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Air-fuel ratio control in gasoline engines has so far relied upon the fact that the stoichiometric air-fuel ratio of gasoline is an identified constant, largely thanks to its consistent chemical composition. In the case of Liquefied Petroleum Gas (LPG), chemical composition is subject to high variability due to geological and economic factors, amongst others. The implication of this variability is unpredictable stoichiometric air-fuel ratio of the fuel supply within any given vehicle, and ultimately degraded control of air-fuel ratio. This paper addresses the problem of stoichiometric air-fuel ratio estimation by evaluating the measurement and modeling of the relative permittivity of fuel, and also the method of iterative computation. For the estimation method proposed in this paper, simulation results are presented to demonstrate its effectiveness.

A phenomenological model having modular formulation is presented for combustion in the open chamber diesel engine. The modules for fuel injection, jet penetration and droplet formation have been calibrated outside the engine in a high pressure, fixed volume chamber by high speed photographic and laser analysis of single spray ‘shots’. In the diagnostic mode of operation the chemical components of the combustion reaction are estimated. In the predictive mode of operation the model is used to estimate engines’ pressure diagrams and various other combustion characteristics of the fuels over a wide range of speed and load conditions. Finally, sensitivity analyses of the reaction rate constants of five fuels namely distillate, sunflower oil, rapeseed oil and methyl esters of sunflower and rapeseed oils, to some of the model inputs are presented.