A diesel particulate trap system using two (2) monolithic ceramic filters and a diesel burner was designed for the 6V-92TA 2-stroke bus engine. The system comprises an electronic controller which controls four (4) valves to direct exhaust flow and burner heat flow. The exhaust passes through one filter, while trapped particulate is being regenerated in the other. The burner control sequence was optimized to avoid overheating of the system components and thermal shock of the traps. The system was tested for 100 hours in a test cell, using the New York Bus Cycle. Engine backpressure showed no noticeable increases from the baseline.
The need to reduce particulate emissions from transit coach engines in the U.S.A. is driven by two forces.
The need to meet the 1991 EPA emission standards for new coach engines.
the need to retrofit in use coach engines, to reduce the particulate burden in the atmosphere of North American cities and assist cities in meeting air quality regulations defined by the Clean Air Act.
Various approaches are under development, including changing the fuel to methanol or natural gas. The use of a diesel particulate trap system offers the advantage to transit operators of maintaining their diesel fuel infrastructure. However, such a system has not yet been proven in service, especially with the Detroit Diesel 6V-92TA engine commonly used in transit coaches, where the two stroke design results in very low exhaust gas temperatures making trap regeneration more difficult. Progress was reported by a number of researchers, however, employing both coated wire mesh traps (1) and ceramic monolith traps (2), and more recently, an engine throttling approach showed promise in periodic forced regeneration of the trap (3). Various trap regeneration approaches were investigated in this laboratory with a Detroit Diesel 2-stroke 6V-71NA coach engine (4), including fuel additives, catalyst coatings, blower by-pass, and diesel burner systems. It was concluded that the combination of a catalyst coated ceramic monolith trap together with a burner regeneration system offered one of the more promising approaches to achieving practical emission control technology. The present paper therefore, describes the development and application of a diesel particulate trap system, using two monolithic ceramic traps and a diesel burner regeneration system, designed for automatic operation on a Detroit Diesel 6V-92TA 2-stroke bus engine.