Structure of propagating edge diffusion flames in hydrocarbon fuel jets

Direct numerical simulations with a C₃-chemistry model have been performed to investigate the transient behavior and internal structure of flames propagating in an axisymmetric fuel jet of methane, ethane, ethylene, acetylene, or propane in normal earth gravity (1g) and zero gravity (0g). The fuel issued from a 3-mm-i.d. tube into quasi-quiescent air for a fixed mixing time of 0.3 s before it was ignited along the centerline where the fuel–air mixture was at stoichiometry. The edge of the flame formed a vigorously burning peak reactivity spot, i.e., reaction kernel, and propagated through a flammable mixture layer, leaving behind a trailing diffusion flame. The reaction kernel broadened laterally across the flammable mixture layer and possessed characteristics of premixed flames in the direction of propagation and unique flame structure in the transverse direction. The reaction kernel grew wings on both fuel and air sides to form a triple-flame-like structure, particularly for ethylene and acetylene, whereas for alkanes, the fuel-rich wing tended to merge with the main diffusion flame zone, particularly methane. The topology of edge diffusion flames depend on the properties of fuels, particularly the rich flammability limit, and the mechanistic oxidation pathways. The transit velocity of edge diffusion flames, determined from a time series of calculated temperature field, equaled to the measured laminar flame speed of the stoichiometric fuel–air mixtures, available in the literature, independent of the gravity level.     

氢、碳氢燃料对向扩散火焰

对氢、正烷烃碳氢燃料与氧的对向扩散火焰,其中正烷烃包含了在工业用燃料中广泛应用的C_nH_2n+2正烷烃CH₄～C1₆H₃₄,对这些燃料的火焰结构进行了分析和比较,系统地分析了压力和拉伸率对火焰行为和热释放率等的影响,其中包含了2115个组分8157个可逆反应．研究结果表明,所有燃料的火焰厚度和热释放率与压力和拉伸率的乘积的平方根成线性关系．在相同工况下,氢的火焰厚度总是大于所有的碳氢燃料,而CH₄～C1₆H₃₄所有的碳氢燃料在相同工况下总是具有几乎相同的燃烧温度分布、燃烧产物分布、火焰厚度和热释放率,该结果表明由这些碳氢燃料组成的混合燃料具有同样的火焰特性.     

Premixed turbulent flame front structure investigation by Rayleigh scattering in the thin reaction zone regime

Premixed turbulent flames of methane–air and propane–air stabilized on a bunsen type burner were studied using planar Rayleigh scattering and particle image velocimetry. The fuel–air equivalence ratio range was from lean 0.6 to stoichiometric for methane flames, and from 0.7 to stoichiometric for propane flames. The non-dimensional turbulence rms velocity, u′/S_L, covered a range from 3 to 24, corresponding to conditions of corrugated flamelets and thin reaction zones regimes. Flame front thickness increased slightly with increasing non-dimensional turbulence rms velocity in both methane and propane flames, although the flame thickening was more prominent in propane flames. The probability density function of curvature showed a Gaussian-like distribution at all turbulence intensities in both methane and propane flames, at all sections of the flame.The value of the term Dκ, the product of molecular diffusivity evaluated at reaction zone conditions and the flame front curvature, has been shown to be smaller than the magnitude of the laminar burning velocity. This finding questions the validity of extending the level set formulation, developed for corrugated flames region, into the thin reaction zone regime by increasing the local flame propagation by adding the term Dκ to laminar burning velocity.     

Strain rate and fuel composition dependence of chemiluminescent species profiles in non-premixed counterflow flames: comparison with model results

A detailed comparison has been conducted between chemiluminescence (CL) species profiles of OH^?, CH^?, and C₂ ^?, obtained experimentally and from detailed flame kinetics modeling, respectively, of atmospheric pressure non-premixed flames formed in the forward stagnation region of a fuel flow ejected from a porous cylinder and an air counterflow. Both pure methane and mixtures of methane with hydrogen (between 10 and 30 % by volume) were used as fuels. By varying the air-flow velocities methane flames were operated at strain rates between 100 and 350 s^?1, while for methane/hydrogen flames the strain rate was fixed at 200 s^?1. Spatial profiles perpendicular to the flame front were extracted from spectrograms recorded with a spectrometer/CCD camera system and evaluating each spectral band individually. Flame kinetics modeling was accomplished with an in-house chemical mechanism including C₁–C₄ chemistry, as well as elementary steps for the formation, removal, and electronic quenching of all measured active species. In the CH₄/air flames, experiments and model results agree with respect to trends in profile peak intensity and position. For the CH₄/H₂/air flames, with increasing H₂ content in the fuel the experimental CL peak intensities decrease slightly and their peak positions shift towards the fuel side, while for the model the drop in mole fraction is much stronger and the peak positions move closer to the fuel side. For both fuel compositions the modeled profiles peak closer to the fuel side than in the experiments. The discrepancies can only partly be attributed to the limited attainable spatial resolution but may also necessitate revised reaction mechanisms for predicting CL species in this type of flame.     

A comparison of computational and experimental lift-off heights of coflow laminar diffusion flames

As a sensitive marker of changes in flame structure, the number densities of excited-state CH (denoted CH^*), and excited-state OH (denoted OH^*) are imaged in coflow laminar diffusion flames. Measurements are made both in normal gravity and on the NASA KC-135 reduced-gravity aircraft. The spatial distribution of these radicals provides information about flame structure and lift-off heights that can be directly compared with computational predictions. Measurements and computations are compared over a range of buoyancy and fuel dilution levels. Results indicate that the lift-off heights and flame shapes predicted by the computations are in excellent agreement with measurement for both normal gravity (1g) and reduced gravity flames at low dilution levels. As the fuel mixture is increasingly diluted, however, the 1g lift-off heights become underpredicted. This trend continues until the computations predict stable flames at highly dilute fuel mixtures beyond the 1g experimental blow-off limit. To better understand this behavior, an analysis was performed, which indicates that the lift-off height is sensitive to the laminar flame speed of the corresponding premixed mixture at the flame edge. By varying the rates of two key “flame speed” controlling reactions, we were able to modify the predicted lift-off heights so as to be in closer agreement with the experiments. The results indicate that reaction sets that work well in low dilution systems may need to be modified to accommodate high dilution flames.     

Temperature and carbon source effects on methane–air flame synthesis of CNTs

We have conducted experimental and numerical studies on flame synthesis of carbon nanotubes (CNTs) to investigate the effects of three key parameters – selective catalyst, temperature and available carbon sources – on CNT growth. Two different substrates were used to synthesize CNTs: Ni-alloy wire substrates to obtain curved and entangled CNTs and Si-substrates with porous anodic aluminum oxide (AAO) nanotemplates to grow well-aligned, self-assembled and size-controllable CNTs, each using two different types of laminar flames, co-flow and counter-flow methane–air diffusion flames. An appropriate temperature range in the synthesis region is essential for CNTs to grow on the substrates. Possible carbon sources for CNT growth were found to be the major species CO and those intermediate species C₂H₂, C₂H₄, C₂H₆, and methyl radical CH₃. The major species H₂, CO₂ and H₂O in the synthesis region are expected to activate the catalyst and help to promote catalyst reaction.     

An experimental and numerical study on the adequacy of CH as a flame marker in premixed methane flames

The CH radical is frequently used as a flame marker because it is relatively short-lived and is present over a narrow region in flames. Discontinuities in the CH field are thus often interpreted as localized extinction of the flame. Recently, however, the adequacy of CH laser-induced fluorescence (LIF) as a flame marker was questioned by an experimental study of flame–vortex interactions in highly N₂-diluted premixed methane flames. We demonstrate both experimentally and numerically that anomalies in the transient response of CH in this earlier study were due to reactant composition variations in the vortex. In addition, we evaluate the adequacy of CH LIF as a flame marker over a much broader range of conditions. Previous numerical studies showed that heat release rate correlates reasonably well with peak [HCO] and the concentration product [OH][CH₂O], but poorly with [CH], in highly N₂-diluted premixed methane flames. Here, the correlation between heat release rate and CH is investigated both experimentally, by performing simultaneous measurements of CH, OH, and CH₂O LIF, and numerically. We consider undiluted and N₂-diluted premixed methane flames over a range of strain rates and stoichiometries. Results are reported for flames subjected to unsteady stretch and reactant composition variations. For all N₂-dilution levels considered, the peak CH LIF signal correlates poorly with heat release rate when the stoichiometry of the reactant mixture changes from rich to lean. However, when flames are subjected to stretch, the correlation between CH and heat release rate improves as the N₂-dilution level decreases. The correlation is reasonably good for undiluted flames with equivalence ratios of 0.8 < Φ < 1.2. This result is particularly encouraging, given the relevance of undiluted flames to practical applications, and it motivates further investigation of the parameter space for which difficulties may exist in using CH as a flame marker.     

Reaction zone structures and mixing characteristics of partially premixed swirling CH4/air flames in a gas turbine model combustor

The mixing, reaction progress, and flame front structures of partially premixed flames have been investigated in a gas turbine model combustor using different laser techniques comprising laser Doppler velocimetry for the characterization of the flow field, Raman scattering for simultaneous multi-species and temperature measurements, and planar laser-induced fluorescence of CH for the visualization of the reaction zones. Swirling CH₄/air flames with Re numbers between 7500 and 60,000 have been studied to identify the influence of the turbulent flow field on the thermochemical state of the flames and the structures of the CH layers. Turbulence intensities and length scales, as well as the classification of these flames in regime diagrams of turbulent combustion, are addressed. The results indicate that the flames exhibit more characteristics of a diffusion flame (with connected flame zones) than of a uniformly premixed flame.     

Lean or ultra-lean stretched planar methane/air flames

Lean premixed combustion has potential advantages of reducing pollutants and improving fuel economy. In some lean engine concepts, the fuel is directly injected into the combustion chamber resulting in a distribution of lean fuel/air mixtures. In this case, very lean mixtures can burn when supported by hot products from more strongly burning flames. This study examines the downstream interaction of opposed jets of a lean-limit CH₄/air mixture vs. a lean H₂/air flame. The CH₄ mixtures are near or below the lean flammability limit. The flame composition is measured by laser-induced Raman scattering and is compared to numerical simulations with detailed chemistry and molecular transport including the Soret effect. Several sub-limit lean CH₄/air flames supported by the products from the lean H₂/air flame are studied, and a small amount of CO₂ product (around 1% mole fraction) is formed in a “negative flame speed” flame where the weak CH₄/air mixture diffuses across the stagnation plane into the hot products from the H₂/air flame. Raman scattering measurements of temperature and species concentration are compared to detailed simulations using GRI-3.0, C₁, and C₂ chemical kinetic mechanisms, with good agreement obtained in the lean-limit or sub-limit flames. Stronger self-propagating CH₄/air mixtures result in a much higher concentration of product (around 6% CO₂ mole fraction), and the simulation results are sensitive to the specific chemical mechanism. These model-data comparisons for stronger CH₄/air flames improve when using either the C₂ or the Williams mechanisms.     

Application of Conditional Source-term Estimation to two turbulent non-premixed methanol flames

Conditional Source-term Estimation (CSE) is a turbulent combustion model that uses conditional averages to close the chemical source term. Previous CSE studies have shown that the model is able to predict the flame characteristics successfully; however, these studies have only focused on simple hydrocarbon fuels mostly composed of methane. The objective of the present paper is to evaluate the capabilities of CSE applied to turbulent non-premixed methanol flames, which has never been done previously. The current study investigates two different types of methanol flames: piloted and bluff-body flames. For the piloted flame, the standard k–ε model is used for turbulence modelling, while the Shear Stress Transport (SST) k–ω model is applied to the bluff-body case. Different values of empirical constants within the turbulence models were tested, and it was found that C_ε1 = 1.7 for the piloted flame and γ₂ = 0.66 for the bluff-body flame provided the best agreement with experimental measurements for the mixing field. Detailed chemistry is included in tabulated form using the Trajectory Generated Low-Dimensional Manifold (TGLDM) method. The predictions including both the Favre-averaged and conditional mass fraction of reactive species and temperature are compared with available experimental data and previous numerical results. Overall, the CSE predictions of conditional and unconditional quantities are in good agreement with the experimental data except for hydrogen. Sources of discrepancies are identified such as the chemical kinetics and neglect of differential diffusion. Large eddy simulations may also help to improve the velocity and mixing field predictions.     

Heat release rate as represented by [OH] × [CH2O] and its role in autoignition

Data from a recent instantaneous, simultaneous, high-resolution imaging experiment of Rayleigh temperature and laser induced fluorescence (LIF) of OH and CH₂O at the base of a turbulent lifted methane flame issuing into a hot vitiated coflow are analysed and contrasted to reference flames to further investigate the stabilization mechanisms involved. The use of the product of the quantified OH and semi-quantified CH₂O images as a marker for heat release rate is validated for transient autoigniting laminar flames. This is combined with temperature gradient information to investigate the flame structure. Super-equilibrium OH, the nature of the profiles of heat release rate with respect to OH mole fraction, and comparatively high peak heat release rates at low temperature gradients is found in the kernel structures at the flame base, and found to be indicative of autoignition stabilization.     

Fuel dependence of benzene pathways

The relative importance of formation pathways for benzene, an important precursor to soot formation, was determined from the simulation of 22 premixed flames for a wide range of equivalence ratios (1.0-3.06), fuels (C₁-C₁₂), and pressures (20-760 torr). The maximum benzene concentrations in 15 out of these flames were well reproduced within 30% of the experimental data. Fuel structural properties were found to be critical for benzene production. Cyclohexanes and C₃ and C₄ fuels were found to be among the most productive in benzene formation; and long-chain normal paraffins produce the least amount of benzene. Other properties, such as equivalence ratio and combustion temperatures, were also found to be important in determining the amount of benzene produced in flames. Reaction pathways for benzene formation were examined critically in four premixed flames of structurally different fuels of acetylene, n-decane, butadiene, and cyclohexane. Reactions involving precursors, such as C₃ and C₄ species, were examined. Combination reactions of C₃ species were identified to be the major benzene formation routes with the exception of the cyclohexane flame, in which benzene is formed exclusively from cascading fuel dehydrogenation via cyclohexene and cyclohexadiene intermediates. Acetylene addition makes a minor contribution to benzene formation, except in the butadiene flame where C₄H₅ radicals are produced directly from the fuel, and in the n-decane flame where C₄H₅ radicals are produced from large alkyl radical decomposition and H atom abstraction from the resulting large olefins.     

Effects of fuel Lewis number on flame spread over solids

Using a detailed two-dimensional numerical model, a systematic investigation has been made to study the effect of fuel Lewis number (Le_F = α/D_F) and mass transfer on flame spread over thin solids. The fuel Lewis number affects the flame spread rates for both concurrent and opposed flames over thin fuels. The dependence of the flame spread rate on Le_F for these two spreading modes is, however, not the same. In opposed flame spreads (zero-gravity, self-propagation, and normal gravity downward propagation), the flame spread rate vs. Le_F curve is non-monotonic with a maximum value occurring at an intermediate value of Le_F = 0.5. In steady, concurrent spread in zero-gravity with low-speed flow and a constant flame length, the flame spread rate decreases with Le_F in a monotonic manner. By using the computational model as a tool, the effects of fuel mass diffusion perpendicular to and parallel with the solid surface are isolated to obtain more physical insight on the two-dimensional aspect of fuel mass transfer on flame spread. In addition, the model has also been used to decouple the solid evaporation process so that the fuel diffusion effect in the gas-phase can be isolated. Both of these theoretical exercises contribute to the understanding of mass transfer effects on the flame spreading phenomena over solids.     

Cup-burner flame structure and extinguishment by CF3Br and C2HF5 in microgravity

The effects of fire-extinguishing agents CF₃Br and C₂HF₅ on the structure and extinguishing processes of microgravity cup-burner flames have been studied numerically. Propane and a propane–ethanol–water fuel mixture, prescribed for a Federal Aviation Administration (FAA) aerosol can explosion simulator test, were used as the fuel. The time-dependent, two-dimensional numerical code, which includes a detailed kinetic model (177 species and 2986 reactions), diffusive transport, and a gray-gas radiation model, revealed unique flame structure and predicted the minimum extinguishing concentration of agent when added to the air stream. The peak reactivity spot (i.e., reaction kernel) at the flame base stabilized a trailing flame. The calculated flame temperature along the trailing flame decreased downstream due to radiative cooling, causing local extinction at <1250 K and flame tip opening. As the mole fraction of agent in the coflow (X_a) was increased gradually: (1) the premixed-like reaction kernel weakened (i.e., lower heat release rate) (but nonetheless formed at higher temperature); (2) the flame base stabilized increasingly higher above the burner rim, parallel to the axis, until finally blowoff-type extinguishment occurred; (3) the calculated maximum flame temperature remained at nearly constant (≈1700 K) or mildly increased; and (4) the total heat release of the entire flame decreased (inhibited) for CF₃Br but increased (enhanced) for C₂HF₅. In the lifted flame base with added C₂HF₅, H₂O (formed from hydrocarbon-O₂ combustion) was converted further to HF and CF₂O through exothermic reactions, thus enhancing the heat-release rate peak. In the trailing flame, “two-zone” flame structure developed: CO₂ and CF₂O were formed primarily in the inner and outer zones, respectively, while HF was formed in both zones. As a result, the unusual (non-chain branching) reactions and the combustion enhancement (increased total heat release) due to the C₂HF₅ addition occurred primarily in the trailing diffusion flame.     

CO2 addition and pressure effects on laminar and turbulent lean premixed CH4 air flames

An experimental study on CH₄–CO₂–air flames at various pressures is conducted by using both laminar and turbulent Bunsen flame configurations. The aim of this research is to contribute to the characterization of fuel lean methane/carbon dioxide/air premixed laminar and turbulent flames at different pressures, by studying laminar and turbulent flame propagation velocities, the flame surface density and the instantaneous flame front wrinkling parameters. PREMIX computations and experimental results indicate a decrease of the laminar flame propagation velocities with increasing CO₂ dilution rate. Instantaneous flame images are obtained by Mie scattering tomography. The image analysis shows that although the height of the turbulent flame increases with the CO₂ addition rate, the flame structure is quite similar. This implies that the flame wrinkling parameters and flame surface density are indifferent to the CO₂ addition. However, the pressure increase has a drastic effect on both parameters. This is also confirmed by a fractal analysis of instantaneous images. It is also observed that the combustion intensity S_T/S_L increases both with pressure and the CO₂ rate. Finally, the mean fuel consumption rate decreases with the CO₂ addition rate but increases with the pressure.     

Quantitative C2H2 measurements in sooty flames using mid-infrared polarization spectroscopy

Quantitative measurements of acetylene (C₂H₂) molecules as a combustion intermediate species in a series of rich premixed C₂H₄/air flames were non-intrusively performed, spatially resolved, using mid-infrared polarization spectroscopy (IRPS), by probing its fundamental ro-vibrational transitions. The flat sooty C₂H₄/air premixed flames with different equivalence ratios varying from 1.25 to 2.50 were produced on a 6 cm diameter porous-plug McKenna type burner at atmospheric pressure, and all measurements were performed at a height of 8.5 mm above the burner surface. IRPS excitation scans in different flame conditions were performed and rotational line-resolved spectra were recorded. Spectral features of acetylene molecules were readily recognized in the spectral ranges selected, with special attention to avoid the spectral interference from the large amount of coexisting hot water and other hydrocarbon molecules. On-line calibration of the optical system was performed in a laminar C₂H₂/N₂ gas flow at ambient conditions. Using the flame temperatures measured by coherent anti-Stokes Raman spectroscopy in a previous work, C₂H₂ mole fractions in different flames were evaluated with collision effects and spectral overlap between molecular line and laser source being analyzed and taken into account. C₂H₂ IRPS signals in two different buffering gases, N₂ and CO₂, had been investigated in a tube furnace in order to estimate the spectral overlap coefficients and collision effects at different temperatures. The soot-volume fractions (SVF) in the studied flames were measured using a He–Ne laser-extinction method, and no obvious degrading of the IRPS technique due to the sooty environment has been observed in the flame with SVF up to ～2×10^?7. With the increase of flame equivalence ratios not only the SVF but also the C₂H₂ mole fractions increased.     

Experimental and numerical study of premixed, lean ethylene flames

Ethylene is a key intermediate in the combustion mechanisms of most practical fuels. It plays also an important role in the formation of aromatic hydrocarbons and soot particules. The latter has motivated many experimental and numerical studies carried out on rich ethylene-air mixtures. Less studies have been devoted to lean mixtures, and the development of strategies based on lean, premixed flames to reduce soot and NO_x production requires additional experimental data in lean conditions. In this work, the chemical structure of lean premixed ethylene-oxygen-nitrogen flames stabilized on a flat-flame burner at atmospheric pressure was determined experimentally. The species mole fraction profiles were also computed by the Premix code (Chemkin II version) and four detailed reaction mechanisms. A very good agreement was observed for the main flame properties: reactants consumption, final products (CO₂, H₂O) and the main intermediates: CO and H₂. Marked differences occurred in the prediction of active intermediate species present in small concentrations. Pathways analyses were performed to identify the origins of these discrepancies. It was shown that the same reactions were involved in the four mechanisms to describe the consumption of ethylene, but with marked differences in their relative importance. C₂H₃ and CH₂HCO are the main radicals formed in this first step and their consumption increases the differences between the mechanisms either by the use of different kinetic data for common reactions or by differences in the nature of the consumption reactions.     

Simulations of laminar non-premixed flames of kerosene with hot combustion products as oxidiser

The effects of hot combustion product dilution in a pressurised kerosene-burning system at gas turbine conditions were investigated with laminar counterflow flame simulations. Hot combustion products from a lean (φ = 0.6) premixed flame were used as an oxidiser with kerosene surrogate as fuel in a non-premixed counterflow flame at 5, 7, 9 and 11 bar. Kerosene-hot product flames, referred to as ‘MILD’, exhibit a flame structure similar to that of kerosene–air flames, referred to as ‘conventional’, at low strain rates. The Heat Release Rate (HRR) of both conventional and MILD flames reflects the pyrolysis of the primary and intermediate fuels on the rich side of the reaction zone. Positive HRR and OH regions in mixture fraction space are of similar width to conventional kerosene flames, suggesting that MILD flames are thin fronts. MILD flames do not exhibit typical extinction behaviour, but gradually transition to a mixing solution at very high rates of strain (above A = 160, 000 s^?1 for all pressures). This is in agreement with literature that suggests heavily preheated and diluted flames have a monotonic S-shaped curve. Despite these differences in comparison with kerosene–air flames, MILD flames follow typical trends as a function of both strain and pressure. Further still, the peak locations of the overlap of OH and CH₂O mass fractions in comparison with the peak HRR indicate that the pixel-by-pixel product of OH- and CH₂O-PLIF signals is a valid experimental marker for non-premixed kerosene MILD and conventional flames.     

Analysis of 205-nm photolytic production of?atomic hydrogen in?methane flames

We investigate the 205-nm photolytic production of atomic hydrogen in methane flames. This process represents a significant interference in two-photon, laser induced-fluorescence (TP-LIF) detection of atomic hydrogen in flames. Relative TP-LIF profiles of the photolytically produced H atoms were measured using a pump-probe technique in atmospheric-pressure, premixed CH₄/O₂/N₂ flames. A high-fluence, non-resonant, nanosecond pump laser created H atoms by photodissociating flame constituents, and a copropagating, non-perturbing picosecond laser probed the photolytically produced Hatoms via TP-LIF. Spatial profiles of photolytically produced H atoms indicate that both intermediate and product species contribute to the interference in all flames. Excellent agreement between simulated and measured interference signals is observed in the product region of the flames. Vibrationally excited H₂O is the dominant source of interference in the product region, but an additional contribution is attributed to vibrationally excited OH radicals. In the flame-front region, CH₃ is the dominant precursor, and photodissociation of C₂H₂ becomes increasingly important in rich flames. Mechanisms for sequential photodissociation of CH₃ and C₂H₂ are presented, indicating that complete dissociation at 205 nm of both precursors is feasible.     

Global reduced mechanisms for methane and hydrogen combustion with nitric oxide formation constructed with CSP data

Reduced mechanisms for methane-air and hydrogen-air combustion including NO formation have been constructed with the computational singular perturbation (CSP) method using the fully automated algorithm described by Massias et al. The analysis was performed on solutions of unstrained adiabatic premixed flames with detailed chemical kinetics described by GRI 2.11 for methane and a 71-reaction mechanism for hydrogen including NO _x formation. A 10-step reduced mechanism for methane has been constructed which reproduces accurately laminar burning velocities, flame temperatures and mass fraction distributions of major species for the whole flammability range. Many steady-state species are also predicted satisfactorily. This mechanism is an improvement over the seven-step set of Massias et al, especially for rich flames, because the use of HCNO, HCN and C₂H₂ as major species results in a better calculation of prompt NO. The present 10-step mechanism may thus also be applicable to diffusion flames. A five-step mechanism for lean and hydrogen-rich combustion has also been constructed based on a detailed mechanism including thermal NO. This mechanism is accurate for a wide range of the equivalence ratio and for pressures as high as 40 bar. For both fuels, the CSP algorithm automatically pointed to the same steady-state species as those identified by laborious analysis or intuition in the literature and the global reactions were similar to well established previous methane-reduced mechanisms. This implies that the method is very well suited for the study of complex mechanisms for heavy hydrocarbon combustion.M This article features supplementary data files available from the supplemental page in the online journal.