Fuel formulation effects on the soot morphology and diesel particulate filter regeneration in a future optimized high-efficiency combustion system

The focus of research is shifting toward development of new engine fuels for optimized combustion systems. The altered chemical structure of these new fuels may impact their thermal decomposition chemistry during the ignition process and hence the in-cylinder conditions for particulate formation and post oxidation. This work fundamentally focuses on the influence of the fuel properties on particulate matter morphology and, thereby, the regeneration behavior of diesel particulate filters. The experiments for particulate analysis were conducted with a single-cylinder diesel research engine designed for future passenger car applications. A detailed analysis of soot characteristics and its consequences on diesel particulate filter behavior were studied at part-load engine operation at EU 6 engine-out nitrogen oxide level. Next to standard EN590 diesel, a paraffinic fuel was investigated as non-oxygenated biofuel candidate. A blend of the 2-methyltetrahydrofuran and di-n-butylether was studied as tailor-made oxygenated biomass-derived fuel candidate. With all fuels, samples of state-of-the-art diesel particulate filter were loaded at the research engine. In succession, the regeneration of the filters was investigated at a laboratory gas bench. Furthermore, the primary particle size, the total number concentration, and size-based number distribution were investigated in detail by means of a transmission electron microscope, condensation particle counter, and Engine Exhaust Particle Sizer™, respectively. Furthermore, the graphitic character of the soot structure was analyzed by optical measurements such as absorption coefficient. It was found that the soot oxidation temperature was decreased by ∼10 °C and ∼65 °C with the paraffinic fuel and the blend of 2-methyltetrahydrofuran and di-n-butylether, respectively, compared to conventional diesel fuel. Overall, the results indicate that with specific tailored fuels not only the total particle mass and number could be reduced but, with altering the soot structure and composition, also the energy requirement for diesel particulate filter regeneration can be reduced.