Lower flammability limits of NH3/H2 mixtures under different initial temperatures and initial pressures

Abstract

In this paper, the lower flammability limits (LFLs) of NH3/H2 mixtures under different initial pressures (50–250 kPa) and initial temperatures (20–100 °C) are experimentally and numerically investigated. The LFLs of ammonia and hydrogen are reduced by the increase of the initial temperature, and the reduction of ammonia LFL is greater than that of hydrogen. An increase in initial pressure decreases the LFL of ammonia but increases the LFL of hydrogen. The LFL of the NH3/H2 mixture is reduced by the increase of H2, which is consistent with Le Chatelier’s Law. When H2 reaches 10%, the LFL trend of the mixture with the initial temperature and initial pressure is similar to that of hydrogen. The LFL prediction models of NH3, H2 and NH3/H2 mixtures under different initial temperatures and initial pressures are established. The changes of OH radicals in elementary reactions are crucial to the effect of LFL. Except for H + O2 = O + OH and 2OH = O + H2O, the main OH ROP of NH3 is NO2 + H = NO + OH, NH2 + OH = NH + H2O and NH3 + OH = NH2 + H2O, while the main OH of H2 ROP is OH + H2 = H + H2O, which may be the reason why the LFLs of NH3 and H2 are different.