As an automotive fuel source, LPG has great promise when compared to petrol (gasoline). Two of the main motivating influences are (1) its simpler chemical composition promises lower emission levels and (2) the lower fuel cost provides improved fuel economy. Currently in Australia, most LPG fueled vehicles are aftermarket conversions to dual-fuel with a gas carburetor system, although recently a dedicated LPG vehicle was released although this still functions on the gas carburetor system. The improved level of fuel delivery control offered by fuel injection (either in liquid or gaseous phase) offers further improvements in both fuel economy and power delivery as was seen in petrol injected vehicles, as well as avoiding problems such as backfire into the intake manifold. Furthermore the tightening of government legislation is also driving the shift towards LPG injection. As a result, future generations of LPG vehicles released by the manufacturers are certain to use injection as the method of fuel delivery. However, the variable composition of LPG (in Australia the mixtures available have been shown to vary between almost pure propane to propane butane ratios of 1:1) introduces an additional challenge for stoichiometric air fuel ratio control over those normally encountered with petrol where the mixture is relatively constant. In this talk I will give an overview to the research at The University of Melbourne into the two of the control issues facing LPG injection, firstly examining the problem of stoichiometric air fuel ratio identification and estimation and then discussing the adaptation of air fuel ratio strategies derived for petrol to apply to LPG.
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