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Emissions of diesel engine are considered to be harmful to health especially particulate emissions. Therefore, the introduction of diesel particulate filters (DPF) were successively forced by government due to reducing the emission limits to a level where inner engine measures are not sufficient anymore. To limit additional fuel consumption by increasing backpressure over the DPF, the collected soot has to be regenerated continuously or discrete by active regeneration. Active regeneration is usually realized by injecting additional fuel either due to the engines injection system into the combustion chamber (late post injection) or via an additional fuel injection device in the exhaust line. This enables increasing exhaust temperature and / or an exothermic reaction in the diesel oxidation catalyst (DOC) of the aftertreatment system.

Full flow particulate filters are a state of the art solution for many serial production diesel engine applications. They are very effective for removing ≻ 90% of particulate mass and ≻ 99% of the particulate number from the exhaust gas of diesel engines. Many diesel engines have to work at load profiles which necessitate active regeneration procedures to ensure continued engine operation and the reliability of the full flow particulate filter. Passive regeneration via NO₂, as a cost-effective solution, cannot be used as the sole method for all applications, due to restrictions such as, insufficient engine-out NOX/PM ratio, low exhaust gas temperature level or occasionally poor fuel quality. To meet the Tier 4 emission legislation casually partial flow particulate filters enable sufficient particulate reduction at boundary conditions where full flow DPF is not applicable.

Many diesel engines have to work at load profiles which, due to the low exhaust gas temperatures, necessitate active regeneration procedures to ensure continued engine operation and the reliability of the particulate filter. An active regeneration may be initiated via inner engine measures such as late injection. However, due to high maintenance interval and run time requirements for non-road applications the combustion of soot accumulated in the diesel particulate filter (DPF) often is realized via downstream processes. Known methods for this purpose are burner systems, systems based on downstream hydrocarbon injection (HCI) and subsequent hydrocarbon (HC)-conversion due to a catalyst or a combination of both. This paper describes an autarkic system using two-stage electro-thermal-supported hydrocarbon conversion. This system is capable to regenerate a DPF within the entire engine operating range and it is less complex than flame burner systems.

For the regeneration of diesel particulate filters with oxygen, temperatures above 550°C are normally required. The increase of the exhaust gas temperature to temperatures above 500°C demands a large amount of energy, so that strategies to reduce the regeneration temperature have to be considered. One option is the injection of a catalyst, which reduces the required regeneration temperature. Hence, a system was developed at HJS Emission Technology GmbH to inject catalyst-precursor into the exhaust gas pipe, whereby the catalysts are generated due to decomposition of the precursor in the hot exhaust gas. A technique based on the calculation of apparent activation energies was developed to characterize the soot combustion on the filter. In the first step metal oxide catalysts, like cerium(IV)oxide, manganese-oxide and iron(III)oxide were investigated after injection of their nitrate precursors dissolved in water.

The operating cycle of many vehicles fitted with diesel particulate filters is such that soot accumulates within the filter and must periodically be oxidised. Work was carried out on a passenger car engine to elucidate how fuel borne catalyst (FBC) to soot ratio, oxygen mass flow rate, temperature and soot loading influence the oxidation rate of soot accumulated in a sintered metal filter (SMF). Results show that soot loading had a major influence; increased soot loading increased the oxidation rate. The other parameter had a smaller influence with increasing oxygen flow rate and FBC/soot ratio each increasing the oxidation rate.