Enhancing the ignition system performance of turbo engines is crucial,with a focus on rapidly and reliably igniting the entire combustor in low-temperature,low-pressure,high-speed inlet flow conditions.This challenge ...Enhancing the ignition system performance of turbo engines is crucial,with a focus on rapidly and reliably igniting the entire combustor in low-temperature,low-pressure,high-speed inlet flow conditions.This challenge has garnered international attention.To address the issue of reliable ignition in the combustors of advanced propulsion system,this paper proposes a Multichannel Jet Enhanced Plasma Igniter(MJEPI) and conducts comparative experimental studies with the conventional spark igniter in a component-level dual-dome swirl combustor.The ignition limit in the combustor is obtained and the ignition processes are recorded.Experimental results demonstrate that the MJEPI significantly improves the ignition performance at high altitude.Specifically,at 0 km and 6 km for ground start-up,ignition limit is extended by 36% and 29%,respectively.At 6 km and 12 km for high-altitude relight,ignition limit is extended by 32% and 21%,respectively.The maximum ignition height is increased by 2.3 km,as determined by the global equivalence ratio of 1.The primary reason for these improvements is attributed to the larger initial flame kernel with greater penetration depth generated by MJEPI,which enables it to withstand more sever conditions such as low temperature,low pressure,and poor kerosene spray quality at elevated altitudes.展开更多
In February 2024,192 lasers at the National Ignition Facility(NIF)in Livermore,CA,USA,began pouring 2.2 MJ of energy into a gold container smaller than the tip of a person’s little finger,heat-ing it to more than thr...In February 2024,192 lasers at the National Ignition Facility(NIF)in Livermore,CA,USA,began pouring 2.2 MJ of energy into a gold container smaller than the tip of a person’s little finger,heat-ing it to more than three million degrees Celsius(Fig.1)[1-4].Inside the container was a tiny fuel capsule containing tritium and deuterium that imploded at more than 400 km·s^(-1)causing atoms to combine and releasing 5.2 MJ of energy[1-4].展开更多
The reignition of aero-engine combustors at high altitudes poses significant challenges due to the low-temperature and low-pressure environment.A novel Long Pulse-Width Plasma Ignition(LPWPI)system has been developed ...The reignition of aero-engine combustors at high altitudes poses significant challenges due to the low-temperature and low-pressure environment.A novel Long Pulse-Width Plasma Ignition(LPWPI)system has been developed to enhance ignition performance.The LPWPI system can effectively prolong the discharge duration time,improve ignition efficacy,and increase the plasma penetration depth.Experimental comparisons with the traditional Spark Ignition(SI)system demonstrate that the LPWPI increased discharge duration to 2.03 ms,which is 45 times longer than that of the SI system,while also doubling the spark penetration depth to 24.1 mm.The LPWPI system achieved a discharge efficiency of 61.1%,significantly surpassing the SI system's efficiency of23.3%.These advancements facilitated an extension of the lean ignition boundary by approximately 22.7%to 39.3%.High-speed camera recordings reveal that the spark duration of the LPWPI system was extended to 2.1 ms,compared to 0.6 ms in the SI system.Ignition progress with LPWPI shows a sustained spark kernel without the flame residence stage observed in the SI system.The impressive performance of the LPWPI system suggests that it is a promising alternative for aero-engine ignition systems.展开更多
Oxide films hinder diffusion and resist external forces,which determines the flame ignition mechanism of magnesium alloys.The effects of the continuity,compactness and mechanical properties of oxide films on the ignit...Oxide films hinder diffusion and resist external forces,which determines the flame ignition mechanism of magnesium alloys.The effects of the continuity,compactness and mechanical properties of oxide films on the ignition mechanism were analyzed,by investigating the flame ignition behaviors of AZ80(ZM5),EZ30K(ZM6)and WE43 Mg alloys.The results show that the rupture of the oxide films caused by liquid gravity was the key to causing ignition.According to thermodynamic calculations,compared with Mg,Al cannot be preferentially oxidized;while Nd can be preferentially oxidized through significant enrichment,resulting in a discontinuous Nd_(2)O_(3)inner layer in the ZM6 alloy;in contrast,Y has a strong preferential oxidation ability,which gives the WE43 alloy a continuous Y_(2)O_(3)inner layer and self-healing ability.In addition,the oxide film of the ZM5 alloy is loose and has poor mechanical properties,so it cannot effec-tively hinder diffusion and resist liquid gravity.Differently,the oxide films of the ZM6 and WE43 alloys are dense and have better mechanical properties,leading to higher ignition temperatures and longer igni-tion times.In addition,a criterion was proposed to predict the ignition time based on the law of energy conservation,and it was simplified to predict the ignition temperature.The errors between the predicted and measured values are within 11%.展开更多
Magnesium and its alloys offer lightweight advantage and have extensive development prospects,particularly in aerospace.However,their flammability poses a significant barrier on the development of Mg alloys.The igniti...Magnesium and its alloys offer lightweight advantage and have extensive development prospects,particularly in aerospace.However,their flammability poses a significant barrier on the development of Mg alloys.The ignition resistance of these alloys often depends on the protectiveness of the oxide film formed on the surface.This paper elucidates the formation mechanism of oxide film from thermodynamics and kinetics,classifying oxide films based on their layered structure to assess their protective properties.Furthermore,it comprehensively reviews the impact of characteristics on the protective effectiveness such as compactness,continuity,thickness,and mechanical properties.The paper also introduces various characterization methods for the microstructure and properties of oxide film.The primary objective of this paper is to enhance the comprehension of oxide film concerning the ignition resistance of Mg alloys and to furnish references for future advancements and research in Mg alloys with heightened ignition resistance.展开更多
The arc ignition system based on charring polymers has advantages of simple structure,low ignition power consumption and multiple ignitions,which bringing it broadly application prospect in hybrid propulsion system of...The arc ignition system based on charring polymers has advantages of simple structure,low ignition power consumption and multiple ignitions,which bringing it broadly application prospect in hybrid propulsion system of micro/nano satellite.However,charring polymers alone need a relatively high input voltage to achieve pyrolysis and ignition,which increases the burden and cost of the power system of micro/nano satellite in practical application.Adding conductive substance into charring polymers can effectively decrease the conducting voltage which can realize low voltage and low power consumption repeated ignition of arc ignition system.In this paper,a charring conductive polymer ignition grain with a cavity geometry in precombustion chamber,which is composed of PLA and multiwall carbon nanotubes(MWCNT)was proposed.The detailed ignition processes were analyzed and two different ignition mechanisms in the cavity of charring conductive polymers were revealed.The ignition characteristics of charring conductive polymers were also investigated at different input voltages,ignition grain structures,ignition locations and injection schemes in a visual ignition combustor.The results demonstrated that the ignition delay and external energy required for ignition were inversely correlated with the voltages applied to ignition grain.Moreover,the incremental depth of cavity shortened the ignition delay and external energy required for ignition while accelerated the propagation of flame.As the depth of cavity increased from 2 to 6 mm(at 50 V),the time of flame propagating out of ignition grain changed from 235.6 to 108 ms,and values of mean ignition delay time and mean external energy required for ignition decreased from 462.8 to 320 ms and 16.2 to 10.75 J,respectively.The rear side of the cavity was the ideal ignition position which had a shorter ignition delay and a faster flame propagation speed in comparison to other ignition positions.Compared to direct injection scheme,swirling injection provided a more favorable flow field environment in the cavity,which was beneficial to ignition and initial flame propagation,but the ignition position needed to be away from the outlet of swirling injector.At last,the repeated ignition characteristic of charring conductive polymers was also investigated.The ignition delay time and external energy required for ignition decreased with repeated ignition times but the variation was decreasing gradually.展开更多
Gas explosions in coal mine goafs are associated with the roof rock fracturing.An experimental system was established to investigate the potential for electrical ignition induced by sandstone fracturing.The electrical...Gas explosions in coal mine goafs are associated with the roof rock fracturing.An experimental system was established to investigate the potential for electrical ignition induced by sandstone fracturing.The electrical responses,luminescent emissions,and ignition characteristics during tensile and compressive failure of sandstones were analyzed in methane/air premixed gas environments.Results indicate that the application of mechanical loading induces the emergence of electrical signals on rock surfaces and in the surrounding atmosphere.This phenomenon is attributed to the generation,accumulation,and subsequent release of free charges during the deformation and fracture within the sandstone.Compressive failure proved to be more conducive to free charge generation than tensile failure,owing to more crack connections.Furthermore,a precipitous increase in surface and external voltages was observed during complete fracturing,a consequence of electron emission from crack tips within the rock structure.Moreover,the ionization induces luminous emissions owing to the collision of energetic electrons released from gas molecules in methane/air mixtures.A strong positive correlation(R2=0.9429)was identified between luminescence intensity and the magnitude of electrical discharge resulting from rock fracture.Notably,such discharge by rock fracturing can be capable of igniting the premixed gas,particularly when the quartz content exceeds 61%.Piezoelectric effects and crack propagation are crucial mechanisms in the causal chain of the charge generation,discharge,and ionization triggered by rock fractures.Based on the above laboratory results,electric ignition of the transient roof fracturing caused by stress mutations can serve as a new potential ignition source for gas explosions in the goaf.These results offer new insights into the prevention and control of gas explosions.展开更多
A numerical and experimental study was conducted to investigate the Laser Ablation(LA)ignition mode in an ethylene-fueled supersonic combustor with a cavity flameholder.Theexperiments were operated under a Mach number...A numerical and experimental study was conducted to investigate the Laser Ablation(LA)ignition mode in an ethylene-fueled supersonic combustor with a cavity flameholder.Theexperiments were operated under a Mach number 2.92 supersonic inflow,with stagnation pressureof 2.4 MPa and stagnation temperature of 1600 K.Reynolds-averaged Navier-Stokes simulationswere conducted to characterize the mixing process and flow field structure.This study identifiedfour distinct LA ignition modes.Under the specified condition,laser ablation in zero and negativedefocusing states manifested two distinct ignition modes termed Laser Ablation Direct Ignition(LADI)mode and Laser Ablation Re-Ignition(LARI)mode,correspondingly.LA ignition in alocal small cavity,created by depressing the flow field regulator,could facilitate the ignition modetransforming from LARI mode to Laser Ablation Transition Ignition(LATI)mode.On the otherhand,the elevation of the flow field regulator effectively inhibited the forward propagation of theinitial flame kernel and reduced the dissipation of LA plasma,further enhancing the LADI mode.Based on these characteristics,the LADI mode was subdivided into strong(LADI-S)and weak(LADI-W)modes.Facilitating the transition of ignition modes through alterations in the local flowfield could contribute to attaining a more effective and stable LA ignition.展开更多
The incorporation of Y significantly improves the fire resistance of the Mg-3Nd-2Gd-0.2Zr-0.2Zn(EV32)alloy.The findings indicate a significant increase in the ignition point of the alloy upon Y addition,notably reachi...The incorporation of Y significantly improves the fire resistance of the Mg-3Nd-2Gd-0.2Zr-0.2Zn(EV32)alloy.The findings indicate a significant increase in the ignition point of the alloy upon Y addition,notably reaching 813.9℃ for the EV32–3Y(wt.%)alloy.Additionally,the calculated residual stresses of the Y_(2)O_(3) and Gd_(2)O_(3) films were 2.732 GPa and 2.569 GPa respectively,showcasing a distinct correlation between Y concentration and improved fire resistance.This enhancement can be attributed to the formation of denser oxide films,especially Y_(2)O_(3) and Gd_(2)O_(3),effectively reducing the susceptibility of the oxide film to thermal stress-induced tearing.The study elucidates the vital role of Y addition in enhancing fire resistance,thoroughly investigating the mechanisms that impact both the formation of oxide films and ignition within the alloy structure.These findings not only contribute to a deeper comprehension of magnesium alloy performance under high-temperature conditions but also offer valuable theoretical guidance for enhancing its fire resistance through alloy design and application.展开更多
Stimulated Raman scattering(SRS)under a new ignition path that combines the advantages of direct-drive(DD)and indirect-drive(ID)schemes is investigated experimentally at the Shenguang-100 kJ facility.The results show ...Stimulated Raman scattering(SRS)under a new ignition path that combines the advantages of direct-drive(DD)and indirect-drive(ID)schemes is investigated experimentally at the Shenguang-100 kJ facility.The results show that collective SRS in the plasma produced by ablating a polyimide film is detected for the ID beams,but is suppressed by adding a toe before the main pulse of the ID beams.The toe also strongly influences SRS of both the ID and DD beams excited in the plasma generated in the hohlraum.When a toe is used,the SRS spectra of the DD beams show that SRS tends to be excited in lower plasma density,which will result in a lower risk of super-hot electrons.Measurements of hot electrons support this conclusion.This research will help us produce a better pulse design for this new ignition path.展开更多
The utilization of graded Al powders offers the possibility to adjust the combustion performance of Al powders,while simultaneously safeguarding their energy properties.In this paper,a series of graded Al powder have ...The utilization of graded Al powders offers the possibility to adjust the combustion performance of Al powders,while simultaneously safeguarding their energy properties.In this paper,a series of graded Al powder have been incorporated into the typical Al@AP composites through the spray drying technique.The thermal behavior,ignition and combustion characteristics were comprehensively evaluated and compared.The experimental results showed that with the varying inclusion of the graded Al,the heat of reaction exhibited a significant change,ranging from 9090 J·g^(-1) to 11036 J·g^(-1),which was strongly dependent on the particle size of Al.The combination of Al with diverse range of particle sizes in graded configuration serves to significantly enhance the decomposition of AP,resulting in the disappearance of the LTD stage and a conspicuous decrease of at least 11.7℃ in the peak temperature of the HTD.Furthermore,the maximum burning rate achieved by the Al-3@AP composite was 33.6 mm·s^(-1),which was exactly twice as high as that of the graded Al-1@AP composite with the lowest burning rate.Diffraction peaks corresponding to unburned Al were detected in the condensed combustion products of Al-1@AP,and the combustion images clearly indicated an incomplete combustion tendency for this sample.In contrast,a well-designed gradation of Al powders,such as a combination of fine Al powders with a particle size below 5μm,has proven to be the most conducive to enhancing the combustion efficiency of the composites.展开更多
During the highly transient process of the direct-start in a four-cylinder GDI engine,each cylinder exhibits specific characteristics in terms of in-cylinder conditions and energy demands,necessitating different contr...During the highly transient process of the direct-start in a four-cylinder GDI engine,each cylinder exhibits specific characteristics in terms of in-cylinder conditions and energy demands,necessitating different control for each cylinder.However,recent studies have paid insufficient attention to cylinders other than the first starting cylinder.This paper proposes a comprehensive control strategy based on experimental data from the direct-start process of the second,third,and fourth cylinders,aiming to enhance the characteristics of combustion and emission performance through the optimization of injection timing,equivalence ratio,and ignition timing.The research findings indicate that the second cylinder should inject fuel approximately 10 ms after the first cylinder ignites to mix thoroughly the fuel with air.The ignition timing of the second cylinder should be close to the highest point of the piston movement to minimize hindrance to the piston compression process.The third and fourth cylinders should adopt a delayed injection timing strategy to prevent the escape of injected fuel caused by low engine speed.The optimal ignition timing for the third cylinder is 20℃A BTDC,while the fourth cylinder should be ignited earlier due to its stronger airflow and faster formation of a mixture that can be ignited.As the fuel injection quantity increases,the power output of the three cylinders enhances,but at the same time,emissions also increase.Therefore,their optimal equivalence ratios are determined as 1.2,1.4,and 1.2,respectively,striking a balance between combustion and emission performances.展开更多
Recent experiments at the National Ignition Facility and theoretical modeling suggest that side stimulated Raman scattering(SSRS)instability could reduce laser–plasma coupling and generate considerable fluxes of supr...Recent experiments at the National Ignition Facility and theoretical modeling suggest that side stimulated Raman scattering(SSRS)instability could reduce laser–plasma coupling and generate considerable fluxes of suprathermal hot electrons under interaction conditions envisaged for direct-drive schemes for inertial confinement fusion.Nonetheless,SSRS remains to date one of the least understood parametric instabilities.Here,we report the first angularly and spectrally resolved measurements of scattered light at laser intensities relevant for the shock ignition scheme(I×10^(16)W/cm^(2)),showing significant SSRS growth in the direction perpendicular to the laser polarization.Modification of the focal spot shape and orientation,obtained by using two different random phase plates,and of the density gradient of the plasma,by utilizing exploding foil targets of different thicknesses,clearly reveals a different dependence of backward SRS(BSRS)and SSRS on experimental parameters.While convective BSRS scales with plasma density scale length,as expected by linear theory,the growth of SSRS depends on the spot extension in the direction perpendicular to laser polarization.Our analysis therefore demonstrates that under current experimental conditions,with density scale lengths L_(n)≈60–120μm and spot sizes FWHM≈40–100μm,SSRS is limited by laser beam size rather than by the density scale length of the plasma.展开更多
The catalytic combustion of methane in a mierochannel whose surface was coated with platinum（Pt） catalyst was studied by numerical-simulation. The effects of gas-phase reactions on the whole catalytic combustion pro...The catalytic combustion of methane in a mierochannel whose surface was coated with platinum（Pt） catalyst was studied by numerical-simulation. The effects of gas-phase reactions on the whole catalytic combustion process were analyzed at a high inlet pressure. A sensitivity analysis of the detailed mechanisms of the surface reaction of methane on Pt revealed that the most sensitive reactions affecting the heterogeneous ignition are oxygen adsorption/desorption and methane adsorption, and the most sensitive reactions affecting the homogeneous ignition are OH and H2O adsorption/desorption. The combustion process of the homogeneous charge compression ignition（HCCI） engine whose piston face was coated with Pt catalyst was simulated. The effects of catalysis and the most sensitive reactions on the ignition timing and the concentration of the main intermediate species during the HCCI engine combustion are discussed. The results show that the ignition timing of the HCCI engine can be increased by catalysis, and the most sensitive reactions affecting the ignition timing of the HCCI engine are OH and H2O adsorption/desorption.展开更多
The arc ignition based on charring conductive polymers has advantages of simple structure,low ignition power consumption and restart capacity,which bringing it broadly application prospect in hybrid propulsion system ...The arc ignition based on charring conductive polymers has advantages of simple structure,low ignition power consumption and restart capacity,which bringing it broadly application prospect in hybrid propulsion system of micro/nano satellite.In order to optimize the performance of arc ignition system,it is essential to have a deeper understanding of the ignition processes and ignition characteristics of charring conductive polymers.In this paper,the thermal decomposition,electrical conductivity and thermal conductivity characteristics of charring conductive polymers with different conductive additives and matrix materials were comprehensively evaluated.An experimental investigation was conducted to determine the ignition behaviors and characteristics of different charring conductive polymers in a visual ignition combustor.The experiment result showed that the ignition delay and external energy required for ignition are negatively correlated with voltage and initial temperature of the ignition grain,but positively correlated with oxidizer flow velocity.Compared with charring conductive polymers containing multi-walled carbon nanotube,the ignition delay of charring conductive polymers with carbon black is significantly higher and the pyrolysis time is relatively longer.However,the ignition and initial flame propagation of charring conductive polymers with carbon black is more violent and more inclined to carbon particle ignition.Finally,the restart characteristic of different charring conductive polymers was studied.The ignition delay and external energy required for ignition of different charring conductive polymers all reduced with the increasing of the number of ignitions.However,the ignition characteristics would not change a lot after repeated ignition.展开更多
To increase the thrust-weight ratio in next-generation military aeroengines,a new integrated afterburner was designed in this study.The integrated structure of a combined strut–cavity–injector was applied to the aft...To increase the thrust-weight ratio in next-generation military aeroengines,a new integrated afterburner was designed in this study.The integrated structure of a combined strut–cavity–injector was applied to the afterburner.To improve ignition characteristics in the afterburner,a new method using a plasma jet igniter was developed and optimized for application in the integrated afterburner.The effects of traditional spark igniters and plasma jet igniters on ignition processes and ignition characteristics of afterburners were studied and compared with the proposed design.The experimental results show that the strut–cavity–injector combination can achieve stable combustion,and plasma ignition can improve ignition characteristics.Compared with conventional spark ignition,plasma ignition reduced the ignition delay time by 67 ms.Additionally,the ignition delay time was reduced by increasing the inlet velocity and reducing the excess air coefficient.This investigation provides an effective and feasible method to apply plasma ignition in aeroengine afterburners and has potential engineering applications.展开更多
Ignition timing control is of great importance in homogeneous charge compression ignition engines. The effect of hydrogen addition on methane combustion was investigated using a CHEMKIN multi-zone model. Results show ...Ignition timing control is of great importance in homogeneous charge compression ignition engines. The effect of hydrogen addition on methane combustion was investigated using a CHEMKIN multi-zone model. Results show that hydrogen addition advances ignition tim- ing and enhances peak pressure and temperature. A brief analysis of chemical kinetics of methane blending hydrogen is also performed in order to investigate the scope of its appli- cation, and the analysis suggests that OH radical plays an important role in the oxidation. Hydrogen addition increases NOx while decreasing HC and CO emissions. Exhaust gas recir- culation （EGR） also advances ignition timing; however, its effects on emissions are generally the opposite. By adjusting the hydrogen addition and EGR rate, the ignition timing can be regulated with a low emission level. Investigation into zones suggests that NOx is mostly formed in core zones while HC and CO mostly originate in the crevice and the quench layer.展开更多
Magnesium alloys have become more attractive because of their low density and electromagnetic shielding effectiveness in the aerospace industry.However,some unpredictable situation may lead to the ignition of magnesiu...Magnesium alloys have become more attractive because of their low density and electromagnetic shielding effectiveness in the aerospace industry.However,some unpredictable situation may lead to the ignition of magnesium alloys.In this review,the thermodynamic conditions and transfer processes of magnesium alloys ignition are analyzed from the point of mechanisms.The criteria of ignition are emphasized.In addition,ignitability and flammability test systems are compared.And a more suitable method to assess the potential ignition and flammability risks of magnesium alloys in extreme environments is recommended.Furthermore,the ignition characteristics of magnesium alloys are discussed in detail.It was found that the ignition of magnesium alloys is a complex process determined by internal properties such as thermo-physical properties,oxide film properties,chemical compositions and geometrical parameters,as well as the external environment such as gas species,oxygen concentration and oxygen pressure.Ignition temperature is not physical constants of materials.It is not simply assumed that ignition may occur when the temperature of Mg alloys reaches a certain ignition point.Finally,the unsolved issues in the ignition of magnesium alloys are pointed out and the future investigation are suggested for improving the safety and reliability of magnesium alloys in the aerospace applications.展开更多
Fuel moisture content is one of the important factors that determine ignition probability and fire behaviour in forest ecosystems.In this study,ignition and fire spread moisture content thresholds of 40 dead fuel were...Fuel moisture content is one of the important factors that determine ignition probability and fire behaviour in forest ecosystems.In this study,ignition and fire spread moisture content thresholds of 40 dead fuel were performed in laboratory experiments,with a focus on the source of ignition and wind speed.Variability in fuel moisture content at time of ignition and during fire spread was observed for different fuels.Matches were more efficient to result in ignition and spread fire with high values of fuel moisture content compared to the use of cigarette butts.Some fuels did not ignite at 15%moisture content,whereas others ignited at 40%moisture content and fire spread at 38%moisture content in the case of matches,or ignited at 27%moisture content and spread fire at 25%moisture content using cigarette butts.A two-way ANOVA showed that both the source of ignition and the wind speed affected ignition and fire spread threshold significantly,but there was no interaction between these factors.The relationship between ignition and fire spread was strong,with R2=98%for cigarette butts,and 92%for matches.Further information is needed,especially on the density of fuels,fuel proportion(case of mixed fuels),fuel age,and fuel combustibility.展开更多
Homogeneous mixtures of CH4/air under moderate or intense low-oxygen dilution（MILD） combustion conditions were numerically studied to clarify the fundamental effects of exhaust gas recirculation（EGR）,espe-cially C...Homogeneous mixtures of CH4/air under moderate or intense low-oxygen dilution（MILD） combustion conditions were numerically studied to clarify the fundamental effects of exhaust gas recirculation（EGR）,espe-cially CO2 in EGR gases,on ignition characteristics.Specifically,effects of CO2 addition on autoignition delay time were emphasized at temperature between 1200 K and 1600 K for a wide range of the lean-to-rich equivalence ratio（0.2~2）.The results showed that the ignition delay time increased with equivalence ratio or CO2 dilution ratio.Fur-thermore,ignition delay time was seen to be exponentially related with the reciprocal of initial temperature.Special concern was given to the chemical effects of CO2 on the ignition delay time.The enhancement of ignition delay time with CO2 addition can be mainly ascribed to the decrease of H,O and OH radicals.The predictions of tem-perature profiles and mole fractions of CO and CO2 were strongly related to the chemical effects of CO2.A single ignition time correlation was obtained in form of Arrhenius-type for the entire range of conditions as a function of temperature,CH4 mole fraction and O2 mole fraction.This correlation could successfully capture the complex be-haviors of ignition of CH4/air/CO2 mixture.The results can be applied to MILD combustion as ＂reference time＂,for example,to predict ignition delay time in turbulent reacting flow.展开更多
基金supported by the Science Center for Gas Turbine Project, China (No. P2022-B-Ⅱ-018-001)。
文摘Enhancing the ignition system performance of turbo engines is crucial,with a focus on rapidly and reliably igniting the entire combustor in low-temperature,low-pressure,high-speed inlet flow conditions.This challenge has garnered international attention.To address the issue of reliable ignition in the combustors of advanced propulsion system,this paper proposes a Multichannel Jet Enhanced Plasma Igniter(MJEPI) and conducts comparative experimental studies with the conventional spark igniter in a component-level dual-dome swirl combustor.The ignition limit in the combustor is obtained and the ignition processes are recorded.Experimental results demonstrate that the MJEPI significantly improves the ignition performance at high altitude.Specifically,at 0 km and 6 km for ground start-up,ignition limit is extended by 36% and 29%,respectively.At 6 km and 12 km for high-altitude relight,ignition limit is extended by 32% and 21%,respectively.The maximum ignition height is increased by 2.3 km,as determined by the global equivalence ratio of 1.The primary reason for these improvements is attributed to the larger initial flame kernel with greater penetration depth generated by MJEPI,which enables it to withstand more sever conditions such as low temperature,low pressure,and poor kerosene spray quality at elevated altitudes.
文摘In February 2024,192 lasers at the National Ignition Facility(NIF)in Livermore,CA,USA,began pouring 2.2 MJ of energy into a gold container smaller than the tip of a person’s little finger,heat-ing it to more than three million degrees Celsius(Fig.1)[1-4].Inside the container was a tiny fuel capsule containing tritium and deuterium that imploded at more than 400 km·s^(-1)causing atoms to combine and releasing 5.2 MJ of energy[1-4].
基金co-supported by the National Natural Science Foundation of China(Nos.52376138 and 52025064)the Science Center for Gas Turbine Project,China(No.P2022B-Ⅱ-018-001)the Foundation Research Project,China(No.1002TJA22010)。
文摘The reignition of aero-engine combustors at high altitudes poses significant challenges due to the low-temperature and low-pressure environment.A novel Long Pulse-Width Plasma Ignition(LPWPI)system has been developed to enhance ignition performance.The LPWPI system can effectively prolong the discharge duration time,improve ignition efficacy,and increase the plasma penetration depth.Experimental comparisons with the traditional Spark Ignition(SI)system demonstrate that the LPWPI increased discharge duration to 2.03 ms,which is 45 times longer than that of the SI system,while also doubling the spark penetration depth to 24.1 mm.The LPWPI system achieved a discharge efficiency of 61.1%,significantly surpassing the SI system's efficiency of23.3%.These advancements facilitated an extension of the lean ignition boundary by approximately 22.7%to 39.3%.High-speed camera recordings reveal that the spark duration of the LPWPI system was extended to 2.1 ms,compared to 0.6 ms in the SI system.Ignition progress with LPWPI shows a sustained spark kernel without the flame residence stage observed in the SI system.The impressive performance of the LPWPI system suggests that it is a promising alternative for aero-engine ignition systems.
基金supported by the National Key Research and Development Program of China(No.2021YFB3501002)the National Science and Technology Major Project(No.J2019-Ⅷ-0003-0165)the National Natural Science Foundation of China(No.52301059).
文摘Oxide films hinder diffusion and resist external forces,which determines the flame ignition mechanism of magnesium alloys.The effects of the continuity,compactness and mechanical properties of oxide films on the ignition mechanism were analyzed,by investigating the flame ignition behaviors of AZ80(ZM5),EZ30K(ZM6)and WE43 Mg alloys.The results show that the rupture of the oxide films caused by liquid gravity was the key to causing ignition.According to thermodynamic calculations,compared with Mg,Al cannot be preferentially oxidized;while Nd can be preferentially oxidized through significant enrichment,resulting in a discontinuous Nd_(2)O_(3)inner layer in the ZM6 alloy;in contrast,Y has a strong preferential oxidation ability,which gives the WE43 alloy a continuous Y_(2)O_(3)inner layer and self-healing ability.In addition,the oxide film of the ZM5 alloy is loose and has poor mechanical properties,so it cannot effec-tively hinder diffusion and resist liquid gravity.Differently,the oxide films of the ZM6 and WE43 alloys are dense and have better mechanical properties,leading to higher ignition temperatures and longer igni-tion times.In addition,a criterion was proposed to predict the ignition time based on the law of energy conservation,and it was simplified to predict the ignition temperature.The errors between the predicted and measured values are within 11%.
基金supported by the National Key Research and Development Program of China(Grant No.2021YFB3501002)the National Natural Science Foundation of China(Grant No.52301059,No.52271009)the Shanghai Post-doctoral Excellence Program(Grant No.2023372).
文摘Magnesium and its alloys offer lightweight advantage and have extensive development prospects,particularly in aerospace.However,their flammability poses a significant barrier on the development of Mg alloys.The ignition resistance of these alloys often depends on the protectiveness of the oxide film formed on the surface.This paper elucidates the formation mechanism of oxide film from thermodynamics and kinetics,classifying oxide films based on their layered structure to assess their protective properties.Furthermore,it comprehensively reviews the impact of characteristics on the protective effectiveness such as compactness,continuity,thickness,and mechanical properties.The paper also introduces various characterization methods for the microstructure and properties of oxide film.The primary objective of this paper is to enhance the comprehension of oxide film concerning the ignition resistance of Mg alloys and to furnish references for future advancements and research in Mg alloys with heightened ignition resistance.
基金the Fundamental Research Funds for the Central Universities(Grant No.30920041102)National Natural Science Foundation of China(Grant No.11802134).
文摘The arc ignition system based on charring polymers has advantages of simple structure,low ignition power consumption and multiple ignitions,which bringing it broadly application prospect in hybrid propulsion system of micro/nano satellite.However,charring polymers alone need a relatively high input voltage to achieve pyrolysis and ignition,which increases the burden and cost of the power system of micro/nano satellite in practical application.Adding conductive substance into charring polymers can effectively decrease the conducting voltage which can realize low voltage and low power consumption repeated ignition of arc ignition system.In this paper,a charring conductive polymer ignition grain with a cavity geometry in precombustion chamber,which is composed of PLA and multiwall carbon nanotubes(MWCNT)was proposed.The detailed ignition processes were analyzed and two different ignition mechanisms in the cavity of charring conductive polymers were revealed.The ignition characteristics of charring conductive polymers were also investigated at different input voltages,ignition grain structures,ignition locations and injection schemes in a visual ignition combustor.The results demonstrated that the ignition delay and external energy required for ignition were inversely correlated with the voltages applied to ignition grain.Moreover,the incremental depth of cavity shortened the ignition delay and external energy required for ignition while accelerated the propagation of flame.As the depth of cavity increased from 2 to 6 mm(at 50 V),the time of flame propagating out of ignition grain changed from 235.6 to 108 ms,and values of mean ignition delay time and mean external energy required for ignition decreased from 462.8 to 320 ms and 16.2 to 10.75 J,respectively.The rear side of the cavity was the ideal ignition position which had a shorter ignition delay and a faster flame propagation speed in comparison to other ignition positions.Compared to direct injection scheme,swirling injection provided a more favorable flow field environment in the cavity,which was beneficial to ignition and initial flame propagation,but the ignition position needed to be away from the outlet of swirling injector.At last,the repeated ignition characteristic of charring conductive polymers was also investigated.The ignition delay time and external energy required for ignition decreased with repeated ignition times but the variation was decreasing gradually.
基金supported by the National Natural Science Foundation of China(Nos.52130411,52174219 and 52174220)the Natural Science Foundation of Jiangsu Province(No.BK20240104)the Fundamental Research Funds for the Central Universities(No.2024-11044).
文摘Gas explosions in coal mine goafs are associated with the roof rock fracturing.An experimental system was established to investigate the potential for electrical ignition induced by sandstone fracturing.The electrical responses,luminescent emissions,and ignition characteristics during tensile and compressive failure of sandstones were analyzed in methane/air premixed gas environments.Results indicate that the application of mechanical loading induces the emergence of electrical signals on rock surfaces and in the surrounding atmosphere.This phenomenon is attributed to the generation,accumulation,and subsequent release of free charges during the deformation and fracture within the sandstone.Compressive failure proved to be more conducive to free charge generation than tensile failure,owing to more crack connections.Furthermore,a precipitous increase in surface and external voltages was observed during complete fracturing,a consequence of electron emission from crack tips within the rock structure.Moreover,the ionization induces luminous emissions owing to the collision of energetic electrons released from gas molecules in methane/air mixtures.A strong positive correlation(R2=0.9429)was identified between luminescence intensity and the magnitude of electrical discharge resulting from rock fracture.Notably,such discharge by rock fracturing can be capable of igniting the premixed gas,particularly when the quartz content exceeds 61%.Piezoelectric effects and crack propagation are crucial mechanisms in the causal chain of the charge generation,discharge,and ionization triggered by rock fractures.Based on the above laboratory results,electric ignition of the transient roof fracturing caused by stress mutations can serve as a new potential ignition source for gas explosions in the goaf.These results offer new insights into the prevention and control of gas explosions.
基金supported by the National Natural Science Foundation of China(Nos.12272408 and 11925207)the Natural Science Foundation for Distinguished Young Scholars of Hunan Province,China(No.2024J12057)。
文摘A numerical and experimental study was conducted to investigate the Laser Ablation(LA)ignition mode in an ethylene-fueled supersonic combustor with a cavity flameholder.Theexperiments were operated under a Mach number 2.92 supersonic inflow,with stagnation pressureof 2.4 MPa and stagnation temperature of 1600 K.Reynolds-averaged Navier-Stokes simulationswere conducted to characterize the mixing process and flow field structure.This study identifiedfour distinct LA ignition modes.Under the specified condition,laser ablation in zero and negativedefocusing states manifested two distinct ignition modes termed Laser Ablation Direct Ignition(LADI)mode and Laser Ablation Re-Ignition(LARI)mode,correspondingly.LA ignition in alocal small cavity,created by depressing the flow field regulator,could facilitate the ignition modetransforming from LARI mode to Laser Ablation Transition Ignition(LATI)mode.On the otherhand,the elevation of the flow field regulator effectively inhibited the forward propagation of theinitial flame kernel and reduced the dissipation of LA plasma,further enhancing the LADI mode.Based on these characteristics,the LADI mode was subdivided into strong(LADI-S)and weak(LADI-W)modes.Facilitating the transition of ignition modes through alterations in the local flowfield could contribute to attaining a more effective and stable LA ignition.
基金supported by the National Key Laboratory for Precision Hot Processing of Metals(Nos.6142909220102).
文摘The incorporation of Y significantly improves the fire resistance of the Mg-3Nd-2Gd-0.2Zr-0.2Zn(EV32)alloy.The findings indicate a significant increase in the ignition point of the alloy upon Y addition,notably reaching 813.9℃ for the EV32–3Y(wt.%)alloy.Additionally,the calculated residual stresses of the Y_(2)O_(3) and Gd_(2)O_(3) films were 2.732 GPa and 2.569 GPa respectively,showcasing a distinct correlation between Y concentration and improved fire resistance.This enhancement can be attributed to the formation of denser oxide films,especially Y_(2)O_(3) and Gd_(2)O_(3),effectively reducing the susceptibility of the oxide film to thermal stress-induced tearing.The study elucidates the vital role of Y addition in enhancing fire resistance,thoroughly investigating the mechanisms that impact both the formation of oxide films and ignition within the alloy structure.These findings not only contribute to a deeper comprehension of magnesium alloy performance under high-temperature conditions but also offer valuable theoretical guidance for enhancing its fire resistance through alloy design and application.
基金supported by the National Natural Science Foundation of China(Grant Nos.12205274,12275251,12105270,12205272,12305262,and 12035002)the National Key Laboratory of Plasma Physics(Grant No.JCKYS2024212803)+2 种基金the Fund of the National Key Laboratory of Plasma Physics(Grant No.6142A04230103)the National Key R&D Program of China(Grant No.2023YFA1608400)the National Security Academic Fund(Grant No.U2430207).
文摘Stimulated Raman scattering(SRS)under a new ignition path that combines the advantages of direct-drive(DD)and indirect-drive(ID)schemes is investigated experimentally at the Shenguang-100 kJ facility.The results show that collective SRS in the plasma produced by ablating a polyimide film is detected for the ID beams,but is suppressed by adding a toe before the main pulse of the ID beams.The toe also strongly influences SRS of both the ID and DD beams excited in the plasma generated in the hohlraum.When a toe is used,the SRS spectra of the DD beams show that SRS tends to be excited in lower plasma density,which will result in a lower risk of super-hot electrons.Measurements of hot electrons support this conclusion.This research will help us produce a better pulse design for this new ignition path.
文摘The utilization of graded Al powders offers the possibility to adjust the combustion performance of Al powders,while simultaneously safeguarding their energy properties.In this paper,a series of graded Al powder have been incorporated into the typical Al@AP composites through the spray drying technique.The thermal behavior,ignition and combustion characteristics were comprehensively evaluated and compared.The experimental results showed that with the varying inclusion of the graded Al,the heat of reaction exhibited a significant change,ranging from 9090 J·g^(-1) to 11036 J·g^(-1),which was strongly dependent on the particle size of Al.The combination of Al with diverse range of particle sizes in graded configuration serves to significantly enhance the decomposition of AP,resulting in the disappearance of the LTD stage and a conspicuous decrease of at least 11.7℃ in the peak temperature of the HTD.Furthermore,the maximum burning rate achieved by the Al-3@AP composite was 33.6 mm·s^(-1),which was exactly twice as high as that of the graded Al-1@AP composite with the lowest burning rate.Diffraction peaks corresponding to unburned Al were detected in the condensed combustion products of Al-1@AP,and the combustion images clearly indicated an incomplete combustion tendency for this sample.In contrast,a well-designed gradation of Al powders,such as a combination of fine Al powders with a particle size below 5μm,has proven to be the most conducive to enhancing the combustion efficiency of the composites.
基金supported by the National Natural Science Foundation of China(grant number 51576129).
文摘During the highly transient process of the direct-start in a four-cylinder GDI engine,each cylinder exhibits specific characteristics in terms of in-cylinder conditions and energy demands,necessitating different control for each cylinder.However,recent studies have paid insufficient attention to cylinders other than the first starting cylinder.This paper proposes a comprehensive control strategy based on experimental data from the direct-start process of the second,third,and fourth cylinders,aiming to enhance the characteristics of combustion and emission performance through the optimization of injection timing,equivalence ratio,and ignition timing.The research findings indicate that the second cylinder should inject fuel approximately 10 ms after the first cylinder ignites to mix thoroughly the fuel with air.The ignition timing of the second cylinder should be close to the highest point of the piston movement to minimize hindrance to the piston compression process.The third and fourth cylinders should adopt a delayed injection timing strategy to prevent the escape of injected fuel caused by low engine speed.The optimal ignition timing for the third cylinder is 20℃A BTDC,while the fourth cylinder should be ignited earlier due to its stronger airflow and faster formation of a mixture that can be ignited.As the fuel injection quantity increases,the power output of the three cylinders enhances,but at the same time,emissions also increase.Therefore,their optimal equivalence ratios are determined as 1.2,1.4,and 1.2,respectively,striking a balance between combustion and emission performances.
基金financial support from the LASERLAB-EUROPE Access to Research Infrastructure Activity (Application No. 23068)carried out within the framework of EUROfusion Enabling Research Projects AWP21-ENR-01-CEA02 and AWP24-ENR-IFE-02-CEA-02+3 种基金received funding from Euratom Research and Training Programme 2021–2025 under Grant No. 633053supported by the Ministry of Youth and Sports of the Czech Republic [Project No. LM2023068 (PALS RI)]by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant Nos. XDA25030200 and XDA25010100)supported by COST (European Cooperation in Science and Technology) through Action CA21128 PROBONO (PROton BOron Nuclear Fusion: from energy production to medical applicatiOns)
文摘Recent experiments at the National Ignition Facility and theoretical modeling suggest that side stimulated Raman scattering(SSRS)instability could reduce laser–plasma coupling and generate considerable fluxes of suprathermal hot electrons under interaction conditions envisaged for direct-drive schemes for inertial confinement fusion.Nonetheless,SSRS remains to date one of the least understood parametric instabilities.Here,we report the first angularly and spectrally resolved measurements of scattered light at laser intensities relevant for the shock ignition scheme(I×10^(16)W/cm^(2)),showing significant SSRS growth in the direction perpendicular to the laser polarization.Modification of the focal spot shape and orientation,obtained by using two different random phase plates,and of the density gradient of the plasma,by utilizing exploding foil targets of different thicknesses,clearly reveals a different dependence of backward SRS(BSRS)and SSRS on experimental parameters.While convective BSRS scales with plasma density scale length,as expected by linear theory,the growth of SSRS depends on the spot extension in the direction perpendicular to laser polarization.Our analysis therefore demonstrates that under current experimental conditions,with density scale lengths L_(n)≈60–120μm and spot sizes FWHM≈40–100μm,SSRS is limited by laser beam size rather than by the density scale length of the plasma.
基金Supported by the National Key Basic Research Development Project of China(No.2001CB209201).
文摘The catalytic combustion of methane in a mierochannel whose surface was coated with platinum（Pt） catalyst was studied by numerical-simulation. The effects of gas-phase reactions on the whole catalytic combustion process were analyzed at a high inlet pressure. A sensitivity analysis of the detailed mechanisms of the surface reaction of methane on Pt revealed that the most sensitive reactions affecting the heterogeneous ignition are oxygen adsorption/desorption and methane adsorption, and the most sensitive reactions affecting the homogeneous ignition are OH and H2O adsorption/desorption. The combustion process of the homogeneous charge compression ignition（HCCI） engine whose piston face was coated with Pt catalyst was simulated. The effects of catalysis and the most sensitive reactions on the ignition timing and the concentration of the main intermediate species during the HCCI engine combustion are discussed. The results show that the ignition timing of the HCCI engine can be increased by catalysis, and the most sensitive reactions affecting the ignition timing of the HCCI engine are OH and H2O adsorption/desorption.
基金Supported by the Fundamental Research Funds for the Central Universities,China(No.30920041102)the National Natural Science Foundation of China(No.11802134).
文摘The arc ignition based on charring conductive polymers has advantages of simple structure,low ignition power consumption and restart capacity,which bringing it broadly application prospect in hybrid propulsion system of micro/nano satellite.In order to optimize the performance of arc ignition system,it is essential to have a deeper understanding of the ignition processes and ignition characteristics of charring conductive polymers.In this paper,the thermal decomposition,electrical conductivity and thermal conductivity characteristics of charring conductive polymers with different conductive additives and matrix materials were comprehensively evaluated.An experimental investigation was conducted to determine the ignition behaviors and characteristics of different charring conductive polymers in a visual ignition combustor.The experiment result showed that the ignition delay and external energy required for ignition are negatively correlated with voltage and initial temperature of the ignition grain,but positively correlated with oxidizer flow velocity.Compared with charring conductive polymers containing multi-walled carbon nanotube,the ignition delay of charring conductive polymers with carbon black is significantly higher and the pyrolysis time is relatively longer.However,the ignition and initial flame propagation of charring conductive polymers with carbon black is more violent and more inclined to carbon particle ignition.Finally,the restart characteristic of different charring conductive polymers was studied.The ignition delay and external energy required for ignition of different charring conductive polymers all reduced with the increasing of the number of ignitions.However,the ignition characteristics would not change a lot after repeated ignition.
基金supported by National Natural Science Foundation of China(Nos.51806245 and 51436008)the Science and Technology Projects of Shaanxi Province(No.2020JM-349)。
文摘To increase the thrust-weight ratio in next-generation military aeroengines,a new integrated afterburner was designed in this study.The integrated structure of a combined strut–cavity–injector was applied to the afterburner.To improve ignition characteristics in the afterburner,a new method using a plasma jet igniter was developed and optimized for application in the integrated afterburner.The effects of traditional spark igniters and plasma jet igniters on ignition processes and ignition characteristics of afterburners were studied and compared with the proposed design.The experimental results show that the strut–cavity–injector combination can achieve stable combustion,and plasma ignition can improve ignition characteristics.Compared with conventional spark ignition,plasma ignition reduced the ignition delay time by 67 ms.Additionally,the ignition delay time was reduced by increasing the inlet velocity and reducing the excess air coefficient.This investigation provides an effective and feasible method to apply plasma ignition in aeroengine afterburners and has potential engineering applications.
基金This work was supported by the Natural Science Foundation of Anhui Province （No.090412030）.
文摘Ignition timing control is of great importance in homogeneous charge compression ignition engines. The effect of hydrogen addition on methane combustion was investigated using a CHEMKIN multi-zone model. Results show that hydrogen addition advances ignition tim- ing and enhances peak pressure and temperature. A brief analysis of chemical kinetics of methane blending hydrogen is also performed in order to investigate the scope of its appli- cation, and the analysis suggests that OH radical plays an important role in the oxidation. Hydrogen addition increases NOx while decreasing HC and CO emissions. Exhaust gas recir- culation （EGR） also advances ignition timing; however, its effects on emissions are generally the opposite. By adjusting the hydrogen addition and EGR rate, the ignition timing can be regulated with a low emission level. Investigation into zones suggests that NOx is mostly formed in core zones while HC and CO mostly originate in the crevice and the quench layer.
基金This project is supported by Fundamental Research Funds for the Central Universities(Grant no.FRF-GF-18-024B).
文摘Magnesium alloys have become more attractive because of their low density and electromagnetic shielding effectiveness in the aerospace industry.However,some unpredictable situation may lead to the ignition of magnesium alloys.In this review,the thermodynamic conditions and transfer processes of magnesium alloys ignition are analyzed from the point of mechanisms.The criteria of ignition are emphasized.In addition,ignitability and flammability test systems are compared.And a more suitable method to assess the potential ignition and flammability risks of magnesium alloys in extreme environments is recommended.Furthermore,the ignition characteristics of magnesium alloys are discussed in detail.It was found that the ignition of magnesium alloys is a complex process determined by internal properties such as thermo-physical properties,oxide film properties,chemical compositions and geometrical parameters,as well as the external environment such as gas species,oxygen concentration and oxygen pressure.Ignition temperature is not physical constants of materials.It is not simply assumed that ignition may occur when the temperature of Mg alloys reaches a certain ignition point.Finally,the unsolved issues in the ignition of magnesium alloys are pointed out and the future investigation are suggested for improving the safety and reliability of magnesium alloys in the aerospace applications.
基金funded by the National Key Research and Development Program of China(2018YFE0207800)the Fundamental Research Funds for the Central Universities(2572019CP10)+1 种基金the National Innovation Alliance of Wildland Fire Prevention and Control Technology of Chinathe Northern Forest Fire Management Key Laboratory of the State Forestry and Grassland Bureau。
文摘Fuel moisture content is one of the important factors that determine ignition probability and fire behaviour in forest ecosystems.In this study,ignition and fire spread moisture content thresholds of 40 dead fuel were performed in laboratory experiments,with a focus on the source of ignition and wind speed.Variability in fuel moisture content at time of ignition and during fire spread was observed for different fuels.Matches were more efficient to result in ignition and spread fire with high values of fuel moisture content compared to the use of cigarette butts.Some fuels did not ignite at 15%moisture content,whereas others ignited at 40%moisture content and fire spread at 38%moisture content in the case of matches,or ignited at 27%moisture content and spread fire at 25%moisture content using cigarette butts.A two-way ANOVA showed that both the source of ignition and the wind speed affected ignition and fire spread threshold significantly,but there was no interaction between these factors.The relationship between ignition and fire spread was strong,with R2=98%for cigarette butts,and 92%for matches.Further information is needed,especially on the density of fuels,fuel proportion(case of mixed fuels),fuel age,and fuel combustibility.
基金Supported by the National Natural Science Foundation of China (50206014)the Shuguang Scholar Program of Shanghai Education Development Foundation (05SG23)
文摘Homogeneous mixtures of CH4/air under moderate or intense low-oxygen dilution（MILD） combustion conditions were numerically studied to clarify the fundamental effects of exhaust gas recirculation（EGR）,espe-cially CO2 in EGR gases,on ignition characteristics.Specifically,effects of CO2 addition on autoignition delay time were emphasized at temperature between 1200 K and 1600 K for a wide range of the lean-to-rich equivalence ratio（0.2~2）.The results showed that the ignition delay time increased with equivalence ratio or CO2 dilution ratio.Fur-thermore,ignition delay time was seen to be exponentially related with the reciprocal of initial temperature.Special concern was given to the chemical effects of CO2 on the ignition delay time.The enhancement of ignition delay time with CO2 addition can be mainly ascribed to the decrease of H,O and OH radicals.The predictions of tem-perature profiles and mole fractions of CO and CO2 were strongly related to the chemical effects of CO2.A single ignition time correlation was obtained in form of Arrhenius-type for the entire range of conditions as a function of temperature,CH4 mole fraction and O2 mole fraction.This correlation could successfully capture the complex be-haviors of ignition of CH4/air/CO2 mixture.The results can be applied to MILD combustion as ＂reference time＂,for example,to predict ignition delay time in turbulent reacting flow.
