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In this work the modeling aspects of fuel vaporization are studied. To start with, the effects of vaporization model on engine simulations are studied. This is done by using two different fuel surrogates. Next a set of non-reacting spray simulations were performed under different ambient and operating conditions and for two different fuels. This was done for spray model validation and to look at the effect of vaporization model on liquid penetration length. Following an observed discrepancy in one of the spray cases, effect of ambient temperature on liquid length, two sensitivity analyses were performed. These analyses take into account the effects of each spray-sub model on vaporization and effects of spray breakup constants on liquid penetration. Using the results from the sensitivity analyses and linearized stability theory an empirical correction factor was developed to correct the spray behavior at low ambient temperatures.

In most large-eddy simulation (LES) applications to two-phase engine flows, the liquid-air interactions need to be accounted for as source terms in the respective governing equations. Accurate calculation of these source terms requires the relative velocity “seen” by liquid droplets as they move across the flow, which generally needs to be estimated using a turbulent dispersion model. Turbulent dispersion modeling in LES is very scarce in the literature. In most studies on engine spray flows, sub-grid scale (SGS) models for the turbulent dispersion still follow the same stochastic approach originally proposed for Reynolds-averaged Navier-Stokes (RANS). In this study, an SGS dispersion model is formulated in which the instantaneous gas velocity is decomposed into a deterministic part and a stochastic part. The deterministic part is reconstructed using the approximate deconvolution method (ADM), in which the large-scale flow can be readily calculated.

A swept-volume method of calculating the volume swept by the flame during each time step is developed and used to improve the calculation of fuel reaction rates. The improved reaction rates have been applied to the ignition model and coupled with the level set G-equation combustion model. In the ignition model, a single initial kernel is formed after which the kernel is convected by the gas flow and its growth rate is determined by the flame speed and thermal expansion due to the energy transfer from the electrical circuit. The predicted ignition kernel size was compared with the available experimental data and good agreements were achieved. Once the ignition kernel reaches a size when the fully turbulent flame is developed, the G-equation model is switched on to track the mean turbulent flame front propagation.