Influence of Engine Operating Parameters and Different Fuels on the Soot Reactivity of Diesel Engines

Abstract

Abstract Strong efforts to reduce CO2 emissions, including in commercial vehicle diesel engines, require the optimization of all processes and engine components that influence fuel consumption. Subsequently, also the additional fuel consumption for particulate regeneration is increasingly focused on. Increasing soot loading of the DPF increases the exhaust back pressure and is therefore deteriorating thermal engine efficiency. Additionally, DPFs are only providing specific maximum soot loading capacities and have to be regenerated accordingly by oxidizing the accumulated soot. The energy or temperature, respectively, which is required for oxidizing the soot to CO2 strongly depends on the physicochemical properties of the soot and is commonly described as particulate reactivity. More reactive soot is advantageous for fuel-efficient regeneration as it can be oxidized at lower temperatures. This work deals with the influence of various engine operating parameters (speed, load, air-fuel ratio, EGR, injection) as well as the influence of fuels on particulate emissions. The associated soot reactivity is compared between conventional fossil diesel (with and without fatty acid methyl ester), regeneratively produced paraffinic diesel fuel HVO (Hydrotreated vegetable oil) and a blend of HVO and oxymethylene ether (OME). All investigations were performed on a single-cylinder research engine. The engine out particle measurements were carried out using a particle size spectrometer and a photoacoustic sensor. Gaseous emissions were recorded using an exhaust gas measuring system and an infrared spectrometer. Additionally, collected engine out soot samples a thermogravimetric analysis (TGA) was implemented to determine the reactivity of the soot. Regardless of the engine operating point set, it was found that the particulate mass for the HVO fuel is significantly lower than the particulate mass of the fossil diesel fuels. In contrast, however, the HVO fuel has an increased number of particles due to smaller particles. A significantly lower particle mass and particle number concentration was achieved with the HVO/OME blend. The NOx emissions were at a similar level regardless of the fuel used. A variation of engine operating parameters showed the same tendencies in terms of soot reactivity, regardless of the fuel used. However, the parameter variations were more or less pronounced depending on the respective fuel. It is particularly noteworthy that, aside from operation at low EGR rates and high air-fuel-ratios, where higher reactivities were observed when using diesel B0, no significant differences in reactivity were evident among the fuels used.