Function Of Equivalence Ratio Research Articles

Hydrogen-Rich Syngas Production from Gasification of Sewage Sludge: Catalonia Case

The continuous tightening of legislation regulating the agricultural usage of sewage sludge in the province of Catalonia (Spain) leads us to propose its gasification to produce hydrogen-rich syngas. A thermodynamic equilibrium model was developed using Aspen Plus® to simulate the air and steam gasification of sewage sludge from a wastewater treatment plant in Catalonia. The syngas generated is analyzed in terms of composition and lower heating value (LHV), as a function of equivalence ratio (ER), gasification temperature (Tgas), steam-to-biomass ratio (SBR), and moisture content (MC). Results show that air-blown gasification finds the highest LHV of 7.48 MJ/m3 at 1200 °C, ER of 0.2, and MC of 5%. Using steam as the gasifying agent, an LHV of 10.30 MJ/m3 is obtained at SBR of 0.2, MC of 5%, and 1200 °C. A maximum of 69.7% hydrogen molar fraction is obtained at 600 °C, MC of 25%, and SBR of 1.2. This study suggests using steam as a gasifying agent instead of air since it provides a higher LHV of the syngas as well as a hydrogen-richer syngas for the implementation of gasification as an alternative method to sewage sludge treatment in the region of Catalonia. Since the economic aspect should also be considered, in this regard, our sensitivity analysis provided important data demonstrating that it is possible to reduce the gasification temperature without significantly decreasing the LHV.

Experimental measurements of soot formation in fuel-rich homogeneous mixtures using an optical rapid compression machine

Advanced combustion strategies are necessary for the use of more environmentally sustainable fuels than traditional diesel. Alcohol fuels and alcohol/gasoline blends are of particular interest as they are readily available in the marketplace. Heavy-duty engines typically use compression ignited, conventional diesel mixing controlled combustion. Mixing controlled combustion features a non-premixed diffusion flame with a wide range of local equivalence ratios, leading to potentially high rates of soot formation. This work studies the sooting behavior of iso-octane and ethanol as a function of equivalence ratio. Measurements are carried out in a rapid compression machine (RCM) and are reported for pre-ignition conditions of 10–30 bar and temperatures of 650–800 K. Theoretical equilibrium and bulk gas temperatures are calculated for both fuels. These data are used to identify the critical equivalence ratio, the lowest equivalence ratio where soot is detected with a single-pass laser extinction diagnostic. The critical equivalence ratio for iso-octane varies between 1.82 and 1.77 for compressed pressures of 10 and 20 bar, respectively. Ethanol, sometimes considered sootless, had a critical equivalence ratio between 2.37 and 2.12 for compressed pressures of 20 and 30 bar, respectively. When characterizing soot formation by oxygenated equivalence ratio, the critical equivalence ratios for ethanol approach those of iso-octane. This suggests the oxygenated nature of alcohol fuels reduces sooting tendency, but other factors such as fuel molecular structure and morphology may play a role. It was observed that ethanol will form soot at equivalence ratios only slightly higher than iso-octane, which could have implications in mixing controlled combustion. It was seen for both fuels that soot formation is pressure sensitive, with the critical equivalence ratio being inversely proportional to compressed pressure and the rate of soot formation. Future work will investigate the sooting behavior of gasoline/ethanol blends.

Flame structure and burning velocity of flames propagating in binary iron aerosols

A numerical study was performed for binary dispersed iron aerosols in air using different particle sizes with constant average particle size. The effects of particle size and density of the two aerosols on flame structure and speed are systematically investigated. Varying the amount of small and big particles results in separated and overlapped flame fronts. For higher values of particle size ratio (ratio between the size of big and small particles) and density of small particles, flame fronts are observed to overlap. The flame speed of the binary mixture is compared with the mono-dispersed case and the difference is analyzed for different particle size ratios. The addition of a small fraction of small particles in the binary mixture is found to result in a substantial increase in the flame speed if the particle size ratio is large. Detailed analyses on the variation of the total amount of fuel shows the particle size ratio determines the equivalence ratio at which the maximum flame speed occurs. The maximum flame speed as a function of equivalence ratio was observed to move from the lean to the rich side for particle size ratio sufficiently large enough.

LFG 엔진의 희박 과급 연소 조건에서 화염 속도 측정 및 계산

In order not to release Landfill gas (LFG) having a high global warming potential into the atmosphere and to burn in an internal combustion engine for power generation, a study was conducted to measure and calculate flame speed under turbocharged and lean burn conditions of spark ignition engine. By changing the ratio between methane and carbon dioxide, which are the main components of LFG, experiments were conducted to measure the flame speed using a constant volume combustion chamber. Also comparative analysis was performed with data obtained using CHEMKIN library with GRI 3.0 mechanisms. In addition, using the data obtained through numerical analysis the correlations were derived to calculate the flame speed as a function of equivalence ratio. This study concludes that the overall trend of LFG flame speed is in good agreement between the experimental and calculated results. Using the correlated equation derived from the results of this study, it is possible to estimate the flame speed of LFG under turbocharged and lean burn of spark ignition engine.

Chemiluminescence signature of premixed ammonia-methane-air flames

This paper reports on the chemiluminescence footprint of premixed ammonia-methane-air flames. The chemiluminescence spectrum of laminar twin-flames stabilized with a counterflow burner were measured between 200 and 457 nm for large ranges of equivalence ratio (0.60 ≤ ϕ ≤ 1.30), ammonia fraction (pure methane to pure ammonia), and strain rate (55/s ≤ a ≤ 300/s). Relevant excited radicals were identified, namely, NO*, OH*, NH*, CN*, CH*, and CO2* and evolutions of their chemiluminescence intensity were analyzed as a function of equivalence ratio, ammonia fraction, and strain rate. These measurements produced an unprecedented database on the chemiluminescence of ammonia-methane-air flames, which could be used in the future for model validation. A total of 15 ratios of chemiluminescence intensity were also considered and 5 ratios showing promise for the development of chemiluminescence-based flame sensors were identified. The CN*/OH* ratio is a potential surrogate for equivalence ratio even if the ammonia fuel fraction in the fuel blend is not known accurately – as long as it exceeds 0.3 by volume. The CN*/NO* ratio is another possible surrogate for equivalence ratio if the ammonia fraction in the fuel blend is below 0.5. The OH*/CH* ratio, often used to sense equivalence ratio in hydrocarbons flames, is not recommended for ammonia-methane flames. The NH*/CN* ratio is a potential surrogate for the ammonia fraction in the fuel blend if equivalence ratio is larger than ϕ = 0.7 and if the ammonia fraction in the fuel blend is below 0.4. Other ratios may be combined to provide a simultaneous measure of equivalence ratio and ammonia fraction in the fuel blend with an extended range of validity, for example NH*/OH* and CN*/NH*.

Jet ignition prediction in a zero-dimensional pre-chamber engine model

This paper presents a multi-chamber, multi-zone engine model to predict the ignition of a lean main chamber by a pre-chamber. The two chambers are connected by small cylindrical holes: the flame is ignited in the pre-chamber, hot gases propagate through the holes and ignite the main chamber through Turbulent Jet Ignition (TJI). The model original features are: (i) separate balance equations for the pre- and main chambers, (ii) a specific model for temperature and composition evolution in the holes and (iii) a DNS-based model to predict the ignition of the main chamber fresh gases by the burnt gases turbulent jets exiting the holes. Chemical reactions during TJI are the result of two competing mixing processes: (1) the hot jet gases mix with the fresh main chamber to produce heated zones and (2) at the same time, these hot gases cool down. (1) increases combustion and leads to ignition while (2) decreases it and can prevent ignition. The overall outcome (ignition or failure) is too complex to be modelled simply and the present model relies on recent DNSs of TJI which provided a method to predict the occurrence of ignition. Incorporating this DNS information into the engine model allows to predicts whether ignition will occur or not, an information which is not accessible otherwise using simple models. The resulting approach is tested on multiple cases to predict ignition limits for very lean cases, effects of H2 injection into the pre-chamber and optimum size for the holes connecting the two chambers as a function of equivalence ratio.

Self-excited noise generation from laminar methane/air premixed flames in thin annular jets

Self-excited noise generation from laminar flames in thin annular jets of premixed methane/air has been investigated experimentally. Various flame shapes were observed in this flow configuration, including conical shaped flames, ring shaped flames, steady crown shaped flames, and oscillating crown shaped flames. Self-excited noise with a total sound pressure level of about 70 dB was generated from the oscillating crown shaped flames for equivalence ratios>0.95. Sound pressure and CH* chemiluminescence were measured by using a microphone and a photomultiplier tube. The frequency of generated noise was measured as a function of equivalence ratio and premixture velocity. A frequency doubling phenomenon has also been observed. The measured CH* chemiluminescence data were analysed and which the corresponding sound pressure has been calculated. By comparing the measured and calculated sound pressures, the noise source can be attributed to the flame front fluctuation near the edge of the oscillating crown shaped flames. The flame stability regime was influenced strongly by the mass flow rate of air through the inner tube.

A comparative study of the explosion behaviors of H2 and C2H4 with air, N2O and O2

Explosions can occur in different oxidizer atmospheres in confined spaces, which should be given attention in regard to the fire safety in process industries. In this study, experiments were carried out in a closed cylindrical vessel (7.3 L) to compare the explosion behaviors of hydrogen (H2) and ethylene (C2H4) with air, nitrous oxide (N2O), and oxygen (O2) at various equivalence ratios. The initial pressures of the hydrogen and ethylene mixtures were 50 kPa and 30 kPa, respectively. Explosion indices such as the maximum explosion pressure (Pmax), maximum rate of pressure rise ((dp/dt)max) and deflagration index (KG) were determined experimentally. The results showed that the pressure evolutions obtained with N2O and O2 exhibited strong oscillations due to flame instabilities and cellular structures. The maximum explosion pressure increased in the order of air, O2 and N2O while the maximum rate of pressure rise increased in the order of air, N2O and O2. Unlike those of air and O2, the maximum values of (dp/dt)max obtained with N2O were found to be at the fuel-lean side. This indicated that the instability feature of N2O supported combustions at the fuel-lean side. Compared with air, the maximum explosion pressure obtained in N2O and O2 atmospheres could be very close to the adiabatic pressure when considering no heat loss during an explosion. Therefore, there was a flame acceleration and deflagration to detonation transition (DDT) mechanism in the explosions with N2O and O2. Additionally, two dimensionless pressure rise coefficients were derived and discussed. The flames in very lean H2-N2O were very unstable, resulting in scattered coefficients as a function of equivalence ratio. At the fuel-rich side, the dimensionless coefficients were very close. In practice, the potential DDT mechanism in the explosions, especially in N2O and O2 atmospheres, needed to be considered.

Flame investigations of a laboratory-scale CECOST swirl burner at atmospheric pressure conditions

Experimental and numerical studies were performed to understand the stabilization of lean premixed natural gas/air flames in a gas turbine model combustor which was equipped with a swirl burner, known as the CECOST burner, designed to replicate the flow and flame structures in an industrial gas turbine engine. The operability range, flame stabilization, and flashback were investigated employing simultaneous OH– and CH2O-PLIF, and high-speed chemiluminescence imaging. Large eddy simulation (LES) was carried out for analysis of the vortex breakdown structures under non-reacting conditions. It was found that the vortex breakdown structures under isothermal conditions were insensitive to the Reynolds number (Re) for Re ≥ 10000; however, the stability of the flames and operability range of the burner were highly sensitive to Re as well as to equivalence ratio (ϕ). The equivalence ratio was varied at various Reynolds numbers to observe different regimes of the flame ranging from the lean blowout (LBO) limit to the flashback limit. The LBO limit was found to be mainly a function of equivalence ratio while being nearly independent of the Reynolds number, whereas the occurrence of flashback showed distinct characteristics for different ranges of the Reynolds number. At low and moderate Reynolds numbers, (Re ≤ 17000), flashback occurred when increasing ϕ from lean towards stoichiometric conditions. The coupling between the flow field and heat release induces vortex breakdown in the mixing tube and initiates flashback. In contrast, at higher Reynolds numbers (Re > 17000) no flashback was observed even when ϕ was increased to stoichiometric conditions. At these conditions with high Re, the increase in the bulk flow velocity affects the vortex breakdown structure, pushing the vortex breakdown downstream, which in turn prevents the flame from flashing back into the mixing tube.

Investigation of Graphite Nozzle Erosion in Hybrid Rockets Using Oxygen/High-Density Polyethylene

A recently developed reconstruction technique is used to investigate graphite nozzle erosion in two scales of hybrid rocket motors, 30-N-thrust class and 2000-N-thrust class, using oxygen as the oxidizer and high-density polyethylene as the fuel. Thermocouple measurements taken from within the nozzles are used to estimate nozzle throat wall temperature. Forty-four static firing tests were conducted under varying experimental conditions to confirm the validity of the reconstruction technique results, to investigate the conditions at the onset of erosion, and to formulate an empirical predictive model of nozzle erosion rate. Results show that a single formula that treats the combustion gas as a single oxidizing agent for which heterogenous rate constants are functions of equivalence ratio can satisfactorily replicate the erosion rate of graphite by a combustion gas containing multiple oxidizing species. Furthermore, the chemical-kinetic-limited conditions of the onset of nozzle erosion are specified by a novel empirical correlation, which shows that erosion begins at lower temperature and pressure in oxidizer-rich combustion gas than in fuel-rich combustion gas.

Numerical Study on JP-10/Air Detonation and Rotating Detonation Engine

JP-10/air two-phase detonation and rotating detonation engine (RDE) are numerically studied to find out their limits of physical values as a function of equivalence ratio, prevaporization, fuel concentration, droplet diameter, and initial pressure and temperature. To find such limits, the JP-10/air two-step chemical reaction mechanism is used and the Eulerian–Eulerian two-phase governing system is developed to simulate those limits. Especially the JP-10/air two-phase detonation velocity and cell size are investigated in detail and the generation of nonreacted region and quenching mechanism of JP-10/air two-phase RDE are simulated. The findings from those studies are that 1) the JP-10/air two-phase detonation and RDE codes are developed and validated to calculate detonation and RDE; 2) the JP-10/air detonation cell size is calculated by the developed code to show a good agreement with the experimental data; and 3) the JP-10/air RDE simulation shows a detonation quenching at the condition when the droplet diameter is larger than and the prevaporization factor is smaller than 20%.

Dynamics of 2D, V-shaped Bluff-body Stabilized Turbulent Premixed Flames near and Away from Blowoff with Different Gaseous Fuels

ABSTRACT V-shaped premixed flames of propane, methane, and ethylene-air mixtures were stabilized on a triangular-shaped flame holder under three different free stream turbulence levels; 4%, 18%, and 34% rms at a nominal burner exit velocity of 10 m/s. Flames were studied at strongly burning and near blowoff conditions to observe the changes in the overall flame dynamics. Flame behavior at different upstream flow turbulence conditions was visualized by simultaneously capturing the end and side views of flame chemiluminescence using high speed (4 kHz) imaging. A gradual shift from symmetric to asymmetric flame structures was observed with reduction of equivalence ratio approaching blowoff. Particle image velocity measurements confirmed the gradual switch of vortex shedding from symmetric varicose mode to the asymmetric sinuous mode as flame blowoff is approached by reduction of the mixture equivalence ratio. It is found that average flame front position crosses the shear layer from its outer location at strongly burning conditions to within the shear layers bounding the recirculation zone as flame blowoff is approached. Transition of flame behavior from “varicose” to “sinuous” oscillations is documented by way of a symmetry index as a function of equivalence ratio and turbulence intensity for the three fuels studied.

Numerical Simulation of Biomass Gasification in an Entrained Flow Cyclone Gasifier

A transient, two-way coupled Eulerian–Lagrangian computational fluid dynamics model has been developed for numerically investigating the gasification process of wood powder inside a cyclone-shaped reactor. The suggested model has considered heat and mass transfer, drying, devolatilization, and homogeneous and heterogeneous reactions. The model is validated using the experimental data from a commercial entrained-flow cyclone gasifier. The changes in gas composition as a function of equivalence ratio and the behavior of gasification process agreed well with the experimental measurement. Trajectories of individual particles were captured, and the behavior, mass fraction, and temperature distribution of several representative particles in different sizes were studied. Moreover, the model was successful in prediction of produced gas lower heating value, cold gas efficiency, and carbon conversion.

Performance analysis of a commercial fixed bed downdraft gasifier using palm kernel shells

This work analyzes the use of palm kernel shells (PKS) produced by the Colombian palm oil mill industry, for purposes of fueling a commercial downdraft fixed bed gasifier (Ankur Scientific WGB- 20) designed to operate with wood chips. Operational parameters such as hopper shaking time, ash removal time, and airflow were varied in order to get the highest gasifier performance, computed as the ratio between producer gas chemical energy over biomass feeding energy. Experiments were carried out following a half fraction experimental design 24-1. Since these parameters affect the equivalence ratio (ER), behavior indicators were analyzed as a function of ER. It was found that the shaking time and airflow had a significant effect on higher-heating-value (HHV) and process efficiency, while the removal time is not significant. The highest performance for palm shell was reached at ER=0.35, where the resulting gas HHV and process efficiencies were 5.04 MJ/Nm3 and 58%, respectively.

Investigation of the partial oxidation of methane/n-heptane-mixtures and the interaction of methane and n-heptane under ultra-rich conditions

The homogeneous partial oxidation of methane is an interesting approach to obtain useful chemicals like synthesis gas, higher hydrocarbons, aldehydes or alcohols. Because of the low reactivity of methane, the homogeneous conversion needs high temperatures to proceed at reasonable reaction rates. Additives like n-heptane form reactive intermediates at comparatively low temperatures and initiate the conversion. To study the kinetics of doped conversion reactions, fuel-rich diluted methane/n-heptane/oxygen/argon-mixtures (2 ≤ Φ ≤ 20) were investigated in a plug-flow reactor at a pressure of 6 bar, at intermediate temperatures between 423 and 973 K and at relatively long residence times (7 ≤ τ ≤ 14 s). The product composition at the reactor outlet is analyzed by gas chromatography and mass spectrometry. Species profiles as a function of equivalence ratio and temperature are compared with simulations, and serve as validation data for different reaction mechanisms. Rates of production and reaction paths are analyzed to investigate the interaction of methane and n-heptane during the oxidation process. They show that the chemical interaction of the oxidation products of both fuels has a promoting effect on the formation of different useful products like carbon monoxide, methanol or ethane. To prove this observation, mole fraction profiles as a function of temperature were compared between experiments with an equivalence ratio of Φ = 8 using neat methane, neat n-heptane and methane/n-heptane mixtures as fuels. The results show that the yields of these species are much higher in case of the methane/n-heptane mixture compared to the yields obtained in the neat methane and neat n-heptane conversions or the sum of both.

Experimental and numerical study of the ignition of hydrogen-air mixtures by a localized stationary hot surface

The ignition of hydrogen-air mixtures by a stationary hot glow plug has been experimentally investigated using two-color pyrometry and interferometry. The ignition process was characterized by the surface temperature at ignition, as well as by the location where the initial flame kernel was formed. The experimental results indicate that: (i) the ignition temperature threshold is a function of equivalence ratio; (ii) the ignition location is a function of the rate at which the glow plug is heated because high heating rates favor non-uniform heating. As a result, ignition occurs on the side rather than near the top face of the glow plug. Comparison with two-dimensional numerical simulations exhibits discrepancies in terms of the temperature threshold value and dependence on equivalence ratio. Simulations performed imposing a non-uniform surface temperature show that a temperature difference between the side and the top of the glow plug as low as 12.5 to 25 K resulted in side ignition for hydrogen-air mixtures. The effect of surface chemistry was estimated numerically by imposing a boundary condition of zero species concentration for intermediate species, H and HO2, at the hot surface, which increased the ignition threshold by up to 50 K for an initial H2 concentration of 70%. The present study shows that surface temperature non-uniformity, heterogeneous chemistry and reaction model used, could influence the experimentally reported and numerically predicted ignition threshold as well as the location of ignition.

Experimental correlation of laminar flame pollutant emission indices with methyl ester fuel degree of unsaturation and equivalence ratio

Fuel unsaturation has been widely cited as a reason for the increased nitric oxide emissions from compression ignition engines when fueled with methyl esters (biodiesels) and their blends with petroleum counterparts. In an earlier study, a parameter called degree of unsaturation (DOU) was established to serve as a common platform across different fuel families (esters/alkanes/aromatics) to quantify the effects of fuel unsaturation, particularly with petroleum/biodiesel blends. DOU can be evaluated based on the average molecular formula of the fuel alone without involving complex and expensive experimental procedures such as those involved in the measurement of iodine number and bromine number. In this article, the fuel unsaturation effects on the emission characteristics from the laminar flames of blends of various pre-vaporized methyl esters, such as methyl oleate, neat biodiesels (from methyl esters of soy, canola, palm and rapeseed feedstock) and biodiesel blends were investigated at four burner-exit equivalence ratios of 0.9, 1.0, 1.2 and 1.5. The selection of these fuels for this study was an attempt to isolate the fuel unsaturation effect of biodiesels, and their blending effect with petroleum fuels. Experimental correlations were developed between DOU (over a range of 1.7–2.5) and global NO and CO emission indices as a function of equivalence ratio. The effects of DOU on EINO were significantly influenced by the equivalence ratio, with the maximum influence at an equivalence ratio of 1.2.

Combustion behavior and stability map of hydrogen-enriched oxy-methane premixed flames in a model gas turbine combustor

The article describes an experimental study and comparison of the combustion behavior and determines the stability map of turbulent premixed H2-enriched oxy-methane flames in a model gas turbine combustor. Static stability limits, in terms of flashback and blow-out limits, are recorded over a range of hydrogen fraction (HF) at a fixed oxygen fraction (OF) of 30% and a particular inlet bulk velocity, and the results are compared with the non-enriched case (HF = 0%). The static stability limits are also recorded for different inlet bulk velocity (4.4, 5.2, and 6 m/s) and the results are compared to explore the effect of flow dynamics on operability limits of H2-enriched flames. The stability maps are presented as a function of equivalence ratio (0.3–1.0) and HF (0%–75%) plotted on the contours of adiabatic flame temperature (AFT), power density (PD), inlet Reynolds number (Re) and reacting mixture mass flow rate (m˙) to understand the physics behind flashback and blow-out phenomena. The results indicated that both the flashback and blow-out limits tend to move towards the leaner side with increasing HF due to the improved chemical kinetics. The stability limits are observed to follow the Reynolds number indicating its key role in controlling flame static stability limits. The results showed that H2 enrichment is effective in the zone from HF = 20% up to HF = 50%, and O2 enrichment is also effective in a similar zone from OF = 20% up to 50%, with wider stability boundaries for H2 enrichment. Axial and radial temperature profiles are presented to explore the effect of HF on the progress of chemical reactions within the combustor and to serve as the basis for validation of numerical models. Flame shapes are recorded using a high-speed camera and compared for different inlet velocities to explore the effects of H2-enrichment and equivalence ratio on flame stability. The equivalence ratio at which a transition of flame stabilization from the inner shear layer (ISL) to the outer recirculation zone (ORZ) occurs is determined for different inlet bulk velocities. The value of the transition equivalence ratio is found to decrease while increasing the inlet bulk velocity. Flame shapes near flashback limit, as well as near blow-out limit, are compared to explore the mechanisms of flame extinctions. Flame shapes are compared at fixed adiabatic flame temperature, fixed inlet velocity and fixed flow swirl to isolate their effects and investigate the effect of kinetic rates on flame stability. The results showed that the adiabatic flame temperature does not govern the flame static stability limits.

Laminar flame speeds of DEMP, DMMP, and TEP added to H2- and CH4-air mixtures

Organophosphorus compounds (OPCs) have long been known to have significant fire suppression capabilities but were outclassed by Halon 1301 due to toxicity concerns. Recent interest in finding replacements for Halon 1301 has provided an impetus to reconsider OPCs. To better understand the mechanism by which OPCs suppress flames, more information about how they interact with fuel/air mixtures via chemical kinetics is needed. In this study, dimethyl methylphosphonate (DMMP), diethyl methylphosphonate (DEMP), and trimethyl phosphate (TEP) were added to hydrogen/air and methane/air mixtures to assess their suppression capabilities at 0.1% and 0.3% (DMMP only) of the total mixture volume. Laminar flame speed experiments were performed in an optically tracked, spherically expanding flame setup at 1 atm and 120 °C. The resulting laminar flame speed data are the first to be recorded using these compounds. Results show a 30% decrease in laminar flame speed for all OPCs at 0.1% on the methane/air parent mixture, and the laminar flame speed curves, as a function of equivalence ratio, tend to be broader than for un-doped mixtures. For the hydrogen/air mixtures, the OPCs differentiate themselves by having an increasing suppression effect corresponding with higher carbon moiety, i.e., TEP (15% overall reduction) > DEMP (13%) > DMMP (9%). The OPCs also have an increasing effect with increasing equivalence ratio on hydrogen/air, but with methane/air, they have a non-monotonic effect. The reduction of laminar flame speeds is comparable to twice the concentration of Halon 1301 and 10 times as much for previously investigated Halon 1301 replacements. These results are ideal for improving existing OPC chemical kinetics mechanisms, and possible applications include both fire suppression technologies and destruction of dangerous OPC compounds.

The pressure dependence of laminar flame speed of 2-methyl-2-butene/air flames in the 0.1–1.0 MPa range

ABSTRACTLaminar flame speeds of 2-methyl-2-butene/air mixtures were measured in a constant volume combustion bomb at T0 = 450 K, p = 0.1–1.0 MPa, and φ = 0.5–1.6. The dependence of laminar flame speed on pressure is described by an empirical formula , where the power exponent β is summarized as a function of equivalence ratios (φ). The maximum β at stoichiometric ratio indicates that the effect of pressure on flame is greater around the stoichiometric ratio and weaker at deviations from the stoichiometric ratio. Furthermore, analysis by chemical kinetic mechanism shows that elevated pressure is more sensitive to the reactions associated with the H and OH radicals and affects their concentration variation, and ultimately the laminar flame speed of 2-methyl-2-butene/air mixtures.