Strategies for active diesel particulate filter regeneration based on late injection and exhaust recirculation with different fuels

Wall flow–type particulate filters are used in diesel vehicle engines to reduce particulate emissions below the limits established in regulations Euro 5 and Euro 6. The soot accumulated in the trap is eliminated during regeneration processes, often combining passive strategies with active ones. Active regeneration is conducted by modifications of the engine control parameters with respect to those set for normal vehicle operation. In this work, three of these parameters were modified to look for an optimized regeneration strategy, considering fuel consumption, gaseous emissions and rate of regeneration. The selected parameters were injection timing (affecting all injection events), exhaust gas recirculation and amount of postinjected fuel. The fuel tested was considered as an additional variable, and therefore, tests were performed with three different fuels: an ultra-low sulfur diesel fuel, a biodiesel fuel produced from animal fat and a gas-to-liquid fuel from low-temperature Fischer–Tropsch process. It was proved that eliminating the gas recirculation is the optimal option for a fast regeneration and reduced fuel consumption and that the late postinjection is essential to keep the temperature conditions needed for an efficient regeneration. Some limits were also proposed for these parameters to prevent from excessively fast or uncontrolled regeneration, to avoid excessive increase in fuel consumption and to reduce the probability of fuel dilution. Finally, the fuel properties were proved to be very relevant to the regeneration process, and therefore, both biodiesel and gas-to-liquid fuels (especially the former) showed un-optimized regeneration processes under the conditions set for regeneration process optimized with diesel fuel.