Abstract
A model to predict soot evolution during the combustion of complex fuels is presented. On one hand, gas phase, hbox {polycyclic aromatic hydrocarbon (PAH)} and soot chemistry are kept large enough to cover all relevant processes in aero engines. On the other hand, the mechanisms are reduced as far as possible, to enable complex computational fluid dynamics (CFD) combustion simulations. This is important because all species transport equations are solved directly in the hbox {CFD}. Moreover, emphasis is placed on the applicability of the model for a variety of fuels and operating conditions without adjusting it. A kinetic scheme is derived to describe the chemical breakdown of short- and long-chain hydrocarbon fuels and even blends of them. hbox {PAHs} are the primary soot precursors which are modeled by a sectional approach. The reversibility of the interaction between different hbox {PAH} classes is achieved by the introduction of hbox {PAH} radicals. Soot particles are captured by a detailed sectional approach too, which takes a non-spherical growth of particles into account. In this way the modeling of surface processes is improved. The applicability and validity of the gas phase, hbox {PAH}, and soot model is demonstrated by a large number of shock tube experiments, as well as in atmospheric laminar sooting flames. The presented model achieves excellent results for a wide range of operating conditions and fuels. One set of model constants is used for all simulations and no case-dependent optimization is required.
Highlights
Low emissions during combustion of hydrocarbon-based fuels are a key criterion for the approval of aero engines
The presented gas phase, polycyclic aromatic hydrocarbon (PAH) and soot model is validated using a large number of experiments with different operating conditions and fuels
The PAH model is validated here indirectly only, using soot data which is linked by the PAHs to the gas phase
Summary
Low emissions during combustion of hydrocarbon-based fuels are a key criterion for the approval of aero engines. The occurrence of cirrus clouds due to condensation trails is significantly enhanced by soot emissions from aero engines. These are only some of many consequences arising from undesired combustion products (Burkhardt et al 2018; Travis et al 2002). Soot radiation in aero engines may cause unwantedly high wall heat loads (Wulff and Hourmouziadis 1997). For these reasons and the upcoming more stringent legal regulations, combustion concepts with higher efficiencies and less pollutant emissions are essential. This requires reliable soot prediction models able to reproduce its complex dependencies on temperature, pressure, fuel, and level of premixing
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