Contribution of multiphysics CFD simulation to the reduction of pollutant emissions from domestic heating appliances: application to a pellet stove

Domestic biomass combustion devices, such as pellet stoves, are important heating sources for many European households. For example, 1.7 million households in France are equipped with pellet stoves for heating or domestic hot water supply. However, these installations are source of pollutants such as carbon monoxide CO, nitrogen oxides NOx and fine particle matter PM.

In order to improve the air quality and comply with French and European standards, this study aims to investigate the parameters influencing the efficiency of a pellet stove and its pollutant emissions. To this end, a 3D multiphysics numerical model of an existing pellet stove (NES10 EVO by Caminetti Montegrappa) was developed using the commercial software ANSYS Fluent.

The steady-state CFD model is based on a detailed coupled flow and heat transfer approach (Conduction-Convection-Radiation) and a simplified two-step combustion mechanism, enriched with User-Defined Functions (UDF) to simulate drying, pyrolysis and char oxidation. Particular attention has been paid to the modeling of radiative heat transfer, which plays a key role in combustion. Due to the strong dependence of the radiative properties of combustion products (, , soot) on their composition, temperature and partial pressures, a multi-band approach was used. The spectrum was divided into 16 bands between 200 and 10000 /cm (i.e., from 1 to 50 μm) in which the absorption coefficient varies with temperature and pressure. The radiative transfer equation was solved using the non-gray Monte-Carlo method. The formation of pollutants such as NOx and soot was also considered.

In parallel, an experimental study was conducted to validate the relevance of the numerical results obtained. A comparison of relevant gas (CO, , O2, NOx) concentrations at the stove outlet, flame temperatures at different heights within the appliance and the stove power has demonstrated the suitability of the multiphysics model.

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