Bernhard Lüers

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.

Tailor Made Biofuels: Effect of Fuel Properties on the Soot Microstructure and Consequences on Particle Filter Regeneration

In recent years a lot of effort has been made to understand the phenomena of Diesel Particulate Filter (DPF) regeneration processes but less attention has been paid to understand the influence of fuel properties on soot reactivity and its consequence on the DPF regeneration behavior.Within the Cluster of Excellence “Tailor-Made Fuels from Biomass (TMFB)” at RWTH Aachen University, the Institute for Combustion Engines carried out a detailed investigation program to explore the potential of future biofuel candidates for optimized combustion systems. These new biofuels are being developed to realize partially homogeneous low-temperature combustion, in order to reduce the emission and fuel consumption to meet future requirements. The chemical structure of these new fuels may impact the thermal decomposition chemistry and hence the in-cylinder particulate formation conditions. This work fundamentally focusses the influence of fuel properties on particulate matter reactivity and, thereby, the regeneration behavior of the diesel particulate filters (DPF).The experiments for particulate measurements and analysis were conducted, under constant engine operating conditions, on a EURO 6 compliant High Efficiency Combustion System (HECS) fuelled with petroleum based diesel fuel as baseline and today’s biofuels like FAME and Fischer Tropsch fuels as well as potential biomass derived fuel candidates being researched in TMFB.Several different methods were used for analysis of mass, composition, structure and spectroscopic parameters of the soot. The graphitic microstructure visible with high resolution transmission electron microscopy (HRTEM) was compared to the results of X-Ray diffraction (XRD), optical light absorption measurement and elementary analysis of samples.The results indicate that combustion with increasing fuel oxygenation produces decreasing engine-out particulate emissions. The ranking of activation energies of soot oxidation analysis from LGB experiments correspond well with the ranking of the soot physico-chemical properties. In comparison to petroleum based diesel fuel, the reduction of engine out soot emission by a factor of five with the use of the future biomass derived fuel candidate was accompanied by ten times reduction of the soot volume based absorption coefficient and two times reduction of carbon to hydrogen ratio. As a result of it, the activation energy of soot oxidation in DPF reduced by ∼ 10 KJ/mol. The reduced engine out soot emission and increased reactivity of the soot from the future biomass derived fuel candidate could cause a significant reduction of thermal DPF regenerations.Copyright