1992-02-01

Development of an I/M Short Emissions Test for Buses 920727

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. These samples are collected over two short test cycles using 30-second sampling intervals, while the bus engine is operated in a specified manner with the brakes locked and transmission in “Drive.” Concentrations of CO, NOx, and O2 are determined using a portable emissions analyzer. Particulate concentrations or smoke levels are assessed by reading the light reflectance of the sample filter (this filter may also be weighed for quantitative determinations). Ideally, “short-test emission factors” can be used to estimate EPA transient cycle emissions of CO, NOx, and particulate as derived for a 1986 DDC 6V92-TA in this work. Additional correlation work to include other engine families is dependent on continued industry interest.

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