Effect of oxygenated and paraffinic alternative diesel fuels on soot reactivity and implications on DPF regeneration

Abstract

A wide range of alternative fuels has recently emerged worldwide, as a means to reduce the dependence on fossil resources and to meet the stringent energy and emissions legislations. In the diesel market, oxygenated biofuels such as biodiesel and e-diesel (low content ethanol-diesel blends) and paraffinic fuels such as those derived from Fischer-Tropsch processes (GTL) or hydro-treatment of vegetable oils (HVO) stand out as the most promising ones. A current challenge that these fuels face is their effect on loading and regeneration performance in diesel particle filters –DPFs–, an aftertreatment technique commonly adopted to abate particulate emissions. This work analyses the oxidative behavior of soot under controlled temperature-atmosphere conditions. Five fuels (conventional diesel fuel, e-diesel, HVO, GTL and conventional biodiesel) were tested in a Euro 5 automotive engine. The effect of the oxidant gas composition (oxygen content and NO2 presence) and the engine injection strategy (small modifications around the original manufacturer setting) were analyzed. Results revealed a greater ability of soot from paraffinic and, especially, oxygenated biofuels to be oxidized under lower temperature conditions. In particular, e-diesel soot needed the lowest temperature and its oxidation pattern was the fastest and the least sensitive to the oxygen concentration in the exhaust gas, which makes feasible the use of exhaust gas recirculation during active regeneration. From the original injection strategy, small advances/delays and/or the presence of a fuel post-injection did not significantly alter the reactivity of soot. NO2 concentration in the exhaust gas showed no significant effect on the soot oxidation process at temperatures higher than 300°C.