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Storage stability of different diesel fuels containing cat-cracked stocks was examined using various aging conditions. The degradation of fuel during storage was monitored through insoluble formation but also through reaction of nitrogen compounds known to be involved in the fuel degradation process. The influence of aging in injector fouling tendency was also investigated on an IDI engine on test bench. Various stabilizer additives (tertiary amines, dispersant…) were tested. Best results were obtained with dispersants which prevent sediment agglomeration making them able to cross the filter mesh. Additives limit indole evolution without inhibiting completely sediment formation, proving that other reactions take place. We showed that fuel oxidability is not modified by additives. None of the tested formulations is effective on fuel darkening. After aging, surfactants remain effective on injector fouling. Another way of improving the storage stability of Diesel fuel is hydrotreatment.

Future fuel formulations including classic refining schemes (hydrotreatment) and synthetic blending stocks like Fischer-Tropsch, oligomerate and high cetane linear ethers were tested for their impact on diesel emissions in various engine conditions (transient and cold operations). CO, HC, Aldehyde, Particulate and PAH emissions are highly sensitive to fuel quality whereas NOx emissions are only slightly modified. Very low level of pollutants is obtained with the Fischer-Tropsch fuel. Oligomerisation fuel induces an increase in CO, HC, aldehyde emissions due to its very low cetane number but presents low emissions of particulates and smoke because of its paraffinic composition. Pentyl ether behaves essentially as a high cetane paraffinic hydrocarbon. The relationships between fuel parameters and emissions were also assessed: CO, HC and aldehyde emissions depend on the cetane number. Particulates, IOF, smoke and PAHs are controlled by aromatic content and density.

Diesel urban buses and refuse trucks are part of the particulate emissions sources that affect city air quality. In order to reduce particulate pollutant emissions, a development program has been carried out based on a Euro 4 engine with a DPF technology. Currently, for Euro 4 compliance, SCR is the favoured technology. To avoid a completely new development, the Exoclean™ DPF system was located after the SCR. Catalyst. The severe operating conditions and the location of the DPF necessitated the development of an active system based on the association of a DPF and a Fuel-Borne Catalyst. A Renault Trucks MD9 engine was used. This work was funded by ADEME (French Agency for Environment and Energy Management). Due to severe stop and go duty cycles and the interest to fit the DPF downstream of the SCR, this study shows the benefit of using an active DPF with an FBC to ensure full regeneration even at low temperatures.

In urban areas, particulate emission from Diesel engines is one of the pollutants of most concern. As a result, particulate emission control from urban bus Diesel engines using particulate filter technology is being introducing in La Rochelle. The Diesel Particulate Filter (DPF) introduction on the existing urban bus fleet has been initiated by the CDA La Rochelle through a voluntary retrofit program. The class of urban bus to be retrofitted is based on EURO 1 and EURO 2 Diesel engines, using a standard European Diesel fuel with 300ppm of Sulphur content. In that case, the appropriated technology for DPF regeneration requires a very flexible strategy for DPF regeneration, such as the use of the Ceria-based Fuel-Borne Catalysts. The paper describes the practical approach developed to install and optimize the DPF System on the urban buses.

Modeling is a precious help to optimize the setting and control of Diesel particulate filter (DPF) regeneration, given the complex phenomena involved. Among those, the fuel-borne catalyst action must be taken into account, because of its prevailing effect on the soot ignition and the regeneration propagation. This paper describes how a 1D model was developed, which simulates the soot heating, ignition and oxidation along the wall-flow filter. The aim is to predict the regeneration of one filter channel, knowing the exhaust gases flow, temperature and oxygen content, and the way the filter was loaded with soot. The reaction mechanism and kinetics were experimentally studied and involve the additive action. Engine bench tests were conducted to highlight the effects of additive content, as well as the regeneration sensitivity to its main parameters (exhaust gases and soot features).

The impact of fuel hydrotreatment on Diesel exhaust emissions is investigated. Several fuels are formulated in a refining pilot unit. By progressively increasing the hydrotreatment severity, sulfur reduction is first achieved, followed by aromatic reduction and cetane enhancement. The operating conditions and the effect on fuel characteristics are detailed. The influence of this hydrotreatment on exhaust emissions of a light-duty prechamber engine is studied under both steady-state and transient conditions. In steady-state operation, a slight effect of fuel on CO and HC emissions appears which increases when the injection timing is retarded. No evidence of fuel influence on particulate emissions is found except for a sharp increase due to sulfate contribution for fuels with high sulfur content. The transient operation enhances the influence of fuel characteristics on pollutants.

To ensure overall optimisation of heavy duty engine performance (with the respect of NOx&PM future European and US emissions standards), the use of a high efficiency NOx after-treatment system such as a NOx trap appears to be necessary. But running in rich conditions, even for a short time, leads to a large increase of particulate emissions so that a particulate filter is required. 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, the fuel penalty and the temperature level of the NOx-trap have been shown as a key parameter. Respective DPF and LNA locations have been studied. The configuration with the NOx-trap upstream provides the best NOx / fuel penalty trade-off since it allows NOx slip reduction and does not disturb the rich pulses.

This paper presents the main properties of a SiC diesel particulate filter bonded with specific ceramic oxides at a markedly lower sintering temperature than normal pure SiC DPF. The elasticity of the bond has been studied to have a good behavior to thermal shock permitting a larger cross section element and a reduction of the number of cement joints in the final monolith. That new product, manufactured at present is composed of seven square elements. Endurance tests have been carried out by laboratory bench testing in two commercial automobile diesel engines. The DPF pore size has been adjusted so that it may be catalyzed or impregnated.

In a few months, small two-stroke engines, which are used in two-wheel vehicles, will require the use of catalysis to achieve more stringent standard levels of emissions in the European Union. Such a kind of severe emission levels already exists in some countries and different catalytic gas after-treatment systems have already been studied. But in the most of cases, the principal aim was to fit in the existing exhaust lines of the corresponding vehicles. Thus, the catalyst parameters were chosen through criteria which were not mainly ‘catalytical’ criteria. Indeed, the performances of a catalytic system depend on many parameters, which are for example the position in the exhaust line, the dimensions of the monolith (diameter, length and cell density), the material (ceramic or metallic, thickness) or the precious metal formulation. An engine bench was equipped with a two-stroke engine and different configurations of the catalyst were considered.