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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.

This updated paper presents chassis dynamometer emissions testing of various heavy duty vehicles with and without retrofitted diesel oxidation catalyst technology. Analysis is provided into both the vehicle emissions baselines and emissions with retrofitted catalyst technology over the New York Composite and Central Business District cycles. The vehicles studied include four urban buses, two school buses and four heavy duty trucks. Some of these vehicles in this study have been followed for up to two years. The paper will discuss in-use heavy duty vehicle emissions issues and the use of diesel oxidation catalyst technologies.