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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.

A 261 kW (350 hp) spark-ignited, turbo-charged and aftercooled Cummins “Big Cam” propane engine was developed and tested for class 8 truck application. Two propane engines were operated in line-haul service for a total of 33 months and almost 350 000 kilometres (217 480 miles). A diesel-powered tractor, in similar service, was monitored for comparison. Fuel economy, oil consumption, maintenance, drivers' comments, and engine refinements were fully documented. Propane fuel economy averaged 94 L/100 km (2.5 mpg), relative to 45 L/100 km (5.2 mpg) with the diesel. Overall reliability was good and driver acceptance excellent; however, further refinements, especially in the turbocharger, ignition, and cooling system, are required to compete with the modern diesel.