Filtration of Diesel Soot Nanoparticles and Reliability in Swiss HDV Retrofitting 2005-26-015

Based on the emission inventory Fig. 1, the Swiss 1998 Ordinance on Air Pollution Control (OAPC) mandates curtailment of carcinogenic diesel particle emissions at type B construction sites [1]. Moreover, particle traps are compulsory at underground workplaces [2]. In compliance, more than 6,000 Diesel engines were retrofitted with various particle trap systems. Many traps surpassed 99% filtration efficiency and secondary emissions were mostly prevented. However, trap failure due to mechanical and thermal damage was initially rather high at about 10%. By the year 2000 the failure rate was halved to about 6%. Thanks to focussed improvements, the year 2003 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%.

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 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 designs, power range and age for all construction machines. 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.