Multi-zone modeling and simulation of syngas combustion under laminar conditions

Abstract

The use of laminar models has been generally accepted, as quench distances in engines and the distances obtained for laminar flame quench calculations could be well correlated. In this work a multi-zone model is presented in order to derive the quenching distance and heat flux in laminar syngas–air flames based on recent developments in the science of combustion. Three typical mixtures of H2, CO, CH4, CO2 and N2 have been considered as representative of the syngas coming from wood gasification, and its laminar combustion is made in a static spherical vessel. The model is validated for the methane–air case and then applied to syngas–air mixtures in order to estimate the heat flux to the walls and quenching distances. Two wall heat transfer models are implemented and compared. The classical Woschni model based on the hypotheses of forced convection and the Rivère model based on kinetic theory of gases. Conclusion could be drawn that the Rivère heat transfer model is capable to better reproduce the heat flux to the walls. Heat flux through the walls is higher for stoichiometric syngas–air mixtures which follows the same behavior of the pressure inside the combustion vessel. Quenching distance of syngas–air mixtures decreases with the heat flux increase, which is consistent with earlier studies. This model could be very useful in predicting the physical conditions of quenching especially for estimation of the quenching distance where the measurement is not possible such as in engines. However, the estimation given should be understood as an order of magnitude, because in turbulent conditions the flame–wall interaction results in lower Peclet numbers than in the laminar case.