Coupling of a NOxTrap and a DPF for Emissions Reduction of a 6-Cylinder HD Engine

Authors

Dipl.-Ing. T. Colliou, Dr. J. Lavy, Dr. B. Martin, Dr. J. B. Dementhon, IFP, Lyon; Dipl.-Ing. G. Pichon, Dipl.-Ing. K. Chandes, Dipl.-Ing. L. Pierron, RENAULT TRUCKS, St. Priest

Year

2003

Print Info

Fortschritt-Berichte VDI, Reihe 12, Nr. 539

Summary

To ensure overall optimization of engine performance (NOx, particulates, efficiency), the use of a NOx after-treatment system appears necessary to meet the European heavy duty vehicle EURO IV emissions standards. Among the identified means, the NOx-trap should offer efficiency comparable to that of reduction by urea, without having the same constraints. The trap works on the basis of the alternation of operating phases with a lean mixture during which NOx are stored and rich phases during which nitrates are destored and treated. The study has been performed on a RENAULT TRUCKS 6-cylinder 6,2 liters heavyduty engine. A first investigation with a NOx-trap only has been carried out to evaluate and optimise the storage, destorage and reduction phases from the NOx conversion efficiency and fuel penalty trade-off. The equivalence ratio level, which affects the regeneration phase duration and efficiency, the fuel penalty and the temperature level of the NOx-trap have been shown as a key parameter. From the results obtained, high equivalence ratio regeneration (around 1.18) provides the best results. The necessity to run in rich condition, even for a short time, leads to an increase of particulate emission level and a DPF is therefore required. The different possible arrangements of the two aftertreatment systems (NOx-trap and Catalysed DPF) have been evaluated in a second part of the study. The NOx–trap upstream the CDPF provides the best NOx / fuel penalty trade-off since it allows NOx slip reduction (reaction with the slipped reductants inside the CDPF) and do not disturb the rich pulses. For low NOx target, the requirement of NOx-trap regeneration frequency reduces the CRT effect efficiency. Thus, for these conditions, specific DPF regeneration strategies are required. The implementation of the CDPF upstream the NOx-trap can eliminate this drawback up to 1 g/kW.h NOx target without any CDPF loading process. Furthermore, the implementation of the CDPF upstream is favourable to avoid soot through the NOx-trap. With this configuration plus an oxidation cat downstream the NOx-trap to limit NOx, HC and CO slip, the fuel penalty is 1.8% for NOx reduction from EURO III to EURO V levels. CO level is also compatible with this target but HC must be further reduced. This can be achieved by the optimisation of the injection settings during rich pulses without any detrimental effect on fuel consumption. Partly funded by FSH (Fond de Soutien aux Hydrocarbures, a French public research fund), this investigation was operated by IFP and RENAULT TRUCKS.

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