The Development and On-Road Performance and Durability of the Four-Way Emission Control SCRTTM System

The progressive tightening of the Heavy Duty Diesel emissions legislation worldwide necessitates the development of pollution control systems capable of enabling engines to meet the incoming legislative requirements. It is clear that to maximise the benefit to the environment, as well as to meet the very stringent future standards (especially the US 2010 limits), systems capable of high simultaneous conversions of all four major pollutants, carbon monoxide (CO), hydrocarbons (HC), oxides of nitrogen (NOx) and Particulate Matter (PM), are required. Very high conversions of CO, HC and PM are achieved using catalyst-based Diesel Particulate Filter (DPF) systems, such as the Continuously Regenerating Technology, CRT, system. High NOx conversions can be obtained using Selective Catalytic Reduction (SCR) systems, in which ammonia (generated from urea) is used to selectively reduce the NOx. This paper summarises the key steps in the development of the four-way SCRT system, which comprises the CRT system followed by an SCR system. Engine bench results obtained during the development of this system are presented and discussed. However, the key to real-world emissions benefit is the actual on-road performance of such systems. It is well established that the CRT system provides very high and durable conversions of CO, HC and PM, so the focus of this current work was to demonstrate the NOx conversion capability and durability of the SCRT system. The SCRT unit was installed on a long-haul truck powered by a 15 litre Cummins engine. On-road NOx emissions performance was measured using NOx sensors located upstream and downstream of the SCRT unit. Over an 850 km evaluation route, the average on-road NOx conversion obtained was up to 82%, even when the urea injection quantity was set to give a maximum NOx conversion of around 85%. The durability of the system has also been assessed. Over the course of 150,000 km, no reduction in the NOx conversion efficiency of the system was observed. The results presented in this paper demonstrate that the SCRT system provides very high on-road NOx conversion, and that the system has excellent durability within real-world applications. * author for correspondence: Dr Andrew P Walker Johnson Matthey plc, Orchard Road, Royston, Herts, SG8 5HE, UK Tel: 44-1763-253349 Fax: 44-1763-253815 e-mail: walkeap@matthey.com INTRODUCTION The progressive tightening of the emissions standards for Heavy Duty Diesel vehicles throughout the world presents challenges for the engine development and emission control communities. In both Europe and North America the major challenges are in PM and NOx control for the legislation to be introduced in 2005 (Euro IV), 2007 (US ’07), 2008 (Euro V), and 2010 (US ’10). Table 1 summarises the evolution of the emissions standards in Europe, and Table 2 outlines the US regulations. Table 1: Emissions Legislation Limits in Europe (ESC Test Cycle; g kW hr)