Development of an Emission Control System for Two-Stroke Diesel Powered Transit Coaches

The development of a system to reduce exhaust particulate emissions from a Detroit Diesel 6V71NA engine used in many existing city transit buses is described. During the development, tests were carried out with a ceramic wall flow monolith diesel particulate trap using both fuel additives and catalyst coatings as primary filter regeneration aids.

Both manganese and copper-manganese fuel additives were found to cause plugging of injector spray nozzles with deposits on the injectors, resulting in unsatisfactory engine performance. Precious metal catalyst coatings allowed partial trap regeneration to occur when the engine was operated over a modified New York City bus cycle on a computer-controlled engine test bed. This has resulted in satisfactory exhaust backpressures being maintained over time periods in excess of 40 hours of operation. A regeneration subsystem is employed to reduce the backpressure to the clean trap condition.

Tests of various regeneration subsystems will be described, and a best overall system will be discussed with respect to integration and field testing in a city bus.