NO_x formation pathways in lean-premixed-prevapourized combustion of fuels with carbon-to-hydrogen ratio between 0.25 and 0.88

Abstract

NOx measurements in jet-stirred reactor (JSR) combustion of seven fuels are modelled using three complete chemical kinetic mechanisms. The two JSRs are operated at 1790 K, 1 atm, 2–4 ms, and the fuel-air equivalence ratio of 0.61. The modelled fuels are methanol, methane, ethane, ethene, propane, n-butane, and toluene. The experimental database also includes C1-C4 alkane mixtures, two light naphtas, four number two diesel oils, and benzene. The fuels and air are premixed, prevapourized, and preheated with a temperature-staged prevapourizer-premixer and an air-heater. Experiments show NOx and CO increase when burning fuels with increasing carbon-to-hydrogen ratio (from 0.25 to 0.88). The data are analysed using three complete chemical kinetic mechanisms: GRI 3.0 Mech., CNRS' C1-C4 hydrocarbon oxidation mechanism, and CNRS' toluene oxidation mechanism. The modelling shows that the increase in NOx with the fuel carbon-to-hydrogen ratio is because of the increase in the NO formation via NNH, Zeldovich, and nitrous oxide pathways. The NNH pathway produces between 25 and 45 per cent of the NO formed. GRI 3.0 Mech. tends to favour this pathway since it forms more O, H, and NNH reactive species than the CNRS' C1-C4 hydrocarbon mechanism. Several rate constants for NNH + O → NH + NO are considered and best agreement using two and three perfectly stirred reactor schemes is found with the rate constant k = 7 × 1013 cm3/mol/s.

Models To Predict Kinetics of NOx Reduction by Chars as a Function of Coal Rank

“…In the last 30 years, remarkable progress has been achieved in reducing the concentration of NO x in the atmosphere: nevertheless, some details of the mechanism and kinetics of NO x reduction by coal, biomass, and char remain unresolved. Fossil fuel combustion represents the main source of atmospheric NO x , , the formation of which proceeds through four chemical mechanisms: the Zeldovich (thermal) mechanism, the Fenimore (prompt) mechanism, the N 2 O intermediate mechanism, and the NNH mechanism. − The four mechanisms become dominant under different conditions, for example, the thermal mechanism dominates at high temperatures (>1800 K) with fuels that contain no fuel-bound nitrogen and the intermediate N 2 O mechanism becomes important in low temperatures.…”

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].…”

Effect of the Geometrical Parameters in a Domestic Burner With Crescent Flame Channels for an Optimal Temperature Distribution and Thermal Efficiency

“…The NO emission values are plotted in the Figure 10. Figure 10 reveals that the NO levels appear to be compliant with the temperature values, which means that the effect of thermal NO mechanism (Zeldovich mechanism) [22,23] are dominant in the simulations. If the temperature exceeds the 1200 K value the dominant reaction pathway becomes the thermally dominated NO formation.…”