships among operational parameters, fuel chemistry, and NOx emissions, and provide further evidence of a link between stoichiometry near the flame lift-off length and formation of NOx. In addition, fuel molecular structure is demonstrated to be a significant factor in NOx emissions, but more robust chemical kinetic mechanisms and soot models for biodiesel are likely needed for improved predictive accuracy in modeling alternative fuels.