A combustion chamber, burning gaseous kerosene, is simulated to investigate the effects of mini-scale flame-holder geometry and its position on the combustion performance and the resulting nano-particulate soot aerosol, carbon monoxide, and carbon dioxide pollutions. To model the complex process of soot nanoparticle formation including the nucleation, coagulation, surface growth, and oxidation, we use a two-equation soot model to solve the soot mass fraction and soot number density transport equations. Considering a detailed chemical kinetic consisting of 121 species and 2613 elementary reactions, we construct the required flamelets library, i.e. the lookup table, and apply the flamelet combustion model, which solves the transport equations of mixture fraction and its variance. We take into account the turbulence-chemistry interaction using the presumed-shape probability density functions PDFs. Applying the two-equation κ-ε turbulence model with round-jet corrections and suitable wall functions, the transport equations of turbulence kinetic energy and its dissipation rate are solved to close the turbulence closure problem. Since it is required to impose the effects of radiation for the most important radiating species, we include the radiation heat transfer of soot and gases assuming the optically-thin flame consideration. In this regard, the radiation heat transfer is determined locally and only affected by the emissions. We evaluate the achieved solutions through our developed method comparing with the data documented in an experimental test, i.e. a gaseous-kerosene/air turbulent nonpremixed flame. The comparisons are provided for the achieved flame structure, i.e., the experimental data reported on the distributions of mixture fraction, temperature, and soot volume fraction. Next, we consider a disk-type mini-scale flame-holder inside the combustion chamber to study its effects on the flow pattern of reacting flow and the distributions of temperature, soot volume fraction, soot particles diameter, CO, and CO2 mass fractions. Our results show that the mounted flame-holder would increase the inside temperature while reduce the temperature, soot volume fraction, CO, and CO2 mass fractions of the exhaust gases. We also study the geometry and position of mini-scale flame-holder numerically in terms of the average values of temperature, soot volume fraction, soot particles diameter, CO mass fraction, and CO2 mass fraction at the outlet of combustion chamber. Our results indicate that increasing the radius of flame holder would lead to a reduction in carbonaceous emissions, i.e. black carbon, CO, and CO2, and the temperature of exhaust gases. Evidently, a maximum temperature increase inside the combustion chamber would augment the combustion performance. We also show that mounting the flame holder at the lower positions above the fuel nozzle exit would lead to the same consequences. The present study provides good informative advices to the researchers who investigate pollution in aero-engine combustion chambers.
Mixture fraction, soot volume fraction, and velocity imaging in the soot-inception region of a turbulent non-premixed jet flame
