Reliability of DPF - Systems : Experience with 6000 Applications of the Swiss Retrofit Fleet

The Swiss 1998 Ordinance on Air Pollution Control (OAPC) mandates curtailment of carcinogenic Diesel particle emissions at construction sites [4]. In addition particle traps are compulsory at underground workplaces [3]. In compliance, more than 6,000 Diesel engines were retrofitted with different particle trap systems. Many traps surpassed 99% filtration efficiency, from the beginning, and secondary emissions were mostly prevented. However, trap failure due to mechanical and thermal damage was initially rather high at about 10%. By Y-2000 the failure rate was halved to about 6%. Thanks to focussed improvements, the Y2003 statistics show yearly failures of “only” about 2%. The Swiss target is to retrofit 15,000 construction machines with traps, fully compliant with environmental directives, having 5,000 operating hours durability and failure rates below 1% . Fig1: Contribution of on-road and off-road Diesel engines to particle emissions in Switzerland. Note the relatively high impact of construction site machines [19], despite much fewer engines than in trucks and agriculture tractors. Construction machines have much higher PM-emission factors than trucks, and are operated more intensely than tractors. Traps must pass the VERT suitability test before deployment. The type certification for a representative example of a trap family comprises very detailed measurements of the filtration characteristics and the tendency to secondary emissions. The trap system is also verified in typical field deployment during more than 2,000 operating hours. Moreover, all construction machines are periodically inspected for emissions and functionality. Trap certification is cancelled when more than 5% failure is detected annually. This paper reports on the filtration quality of VERT-Test compliant traps, both in the new state and after prolonged deployment of at least 2,000 operating hours. The paper examines trap failures, their causes and prevention based on information from manufacturers, retrofitters and independent inspections. The work was performed in close collaboration with the regulatory authorities and the trade association AKPF of the trap manufacturers and retrofitters. The experience with this large retrofitted fleet shows the applicability of traps for Diesel engines of various design, power range and age for all construction machines – the directive includes no exceptions. The particle trap technology is demonstrated as technically, operationally and economically feasible. However there are several important prerequisites: comprehensive suitability testing, careful function monitoring and regular field inspection. Thus the targeted effectiveness and dependability are ensured.