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The recent tightening of emission standards for new heavy duty engines has lead to the development and implementation of alternative fuel engines, particularly for urban transit bus applications. Alternative fuels are intended to offer a potential emissions benefit with regards to the regulated emissions, and especially the particulate matter, which has received the greatest degree of regulatory action. However, the entire composition of the engine emissions should be considered when evaluating the environmental benefits of these new fuels, and also the continued performance of these engines in actual fleet service. In this study the exhaust emissions from methanol, ethanol, and diesel - powered buses were determined during transient operation of the vehicles on a heavy duty chassis dynamometer. The tests of the alcohol fuelled buses, and a control diesel bus were conducted as the buses accumulated mileage in revenue generating service.

The Province of BC requires all light duty vehicles in the lower mainland to pass or conditionally pass an emissions inspection as a condition of license and insurance renewal. Vehicles converted to natural gas and propane fail emissions tests at higher rates than comparable vehicles run on gasoline. Work is described to investigate the emissions performance of vehicles fitted with after-market conversions. FTP 75, Hot 505 and BC AirCare test cycles (total 74) were performed on a variety of vehicles (total 20) which were split between dual-fuel and mono-fuel using propane or natural gas along with gasoline. All but three vehicles were supplied by the manufacturer to run on gasoline with closed-loop air/fuel ratio feedback. The after market conversions consisted of both open-loop and closed-loop feedback systems for the gaseous fuel systems.