Modelling of hydrogen cyanide formation in room fires

A chemical kinetics model for calculation of the formation of hydrogen cyanide (HCN) has been made. The combustion of a mixture of methylamine and ethylene has been modelled using the stationary laminar flamelet concept. The flamelet calculations are based on several thousand elementary reaction steps including the chemical kinetics of HCN in combustion. The flamelets for both cold (293 K) and hot (1000 K) combustion product recycling have been calculated. The effect of strain is also included in the flamelet calculations. Scalar dissipation rates from 0.01 s(-1) to extinction values have been varied. Also the effect of radiation is included in the flamelet state relationships. Separate flamelet sets for various levels of radiation, from adiabatic up to 30% radiation losses, incremented by 1%, have been made. In the flow field calculation, the flamelet options may be used either as adiabatic, constant radiation or an interpolation between flamelet sets of different radiation. The chemical kinetics model, incorporated into a Reynolds-Averaging Navier-Stoke (RANS) type CFD code, has been used to simulate two laboratory fire tests of the combustion of nylon. Changing the size of the opening in the test room varied the ventilation between the two tests. Flamelet sets for a mixture of methylamine and ethylene with nitrogen content close to that of nylon were used in these simulations. The simulations were made with and without recycling the combustion products back to the fire. The calculations show that recycling of the combustion products to the fire increases the formation of HCN and CO. Similarly, a lowered ventilation rate increases the formation of these species. The calculated temperatures and main species concentrations, including HCN, agree reasonably well with the trends in the laboratory measurements