Decrease In Ignition Delay Time Research Articles

Kinetic insights into ammonia-hydrogen doped ignition and emission assisted by nanosecond pulsed discharge

Non-equilibrium plasma is applied for the first time to ignite the ammonium-hydrogen mixture and reduce the NOx/N2O emission with effect in this work. Gas chromatography (GC) experiments as well as a detailed kinetic model, including neutral molecules, free radicals, charged particles, vibratory excited states, and electron excited states, are integrated to investigate the kinetic process of ammonia-hydrogen doped ignition and NOx/N2O emission facilitated by nanosecond pulsed discharge. The numerical model closely matches the GC-measured values of NH3 consumption, H2 increase, and N2O production. Pathway fluxes of important species and sensitivity analysis of ignition delay time reveal that the addition of non-equilibrium plasma has an obvious promotion effect on ammonia and hydrogen-doped oxidation and ignition. The initial ignition temperature significantly impacts the ignition delay time, with a more pronounced plasma-promotion effect observed at lower temperatures. Conversely, as the hydrogen mixing ratio increases, the ignition delay time decreases, yet the generation of NO and N2O increases. This is attributed to the heightened production of H and NH through elementary reactions such as NH3+HNH2+ H2, H + O2O + OH, and OH + H2H + H2O. Nevertheless, NO and N2O emissions are reduced by 1-2 orders of magnitude with plasma assistance compared to auto-ignition. The reduction in NO emissions can be attributed to increased consumption in the pathway of NO + NH2N2 + H2O and decreased formation in the pathways of HNO + O2HO2 + NO and NH + NON2O + H. Additionally, it was discovered that the electron attachment dissociation reaction e + N2O → O− + N2 predominantly contributes to the reduction of N2O. These research findings significantly contribute to advancing our understanding of the kinetics involved in ammonia-hydrogen doped ignition and emissions, particularly with plasma assistance, for potential engine applications.

Experimental Studies on Thermal Oxidation and Laser Ignition Properties of Al-Mg-Li Powders.

Powder ramjets are a kind of vehicle propulsion system with high specific impulse and efficiency. They provide significant benefits in terms of extended propulsion and thrust adjustment. The pursuit of a highly reactive fuel appropriate for powder ramjets is likely to stimulate advancements in innovative propulsion systems, which are crucial for deep space exploration and long-term space missions. This work presents experimental studies on the thermal oxidation and laser ignition performance of aluminum-magnesium-lithium powders at atmospheric pressure. TG-DSC curves of powders in three heating rates were obtained. The ignition processes and ignition delay times were recorded by a CO2 laser ignition experiment system at a laser power of 10~60 W. The results show that at a lower heating rate of 10 K/min, the powder's thermal hysteresis is less, and the powder energy released in stage I is more concentrated. However, the degree of heat release concentration approached a similar level at heating rates of 30 K and 50 K. The ignition delay time decreased as the laser flux density increased. When the laser flux density exceeds 80 W/cm2, the effect of laser power on the ignition delay time decreases. At atmospheric pressure, the mathematical relationship between ignition delay time and laser flux density is given. Finally, the powder ignition processes at different laser powers are represented graphically.

Thermodynamic analysis of employing argon as the diluent and adding hydrogen in an HCCI ammonia engine: Ignition characteristics and performances of combustion and NO emissions

Ammonia is an efficient hydrogen energy carrier and a potential zero-carbon fuel for internal combustion engines. However, the poor ignition and combustion performances of ammonia limit its further application in homogeneous charge compression ignition engines. This study proposes to employ an inert gas argon as a diluent to improve ammonia's ignition and combustion performances. Furthermore, the effect of adding hydrogen is also investigated under a wide calculation range of compression ratio, excess oxygen ratio, and argon ratio through thermodynamic analysis. The calculation results indicate that replacing nitrogen with argon can significantly shorten the ignition delay time and promote the thermal conversion efficiency and power density. Under a specific condition (compression ratio = 19 and excess oxygen ratio = 3.0), when replacing air with an argon-oxygen mixture of argon/oxygen ratio = 79: 21, the ignition delay time of pure ammonia reduces from 700 ms to 0.31 ms, the thermal conversion efficiency increases from 65.1% to 78.2%, and the power density raises by approximately 20%. Nevertheless, the NO volume fraction grows by 1179 × 10−6 VOL due to the high temperature. The ignition delay time drops with the increase of hydrogen blend ratio. With an initial condition of 1250 K and 3.0 MPa, the ignition delay time decreases by 81%–95% when the hydrogen blend ratio is elevated from 5% to 20%. However, adding hydrogen also falls the thermal conversion efficiency and elevates the NO volume fraction. A hydrogen blend ratio of 5% is an excellent tradeoff value.

Autoignition of two-phase n-heptane/air mixtures behind an oblique shock: Insights into spray oblique detonation initiation

Autoignition of n-heptane droplet/vapor/air mixtures behind an oblique shock wave are studied, through Eulerian-Lagrangian method and a skeletal chemical mechanism. The effects of gas/liquid equivalence ratio (ER), droplet diameter, flight altitude, and Mach number on the ignition transient and chemical timescales are investigated. The results show that the ratio of chemical excitation time to ignition delay time can be used to predict the oblique detonation wave (ODW) transition mode. When the ratio is relatively high, the combustion heat release is slow and smooth transition is more likely to occur. In heterogeneous ignition, there are direct interactions between the evaporating droplets and the induction/ignition process, and the chemical explosive propensity changes accordingly. The energy absorption of evaporating droplets significantly retards the ignition of n-heptane vapor. In the two-phase n-heptane mixture autoignition process, the ignition delay time decreases exponentially with flight Mach number and increases first and then decreases with the flight altitude. As the liquid ER increases, both ignition delay time and droplet evaporation time increase. With increased droplet diameter, the ignition delay time decreases, and the evaporation time increases. Besides, when Mach number is less than 10, the ratio of the chemical excitation time to ignition delay time generally increases with the flight altitude or Mach number. It increases when the liquid ER decreases or droplet diameter increases. When the Mach number is sufficiently high, it shows limited change with fuel and inflow conditions. The ODW is more likely to be initiated with a smooth transition at high altitude or Mach number. Abrupt transition mode tends to happen when fine fuel droplets are loaded. The results from this work can provide insights into spray ODW initiation.

Effects of Hydrogen Addition on Premixed Combustion of Kerosene in SI Engine

Spark ignition (SI) engines fueled with kerosene have broad application prospects in unmanned aviation vehicles. The knock phenomenon of kerosene in SI engines is a huge challenge, leading to a much lower power output than gasoline engines. In this context, the combustion characteristics of kerosene blending with hydrogen are analyzed numerically regarding the working conditions of an SI engine. First, the ignition delay time of a kerosene/hydrogen mixture is estimated for temperatures of 600–1000 K and pressures of 15–35 bar using the Tay mechanism. The effects of hydrogen addition are evaluated with a ratio of 0–0.4. The sensitivities of the main reactions that affect the ignition delay time are discussed. Then, the laminar flame speed is predicted using the HYCHEM-SK mechanism, and the effects of hydrogen addition on the net reaction rates of the main reactions are analyzed. The results indicate that the ignition delay time is shortened and the laminar flame speed is increased as the hydrogen addition ratio rises. Meanwhile, the ignition delay time decreases except for the NTC range, and the laminar flame speed increases evidently as the temperature rises. In addition, the ignition delay time decreases obviously as the pressure increases with a temperature greater than 750 K. However, the laminar flame speed declines at 600 K and 800 K, while an opposite trend exhibits at 1000 K as the pressure rises. The laminar flame speed increases by 23.85–24.82%, while the ignition delay time only decreases by 4.02–3.59% at 1000 K as the hydrogen addition ratio rises from 0 to 0.4, which will be beneficial for knock suppression.

Theoretical and numerical study of the combustion properties of premixed hydrogen/natural gas/air at a sub-atmospheric pressure of 0.849 Bar

Due to the energy transition worldwide, renewable energy sources complementary to fossil fuels are being sought. Considering that hydrogen generates only water when reacting with air, the application of hydrogen can play a leading and complementary role in the reduction of greenhouse gas (GHG) emissions. This work conducts a theoretical and numerical evaluation of the effect of adding hydrogen to natural gas (NG) combustion. Eight fuels, from 0% H2 up to 100% H2, by volume, were evaluated in 15% intervals. The volumetric and mass air requirement, H2O and CO2 production, wet and dry combustion products, as added to the heating value, Wobbe index, flammability ranges, dew point, and specific gravity, were calculated for each mixture at stoichiometric conditions. Some premixed flame combustion properties were calculated numerically for equivalence ratios from 0.5 to 1.5, using Medellín’s atmospheric conditions. These properties include the minimum ignition energy, critical quenching distance, diffusive thickness, laminar burning velocity, adiabatic flame temperature, flame structure, and ignition delay time. The latter property considered reagent preheat temperatures between 1000 K and 1600 K, finding an inverse relationship. Furthermore, increased hydrogen content showed an increase in flame temperature and laminar deflagration velocity, and a decrease in ignition delay time, flame thickness, critical quenching distance, and minimum ignition energy. Finally, the maximums and minimums of the properties considered were found to center at stoichiometric conditions for 100% natural gas, while the addition of hydrogen shifted the trend towards richer mixtures.

Ignition and oxidation performance of SnO2 coated boron particles: A solid fuel for energetic applications

The ignition performance of boron is limited by the presence of a natural oxide layer on its surface. As a result, despite its high volumetric and gravimetric heat of combustion, its use in high energetic applications remains rare. To improve its ignition performance, and its eventual use in energetic applications, we coated micro sized boron particles with nanometer sized SnO2 nanoparticles using a simple chemical precipitation method. Several samples were prepared by varying the chemical precipitation time on the boron surface. A structural study of the SnO2 coated boron particles determined the formation of nanocrystalline SnO2 nanoparticles on the surface of the boron particles. Surface morphology showed the small sized SnO2 nanoparticles were distributed over the boron surface. EDS and XPS techniques confirmed the presence of B, Sn, and O elements in the SnO2 coated boron samples. TEM analysis supported the results of the surface morphology, and confirmed the apparent size of SnO2 nanoparticles to be in the range of 3–20 nm. TGA was used to study the oxidation behavior of the boron and SnO2 coated boron particles in an air atmosphere. It showed an approximate 20% reduction in the mass gain of boron at 1000 °C, as well as a shift, 160 °C lower, in the onset oxidation temperature after the coating of SnO2 nanoparticles. A shock tube study measured a significant enhancement in the ignition performance of boron. The SnO2 coated boron particles resulted in a 19% decrease in ignition delay time compared with pure boron particles.

Experimental Investigations on the Ignition Delay Time of Freely Falling Liquid Fuel Droplets

The ignition delays of freely falling liquid fuel droplets in a high-temperature environment were determined experimentally as a function of the surrounding parameters and droplet composition. Two different groups of fuels have been categorized based on the viscosity and volatility of each fuel. In the first group, for diesel and kerosene, the ignition delay time decreases with increasing system temperature due to low viscosity and thereby high volatile nature of fuels. Whereas, in the second group, C-heavy oil and blended renewable fuel shows an increase in the ignition delay time with increasing the system temperature and thereby shows the negative temperature coefficient (NTC) behavior due to high viscosity and low volatile characteristics of those fuels. In the case of low viscosity carbon residue fuels with low ignition temperature, they may vaporize early and decrease in the ignition delay time. But for high viscosity carbon residue fuels and with high ignition temperature, it may prolong the vaporization time and thereby physical delay. Evidently, the physical parameters and therefore the physical delay are the predominant factors in the NTC behavior of such high hydrocarbon liquid fuel droplets.

Experimental study of ignition behaviors of pyrolysis gas of kerosene‐based endothermic hydrocarbon fuel

The pyrolysis gas consisting of 29.4% CH4, 21.3% C2H4, 30.8% C2H6, and 18.5% C3H6 in mole fraction is presented, as the surrogate of the actual gaseous pyrolysis products. At the conditions of TC = 877.7-963 K, PC = 3.22-4.37 MPa, φ = 0.5 and 1.0, the ignition delays of pyrolysis gas/air (diluted with 52% Ar) have been measured. With TC or PC increasing, the ignition delay time decreases. The auto-ignition of φ = 1.0 is faster than that of φ = 0.5. Furthermore, two widely used small hydrocarbons chemical mechanisms are validated with the measured results. The USC-II mechanism can well predict experimental results at high-T regimes, but fails at low-T regimes. By sensitivity analysis of temperature, the two elementary reactions C2H6 + OH = C2H5 + H2O (negative sensitivity coefficient) and C3H6 + OH = aC3H5 + H2O (positive sensitivity coefficient) have been identified, which have higher reactivity at low-T and lower reactivity at high-T. Considering the extreme uncertainty of rate constants of C3H6 + OH = aC3H5 + H2O, the kinetic parameters have been modified for improving the predictions. The validated results indicate that the optimized mechanism improves predictions of the auto-ignition behavior at low temperature regimes.

Numerical modeling of ignition enhancement by repetitive nanosecond discharge in a hydrogen/air mixture II: forced ignition

Non-equilibrium plasma has promising applications in combustion enhancement. In this study, 1D simulations are conducted for the forced ignition process using non-equilibrium plasma generated by repetitively pulsed nanosecond discharge (NSD). The ignition kernel is induced by a discharge area with NSD and it develops and propagates in a static stoichiometric hydrogen/air mixture. The objective is to assess how the characteristics of NSD affect the ignition delay time and ignition kernel development during the forced ignition process. Similar to the homogeneous ignition considered in part I, the forced ignition process is found to be strongly affected by the pulse number, discharge frequency, discharge radius, total input energy, and input energy per pulse of NSD. For a fixed input energy per pulse, the ignition delay time decreases and the propagation speed of the initial ignition kernel increases with the pulse number, discharge frequency and discharge radius. However, for a fixed total input energy, the ignition delay time increases and the propagation speed of the initial ignition kernel decreases with the pulse number. Furthermore, it is found that the promotion of ignition kernel development and propagation in the forced ignition by NSD are mainly due to the kinetic effect rather than the thermal effect.

Numerical Simulations and Experiments of Ignition of Solid Particles in a Laminar Burner: Effects of Slip Velocity and Particle Swelling

Ignition and combustion of pulverized solid fuel is investigated in a laminar burner. The two-dimensional OH radical field is measured in the experiments, providing information on the first onset of ignition and a detailed characterization of the flame structure for the single particle. In addition, particle velocity and diameter are tracked in time in the experiments. Simulations are carried out with a Lagrangian point-particle approach fully coupled with an Eulerian solver for the gas-phase, which includes detailed chemistry and transport. The numerical simulation results are compared with the experimental measurements in order to investigate the ignition characteristics. The effect of the slip velocity, i.e. the initial velocity difference between the gas-phase and the particle, is investigated numerically. For increasing slip velocity, the ignition delay time decreases. For large slip velocities, the decrease in ignition delay time is found to saturate to a value which is about 40% smaller than the ignition delay time at zero slip velocity. Performing a simulation neglecting the dependency of the Nusselt number on the slip velocity, it is found that this dependency does not play a role. On the contrary, it is found that the decrease of ignition delay time induced by the slip velocity is due to modifications of the temperature field around the particle. In particular, the low-temperature fluid related to the energy sink due to particle heating is transported away from the particle position when the slip velocity is non-zero; therefore, the particle is exposed to larger temperatures. Finally, the effect of particle swell is investigated using a model for the particle swelling based on the CPD framework. With this model, we observed negligible differences in ignition delay time compared to the case in which swelling is not included. This is related to the negligible swelling predicted by this model before ignition. However, this is inconsistent with the experimental measurements of particle diameter, showing a significant increase of diameter even before ignition. In further simulations, the measured swelling was directly prescribed, using an analytical fit at the given conditions. With this approach, it is found that the inclusion of swelling reduces the ignition delay time by about 20% for small particles while it is negligible for large particles.

Ignition of nickel coated aluminum agglomerates using shock tube

Al is used as additives for solid propellants due to its high energy density. However, Al is difficult to ignite since it is covered with a protective oxide film having a high melting point. One method suggested to solve this problem is surface coating with other metal particles. Thus, in this study, Al particles were coated with Ni nanoparticles by a simple spray drying technique. The coating process was carried out by varying the weight percent of Ni to Al particles. The crystalline structure of Ni-coated Al particles was retained without any intermetallic or additional phase formation, as identified by XRD. SEM and EDS results show uniform and continuous coating of Ni-nanoparticles on the surface of 10 µm Al particles was formed when the sample was prepared using an equal weight percentage ratio of Ni and Al. When the ratio of Ni to Al was decreased, the Ni-nanoparticles only partly covered the surface of the Al particles. The presence of elements was confirmed from the XPS analysis with strong surface interaction between Ni nanoparticles and Al particles. Ni-coated Al particles in an air atmosphere showed higher exothermic energy than pure Al particles. Ignition performance of Ni-coated Al particles obtained from a shock tube experiment at high temperature demonstrated the significant decrease in ignition delay time as the Ni content in the sample increased.

Influence of quadricyclane additive on ignition and combustion properties of high-density JP-10 fuel

With the development of supersonic aerospace propulsion, the demand for high-density fuels with excellent ignition and combustion performance has become imperative. This work will explore the influence of strained quadricyclane (QC) on ignition and combustion properties of high-density fuel JP-10 utilizing shock tube, hot-plate ignitions, and oxygen bomb combustion. Shock tube test shows that 1% QC/JP-10 blended fuel gives a 40% decrease of ignition delay time and a 17% decrease of apparent ignition activation energy compared with pure JP-10, respectively. Hot-plate ignition test shows that adding 1% QC in JP-10 can decrease the ignition delay time by 20% and reduce the lowest ignition temperature by 20 °C. Oxygen bomb calorimetric test shows that 1% QC/JP-10 blended fuel gives the highest heat of combustion and the highest combustion efficiency in air excessive ratio range of 1.2–2. The most significant effect of 1% QC addition is attributed to the easy flammability and low activation energy of QC. This work also suggests QC as a good additive to enhance the combustion performance of high-density fuels.

The influence of chemical composition on ignition delay times of gasoline fractions

Tailoring fuel properties to maximize the efficiency of internal combustion engines is a way towards achieving cleaner combustion systems. In this work, the ignition properties along with the chemical composition (expressed as functional groups) of various light distillate (e.g., gasoline) cuts were analyzed to better understand the properties of full boiling range fuels. Various distillation cuts were obtained with a spinning band distillation system, which were then tested in an ignition quality tester (IQT) to obtain their global chemical reactivity (i.e., ignition delay time (IDT)). The distillates were further analyzed with 1H nuclear magnetic resonance (NMR) spectroscopy to identify and quantify various functional groups present in them. Various gasolines of research grade with specific target properties set forth by the Coordinating Research Council (CRC) that are known as FACE (fuels for advanced combustion engines) gasolines were distilled. When fuels with low aromatic content were distilled, the higher boiling point (BP) range (i.e., higher molecular weight) fractions exhibited lower IDT. However, distilled fractions of fuels with high aromatic content showed an initial decrease in IDT with increasing BP, followed by drastic increase in IDT primarily due to increasing aromatic groups. This study provides an understanding of the contribution of various volatile fractions to the IDTs of a multicomponent fuel, which is of relevance to fuel stratification utilized in gasoline compression ignition (GCI) engines to tailor heat release rates.

A Shock Tube Study of Ethylene/Air Ignition Characteristics over a Wide Temperature Range

ABSTRACT As a key intermediate product, ethylene plays an important role in the combustion of heavy hydrocarbons. Very limited experiments have focused on the high temperature (>1000 K) ethylene ignition at the real fuel–air condition, but no one on the ethylene/air ignition at low temperatures (<1000 K). In the present work, ignition delay times of ethylene/air mixtures were measured at temperatures of 721 to 1307 K, pressures of 0.97 to 20.54 atm, and equivalence ratios of 0.5, 1.0 and 2.0，and ignition characteristics of ethylene/air were discussed. The high-temperature results show that ignition delay times decrease with the increase of temperature monotonously; the ignition delay of fuel-lean mixture exhibits an unusual behavior of almost zero pressure dependence, and stoichiometric and fuel-rich mixtures still have ordinary pressure dependence, with a pressure increase producing a decrease of ignition delay time. The results at wide temperatures indicate that ethylene/air ignition delay shows no negative temperature coefficient (NTC) behavior at low temperatures, and has an inflection point at the temperature of about 1000 K, showing a two-region ignition feature. The ignition delay times at two regions can be described by Arrhenius-type formulas, respectively, and the ethylene/air ignition delay is much less sensitive to the temperature at the low-temperature region. A good agreement is found between current data and another experimental data for high-temperature ignition. The mechanism used predicts the ethylene/air ignition delay well at high temperatures but must overpredict the ignition delay times at low temperatures. This work contributes to understanding the ethylene ignition properties at a wide temperature range and provides experimental data valuable for validating and refining the chemical kinetics mechanism of ethylene.

The study of co-combustion characteristics of coal and microalgae by single particle combustion and TGA methods

The co-combustion characteristics of coal and microalgae with different blending ratios and under different atmospheres are studied by single particle combustion and thermogravimetric analysis methods. The combustion processes of coal, microalgae and their blends in the single particle combustion experiment have two stages, while the combustion process of coal in the thermogravimetric analysis experiment only has one stage. With the increasing blending ratio of microalgae, flames of volatiles and char of fuels become dimmer and smaller, and the average flame temperature decreases from about 1400 °C to about 1200 °C. The ignition delay time decreases from 200 ms to 140 ms, and the experimental ignition delay time of blended fuels is lower than the theoretical ignition delay time, which demonstrates that the synthetic effect between coal and microalgae exists. To analyze the influence of oxy-fuel atmosphere on the combustion characteristics, the air is replaced by the O2/CO2 atmosphere. The replacement decreases the luminosity, size and average temperature of flames. The average flame temperature of volatiles decreases from 1449.4 °C to 1151.2 °C, and that of char decreases from 1240.0 °C to 1213.4 °C. The replacement increases the ignition delay time of fuel from 80 ms to 100 ms. Increasing mole fraction of O2 in O2/CO2 atmosphere can offset these influences. With the increasing mole fraction of O2, flames of volatiles and char of fuels become brighter and larger, the average flame temperature increases from about 1100 °C to about 1300 °C, while the ignition delay time decreases from 100 ms to 77 ms.

Influence of high ethane content on natural gas ignition

The effect of ethane on combustion and natural gas autoignition was studied in the present paper. Two fuel mixture of natural gas with high ethane content were considered, 75% CH4 – 25% C2H6 (mixture 1), and 50% CH4 – 50% C2H6 (mixture 2). Natural gas combustion incidence was analyzed through the calculation of energy properties and the ignition delay time numerical calculations along with an ignition mode analysis. Specifically, the strong ignition limit was calculated to determine the effect of ethane on natural gas autoignition. According to the results, ignition delay time decreases for both mixtures in comparison with pure methane. The strong ignition limit shifts to lower temperatures when ethane is present in natural gas chemical composition.&#x0D;

Nanosecond discharge ignition in acetylene-containing mixtures

We study experimentally and numerically the kinetics of ignition in lean and stoichiometric C2H2 : O2 : Ar mixtures after a high-voltage nanosecond discharge. The ignition delay time is measured behind a reflected shock wave with and without the discharge using detection of CH radiation. Generation of the discharge plasma is shown to lead to a decrease in ignition delay time. Discharge processes followed by chain chemical reactions with energy release are simulated during ignition in the C2H2 : O2 : Ar mixtures. The generation of atoms, radicals and excited and charged particles in the discharge phase is numerically simulated. The calculations are based on the measured time-resolved discharge current and electric field. The calculated densities of the active particles produced in the discharge on a nanosecond time scale are employed as input data to simulate plasma-assisted ignition on a microsecond scale. The calculated ignition delay times are compared with the experimental data. It is shown that the effect of the discharge plasma on ignition of the acetylene-containing mixtures is associated with active species production in the discharge phase rather than with gas heating during the discharge and in its afterglow. A sensitivity analysis is made to determine limiting reactions in acetylene autoignition and ignition after the discharge under the conditions studied.

Study on Laser Ignition Characteristics of NEPE Propellant

The ignition process of NEPE propellant by a CO2 laser ignition system has been investigated experimentally. The effect of laser heat flux density on the ignition delay time of NEPE propellant was examined. The ignition delay time of NEPE propellant was decreased along with the increase of laser heat flux density. The effect of ignition heat flux density on ignition delay time decreases when the laser heat flux density is more than 290 W/cm2. This heat flux density value can be used as igniter design reference value. The ignition delay time increases dramatically along with the decrease of laser heat flux density when the laser heat flux density is lower.

G060041 非予混合火炎の着火遅れに対するスカラー散逸率の影響([G06004]熱工学部門一般セッション(4):着火)

The objective of this study is to suggest a new method to predict the stability limit of high temperature air combustion. For the first stage of this study, the flamelet equation is solved numerically to investigate the effects of the scalar dissipation rate and the dilution with burned gas on ignition delay. Methane was used as fuel. Ignition time is defined as the time at which a temporal increase of maximum temperature becomes maximum. The ignition delay time increases with the scalar dissipation rate in the higher range of x. However, in the lower range of x, the time decreases with x. The ignition delay time based on the maximum temperature includes durations of radical pool growth and of movement of most reactive region. In the lower range of x, the increase in the movement speed decreases the ignition delay time with x. With the increase in the dilution ratio K, the ignition delay time decreases, and then increases. This trend is attributed to the increase in temperature and the decrease in species concentration with K. The introduction of chemical characteristics time provides the generalization of ignition delay time for all dilution ratios.