The Development and In-Field Performance of Highly Durable Particulate Control Systems 2004-01-0072

The tightening of Heavy Duty Diesel (HDD) emissions legislation throughout the world is leading to the development of emission control devices to enable HDD engines to meet the new standards. One system which has shown great promise in controlling PM emissions is the Continuously Regenerating Trap (CRT^®) system. This system will be referred to as the CR-DPF for the remainder of this paper.

Stringent durability requirements will be introduced alongside the new legislative emission limits, so it is essential that DPF systems are made to be as robust as possible. In Europe the systems are expected to need to meet a durability target of 500,000 km, while in the US this will be approximately 700,000 km (435,000 miles).

This paper reports on the development of a greatly improved oxidation catalyst for these CR-DPF applications. Field and engine bench studies revealed that the previous catalyst could be poisoned by sulfur build-up during prolonged operation at low temperatures. A new, more sulfur-tolerant catalyst was developed in an engine bench study, and field trials were then carried out to compare the real-world performance of the new and old catalysts within the CR-DPF system. These trials have demonstrated that the new catalyst is far more active than the previous catalyst following 80,000 km of real-world operation. In addition, far less sulfur was present on the new catalyst after this field ageing, demonstrating that the catalyst design strategy was successful.

We have previously shown that superior low temperature passive PM regeneration can be obtained in engine bench tests by combining an upstream Oxidation Catalyst with a Catalysed Soot Filter (CSF) within the CR-DPF configuration. This Catalysed CRT (CCRT™) system will henceforth be referred to as the Oxicat + CSF system. The passive, in-field durability of the CR-DPF and Oxicat + CSF systems have been compared over challenging, low temperature duty cycles, and it has been shown that the Oxicat + CSF system significantly out-performs the CR-DPF system within such applications. This is the case even when the total amount of active metal component is the same in the two systems. Therefore, the real-world durability of the Oxicat + CSF system is significantly better than that of the CR-DPF system over very low temperature duty cycles.