Investigating of fuel condensation processes under non-reacting conditions in an optically-accessible engine 2019-01-0197
Many engine experimental researches have concluded the importance of fuel condensation on determining the emission characteristics of low temperature combustion. However, direct experimental evidence has not reported in the literature. In this paper, the in-cylinder condensation processes observed in optically accessible engine experiments are illustrated at first. The observed condensation processes are then simulated using state-of-the-art multidimensional engine CFD simulations with a phase transition model that incorporates a well-validated phase equilibrium numerical solver, in which a thermodynamically consistent phase equilibrium analysis is applied to determine when mixtures become unstable and a new phase is formed. The model utilizes fundamental thermodynamics principles to judge the occurrence of phase separation or combination by minimizing the system Gibbs free energy. It is shown that thermodynamically unstable mixtures are formed during the late expansion stroke for the conditions of the experiments. Close agreement on the beginning of condensation is observed between the simulations and available experiments. Sensitivity analyses show that the condensed fuel mass will decrease if initial temperature decreases or pressure increases.
Lu Qiu, Rolf Reitz, Ethan Eagle, Mark Musculus
University of Wisconsin Madison, Wayne State University, Sandia National Laboratories