Collaborative Research: NSF/DOE Advanced Combustion Engines: Radiation Heat Transfer and Turbulent Fluctuations in IC Engines - Toward Predictive Models to Enable High Efficiency

CBET-1258613

Daniel C. Haworth

The Pennsylvania State University

Michael F. Modest

University of California-Merced

Radiation heat transfer is important in most combustion systems, by virtue of their high temperatures. In practical applications, combustion usually occurs in a turbulent flow environment, where turbulent fluctuations in composition and temperature can significantly alter the radiative transfer rates. The importance of these ?turbulence-radiation interactions? (TRI) is increasingly being recognized. Computational models that neglect radiation and/or TRI, or that treat them in an over-simplified manner, can give inaccurate predictions of important quantities including heat transfer rates, temperatures, and pollutant emissions. Radiation is known to be responsible for up to half of the in-cylinder heat losses during the combustion event in compression-ignition internal combustion engines. Accurate determination of radiative transfer rates is exceedingly difficult, requiring the solution to a five-dimensional radiative transfer equation, and further exacerbated by strong spectral variations of radiative properties. The problem reaches another level of difficulty when interactions with turbulence are considered. Consequently, radiation and TRI in engines have received little attention to date. The purpose of this research project is to quantify the extent to which radiation and TRI influence the efficiency and emissions characteristics of compression-ignition engines, and to develop predictive computational models that can be used for engine combustion system development and design. Next-generation high-efficiency engines are expected to function close to the limits of stable operation, where even small perturbations to the energy balance can have a large influence on system behavior. It is expected that radiation and TRI may be particularly important for such engines. To this end, advanced multiphase spectral radiation models and radiative transfer equation solution methods will be extended to the highly transient, high-pressure combustion environments that are representative of current and next-generation compression-ignition engines. The models will be exercised to establish conditions where radiation and/or TRI are important, and where they may safely be neglected. Outcomes of the proposed project will include new physical models and numerical strategies for radiative transfer in high-pressure multiphase systems, new physical insight into radiation and TRI in combustion environments of practical interest, and validated models that have been connected to multiple underlying computational fluid dynamics codes.

Energy conversion involving turbulent combustion processes will remain important in global propulsion and power generation applications for the foreseeable future. This includes road vehicles, where ambitious near-term engine efficiency targets have been established that have the potential to significantly reduce energy and fossil fuel consumption. Radiation heat transfer is important in most combustion systems, but has received relatively little attention because of its extreme complexity. This project will provide advanced radiation models that will be part of the predictive computational tools that are required to develop high-efficiency engines. The physical insight and models that are developed will be relevant for other advanced combustion systems, including gas-turbine combustors.