Comprehensive soot particle size distribution modelling of a model Rich-Quench-Lean burner

Abstract

Soot particle size distribution (PSD) evolution in an ethylene lab-scale swirl Rich-Quench-Lean (RQL) combustor is investigated using a detailed physicochemical sectional soot model coupled with the Conditional Moment Closure turbulent combustion model and Large Eddy Simulation. The aim is to develop predictive capability for the local soot PSD and to explore differences in soot PSDs with different conditions of a burner configuration widely used in practice for emissions control. Two such conditions are studied by varying the airflow provided in the burner primary and dilution regions, which has a drastic effect on soot emission as shown by previous experiments. The results show a reasonably good agreement with experiments for the mean reaction zone and soot locations and their variations with dilution. The predicted PSDs at the burner exit are fairly well captured for the high-dilution condition but show too few and too small particles for the dilution-free condition, which may be due to an overprediction of the oxidation rates or the unity Lewis number assumption used here that enhances penetration of soot towards the oxidiser stream. The results are analysed to reveal the hierarchy of reaction pathways during soot evolution and indicate how dilution air modifies the soot PSD within the primary zone. In particular, the presence of dilution leads to a broadly sustained uni-modal soot

Soot Emission Simulations of a Single Sector Model Combustor Using Incompletely Stirred Reactor Network Modeling

“…As discussed in Refs. [11,20,21], conditional quantities related to soot evolution show strong spatial dependence. Therefore, it is necessary to extend the approach to a network of ISRs spanning the whole combustor under investigation.…”

“…Soot Emission Simulations of a Single Sector Model Combustor Using Incompletely Stirred Reactor Network Modeling particle size distribution (PSD). In this direction, we couple the recently developed hybrid chemistry (Hy-Chem) approach for kerosene combustion [24,25] with a reaction subset for molecular growth up to pyrene and a detailed physicochemical sectional soot model initially developed for ethylene [10,11]. This allows for a demonstration of the ISRN potential in handling complex chemical mechanisms and soot models, but it also allows for an estimation of the soot PSD at the combustor exit.…”

“…The ISRN equations are then solved using an in-house unstructured finite volume code, initially developed for CMC modeling (see [10,23,27,28] and references therein The procedure is very similar to the one followed every time-step in existing CMC codes (e.g., [27]…”

“…However, larger Polycyclic Aromatic Hydrocarbons (PAH) species are not considered, but they are typically required by comprehensive soot models, like the Napoli sectional (NAPS) soot model employed in this work. Therefore, the HyChem combustion chemistry is combined here with additional PAH growth routes, extracted from a detailed mechanism calibrated for ethylene [10,11], which is also the base gas-phase scheme for the NAPS soot model. These reactions consider the sequential addition of acetylene molecules and the self-combination of resonantly stabilized radicals to account for the molecular growth of aromatic cycles up to pyrene (A4).…”

“…Nevertheless, recently developed comprehensive soot models [7][8][9][10][11] cannot easily be used in conjunction with high-fidelity CFD simulations to perform parametric studies during the design phase of combustors,…”