Optimisation of the Post-injection during the Particle Filter Regeneration can reduce the Fuel Entry into the Engine Oil of Passenger Car Diesel Engines

The effects of the splitting of the engine-internal „late” post-injection in regeneration mode during the operation with the fuel blends B7, B10 and B30 (admixture content of RME from 7, 10 and 30 %-vol.) on the fuel entry into the engine oil as well as on the change in the oil viscosity were examined in stationary test runs at the Institute for Mobile Systems IMS, Chair of Reciprocating Machines at the Otto-von-Guericke University Magdeburg. The project was financed by the Union zur Förderung von Öl- und Proteinpflanzen e.V. (UFOP).

The bench tests, which were carried out in an operating point with small engine load in the regenerating mode, showed that the fuel entry increased into the engine oil with increasing RME content of the fuel. In this case the RME-concentration increased in the engine oil whereas the DF-concentration decreased.

The splitting of the late post-injection in two partial injections lowered the fuel entry into the engine oil in comparison with a late undivided post-injection during operation of the engine with B7 by approx. 20 % and with B30 by approx. 27 %. In this case also the injection data of the late post-injection were optimised apart from the fuel mass. The splitting affected specially positively with high RME contents in the fuel.

The stationary test bench tests revealed that the optimisation of the late post-injection in the area of the exhaust stroke can reduce the fuel entry into the engine oil. However, they also clearly demonstrated that the early post-injections subsequent to the main injection can have a considerable share in the engine oil dilution if partial amounts of the fuel jets encounter the cylinder wall. The early post-injections should be incorporated in future potential investigations. However, the emissions, the consumption and the vehicle handling must not impact negatively.


Diesel particle filters (DPF) in passenger cars and light commercial vehicles require an active regeneration in order to burn the soot, which was retained from the filter during the normal driving. Since the exhaust-gas temperature does not suffice frequent in spite of the catalyst coating of the filter material, fuel is injected if needed into the cylinder after the actual combustion procedure. This so-called engine-internal post-injection is leading, however, to a forced fuel entry into the engine oil. Due to the higher boiling-range of the biodiesel this effect leads to a critical engine oil dilution during the operation with high biodiesel additions.

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