Development And Application Of PAH Skeletal Models And A Phenomenogical Soot Model For Diesel Surrogate Fuel Combustion

As the regulation on the number and size of particulate matter (PM) emitted from the combustion process of internal combustion (IC) engines becomes more and more stringent, it is necessary to improve continuously engine performance. Numerical simulation with advantage in reducing research cost and shorting development times has been regarded as an important approach of engine development. The complex processes of soot formation and oxidation include gaseous chemical kinetic mechanisms and soot particle dynamics. The soot emission process depends on fuel type, temperature, pressure and equivalence ratio. Thus, it is a very difficult and challenging work to simulate soot formation and oxidation in IC engines. For the diesel engine simulation, multi-components surrogate fuel have been more and more widely used to predict the combustion process of diesel fuel. It is worth noting that, although several phenomenological soot models have been constructed to simulate the soot formation and oxidation, most of them focus only on a single fuel. The purpose of this thesis is to construct a phenomenological soot model for different types of fuels with the consideration of the variation in PAH characteristics. For this target, PAH skeletal models have been developed for several fuels. Based on these PAH models, a phenomenological model for soot formation and oxidation has been constructed. The new PAH skeletal models and soot model were validated against related measurement data in fundamental reactors, constant-volume combustion chamber and diesel engines, which showed good performance of the new models. Research work completed in this thesis is as following.1. Recent advancement and achievements in the phenomenological soot formation and oxidation models is reviewed systematically. The characteristics and trend of diesel surrogate fuel is summarized. Recent detailed and skeletal mechanisms of PAHs for different fuel types are reviewed and discussed.2. Through an analysis of the effects of fuel type on PAHs and soot formation, the necessary of using PAHs as soot precursor species is recognized. By using a skeletal PAH model introduced into soot model to describe the formation process of soot precursor mechanism, the influence of different molecular structures of fuels on soot formation characteristics can be predicted. Based on this idea, a new phenomenological soot model has been developed for multi-component fuels.3. By reviewing recent mechanisms for the formation of PAHs up to4ring molecules, important pathways were identified and used to construct the initial skeletal PAH models for fuels with different molecular structure. A new PRF-PAHs model was developed by combining the optimized PAH model with the previously developed PRF oxidation model. The model is validated against measurement data from shock tube, premixed laminar flames and counter-flow diffusion flames. Furthermore, the PRF-PAHs model is incorporated into a soot model, which is also validated against experiment data in shock tube, and applied to3D-CFD simulations of a constant-volume combustion chamber and diesel engines.4. By incorporating an oxidation model of toluene into the PRF-PAHs model, a new TRF-PAHs model for diesel surrogate fuel is constructed and validated and optimized by comparison with shock tube, flow reactor and jet stirred reactor experiments. The final TRF-PAHs model includes73species and207reactions, it can accurately predict the ignition delay time and mole fractions of species. Based on the TRF-PAHs model, a soot model is developed and validated against experiment data in shock tube, and applied to3D-CFD simulation of diesel engines.5. Skeletal models of oxidation and PAHs formation for n-decane and methyl cyclohexane are developed. By coupling them with toluene and iso-octane oxidation models, a skeletal model for multi-component diesel surrogate fuel with88species and224reactions was built. The new model has been validated against experimental data, and finally, in coupling with the soot model, is applied to simulate the combustion process and soot emission from a constant-volume combustion chamber and diesel engines.