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Emissions from existing diesel-powered urban buses are increasingly scrutinized as local, state, and federal governments require enforcement of more stringent emission regulations and expectations. Currently, visual observation of high smoke levels from diesel-powered equipment is a popular indicator of potential emission problems requiring tune-up or engine maintenance. It is important that bus inspection and maintenance (I/M) operations have a quality control “test” to check engine emissions or diagnose the engine state-of-tune before or after maintenance. Ideally, the “emission test” would be correlated to EPA transient emissions standards, be of short duration, and be compatible with garage procedures and equipment. In support of developing a useful “short-test,” equipment was designed to collect samples of raw exhaust over a short time period for gaseous and particulate emissions.

Emissions regulations for 2007 will likely require engine manufacturers to use a diesel particulate filter (DPF) to meet particulate matter (PM) emission requirements. With the lower operating temperatures of light-duty diesel engines, some form of catalyst will be required to facilitate oxidation of accumulated soot PM to regenerate the DPF. This catalyst can either be permanently applied to the filter substrate in the manufacturing process, or be continuously delivered via the diesel fuel. In this study we examined the impact of using both forms of catalyst. A recently published study of the fuel-borne catalyst additive MMT [1] (Methylcyclopentadienyl Manganese Tricarbonyl), reviewed the performance of MMT in conjunction with an uncatalyzed DPF [2].