Oxidation Of HCN Research Articles

NOx emissions during oxygen-enriched combustion of sewage sludge and corresponding hydrochar

This study proposed an oxygen-enriched combustion technology for the resource utilization of hydrochar prepared from sewage sludge (SS) through hydrothermal carbonization (HTC). However, its application potential relies heavily on NOx emissions. To investigate NOx emissions during oxygen-enriched combustion of hydrochars prepared at different temperatures (200 °C, 240 °C, and 280 °C), real-time NOx concentrations were recorded under varying conditions, including different carrier gases (N2 and CO2), temperatures (600 °C, 800 °C, and 1000 °C), and oxygen concentrations (20 %, 30 %, and 40 %). In comparison to air combustion processes, the NOx emissions during the devolatilization stage were considerably depressed in oxygen-enriched combustion. A high concentration of CO2 inhibited NH3 production and HCN oxidation, and generated increased amounts of CO to facilitate NOx reduction. Elevated temperatures also reduced the NOx release during the oxygen-enriched combustion of SS and hydrochar, as the accelerated oxygen consumption weakened the oxidation reactions of HCN and NH3; the enhanced reduction reaction rate and increased CO production also promoted NOx reduction. Elevated oxygen concentrations, however, promoted NOx release owing to the increased NH3 and HCN oxidation by an increased number of oxidizing groups. Additionally, the reduction of reducing gases and rapid char combustion hindered NOx reduction. The NOx-N conversion of the hydrochars was much lower than that of SS under different conditions. HTC effectively reduced the nitrogen content of SS, with nitrogen in HC-280 existing as stable heterocyclic -N. HC-280 showed significantly less nitrogen conversion at low temperatures (9.03 % reduction at 600 °C) and high oxygen concentrations (2.01 % reduction at 40 % O2) compared to SS, highlighting the potential of combining HTC and oxygen-enriched combustion.

Enhanced C2-CN sub-mechanism: Impact on NO/N2O and soot precursor yields during C2H2/HCN oxidation

The combustion of hydrocarbon-ammonia fuels poses challenges related to the formation of soot and nitrogen oxides (NOx) emissions. Various kinetic mechanisms have been developed to describe the pathways of soot and NOx formation, but limited attention has been paid to the role of the C2-CN species, such as HC3N and CH2CHCN, in influencing the yields of soot and NOx. To address this gap, we present a detailed C2-CN sub-mechanism integrated into a NOx and polycyclic aromatic hydrocarbons (PAHs) kinetic model. The rate constants of the barrierless association reactions of C2H+CN, C2H3+CN, C2H5+CN, and CH3+CH2CN were updated using the variable reaction coordinate transition state theory (VRC-TST). We numerically investigated the oxidation of C2H2 and HCN at equivalence ratios of 2.0 and 3.0, which are major precursors for NOx and PAHs, in a perfectly stirred reactor (PSR) employing two kinetic models (with/without the developed C2-CN sub-mechanism). By comparing the rates of production (ROPs) obtained via both models, we analyzed the formation pathways of NO/N2O and Benzo(ghi)fluoranthene (BGHIF). Our findings reveal temperature-dependent trends in the calculated rate constants of C2H5+CN and CH3+CH2CN associations (positive dependence) as well as C2H+CN and C2H3+CN associations (negative dependence). The peak mole fractions of BGHIF at equivalence ratio (φ) of 2.0 and 3.0 predicted by the updated mechanism were 18.4 % and 13.6 % lower than the base mechanism. This reduction can be attributed to an additional consumption channel of C2H2 (C2H2+CN=HC3N+H) predicted by the C2-CN sub-mechanism. Furthermore, the C2-CN sub-mechanism exhibited a stronger suppression effect on N2O formation compared with NO formation at φ=2.0 and 3.0. This limitation can be explained by an additional consumption channel of CN via CN+C2H2=HC3N+H, resulting in decreased NO/N2O through the reaction sequence CN→NO→N2O and CN→NCO→HNCO→NH2→HNO→NO→N2O.

Interactions of HCN with NO in pressurized oxy‐combustion

AbstractThe process of recycling flue gas to the boiler of a pressurized oxy‐combustion system could affect the final concentration of NOx, which is very important for an appropriate design of the carbon capture process. During the recycling process, HCN, as the main intermediate of the reburn reaction, may interact with NO significantly to determine the final NO emissions. The current study aims to assess the gas‐phase interactions of HCN and NO in a CO2 atmosphere, which is customary to pressurized oxy‐combustion conditions. A kinetic modeling study of the oxidation of HCN in the presence of NO has been performed under POC conditions and in the 973–1473 K temperature range. The influences of the stoichiometry, pressure, H2O concentration, and NO inlet concentration are analyzed. The results show that the HCN–NO interaction reduces both HCN and NO and that the interaction increases as pressure increases when the temperature is above 1073 K, whereas the opposite is found in low‐temperature regions. The effect of stoichiometric parameters also strongly depends on temperature but follows the opposite trend compared with the effect of pressure. These differences contribute to the suppressive effect on O2 decomposition and the positive effect on H2O decomposition at elevated pressures. An optimal temperature for NO reduction is shifted to lower temperature with increasing pressure and H2O concentration. The analysis of the total fixed nitrogen (TFN) indicates that for an actual boiler (5% O2), the temperature should be controlled at 1373, 1223, 1173, and 1173 K, respectively, as the pressure increases from 1 to 15 atm. Finally, a 21‐species and 69‐step reduced chemistry is developed and validated to accurately predict the interaction of HCN with NO at elevated pressures.

The role of H2O in NO formation and reduction during oxy-steam combustion of bituminous coal char

To improve the CO2 capture efficiency and reduce energy penalties in conventional oxy-fuel combustion systems, one possibility is to eliminate the use of recycled flue gas, by using steam and O2. This is known as oxy-steam combustion. However, the role of H2O in NO formation and reduction under oxy-steam combustion is not yet clear. Here, NO emissions during oxy-steam and air combustion of coal char were compared using both experiments and theoretical calculations, with an emphasis of the role of H2O and its resulting radicals in NO formation and reduction reactions. High concentration of H2O promotes both OH radicals and hydroxyl groups formation during oxy-steam combustion, which in turn effects NO formation and reduction reactions and eventually NO emissions. Specifically, NO formation under air combustion is largely determined by HCN conversion to NCO and then NO, whereas under oxy-steam combustion, high concentrations of OH radicals cause HCN to form NH2 and eventually NO as the dominant route. However, the conversion of HCN to NH2 and then NO is faster, and hence these OH radicals accelerate HCN oxidation to NO under oxy-steam combustion. Given that OH radicals and hydroxyl groups have little influence on NO reduction to N2, there is more NO production in oxy-steam combustion that air combustion.

A reactive molecular dynamics study of HCN oxidation during pressurized oxy-fuel combustion

In the present work, HCN oxidation during pressurized oxy-fuel combustion is studied using reactive molecular dynamics (ReaxFF MD) simulations. The effects of CO2, pressure, and O2 concentration on HCN oxidation are investigated. Under fuel-rich conditions, CO2 reduces the overall oxidation rate of HCN due to the lower diffusion coefficient of O2 in O2/CO2 environment. On the other hand, CO2 increases the amount of OH radicals through the reaction of CO2 + H → CO + OH at high temperatures. Although high pressure reduces the diffusion coefficient of O2, the oxidation rate of HCN still increases with the increase in pressure due to the higher partial pressure of O2. Moreover, NO emissions decrease with the increase in pressure because high pressure promotes the conversion of NO to N2. Furthermore, CO2 reduces the amount of CN, which is an important intermediate for the reduction of NO at high temperatures. Due to this reason, a positive effect of CO2 on the emissions of NO is observed. Additionally, the oxidation rate of HCN increases with the increase in the concentration of O2. Unlike fuel-rich conditions, CO2 exhibits an inhibitory effect on the emissions of NO under high concentration of O2.

DFT study on the interactions between HCN and NO over char

A noteworthy part of HCN conversion is in reference to its potential behavior in NO reduction. In this work, a comprehensive density functional theory (DFT) study was carried out to obtain new insight into the mechanisms of HCNNO reaction on the char surface. A model modified with the hydroxyl group contributes to a better understanding of NO reduction with HCN oxidation. The adsorption modes are found to influence the adsorption energies and reaction paths significantly. For single adsorption, the HCN adsorption in dual-site mode is the most thermally favorable. The co-adsorption of HCN and NO is dramatically more significant than the sum of the corresponding single adsorption, mainly due to the reaction of adsorbates on the surface. In addition, the microscopic reaction paths for CO and N2 formation are summarized based on the most energetically stable adsorption and co-adsorption structures separately. The canonical variational transition-state theory (CVT) is adopted here to provide fruitful kinetic implications in the temperature range of 500–1800 K. The analysis indicates that the occurrence of HCN oxidation decreases the reaction energy barriers evidently, which is also responsible for the rates increasing. The co-adsorption mechanism is favorable for NO conversion, especially for the release of CO. The findings from this work are beneficial for better understanding and illustrating the ultra-low NOx emission processes. The co-adsorption mechanism that was always neglected before is strongly suggested in future computational studies.

Numerical study on combustion characteristics and heat flux distributions of 660‐MW ultra‐supercritical double‐reheat tower‐type boiler

AbstractUltra‐supercritical double‐reheat technology, as one of the most advanced coal‐fired power generation technology, is an important direction for emission reduction and energy saving in the world. In this study, the numerical calculation was executed in a 660‐MW ultra‐supercritical double‐reheat tower‐type boiler under deep‐air‐staging conditions. The refined HCN oxidation model was adopted to substitute the default model implemented by the user‐defined functions to calculate the NOx emission. The influences of the boiler load, over‐fire air (OFA) ratio, and excess air coefficient on temperature, species, and heat flux distributions were investigated. Results show that the decrement of the boiler load from boiler maximum continuous rating to 50% turbine heat acceptance gives rise to an increase of NOx emission. The heat flux distributions along with the furnace width direction present bell shaped. When the OFA ratio rises from 17% to 43%, NOx emission descends from 357.7 to 179.3 mg m−3 at the furnace outlet, and the heat flux distributions become more uniform along with the furnace width direction with lower peaks. Temperatures, species, and heat flux distributions are similar under the three different excess air coefficients. The NOx emission is the lowest when the excess air coefficient is 1.15. The results could provide a reference for combustion characteristics optimization and hydrodynamic calculation of ultra‐supercritical double‐reheat tower‐type boiler.

Catalytic oxidation and hydrolysis of HCN over LaxCuy/TiO2 catalysts at low temperatures

Abstract A series of LaxCuy/TiO2 catalysts were prepared by sol-gel method to remove HCN under the conditions of 1% O2 and 10% relative humidity. Samples were characterized by BET, XRD, XPS, H2-TPR, NH3/CO2-TPD and FT-IR. NH3-SCR reactions were carried out to verify the results of the catalyst activity tests and explore N2 formation mechanism. La/Cu ratios had a prominent impact on the catalyst performance. La1Cu9/TiO2 had the best catalytic activity: its conversion of HCN and N2 selectivity were 100% and 62.24% at 150 °C, respectively. The characterization results indicated interactions between La and Cu, catalytic redox activity and existence of abundant acidic and basic sites on the catalyst surface. Low content of La significantly improved catalytic redox ability and total acidity as well bring about the catalyst medium strong acid sites with a lower temperature. Synergistic effects of La and Cu oxides provided La1Cu9/TiO2 catalysts with remarkable activity at low temperatures.

Promotional effect of Ce and Fe addition on Cu-based extruded catalyst for catalytic elimination of co-fed acrylonitrile and HCN

The promotional effect of Ce and Fe modified Cu-based extruded catalysts on their performance for the catalytic elimination of co-fed acrylonitrile and HCN was investigated. The CuCeFe-ZTA catalyst exhibited great catalytic performance and stability. The introduction of Ce led to an increase in the amount of active oxygen species and better reducibility of the catalyst, while more strong acid sites were formed upon further modification of the catalyst upon addition of Fe. These features are critical in promoting catalyst performance for nitrile and HCN oxidation reactions, and the results of this work may facilitate the research in developing industrial catalysts for the purification of nitrile and HCN-containing exhaust gas streams.

Mn based catalysts for driving high performance of HCN catalytic oxidation to N2 under micro-oxygen and low temperature conditions

In this work, a series of MnOx/TiO2-Al2O3 oxides synthesized via sol–gel method were evaluated for catalytic oxidation of HCN under micro-oxygen and low temperature conditions. The reaction temperature, oxygen concentration, Mn content, relative humidity and calcination temperature of catalysts were the five crucial factors that were determined during the study. 15wt% of MnOx/TiO2-Al2O3 performed excellently on HCN catalytic oxidation, and nearly 100% HCN conversion and 70% N2 yield were obtained at 200°C. The comparison of H2-TPR, BET, FTIR and XPS results from fresh and used catalysts revealed that both oxygen types, namely chemisorbed and lattice oxygen, as well as adsorbed water molecules and several chemical states of Mn, including Mn4+, Mn3+ and Mn2+, were the main active species on the catalyst’s surface.It was found that the occurrence of hydrolysis of HCN was accompanied by the HCN catalytic oxidation process. In HCN catalytic oxidation process, the catalytic hydrolysis of HCN that occurred could be ascribed to two sources of adsorbed water molecules: (i) the catalyst itself, which contained adsorbed water molecules; (ii) the re-adsorption of water molecules that produced by HCN oxidation reaction. The water vapor introduced had obvious inhibition to HCN conversion and N2 yield may be due to the competitive adsorption between water molecules and HCN.Based on XPS, FTIR results and early studies, HCN pre-reacted with water molecules from the catalyst’s surface to produce NH3 and CO. Both of these products were readily further oxidized to produce N2, H2O and CO2 under low temperatures, but they were oxidized to NO instead at high temperatures. Meanwhile, only a small amount of N2O as an undesirable by-product produced in this reaction process.

Coupling catalytic hydrolysis and oxidation of HCN over HZSM-5 modified by metal (Fe,Cu) oxides

Abstract In this work, a series of metal oxides (Fe,Cu) modified HZSM-5 catalysts were synthesized by incipient-wetness impregnation method and then characterized by XRD, N 2 adsorption-desorption, H 2 -TPR, NH 3 -TPD, UV-vis, FT-IR and XPS measurements. The catalytic hydrolysis and oxidation behaviors toward HCN were investigated. The results indicated that the Fe-Cu/HZSM-5 catalysts exhibited more excellent performence on coupling catalytic hydrolysis and oxidation of HCN than HZSM-5, Fe/HZSM-5, Cu/HZSM-5, and both nearly 100% HCN conversion and 80% N 2 selectivity were obtained at about 250 °C. The improved catalytic performance could be ascribed to the creation of highly dispersed iron and copper composites on the surface of the HZSM-5 support, the excellent redox and regulated acid properties of the active ingredients. Moreover, the highly N 2 selectivity could be attributed to the good interaction between the Fe and Cu nanocomposites which was facilitated to the NH 3 -SCR (selective catalytic reduction of NO by NH 3 ) reaction.

Structural evolution of nitrogen-doped carbon nanotubes: From synthesis and oxidation to thermal defunctionalization

Mechanism of the oxidation and thermal defunctionalization of nitrogen-doped carbon nanotubes (N-CNTs) was studied. TGA-MS, low temperature nitrogen adsorption, Raman spectroscopy, TEM and XPS were used to trace the changes in the morphology, surface properties and defectiveness of N-CNTs during HNO3 treatment. The first hour of treatment resulted in the intensive oxidation of N-CNTs due to the transformation of surface nitrogen groups into oxidized pyridone ones. Complete destruction of segmented structure of N-CNTs and a decrease in both oxygen and nitrogen content was observed after prolonged oxidation. The changes in the defectiveness were confirmed by the increase in ID1/IG and the decrease in ID3/IG ratio in Raman spectra. The thermal stability of nitrogen species in N-CNTs was found to increase in the following sequence: pyridone, pyridine and graphitic nitrogen. Decomposition of pyridone nitrogen starts at 200–400°С resulting in the formation of pyridine and pyrrolic nitrogen species. Above 500 °C these two nitrogen species transform into graphitic nitrogen which decomposes at temperatures above 1000°С. NO release in different temperature ranges was associated with both the destruction of nitro-, nitrito-, nitroso-groups and oxidation of HCN. The mechanism of functionalization and thermal destruction of oxygen- and nitrogen-containing groups was proposed.

Removal of HCN over Mn based catalysts under low temperatures

Mn-based catalysts were synthesized by a sol-gel method and implied to removal of HCN under low temperature and micro-oxygen conditions. The results show the catalysts that modified by manganese oxide have superior catalytic oxidation activity for HCN conversion. Furthermore, the introduction of barium can promote the selective catalytic oxidation of HCN to N2. The introduction of H2O apparently inhibited the conversion efficiency of HCN, and the H2O could restrain the production of N2 yield at lower temperature but it nearly had no effect on N2 yield at higher temperatures.

微粉炭燃焼におけるNO<sub>x</sub>統括反応モデルの改良

The global reaction rate expressions for N intermediates (HCN and NH3) proposed by De Soete were frequently used in NOx simulation of pulverized coal (PC) combustion. However, the oxidation rate of HCN calculated by De Soete's expressions is largely underestimated in the typical condition of PC combustion. In this study, the oxidation rate of HCN is recommended to be increased. The modified NOx model was used to simulate the NOx concentration distribution for two coals in a down-fired autothermal test furnace. A satisfactory agreement for the NOx concentration distributions between simulation and measurement could be obtained using the increased HCN oxidation rate, if proper char surface area values (S) were chosen. It was found that the S leading to the best simulation results for two coals were both proportional with those measured by Hg porosimetry.

Modeling of NO formation in low pressure premixed flames

In this paper a detailed sub-mechanism NOMecha2.0 for NOx chemistry at high temperature is validated on a large experimental database obtained in flames, a jet-stirred reactor (JSR) and a plug-flow reactor under sub-atmospheric and atmospheric conditions. This sub-mechanism mainly based on the one implemented in the GDFkin®3.0_NCN model for prompt-NO formation has been thoroughly updated. Prompt-NO formation results from the reaction between CH and N2 yielding NCN and H. Then, NCN radicals react with H and O-atoms yielding HCN + N and CN + NO, respectively. Care was taken in the choice of the enthalpy of formation of the N-species, especially for NCN radicals for which the enthalpy values reported in the literature differ by more than 10 kJ mol−1. Critical rate constant values for the two main reactions (CH + N2 → NCN + H and NCN + H → HCN + N) and the branching ratio of the reactions NCN + H → products are discussed. Validation focuses mainly on prompt-NO formation in low pressure flames stabilized with different fuels (CH4, C2H6, C3H8 and C2H2) using data from the literature. It draws in particularly on the extended experimental database, including species profiles (CH, NCN, CN, HCN, NCO and NO) previously obtained in Lille in CH4 and C2H2 flames, which was extended in this work. Validation also considers experiments dedicated to HCN oxidation in a JSR or in flames, and to HNCO oxidation performed in a plug-flow reactor. In order to improve the prediction of HNCO, HCN/HNC isomerization has been implemented in NOMecha2.0. Finally the NOMecha2.0 sub-mechanism was satisfactorily coupled to a detailed chemical mechanism from the literature dedicated to the oxidation of acetylene at high temperature to predict NO formation.

Interactions of HCN with NO in a CO2 Atmosphere Representative of Oxy-fuel Combustion Conditions

The knowledge of NOx concentration in the exhaust gas of an oxy-fuel combustion system is very important for an appropriate design of the subsequent carbon capture process. NOx final emissions in oxy-fuel combustion depend on the reburn reactions of the recycled NO when it returns to the boiler. HCN is the main intermediate during this process, and thus, it may interact with NO significantly. The present work aims to evaluate the gas-phase interactions between HCN and NO in a CO2 atmosphere, characteristic of oxy-fuel conditions. A flow reactor experimental and kinetic modeling study of the oxidation of HCN in the presence of NO has been performed in a CO2 atmosphere and in the 973–1423 K temperature range. The influence of the stoichiometry and NO inlet concentration is analyzed. The results indicate that the HCN–NO interaction results in the diminution of both HCN and NO in a CO2 atmosphere. The conversion of NO is higher as temperature, oxygen concentration, and HCN/NO inlet ratio increase. The maximum...

NO Formation during Oxy-Fuel Combustion of Coal and Biomass Chars

The yields of NO from combustion of bituminous coal, lignite, and biomass chars were investigated in O2/N2 and O2/CO2 atmospheres. The experiments were performed in a laboratory-scale fixed-bed reactor in the temperature range of 850–1150 °C. To minimize thermal deactivation during char preparation, the chars were generated by in situ pyrolysis at the reaction temperature. The NO yield clearly decreased and the CO yield increased when the atmosphere was altered from O2/N2 to O2/CO2 at 850 °C, but only small differences in NO and CO yields were observed between the two atmospheres at 1050–1150 °C. To examine how CO influences the NO yield, the effect of CO on NO reduction over char as well as NO reduction by CO over ash was investigated in the fixed-bed reactor. Furthermore, the influence of CO on the homogeneous oxidation of HCN, possibly a product of the char-N oxidation, was evaluated using a detailed chemical kinetic model. The results indicate that CO influences the NO yield from char combustion throu...

Improvement of NOx formation model for pulverized coal combustion by increasing oxidation rate of HCN

The NOx formation simulation during pulverized coal (PC) combustion has been studied for several decades. In these studies, the global reaction rate expressions for N intermediates (HCN and NH3) proposed by De Soete were frequently used. Using De Soete’s expressions, the calculated reaction rates of HCN and NH3 in the typical temperature range of 1750–2000K for PC combustion show that HCN has obviously lower conversion rate to NO (or oxidation rate of HCN, HCN+O2→NO+⋯) than that to N2 (HCN+NO→N2+⋯) as well as obviously lower conversion rate to NO than NH3 does (NH3+O2→NO+⋯). This is completely in contradiction with the well-recognized conclusions in the publications. Thus, in this study, the oxidation rate of HCN is recommended to be increased by about 13 times according to related literature data. The modified NOx model was integrated into coal combustion model to simulate the NOx concentration distribution for three coals (two sub-bituminous coals and one lignite) in a down-fired autothermal test furnace. The input kinetic data of coal devolatilization and char combustion for coal combustion model were all obtained from the experiments in a drop tube furnace, which ensured the good agreements of gas temperatures and compositions between prediction and measurement in the test furnace. According to the simulated results, it was nearly impossible to accurately reproduce the NOx concentration profile in pc furnace using the original De Soete’s HCN oxidation rate, since the NOx concentrations in the high-temperature flame zone were greatly underestimated. Nevertheless, a satisfactory agreement for the NOx concentration distributions between prediction and measurement could be obtained using the increased HCN oxidation rate, if proper char surface area (S) values were chosen. Via using different S values, it was found that the S leading to the best simulation results for three coals were all about 17.5 times higher than those measured by Hg porosimetry (SHg), but they could not correlated well with that measured with low-temperature N2 adsorption (SBET). This indicated that SHg was a better surface basis for normalizing char reactivity with NO than SBET for different coals in the NOx simulation under the conditions of PC combustion.

Computational study on the mechanism and thermodynamic of atmospheric oxidation of HCN with ozone

Oxidation of hydrogen cyanide with ozone on the singlet potential energy surface is carried out using the MP2 and CCSD(T)//MP2 theoretical approaches in connection with the 6-311++G(d,p) basis set. In this reaction, energy barrier of transition states are low, so the reaction of HCN with ozone can occur easily at atmospheric condition. With variety of pre-reactive complex, five types of products are obtained at the MP2 method which four types of them have enough thermodynamic stability at the standard condition. CO2 + HNO are final adducts in a process that is computed to be exothermic by −132.605 kcal/mol in standard enthalpy and spontaneous by −144.166 kcal/mol in Gibbs free energy of reaction. In kinetic viewpoint, the production of OCN + HO2 adducts path with one low level transition state is the most favored path.

A kinetic study on the potential of a hybrid reaction mechanism for prediction of NOx formation in biomass grate furnaces

This paper presents the verification of a hybrid reaction mechanism (28 species, 104 reactions) by means of a kinetic study with a view to its application for the CFD-based prediction of gas phase combustion and NOx formation in biomass grate furnaces. The mechanism is based on a skeletal kinetic scheme that includes the subsets for H2, CO, NH3 and HCN oxidation derived from the detailed Kilpinen 97 reaction mechanism. To account for the CH4 breakdown two related reactions from the 4-step global mechanism for hydrocarbons oxidation by Jones and Lindstedt were adopted. The hybrid mechanism was compared to the global mechanism and validated against the detailed Kilpinen 97 mechanism. For that purpose plug flow reactor simulations at conditions relevant to biomass combustion (atmospheric pressure, 1200–1600 K) for approximations of the flue gases in a grate furnace at fuel lean and fuel rich conditions were carried out. The hybrid reaction mechanism outperformed the global one at all conditions investigated. The most striking differences obtained in predictions by the hybrid and the detailed mechanism at the residence times prior to ignition were attributed to the simplified description of the CH4 oxidation in the case of the former. The overall agreement regarding both combustion and NOx chemistry between the hybrid and the detailed mechanism was better at fuel lean conditions than at fuel rich conditions. However, also at fuel rich conditions, the agreement was improving with increasing temperature. Moreover, it was shown that an improvement in the prediction of NOx formation by the N-subset of the hybrid reaction mechanism can be achieved by replacing its C–H–O subset with that of the detailed one.