Catalysed Diesel particulate filter: study of the reactivity of soot arising from biofuel combustion

Nora  Lamharess, IFP Energies nouvelles -Lyon

Abstract for Cleers 2011
Cross-Cut Lean Exhaust Emissions Reduction Simulations
Catalysed Diesel particulate filter: study of the reactivity of soot arising from biofuel combustion
Nora Lamharess1*, Claire-Noelle Millet1, Laurie Starck2, Patrick Da Costa3

1IFP Energies nouvelles, Rond-point de l'?changeur de Solaize, BP 3, 69360 Solaize, France
2IFP Energies nouvelles, 1-4 avenue de Bois-Pr?au, 92852 Rueil-Malmaison, France
3Institut Jean le Rond d'Alembert, universit? Pierre et Marie Curie, 2 place de la gare de ceinture 78210 Saint Cyr l'?cole, France

*corresponding author : nora.lamharess@IFPEN.fr

Nowadays the challenge consists in reducing vehicle greenhouse gases, polluting emissions and dependence on fossil oil energy. Governments are thus increasingly mandating the use of various types of biofuels which would partly resolve this environmental and economic problem.
This work aims to study firstly the impact of biofuels on polluting emissions, focusing on soot particulate matter (PM), and secondly the reactivity of soot which is trapped in a catalysed Diesel particulate filter (CDPF).
The fuel matrix is as follows:
*An ultra low sulfur diesel ("ULSD") which contains less than 10 wt ppm sulfur, no oxygen, and 22 wt% aromatics. This fuel is typical of a conventional European Diesel fuel.
*A blend "B30" made with 30% of biodiesel and 70% of ULSD fuel. Notice that biodiesel is mainly composed of RME (Rapeseed Methyl Ester).
*A blend "FT30" done with 30% of synthetic Fischer-Tropsch fuel derived from a gas-to-liquid process and 70% of ULSD fuel.

A DW10B common-rail Diesel engine from PSA was operated at 1500 rpm and 5 bar of BMEP and equipped with a catalysed diesel particulate filter. The three test fuels and the corresponding polluting emissions were analysed. PM samples were characterised in terms of composition and structure. Their reactivity was evaluated on a synthetic gas bench by temperature programmed and isothermal oxidation tests.
On the engine bench, no differences between pollutant emissions were observed between FT30 and ULSD fuels. Whereas a reduction of about 36% of PM and 34% of CO emissions was obtained with B30 biofuel compared to ULSD fuel. It was attributed to the higher oxygen amount of B30 fuel.
Reactivity tests were made on a synthetic gas bench (SBG) in the presence and absence of soot. The goal is to determine the effect of each soot on the CDPF behaviour towards HC and CO oxidation. The catalyst used is the "DPNR" commercialized by Toyota, which is capable to treat at the same time the four pollutants: HC, CO, NOx and soot. The gas mixture was chosen as representative of the exhaust gas.
Unlike ULSD, FT30 and B30 soot can inhibit, in some cases, CO and HC conversion around 300 ?C (Fig. 1). This effect is explained by the competition for Pt catalytic sites between the oxidation of CO and HC from the inlet feed and those of the additional CO stemming from partial soot oxidation by NO2.
We also found that the presence of soot can partly destabilize NOx storage. In a recent paper, Castoldi and al. [1] also highlighted the negative influence of soot on the NOx storage capacity of such a catalyst.

Fig. 1: Comparison of 4WCC conversion efficiency obtained during a light-off test on a soot loaded sample (w/soot) and an unloaded sample (w/o soot) – equivalence ratio = 0.3

[1] L. Castoldi, N. Artioli, R. Matarrese, L. Lietti & P. Forzatti. Catalysis Today. 157.(2010) 384?389