Walls, M., Joo, M., and Ross, M., "Impact of the Direct Injection of Liquid Propane on the Efficiency of a Light-Duty, Spark-Ignited Engine," SAE Technical Paper 2017-01-0865, 2017, doi:10.4271/2017-01-0865.
Liquefied petroleum gas (LPG) is commonly known as autogas when used as a fuel for internal combustion engines. In North America, autogas primarily consists of propane, but can contain small amounts of butane, methane and propylene. Autogas is not a new fuel for internal combustion engines, but as engine technology evolves, the properties of autogas can be utilized to improve engine and vehicle efficiency. With support from the Propane Education & Research Council (PERC), Southwest Research Institute (SwRI) performed testing to quantify efficiency differences with liquid autogas direct injection in a modern downsized and boosted direct-injected engine using the production gasoline fuel injection hardware.Engine dynamometer testing demonstrated that autogas produced similar performance characteristics to gasoline at part load, but could be used to improve brake thermal efficiency at loads above 9 bar Brake Mean Effective Pressure (BMEP). This improvement was attributed to the favorable octane rating of autogas. At higher loads, where the engine was knock limited on gasoline, autogas allowed operation at or near Minimum advance for Best Torque (MBT) timing and reduced the need for fuel enrichment to control exhaust temperature. At full load, the engine was capable of operating at a stoichiometric air-to-fuel ratio on autogas up to 4000 RPM, without exceeding the turbine inlet temperature limit.