Modelling of liquefied petroleum gas spray development, evaporation and combustion

Abstract

The research reported in this paper is the computational part of a joint experimental/computational investigation of the possible utilization of liquefied petroleum gas (LPG) in a direct injection internal combustion engine. Many aspects of spray modelling have been investigated in the research. This paper concentrates on the implementation of three aspects, namely (a) the incorporation of LPG (butane or propane) physical and chemical properties, (b) the development of a flash evaporation model and (c) the application of a laminar flamelet model of combustion, extended to handle mixtures with equivalence ratios other than unity and implemented here for the first time to simulate spray combustion. The latter two aspects of the research are dealt with in some detail, with the models given prominence in the paper. The solution procedures for the whole model are also outlined. The model is tested by simulating a number of non-evaporating and evaporating LPG sprays. The flash evaporation model is shown to produce both quantitative and qualitative results that are realistic and have a reasonable degree of accuracy, where this is currently measurable. Non-flashing LPG sprays are also shown to be well simulated. The combustion of a number of LPG sprays and a diesel spray is shown to be simulated realistically. The combustion model is found not to require ‘tunable’ constants in order to obtain a reasonable level of agreement with reaction rates for both fuels. Various suggestions for improvements to the models are advanced as well as a series of suggestions for further research in order to enhance the accuracy and capabilities of the models.