Laminar flame speed correlation of ammonia-based fuels with functional group contribution method

Abstract

Appropriate design of ammonia (NH3)-based fuels is required to match the combustion performance requirements of practical combustion equipment. As one of the most important parameters, laminar flame speed (SL) has to be considered in the combustion reacting flow and kinetic analyzing, and its correlation plays an important role in the combustion process modeling and fuel design. But until now, there is no a common SL correlation for NH3-based fuel. In this study, a SL correlation of NH3-based fuels, including pure NH3, NH3/hydrogen (H2)/air, NH3/C1-C4 n-alkanes/air, and NH3/C1-C2 oxygenated fuels/air mixtures, was proposed based on the functional group contribution method and a SL database with 20,260 data points generated through one-dimensional flame simulations. Comparative results of this correlation against detailed reaction mechanisms, literature correlations, and experimental data indicate that the correlation has good predictive capability for SL of the target NH3-based fuels within the considered conditions. Sensitivity analysis and one-dimensional flame simulation results show that when blending a small amount (mole fraction <10 %) of considered fuel into NH3, the enhancement effect of methyl (-CH3) on the SL of NH3 is stronger than that of H2 and methylene (-CH2-). In addition, when the above-mentioned hydrocarbon groups in the blended fuel are substituted by hydroxyl (-OH) or ether group (-O-), the enhancement effect is reduced. As the mole fraction of blended fuel increases, the effective abilities of functional groups in influencing the SL of NH3-based fuels continually strengthen. The proposed correlation provides an effective means for quickly predicting the combustion characteristics of NH3-based fuels and is expected to play an important role in the design of NH3-based fuels.