LPG Direct Injection: An Alternative Fuel Solution to the Two-Stroke Emissions Problem 2007-32-0024

Despite high fuel consumption and poor emissions two-stroke engines are a popular power source in developing countries due to their high power to weight ratio and low cost. To meet more rigid emissions requirements some manufacturers have switched from carburetion to Direct fuel Injection (DI). DI greatly reduces the emissions while simultaneously improving fuel economy. An alternative to this is the direct injection of a gaseous fuel such as Compressed Natural Gas (CNG) or Liquid Petroleum Gas (LPG), both of which may cost less than the equivalent amount of gasoline. A gaseous fuel DI system may also cost less than an air-assisted gasoline DI system as the gaseous system does not require a fuel pump, air pump or liquid fuel injector. In this paper we compare gasoline and premixed LPG as an alternative fuel for retrofit application to a 110cc two-stroke motorcycle. Engine performance, emissions and fuel consumption are measured on a dynamometer at various speeds and throttle settings. Results are compared for the original gasoline engine and the same engine running on pre-mixed LPG and air. Initial results are also presented with the engine operating on Direct Injected LPG at idle. Results indicate that HC emissions (on a mass basis) and fuel consumption similar for premixed LPG and gasoline. At idle HC and CO emissions are greatly reduced with Direct Injection of the LPG fuel.