Experience of Continuously Regenerating Particulate Traps on City Buses in Europe

Experience from more than 16000 Continuously-Regenerating Trap Systems (CRT®) fitted to city buses over an eight-year period is described. The widespread adoption of particulate filters for diesel buses in European cities has been due to their high effectiveness in emissions reduction, but has depended on the relative simplicity of fitting a device that does not usually need interconnection with the engine controls. In conditions giving good passive regeneration (particulate oxidation by NO 2 under the normal exhaust conditions), the inherent durability is excellent. Almost all failures have been due too much soot accumulating in the traps, few of which yet have active regeneration systems. Such failures are usually spasmodic, and often due to high smoke from faulty engines, but a few bus fleets have suffered serious failure frequencies. These problems have been investigated and cured. Prevention being better than cure, engineering methods have been developed to predict passive regeneration performance in any application. Satisfactory trap durability requires adequate vehicle and trap maintenance. Recent developments in on-board filter condition monitoring and off-vehicle filter cleaning have reduced failure rates and extended the range of operation where passive regeneration is satisfactory.