Spherically expanding flame in silane–hydrogen–nitrous oxide–argon mixtures

Abstract

The effect of silane addition on the laminar flame speed (Su0) of flames propagating in hydrogen–nitrous oxide–argon mixtures has been investigated experimentally for the first time using the spherically expanding flame technique in a constant volume combustion chamber. Replacing hydrogen by silane and maintaining the equivalence ratio constant, much higher flame speeds, explosion peak pressures, and pressure rise coefficients were measured. A previously developed detailed reaction model has been updated based on ab initio thermodynamic properties calculations and collision limit violation analysis. The improved reaction model demonstrates encouraging performance in predicting the flame speed, with a mean absolute error below 11%. To explain the effect of silane addition on the flame dynamics, a number of parameters have been calculated including OH and H rate of production, heat release rate per reaction, and sensitivity coefficient on Su0. The dynamics of freely propagating flames in SiH4–H2–N2O–Ar mixtures is essentially controlled by reactions of the H–O–N chemical system: N2O+H=N2+OH, OH+H2=H2O+H, and N2O(+M)=N2+O(+M). Whereas silane addition does not influence much the rate of production of OH, it significantly modifies that of H with a number of pyrolytic chemical pathways of silicon hydrides, such as SiH+H2=SiH2+H and Si+H2=SiH+H, which act as sink of H atom as they proceed in the backward direction. The reactions forming SiO(s) and SiO2(s), such as SiO+OH=SiO2(s)+H and 2SiO=2SiO(s), are exothermic and significantly contribute to the temperature increase. The adiabatic, constant pressure flame temperature for mixture containing silane is significantly higher, up to several 100’s K. The increase of Su0 induced by silane addition seems to be mostly related to the large increase of the flame temperature which leads to higher energy release rate.