Chemical Kinetic Modeling of the Autoignition Properties of Ammonia at Low–Intermediate Temperature and High Pressure using a Newly Proposed Reaction Mechanism

Abstract

Global emissions can be significantly reduced with the use of zerocarbon emission fuels. Ammonia is now at the center of attention because of its promise as a carbon-free energy fuel. So, a detailed study on ammonia's combustion and emission characteristics is necessary, especially at low− intermediate temperature and high-pressure conditions. Very few reaction models are available for low−intermediate-temperature ammonia chemistry, and most of them could not show reasonable agreement with the experimental conditions. In the present work, a new ammonia oxidation reaction model has been proposed by referring to the previous available literature for low−intermediate temperature and high-pressure ammonia oxidation chemistry, and also a comprehensive chemical kinetic modeling for the autoignition characteristics and NO x emissions is performed for an ammonia/air mixture using the newly proposed mechanism. The newly proposed ammonia reaction model consists of 32 species and 259 reactions. The proposed mechanism has also been tested by performing the computational fluid dynamics (CFD) modeling for a premixed NH 3 /air mixture in a microflow reactor with varying wall temperature at equivalence ratios of 0.8, 1, and 1.2, and the model validation has been carried out by comparing the mole fraction profiles of species NH 3 , O 2 , and H 2 O with the available experimental results. The proposed reaction model was able to predict the formation of steady weak flames of the NH 3 /air premixed mixture within the computational domain. An excellent agreement is observed between the computational and experimental results for autoignition properties and CFD model validation using the newly proposed reaction model.

Effect of Intermediate Radicals on NOx and De‐NOx Characteristics of NH3/H2/Air Flames at High Pressure

“…The relation of O/H radical to NO x production in ammonia flames have been widely discussed in various reports 5, 8, 10, 17, 18. However, less literature is published about the role of nitrogen‐based intermediate radicals such as NH 2 , HNO, and NH on NO x formation or consumption in NH 3 /H 2 /air flames at higher pressure.…”

“…The total NO x consists of NO, NO 2 , and N 2 O. Previous studies [5,8,15] suggest that in ammonia flames the NO significantly contributes to the total NO x production compared to N 2 O and NO 2 . Therefore, the NO 2 and N 2 O analysis can be neglected.…”

“…Several other studies [5,7,8,11] also demonstrated that the recombination reactions of N 2 H x (x = 2, 3, and 4) are crucial for understanding NH 3 oxidation chemistry at low-intermediate temperatures and high pressure. In combustion, nitrogen oxides are formed as either a result of oxidation of chemically fuel-bound nitrogen or in a high-temperature environment by fixation of nitrogen in the combustion air.…”

“…Previous studies [8][9][10] reported that the hydrogen addition to NH 3 /air flames increases NO x production and positively affects the heat release rate, adiabatic flame temperature, and laminar burning velocity of the premixed mixture. A recent study carried out by Li et al [10] and Singh et al [5,8] concluded that NO production in ammonia combustion is strongly influenced by fuel-bound nitrogen, and intermediate radicals such as OH, HNO, NH 2 , and NNH play a significant role in NO production and reduction chemistry.…”

Adaptability of different mechanisms and kinetic study of methane combustion in steam diluted environments

“…Each mechanism is not suitable for all ranges of operating conditions and needss to be compared with the experimental results for its applicability. Recent studies 18 , 19 show the requirement for modifications of existing mechanism files to predict the combustion chemistry at different mixture compositions. Thus, the numerical schemes should accurately capture the chemical and thermal effect of steam dilution to allow further analysis using steam dilution conditions.…”