Ammonia conversion and NOx formation in laminar coflowing nonpremixed methane-air flames

Abstract

This paper reports on a combined experimental and modeling investigation of NO x formation in nitrogen-diluted laminar methane diffusion flames seeded with ammonia. The methane-ammonia mixture is a surrogate for biomass fuels which contain significant fuel-bound nitrogen. The experiments use flue-gas sampling to measure the concentration of stable species in the exhaust gas, including NO, O 2 , CO, and CO 2 . The computations evolve a two-dimensional low Mach number model using a solution-adaptive projection algorithm to capture fine-scale features of the flame. The model includes detailed thermodynamics and chemical kinetics, differential diffusion, buoyancy, and radiative losses. The models shows good agreement with the measurements over the full range of experimental NH 3 seeding amounts. As more NH 3 is added, a greater percentage is converted to N 2 rather than to NO. The simulation results are further analyzed to trace the changes in NO formation mechanisms with increasing amounts of ammonia in the fuel.

The role of NNH in NO formation and control

“…A subsequent reaction NNH + O = NH + NO then offers a high temperature pathway for NO formation, the so-called NNH mechanism. A number of experimental and modeling studies [27][28][29][30][31][32] support the existence of the NNH mechanism, and kinetic modeling indicates that it is of importance in premixed and non-premixed flames of both hydrogen [33][34][35][36] and hydrocarbons [37][38][39][40][41][42].…”

Stochastic algorithms for the analysis of numerical flame simulations

“…This mechanism, which includes detailed nitrogen chemistry, contains 65 species and 447 reactions. The case we consider here was part of a combined experimental and numerical study of the effect of fuel-bound nitrogen in the form of NH 3 on NO x formation [6,18]. Here we consider only the case with no added NH 3 .…”

“…Smooke and his co-workers [1][2][3][4][5] have performed a number of studies of laminar methane diffusion flames with detailed kinetics. Sullivan et al [6] have studied nitrogen chemistry in ammonia-enriched methane flames. For premixed flames, Najm and co-workers [7][8][9], and Bell et al [10], have studied vortex flame interactions with detailed methane chemistry.…”

A taxonomy of integral reaction path analysis

“…The path that consumes water occurs on the centerline below the middle flame sheet shown in Figure 6(b). This is a very warm region where some mildly endothermic carbon reactions also occur [39]. Figure 10 reveals the interesting fact that virtually all oxygen atoms pass through hydroxyl.…”

“…Evidently some nitrogen atoms cycle between carbon-bearing and carbon-free species before leaving the flame as either nitric oxide or molecular nitrogen. The reactions responsible for the various paths are identified in [39]. A stochastic particle analysis of the computational results is given in [5].…”