Advanced Soot Model for Aeronautics and Piston Engines – ASMAPE

Soot particles are formed during the combustion of hydrocarbon/air mixtures in most combustion devices related to transportation. They are regulated for Diesel engines, and will soon be for spark-ignition (SI) engines and gas turbines (GT). These regulations will concern not only the soot mass emission, but also the number of particles and finally the number of the smallest (most harmful) ones. Diesel engines are today equipped with particle filters (PF) that allow to suppress particles at the engine exhaust. On the contrary, reducing soot emissions at the source could avoid fitting SI engines with PF, as is the case today. Even if a PF is used, there still is a strong interest in reducing soot emission at the source for Diesel and SI engines because this would allow improving the fuel efficiency and to reduce the high cost of after-treatment systems. In the aeronautical domain, reduction at the source is the unique way to reduce soot emissions.
In this context, engine manufacturers of piston engines (PE) and aircraft GT will need reliable experimental and numerical tools to evaluate both the total soot volume fraction (SVF), as well as the Soot Number Density Function (SNDF) at the engine exhaust. Besides, due to the scarcity of fossil fuels, the contribution of bio-sourced fuels will become dominant in the future. A key issue is then to be able to evaluate the impact of fuel formulation on soot emissions.
The objective of ASMAPE is the development of validated predictive Computational Fluid Dynamics (CFD) models for the formation and evolution of soot during the turbulent combustion processes, in both PE and GT. The ambition is to address the three main commercial fuels (CF) relevant for a present usage: Gasoline, kerosene and Diesel fuel. The predictive capability of the models to be developed will concern both the SVF and SNDF.
The originality of ASMAPE is to propose an innovative integrated research work bringing together advanced optical diagnostics, chemical kinetics and turbulent combustion modelling, as well as work on numerical methods, applied to a wide spectrum of studies ranging from basic laminar flames to real-size PE and GT.
The starting point will be the acquisition of a well defined sooting laminar flames experiments using advanced optical diagnostics, and its analysis in order to gain detailed insight into the chemistry of polycyclic aromatic hydrocarbons (PAH) and soot nucleation, and to develop surrogate fuel (SF) chemical mechanisms able to predict them for the CF considered.
The proposed mechanisms will then be exploited in order to formulate a sectional and an alternative pretabulated soot model, available in the project's CFD codes. Presently, they rely on ad-hoc soot gas phase chemistry and are thus strongly limited in terms of predictive capabilities. ASMAPE aims at improving them by developing methods for accurately coupling the soot models with the turbulent combustion models used for the different applications within the project. This modelling work will concern both RANS codes for PE and GT, and a LES research code widely used in both domains.
Furthermore, the acquisition of two experimental databases on turbulent sooting flames will provide reliable data for extensively validating the project's soot models. The capacity of these models to predict soot formation and evolution in real-size PE and GT will be demonstrated at the project end.
Finally, work will be undertaken in the view of extending the predictive capacities of future soot models to cover not only the SVF and SNDF but also aspects as particle shape or composition, while reducing the related CPU time overhead.
The developed CFD soot models will directly be available at the project end for the French automotive and aeronautical industry to support design work aimed at limiting soot production at the source.