As emission regulations for off-road engines become more and more stringent, alternative fuel off-road engines are being developed rapidly. This paper studies a closed-loop controlled LPG system, which was developed and tested on four lawn and garden engines.
The four engines studied are Kohler 18hp, Kohler 13 hp, Briggs & Stratton 6 hp, and Briggs & Stratton 5hp engines, which power Toro walk-behind commercial lawn mowers, John Deere lawn tractors, John Deere walk-behind commercial lawn mowers, and Toro walk-behind commercial lawn mowers, respectively. All engines are four-stroke, spark-ignited and air-cooled. The fuel management system is an air valve based closed-loop controlled dedicated LPG system. The emissions and durability test results are presented. It was found that all engines operating on propane had significantly lower exhaust emissions than those of gasoline baselines. Durability tests were conducted on the Kohler 18hp, Kohler 13hp and Briggs & Stratton 6hp engines under the SAE J1088 A cycle for 250, 250, and 500 hours, respectively. The durability tests revealed that all three engines showed no substantial deterioration of emissions or performance.