Mark Stephen Brogan

Development of a rapid sulfation technique and fundamental investigations into desulfation process

Effective implementation of lean NOx trap (LNT) technologies requires the development of desulfation strategies to prevent significant degradation of LNT performance as a result of sulfur poisoning. Key to desulfation investigations is the requirement for a controllable and realistic sulfur loading model. The use of market based fuels can give inconsistent results due to variation of sulfur levels, and increased engine development times. Traditionally, increasing the sulfur level in the fuel via a specific sulfur based dopant has been used to accelerate the sulfation. This research used a different approach, in which sulfur dioxide was rapidly injected immediately prior to the LNT. The ability to replicate slow sulfur accumulation, as well as the benefits of injection control are demonstrated on a gasoline direct injection spark ignition (DISI) engine with LNT aftertreatment, tested on a dynamic dynamometer facility. The development of the sulfation injection technique enabled a series of sulfur loads and desulfation (DeSOx) experiments to be run. This study investigated the effect of sulfur loading, LNT temperature, and air:fuel ratio (AFR) on the DeSOx efficiency. The study shows that LNT DeSOx rate is fundamentally linked to the LNT temperature; and that other parameters, such as sulfur load, are far less critical to desorption rate.

The Effect of Different Ageing Conditions on Spatial Variations in Emissions Across the Radius of a Close-coupled After-treatment System

Using local emissions measurements immediately downstream of a close-coupled catalyst, spatial variations in emissions have been analysed for close-coupled catalysts with different ageing histories. Comparison of the radial emissions profiles between a uniformly-aged (oven-aged) catalyst and two vehicle-aged parts suggests that the vehicle-aged parts have substantial variations in catalyst damage across the radius of the catalyst. The radial variations in damage were confirmed by bench reactor and post-mortem studies. The radial catalyst damage profiles inferred from engine-based evaluations of vehicle aged catalysts show broad correlation with high flow areas identified by CFD predictions and high temperature regions as measured during engine tests. Assessment of the results obtained from CFD analyses, engine-based evaluations, bench reactor evaluations and post-mortem suggests that flow non-uniformity creates high thermal gradients, leading to localised damage of the brick, thus degrading overall catalyst performance.