Conversion of gasoline Saturn SL-1 to dedicated compressed natural gas use

This thesis project investigates the viability of creating a practical, low-cost conversion of a light-duty vehicle to dedicated natural gas service. The vehicle used in the study is a 1991 Saturn SL-1.

The paper focuses on three main aspects: installation of conversion hardware, use of an electronic controller to tailor engine performance, and measuring performance of the final vehicle.

The conversion hardware consists primarily of a single compressed natural gas tank with brackets; valves, tubing, a pressure regulator, fuel injectors, and other components to create a fuel delivery system. Engine conversion involves substitution of original pistons with "flat-top" pistons, raising the compression ratio to 11.0:1.

An aftermarket electronic engine controller with comprehensive software manages all basic engine functions using existing engine sensors and output devices. The OEM controller is left only non-engine tasks to perform.

Initial performance data reveal a 7% decrease in engine torque, but a vehicle highway range (at 3600 psig initial fill) of 250 miles. Further testing and evaluation of the conversion are recommended.