Towards Securing the Particulate Trap Regeneration: A System Combining a Sintered Metal Filter and Cerium Fuel Additive 982598

The paper reports on a study performed as a joint project between Rhodia, Renault Automobiles and AVL and deals with the application of a sintered metal trap (SMT) whose regeneration is supported by the use of a Ce-based fuel-borne catalyst installed on a delivery van equipped with a conventional IDI/NA diesel engine. For demonstration purpose, a trap protection strategy was developed with the aim to minimize the trap loading and thus the consequent fuel consumption penalty that can be observed for worst-case low speed driving scenarios. Measures to temporarily increase the exhaust gas temperature during inner-city driving and therefore to initiate the start of regeneration were successfully applied.

MAJOR EFFORT IS BEING currently undertaken to develop and apply advanced aftertreatment systems to meet future proposed exhaust gas emission standards for passenger cars, LDT and HD diesel engines.

Fig. 1 shows as an example the potential of HSDI engines with respect to achieving different US emission standards depending on vehicle weight. With advanced HSDI diesel engines, the emission standards for NOx and particulate could be met when using electronically controlled EGR and oxidation catalysts up to certain vehicle weights. Further improvements may be expected by new technology elements currently being pursued /1/ such as improved fuel injection equipment, highly dynamic EGR systems, cooled EGR etc. However, since emission levels generally increase proportional to the vehicle weight, the introduction of advanced exhaust gas aftertreatment systems besides the oxidation catalysts will primarily be a necessity of heavier vehicles.

In addition to the beneficial effects of improved fuel quality on emissions, possible strategies to reduce NOx and particulates (as the main pollutants in diesel exhaust) are summarized in Fig.2.

By the application of electronically controlled EGR together with oxidation catalyst and the further improvement of the combustion process, in some cases the legislative emission targets could be met. However, as emission standards of NOx and particulate will be tightened further in the future, additional measures besides in-cylinder control and oxidation catalyst will be needed.

Both particulate trap system and DENOx catalyst are seriously considered as additional strategies to reduce NOx and particulates /2/. In order to meet the fictitious emission targets, basically two routes may be adopted:

• Reduction of particulate emissions to the target level by measures on the engine (e.g. fuel injection with high pressure) and the application of a DENOx catalyst requested to offer high NOx efficiency (e.g. SCR or NOx storage catalyst with more than 60% reduction. However, such systems are not yet proven to offer such an high efficiency.
• Reduction of NOx emission to the target level by engine measures (e.g. cooled EGR with high rates) and application of particulate trap /3/.

Which of these strategies could be applied as a serial solution in the future is a currently still open question.

Considering only the use of particulate traps in the following, it is worth noting that it would be beneficial not only for achieving future standards or even current regulations /4/, but also as a retrofit solution to improve the environmental situation in inner cities - application to busses /5,6,7/ and/or vans transporting goods - resulting in the reduction of visible and therefore disturbing black smoke. However, many problems must be overcome.

Only particulate trap systems which are cost-effective and therefore self-regenerating without any external and costly measures and durable might be used on a large scale.

One of the possible ways how to manage such an application is being described in this paper.