| This study involves developing a multicomponent fuel vaporization model in the three-dimensional KIVA-II code to be used to study the effects of multicomponent fuel vaporization on diesel engine performance. The research was organized in three phases. First, the model was developed and applied to single droplets and compared to experimental results. In the second phase, the model was extended to handle multicomponent fuel sprays after modifying the spray submodels. The third stage involved applying the model to engine cases under standard and cold-starting conditions with an improved multistep kinetics ignition model. The KIVA-II code has also been already updated with state-of-the-art submodels including: a wave breakup atomization model, drop drag with drop distortion, spray/wall interaction with sliding, rebounding, and breaking-up drops, laminar-turbulent characteristic time combustion, and a crevice flow model.; The vaporization model, besides being able to describe bicomponent fuels, accounts for high pressure effects, variable properties, and variable Lewis numbers. Comparisons between the model results and the available experimental data for single droplets are satisfactory. The multicomponent fuel vaporization model was extended to model diesel sprays under typical diesel engine conditions. The spray results indicate the importance of multicomponent fuel effects at relatively low ambient temperatures.; The improved code was applied to engine computations to study the effect of various fuel parameters on engine performance. The computed results under standard or warm conditions are compared with experimental data from a Caterpillar engine equipped with a high-pressure, electronically-controlled fuel injector. Results agree reasonably well with the experimental data. The ignition model was modified to account for fuel composition effects by modifying the Shell ignition model. The effect of multicomponent fuel droplet vaporization on diesel engine cold-starting is studied, with particular attention to the effects of the air intake temperatures, fuel cetane number, injection timing and duration. The effect of fuel residual from previous cycles and from split injections was also studied and was found to be important. Another factor that was investigated was engine geometry and how it can be modified to improve on diesel cold-starting. |
