Approximation of laminar flame characteristics on premixed ammonia/hydrogen/nitrogen/air mixtures at elevated temperatures and pressures

Ammonia shows a promising potential to be a carbon-free and sustainable fuel for gas turbines and internal combustion engines. The design of such complex combustion systems using computational reactive fluid dynamics in combination with detailed reaction mechanisms is a time-consuming challenge. Combustion models are a solution to reduce the computation time, but require data of fundamental laminar flame characteristics. In order to provide such data, in this present study correlations of laminar flame speed and flame thickness for ammonia/hydrogen/nitrogen/air mixtures based on a prior selected detailed reaction mechanism were developed. A validation study for three detailed chemical schemes was conducted using experimentally obtained laminar flame speed data from literature to determine one mechanism with the best predictive capabilities. A database with 222250 data entries of laminar flame speed and flame thickness was generated by performing numerical one-dimensional simulations using the selected mechanism. From that correlations were derived. The database as well as the derived correlations contain a broad range of initial conditions: air/fuel equivalence ratio: (0.5-1.7), ammonia: (0-100) mol%, hydrogen addition: (0-60) mol%, nitrogen addition: (0-20) mol%, fresh gas temperatures: (300-1100) K and pressures: (0.1-25) MPa. For the substitution of fuel within existing burners or engines which so far are operated with methane, it is of special interest, if a defined ammonia/hydrogen/nitrogen/air mixture could be used with similar properties. For that it is shown that such a mixture composition can be found which has a similar laminar flame speed than methane, depending on the given initial conditions.