Effects Of Equivalence Ratio Research Articles

Fuel-air ratio effect on hydrogen-methane flames in a high pressure burner for gas turbines

This numerical simulation studied the effect of H2-CH4 flame equivalence ratio on turbulent premixed combustion at 50%-50% concentration (by volume). The equivalence ratio was varied from 0.45 to 1.0 in 0.5 increments for 126 kW operating power, matching a 3.3 bar inlet reactant pressure. Tests utilized a gas turbine combustor. The thermal field, flow field, and pollutant emissions (NOx and CO) underwent rigorous analysis. The modelling framework applied steady Reynolds-Averaged Navier-Stokes (RANS) equations coupled to a probability density function (PDF) approach for turbulence-chemistry interactions and a NOx formation model. Results showed increasing equivalence ratio from 0.45 to 1.0 elevated temperature approximately 900 K, significantly promoting NOx up to 1600 ppm and CO beyond 1900 ppm. However, equivalence ratio changes minimally impacted the overall flow field, maintaining stabilized flames. These findings provide new insight on thermochemical effects and flame stability in gas turbine (G.T) combustors across a range of equivalence ratios relevant for clean, high-pressure H2-CH4 combustion. The combined RANS-PDF methodology enables predictive simulation of turbulence, kinetics, emissions, and flame stability to guide optimal fuel-air ratio selection and low-emission combustor design.

Structures of Laminar Lean Premixed H2/CH4/Air Polyhedral Flames: Effects of Flow Velocity, H2 Content and Equivalence Ratio

Polyhedral Bunsen flames, induced by hydrodynamic and thermo-diffusive instabilities, are characterized by periodic trough and cusp cellular structures along the conical flame front. In this study, the effects of flow velocity, hydrogen content, and equivalence ratio on the internal cellular structure of premixed fuel-lean hydrogen/methane/air polyhedral flames are experimentally investigated. A high-spatial-resolution one-dimensional Raman/Rayleigh scattering system is employed to measure the internal scalar structures of polyhedral flames in troughs and cusps. Planar laser-induced fluorescence of hydroxyl radicals and chemiluminescence imaging measurements are used to quantify the flame front morphology. In the experiments, stationary polyhedral flames with varying flow velocities from 1.65 to 2.50 m/s, hydrogen contents from 50 to 83%, and equivalence ratios from 0.53 to 0.64 are selected and measured. The results indicate that the positively curved troughs exhibit significantly higher hydrogen mole fractions and local equivalence ratios compared to the negatively curved cusps, due to the respective focusing/defocusing effect of trough/cusp structure on highly diffusive hydrogen. The hydrogen mole fraction and local equivalence ratio differences between troughs and cusps are first increased and then decreased with increasing measurement height from 5 to 13 mm, due to the three-dimensional effect of the flame front. With increasing flow velocity from 1.65 to 2.50 m/s, the hydrogen mole fraction and local equivalence ratio differences between troughs and cusps decrease, which is attributed to the overall decreasing curvatures in troughs and cusps due to the decreased residence time and increased velocity-induced strain. With increasing hydrogen content from 50 to 83%, the hydrogen mole fraction and local equivalence ratio differences between troughs and cusps are amplified, due to the enhanced effects of the flame front curvature and the differential diffusion of hydrogen. With increasing equivalence ratio from 0.53 to 0.64, a clear increasing trend in hydrogen mole fraction and equivalence ratio differences between troughs and cusps is observed at constant flow velocity condition, which is a trade-off result between increasing effective Lewis number and increasing curvatures in troughs and cusps.

Numerical Research of Flame Propagation Process in a Supersonic Combustor with Multi-Strut

ABSTRACT The flame processes and the influence of different factors on the cross flame propagation width in a supersonic combustor equipped with multi-strut fueled with kerosene were analyzed to deepen the understanding of supersonic flame characteristics. Under the conditions of T t = 1680K, P t = 1.64Mpa, and Ma = 2.7, the numerical calculations using the multi-step combustion reaction mechanism were carried out. The mixing performance and flame propagation width could be improved by increasing the number of struts. In the multi-strut injection method, the cross flame was observed outside the central flame. The mechanism of cross flame formation was revealed. The establishment of the cross flame had a maximum spacing requirement between injection struts, but this limit could be expanded by the high temperature zone formed by the narrow-distance injection strut. The effects of igniter energy and ignition strut equivalence ratio on the flame diffusion process were studied. Then the boundary conditions required for the cross flame propagation were obtained. The results of this study are highly significant for enhancing the performance of large-scale supersonic combustors in the future.

Overall scheme design of a closed solid oxide fuel cell hybrid engine for ships

A scheme of compact closed solid oxide fuel cell hybrid engines for ship power and propulsion on ships is proposed. A zero-emission closed engine at the effective equivalence ratio of 1 is achieved by recirculating water and fuelling by liquid hydrocarbon fuel and oxygen. The adiabatic pure oxygen reforming temperature of the reformer is higher than the specified anode inlet temperature. A turbine is placed in front of the solid oxide fuel cell anode. Detailed potential distributions are considered using a two-dimensional solid oxide fuel cell model, and thermodynamic models of the hybrid engine are built. The performance of the reformer is more sensitive to the oxygen-carbon ratio rather than the steam-carbon ratio, which leads to a huge change of the pressure ratio of the turbine. Therefore, the power ratios of turbines and SOFC are also affected by the oxygen and steam carbon ratio and excess oxygen coefficient. The optimized power ratio is 1.02–1.13, which results in a significant change in the efficiency of the engine. Under the specified operating conditions, the engine can achieve a high efficiency of 67 %. Under the off-design conditions, with the increase of the mass flow of fuel or the current density, the power of the engine can be changed from 20 % to 160 % of the designed power.

Effects of Hydrogen Blending Ratio and Equivalence Ratio on the Dynamic Characteristics of Deflagration Shock Waves of CH4/H2 Mixtures

Effects of Hydrogen Blending Ratio and Equivalence Ratio on the Dynamic Characteristics of Deflagration Shock Waves of CH₄/H₂ Mixtures

Numerical investigation of equivalence ratio effects on Flex-Fuel mixing controlled combustion enabled by prechamber ignition

There is interest in adapting renewable and low-carbon intensity fuels to heavy-duty engines to help displace criteria and greenhouse gas emissions associated with diesel combustion. Low-carbon fuels have inherently low cetane numbers and thus pose a significant challenge when considering direct substitution in diesel combustion systems. Use of an actively fueled prechamber as an ignition source to initiate mixing-controlled combustion (PC-MCC) of low-cetane fuels is becoming an attractive combustion mode to alleviate the identified reactivity deficit. This work focuses on the utilization of an active prechamber to facilitate diesel-like combustion of bioethanol-gasoline fuel blends in a heavy-duty engine. Recent results in this emerging technology suggest that ignition quality is uniquely coupled to prechamber equivalence ratio. In this numerical study, the fundamental implications of prechamber equivalence ratio on the ignition performance of direct injected fuels ranging from E10 to E100 are investigated using CONVERGE. Parametric studies of the prechamber operating strategy were assessed at diesel-like conditions to characterize the performance trends relative to a diesel baseline at the same boundary conditions. Simulation results indicate that PC-MCC is flex-fuel capable and achieves diesel-like ignition qualities and combustion processes for all fuels considered under stoichiometric and rich prechamber conditions. To characterize the equivalence ratio trends observed, a novel inflow boundary modeling technique was utilized to prescribe turbulent jets in place of the prechamber where selective speciation of the jet composition was conducted to isolate the ignition contributions of radical and reacting species in lean, stoichiometric, and rich jets. The inflow boundary modeling suggests that excess fuel and combustion intermediates present in jets produced from stratified and fuel-rich prechamber operation promotes higher jet temperatures and as such are superior ignition sources. Relative to a lean prechamber jet, the peak temperature of a reacting jet from a rich prechamber was up to 600 K hotter at fixed distances from the orifice exit. Radicals also demonstrated an influence on the ignition process, but the combustion mode was identified to be thermally dominant.

Effect of Ethanol and Iso-Octane Blends on Isolated Low-Temperature Heat Release in a Spark Ignition Engine

<div>Low-temperature heat release (LTHR) is of interest for its potential to help control autoignition in advanced compression ignition (ACI) engines and mitigate knock in spark ignition (SI) engines. Previous studies have identified and investigated LTHR in both ACI and SI engines before the main high-temperature heat release (HTHR) event and, more recently, LTHR in isolation has been demonstrated in SI engines by appropriately curating the in-cylinder thermal state during compression and disabling the spark discharge. Ethanol is an increasingly common component of market fuel blends, owing to its renewable sources. In this work, the effect of adding ethanol to iso-octane (2,2,4-trimethylpentane) blends on their LTHR behavior is demonstrated. Tests were run on a motored single-cylinder engine elevated inlet air temperatures and pressures were adjusted to realize LTHR from blends of iso-octane and ethanol without entering the HTHR regime. The blends were tested with inlet temperatures of 40°C–140°C at equivalence ratios of 0.5, 0.67, and 1.0 with boosted (1.5 barA) conditions. The measured LTHR decreased with increasing ethanol content for all conditions tested; iso-octane–ethanol blends with above 20% ethanol content (by volume) showed minimal LTHR under engine conditions. These net effects resulted from the combination of thermal effects (charge cooling) and chemical effects (reactivity changes at low temperatures). The effect of temperature, pressure, fuel composition, and equivalence ratio on ignition delay times calculated from chemical kinetic modeling are presented alongside pressure–temperature trajectories of the in-cylinder gases to explain the trends. The underlying cause of the trends is explained by using a sensitivity analysis to determine the contribution of each reaction within the chemical kinetic mechanism to first-stage ignition, revealing the effect of introducing ethanol on the OH radical pool and resulting LTHR intensity.</div>

Effects of Copper Foam Wall/Obstacles on the Deflagration-to-Detonation Transition

To investigate the process of deflagration-to-detonation transition (DDT) of the copper foam wall in the pulse detonation engine, detonation combustion experiments were carried out using ethylene and oxygen-enriched air (oxygen concentration: 40%) as fuel and oxidant. The effects of copper foam pore size, thickness, installation length, and structure on the flame acceleration were studied experimentally, as were the effects of blockage ratio and mixture equivalence ratio. The results show that among the four pore sizes selected, the 10 PPI case produces the fastest flame development on the porous flat wall. For conditions with successful detonation, the 10 PPI case reduces the DDT distance and time by 34.97 and 42.57%, respectively, compared with the 40 PPI case. Regarding the installation length of copper foam, it is found that copper foam with a large pore size (10 PPI) and a short installation length achieves stable detonation. The general structure of copper foam was also analyzed, including the porous flat wall, porous obstacle, and solid obstacle with the same installation length. These three structures effectively accelerate the initiation of detonation. Particularly, porous obstacles show more pronounced effects on flame acceleration than the commonly used solid obstacles. These results are instructive for optimizing the short-distance ignition ability of pulsed detonation engines.

Investigation on self-excited thermoacoustic instability and emission characteristics of premixed CH4/NH3/air flame

Ammonia is one of the promising carbon-free alternative fuels for low-carbon power generation. This study investigated the self-excited thermoacoustic instability of premixed CH4/NH3/air flame in a swirl burner. The work aims to determine the effects of ammonia mole fraction (χNH3), equivalence ratio (Ф) and combustion chamber length (CL) on flame morphology and self-excited flame dynamics. In addition, the emission characteristics of CH4/NH3/air flame were also investigated. Results show that the thermoacoustic instability of the 1/4 wave mode is excited when 0.8≤Ф≤1.2 and χNH3 ≤ 0.3. There are apparent pressure fluctuations and heat release fluctuations in the combustion chamber. The fluctuating frequency decreases with increasing CL. The maximum fluctuating frequency and oscillation intensity appear near Ф=1.0. When χNH3 increases, the amplitude of fluctuating pressure and heat release rate decrease obviously, and the instability range narrows to Ф=1.0–1.1 simultaneously. The low-order acoustic network model successfully predicted the instability transition and frequency decreasing trend caused by increasing ammonia. The increase in the convective time delay is responsible for this transition. Emission analysis indicates that NOx emission can be controlled within 100 ppm under fuel-rich conditions, but the CO emission increases sharply. Thermoacoustic instability and nitrogen oxides can be simultaneously controlled under fuel-rich conditions when χNH3>0.3. However, this will be limited by unburned reactants.

Analyzing the combustion characteristics of premixed methane-oxygen with different hydrogen addition ratios in a catalytic micro-combustor

Experimental and numerical study of premixed methane-oxygen combustion characteristics in a catalytic micro-combustor with different hydrogen addition ratios has been presented in this paper. The objective is to examine the effects of platinum catalysts and hydrogen additions on methane and oxygen combustion. The simulation of a three-dimensional micro rectangular model was carried out with a gas phase reaction mechanism combined with a surface reaction mechanism, and the model was validated with experimental results with a maximum deviation of just 1.56 percent. In the experimental phase, the effects of flammability limit, equivalence ratio, and inlet velocity were studied, while in the numerical phase, the effect of hydrogenation on combustion characteristics was investigated. Experimental results show that adding 10 % hydrogen to a premixed methane-oxygen mixture significantly increases its flammability limit. The maximum external wall temperature along the centerline was observed at an equivalent ratio of 1. Additionally, an increase in the inlet velocity leads to a corresponding increase in the external wall centerline temperature. Catalytic reaction wall temperatures show a gradual decline, with the highest temperatures located at the inlet. An observed trend revealed a decrease in the external wall centerline temperature as the hydrogen addition increased from 0 % to 40 % due to the reduced total heating value of the blended fuel. Due to its higher reactivity and ability to promote complete combustion, hydrogen also plays an important role in CH4 and O2 conversion. In addition, CO and CO2 emissions decreased with increased hydrogen percentage in fuel mixtures. Furthermore, hydrogen addition can reduce external wall heat losses as well. After adding 0–40 % hydrogen to a premixture of (CH4–O2) fuel, the total heat loss of the external wall was reduced from 19.48 W to 17.11 W.

Effect of Equivalent Ratio and Hydrocarbon Ratio on Explosive Characteristics of Synthetic Gas

With the development of society, the importance of energy is increasing day by day, and more and more people realize the importance of energy for social development.Therefore, people began to explore energy utilization, energy exploitation, clean energy and other fields.Therefore, in order to use coal resources cleanly and efficiently and reduce the damage to the environment, the development of clean coal technology is particularly important.As a kind of clean energy, syngas has been paid more and more attention, so people pay more and more attention to the safety application of syngas. This paper explores its influence on syngas explosion by changing the equivalent ratio of syngas and the ratio of hydrogen and hydrogen.The results show that the maximum explosion pressure of syngas occurs near the equivalent ratio 1.2, the maximum explosion pressure rise rate reaches the maximum near the equivalent ratio 1.5, and the maximum explosion pressure time reaches the minimum near the equivalent ratio 1.5.The change of hydrocarbon ratio does not shift the equivalent ratio of the above result, but only changes its value. The prediction equations for predicting the maximum explosion pressure under different equivalent ratios are obtained

The effects of different equivalence ratios and initial pressures on the explosion of methane/air premixed gas in closed space

Methane/air is a widely used fuel. The effects of equivalent ratio (0.8–1.2) and initial pressure (1.0 atm–1.2 atm) on the flame propagation process and explosion overpressure of methane/air premixed gas were studied using a high-speed camera and pressure sensor in a rectangular closed container. Four flame modes in the late propagation stage are distinguished according to the different modes of secondary cup movement. The flame propagation velocity and structure evolution are analyzed by defining the characteristic times. The relationship between the flame structure evolution and the growth of flame propagation velocity and explosion overpressure is revealed. The results show that, in lean combustion, the maximum flame propagation velocity increases with initial pressure increase, and the explosion overpressure fluctuates more significantly. However, the opposite is true with fuel-rich combustion. The interaction between pressure waves and flame fronts can enhance the growth of explosion overpressure in fuel-rich combustion but can inhibit the growth in lean combustion. This work can provide more data support and reference for the application prospect and safe application of methane.

Numerical simulation on combustion characteristics of methane/hydrogen blended fuel for non-premixed conical bluff body burner

Blending hydrogen into methane impacts flame stability, morphology, and pollutant emissions. This study, set against the backdrop of hydrogen-enriched natural gas combustion technology, employs a non-premixed coaxial burner with conical bluff body to create recirculation zones for flame stabilization. Combining EDC and GRI-Mech 3.0, the research fills in the gap of effects of hydrogen blending ratio (0–100%) and equivalence ratio vary (0.4–1.4) within a wide range. Keeping equivalence ratio and fuel volume flow rate as constants, as increasing hydrogen blending ratio, the mean velocity in the chamber decreases, the size of vortex structure located in outer recirculation zones reduces, and the flame length is shortened, illustrating the reaction zone shifts to chamber inlet. Furthermore, when Ф = 1.4, average temperature and temperature uniformity are averagely larger 59.82% and 4.21% than that under Ф = 0.4. The CO2 emission at XH2 = 80% is 54.70% averagely lower than that at XH2 = 0%, but peak concentration of NO increases.

Investigation of the total pressure gain in rotating detonation combustors with dilution holes

An investigation of the total pressure gain (TPG) in rotating detonation combustors (RDCs) with dilution holes is conducted by the experimental method in this study. The effects of pressure ratios (PR = 4.2–7.2) and equivalence ratios (ER = 0.5–1.5) on the total pressure gain are analyzed in four models, i.e., models A–D, of different throat areas A3.1 and dilution hole area A3.5. When the PR is small, the lowest ER causes the highest TPG, and when the PR is high, the highest ER leads to the highest TPG in Model A. While in models B–D, as ER increases, the TPG increases gradually in all the cases. Comparing the level of TPG between the four models, it is found that the increment of A3.1 and A3.5 results in the enhancement of the TPG. The present study's TPG shows superiority when compared with that of traditional RDC, which indicates that the RDC with dilution holes is more promising for achieving positive TPG in specific configurations. An empirical model considering the throat area A3.1, dilution hole area A3.5, outlet area A8, and heat (released by the fuel combustion) release rate Qv is proposed to better predict the performance of different RDC configurations. Positive total pressure gain is inferred to be promisingly attained at a high A3.1/A8, low A8/A3.5, and a high Qv. Total pressure measured by total pressure rake is verified by comparing with the data calculated by Mach-corrected-static-pressure and mass flow function methods, with relative errors in ±4% and ±15%, respectively.

An experimental investigation into ammonia dissociation, oxidation and NO emission in a vertical flow reactor

Ammonia (NH3) dissociation, oxidation, and associated nitric oxide (NO) emission in a vertical cylindrical quartz reactor is investigated to establish the effect of temperature (1000 K–1400 K), initial NH3 concentration (2%, 4%, 6%, 8%, 10%) and flowrate (250 mL/min, 500 mL/min, 750 mL/min). Ammonia oxidation experiments also examine the effect of equivalence ratio (ɸ = 0.8, 0.9, 1.0, 1.1). The NH3 and O2 conversions, N2 yield, and NO emission are determined by analysing the reactor effluent compositions. Ammonia dissociation of <6% is observed for all conditions tested. Ammonia oxidation is initiated at ∼1100 K, with majority of NH3 conversion occurring at 1200 K–1300 K before completion at ∼1325 K. NO emission becomes significant at temperatures >1300 K for ɸ ≤ 1.0 and increases with decreasing equivalence ratio. Under fuel-lean conditions, increasing initial NH3 concentration increases NO emission. Fuel-rich conditions return negligible NO, attributed to the reductive effect of excessive NH3.

Experimental investigation on heat transfer characteristics of an annual jet flame in a pore-array spray gun

Oxyacetylene ablation is widely used to assess high-temperature thermal protection materials. This study investigated the heat transfer characteristics of an oxyacetylene spray gun structured with pore arrays for long-term ablation. The effects of oxyacetylene test parameters (Reynolds number (Re), equivalence ratio (φ), and ablation distance (H)) on the flame shape and heat flux distribution were studied to explore heat transfer behavior. Subsequently, ablation experiments were performed to verify the heat transfer characteristics under different operating conditions. The following conclusions were obtained: (1) The flame shape is characterized by the base flame, flame neck, and main flame, depending on the mixedness of the inner and outer jets. (2) The position of peak heat flux occurred in the radial direction, and the peak heat flux reached 4792 kW/m2 when the Reynolds number, impingement distance, and equivalence ratio were 77700, 20 mm, and 0.72, respectively. (3) The suggested ablation distance is Hs = (57.65–61.98) × [MR]−0.56 (MR: momentum ratio). This study provides useful data for high-enthalpy, long-duration ablation.

Experimental study of CO2/H2/NH3 influence on CH4 flameless combustion process in semi-industrial furnace

A flameless combustion mode was employed in a semi-industrial furnace to investigate the effect of NH3 on CH4, which was diluted by CO2/H2 combustible mixtures, serving as the primary fuel. Emission characteristics, as well as toxic compounds and temperature distribution maps, were presented for selected fuels. The combustion system was tested at a constant firing rate of 150 kWth and a constant fuel bulk velocity of 85 m/s. We investigated the effects of equivalence ratio, fuel composition and volume share of NH3 in the fuel. It was found that the equivalence ratio and NH3 amount have the most significant impact on the emission of fuel nitric oxide in the flameless combustion process. The dilution of CH4 with CO2 affects the stretch rate, resulting in an increase in CO levels as well as promoting NO level growth. The calculated dimensionless Conversion Factor (CF) shows that the dilution gas, CO2, significantly impacts the reduction of NH3 to NO, but only for low-content fuel-bound nitrogen (up to 1%). The lowest values of CF were measured for a high equivalence ratio, corresponding to the typical oxygen content for flameless combustion process.

Combustion performances of a novel micro-combustor with a backward facing step and an exhaust gas recirculation channel

A novel micro-combustor with a backward facing step and an exhaust gas recirculation (EGR) channel was developed to operate at low mass flow rates of H2/air mixtures (1.33–5.34 × 10−6 kg/s). The function of EGR was realized by a high-speed jet issued from the combustor inlet with a diameter of 0.2 mm. Effects of inlet velocity (Vin) and equivalence ratio (ϕ) on combustion performances and EGR ability were investigated numerically. With the increase of inlet velocity, flame moved downstream and splitted at a critical velocity, and the flame temperature and outer wall temperature rise simultaneously. An increase in the equivalence ratio led to a larger reaction zone and higher flame temperature and wall temperature. The mass fractions of NOx emissions are very low with an order of magnitude of 10−10. Both the mass recirculation ratio (εm) and enthalpy recirculation ratio (εh) increased with the increase of incoming mass flow rate. However, for an identical mass flow rate, both εm and εh decreased with equivalence ratio. A dimensionless number, Fa, which was defined as the ratio of pressure difference between the inlet and outlet of EGR channel to the dynamic head of the jet flow, was introduced to evaluate the driving force of EGR. The Fa number decreased with the increase in the mass flow rate of jet flow, but exhibited a non-monotonic variation with equivalence ratio. The variation trends of εm, εh and Fa were interpreted by analyzing the variation regularities of parameters involved in their definitions.

Experimental and kinetic study of ammonia oxidation and NOx emissions at elevated pressures

To investigate the effects of pressure and equivalence ratio on ammonia oxidation and the emission of NOx, experiments were conducted in a flow reactor at atmospheric pressure and 5.0 MPa between 600 and 1250 K, with equivalence ratios ranging from 0.125 to 1.0. In addition, a kinetic model applicable to ammonia oxidation under high-pressure conditions was developed and validated against the performance of other recently published kinetic models with reference to several parameters associated with the ammonia oxidation and the emission of NOx under high-pressure conditions. The developed model was also validated against previously published experimental data collected under high-pressure conditions, and it can accurately capture the data obtained. The study found that the increase in pressure and oxygen content significantly enhanced the reactivity of NH3 and consequently resulted in increased NO and N2O concentrations at low temperatures. Based on a kinetic analysis using the developed model, the HO2 content was identified as the key factor influencing the difference in reactivity between atmospheric and high pressure. Sensitivity analysis revealed that H + O2 (+M) = HO2 (+M) inhibits NH3 consumption at atmospheric pressures but has a promoting effect at high pressures, because at high pressures the reaction generates a significant amount of HO2 radicals at low temperatures, increasing the reaction activity and reducing the onset temperature of ammonia oxidation. The H2NO system becomes even more critical under higher pressure, as more NH2 and O2 are converted to H2NO and NO. H2NO, NO, and N2O act as chain carriers in the reaction sequence, converting NH2 and O2 to OH and NO and accelerating the process of ammonia oxidation. At the same time, higher pressure enhances the NOx formation pathway due to the large amount of HO2 generated. However, as temperatures increase, O and OH radicals increase and DeNOx pathways dominate, resulting in lower NO and N2O contents. In the context of the equivalence ratios, the increase in the O2 content enhances the generation of HO2, leading to a greater tendency for NH2 to be converted in the NH2 + HO2 = HNO + H2O and NH2 + HO2 = H2NO + OH reaction pathways to HNO and H2NO, respectively. The HNO and H2NO produced are subsequently converted to NOx.

The properties of sustainable aviation fuel II: Laminar flame speed

This work reports on the study of flame characteristics and laminar flame speeds (LFS) of sustainable aviation fuel (SAF) and conventional fuels (Jet-A1 and JP-5) premixed with air at elevated pressures. The experimental facilities included the constant volume combustion chamber (CVCC) and used a shadowgraph system to quantify the LFS. The effects of equivalence ratio and ambient pressure on the flame speeds were examined by varying the initial pressure 1, 2, and 3 bar (in addition to 0.1 and 0.5 bar for flame morphology) and the equivalence ratio from 0.8 to 1.8 at 423 K of temperature. The results indicated that JP-5 had the highest LFS value (90.1 cm/s) compared to the other two fuels. Jet-A1 and SAF have the same LFS result, which is less than a 15% difference, excluding the high equivalence ratio and initial pressure. The higher the initial pressure, the lower the LFS for all conditions. The equivalence ratio of 1.2 resulted in the highest LFSs. In addition, in order to understand the laminar flame speed of SAF and its combustion chemical kinetics. Therefore, the sensitivity analysis of SAF was performed. Results indicated that the chain branching reaction (O2 + HOH + O) positively enhanced flame speed as equivalence ratios (φ) increased, while chain propagation reactions, notably O2 + HHO2 (+M), had a negative effect on flame speed, particularly diminishing their influence at higher φ due to limited oxygen availability.