Liquid State LPG Conversion of an Older Vehicle 2014-01-2613

A conversion to LPG of a SI engine that was originally carbureted gasoline is reported in this work. The conversion was implemented on a 1988 Skoda 120L with a 1174cc rear engine. The conversion to run on Liquefied Petroleum Gas (LPG) was carried out using a programmable Engine Control Unit (ECU) that operated a single point fuel injection system. The LPG used was a commercially available mixture of butane and propane. The fuel injection system was designed to operate with the LPG in the liquid state. A circulating pump was used to maintain availability of LPG in liquid state at the inlet to the fuel injector. This made possible the use of similar fuel injection parts as in a gasoline system. Injection of the fuel in the liquid state provided cooling to the intake air as measured during driving of the vehicle and also on chassis dynamometer runs. Engine power output measured on the chassis dynamometer showed equal power between gasoline and LPG around mid RPM of 2500 RPM with a slight decline (4%) in power of the LPG system at 5000 RPM. The conversion was so designed such that the vehicle could cold start on LPG. However the engine could also be reverted to run on gasoline by the changeover of an electrical switch. The dual fuel strategy was adopted due to the fact that the LPG storage container used was relatively small compared to the size of the gasoline tank.