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This paper describes a study into the emissions performance of a passenger car running on natural gas and liquified petroleum gas. The gasoline engine was modified to allow the introduction of the alternative fuels into the engine. The effect of fuel system hardware on emissions was investigated. Modifications were carried out to the gasoline EMS to allow control of the alternative fuel systems. A number of changes were made to the gasoline calibration to allow operation on the alternative fuels. Emissions tests were conducted on commercial grade natural gas and liquid petroleum gas. The results were compared with gasoline emission results of an equivalent vehicle.

A multiplex communication system has been developed for the Ford Alternative Fuel Qualified Vehicle Modifier (QVM) program, linking the vehicle's powertrain control module (PCM) to the alternative fuel (natural gas or propane) control module (AFCM). The system allows precalibrated diagnostic routines (OBD and non-OBD) to be selectively modified and disabled which otherwise would be affected by alternative fuel operation. The system enables the broadcasting of selected information from the PCM for use by the AFCM. An additional benefit is smoother transition between alternative fuel and gasoline operation when the gaseous fuel is depleted. Also, improved emissions on the alternative fuel have been noted due to the link. System development and function are detailed in this paper.