Influence Of Equivalence Ratio Research Articles

Laminar burning velocity, radiative heat loss and cellular instability for NH3/biogas/H2/air premixed flame

This study presents, for the first time, a comprehensive investigation into the laminar flame propagation of ammonia/biogas/hydrogen/air mixtures. The laminar burning velocities (LBVs) were determined using the outwardly propagating spherical flame method under atmospheric temperature and elevated pressures across various equivalence ratios. The Okafor and CEU–NH3–Mech-1.1 mechanisms showed the best agreement with flame speed measurements. The influence of equivalence ratio, hydrogen ratio, and initial pressure on LBV was examined. Results indicate that LBV varies non-monotonically with the equivalence ratio, decreases with increasing pressure, and increases with higher hydrogen ratios. The enhancement of LBV due to hydrogen addition is mainly attributed to chemical effects, with thermal effects also playing a role. Given the significant CO2 content in biogas, which is a key radiative species, the study also analyzed the radiative heat loss of ammonia/biogas/hydrogen mixtures. It was found that as the equivalence ratio nears the flammability limit, LBV is more affected by radiative heat loss, with a lower hydrogen ratio increasing this effect. Additionally, higher CO2 mole fractions in biogas increase radiative heat loss. Detailed analysis of cellular instability, considering factors such as thermal expansion ratio, flame thickness, effective Lewis number, the logarithmic growth rate of perturbations and in conjunction with schlieren images, revealed that flame instability is enhanced with higher initial pressure and hydrogen ratios, while higher equivalence ratios inhibit instability.

Computational investigation of equivalence ratio effects on performance and emissions in a dual-fuel homogeneous charge compression ignition (HCCI) engine with 90% n-dodecane and 10% ethanol

As the automotive industry seeks environmentally friendly and fuel-efficient solutions, a significant transformation towards the Dual Fuel Homogeneous Charge Compression Ignition (DF-HCCI) Engine. It emerges as a highly promising and revolutionary approach to internal combustion engines. This paper provides a comprehensive Computational Investigation on the influence of Equivalence Ratio (ϕ) variations on the performance and emissions of a DF-HCCI engine, utilising a blend of 90% n-dodecane (premix) and 10% ethanol (spry injection). Through simulations, the study explores ϕ ranging from 0.45 to 0.70, providing a detailed analysis of their impact on crucial engine parameters. Results indicate a non-monotonic behaviour in piston work, with an initial increase followed by a decline beyond an optimal point due to incomplete combustion. CO emissions exhibit a general increase with higher ϕ, attributed to reduced air availability for complete combustion. CO2 emissions display a non-monotonic trend, peaking at ϕ = 0.5, indicative of a complex interplay between combustion temperature and completeness. NOx emissions decrease with rising ϕ, as higher temperatures favour NOx formation. Soot emissions decrease with increasing ϕ , correlating with lower combustion temperatures. This investigation provides insights into the relationship between ϕ and DF-HCCI engine characteristics, offering an optimising engine efficiency and mitigating environmental impact.

Lean Biogas-Air Mixture Combustion on Porous Burner with a Flamethrower Ignition System

ABSTRACT Combustion in a porous medium burner is an effective technology that deals with low heat capacity fuels, producing low emissions of pollutant gases. Experimental investigations of filtration combustion were carried out on a laboratory-scale prototype developed by our research group. This prototype is outfitted with a novel spark ignition system attached in the middle of the reactor, which does not change the porous medium properties because it works as a flamethrower. The ignition system produces a flame front into the porous matrix that quickly reaches the operational combustion temperature of 1200 K. By applying pure methane and biogas with different CO2 contents (15% − 40%) for combustion processes, the influence of equivalence ratio, gas flow velocity, energy extraction efficiency and NOx emissions was evaluated. Experimental results such as temperature profiles, reaction stability and flammability limits also have been evaluated. According to the operational parameters tested in this study, this prototype setup presented a low time-consuming process to reach the temperature of combustion, almost ten times faster than those with electrical resistance. Furthermore, the prototype was capable of operating at an equivalence ratio of 0.4 and gas flow velocity of 0.2 m/s, maintaining high CO2 content in the fuel, to reach NOx emission values lower than 1.0 ppm.

Study on the mechanism of nitrogen conversion in NH3-doped methane premixed flame based on multi-spectral analysis methods

It is essential to obtain the in-situ key radicals and components in the combustion process of NH3 oxidation to reveal the volatile nitrogen conversion mechanism. In this work, multi-spectral analysis methods, including image spectroscopy, Tunable diode laser absorption spectroscopy (TDLAS), and plane laser-induced fluorescence (PLIF) were used to obtain the spatial distribution characteristics of the main excited radicals (C2*/CH*/CN*/OH*), H2O, and NO in NH3-doped methane flames, respectively. Furthermore, the kinetic simulation was combined to obtain the key reactions and main pathways of nitrogen conversion. The experimental results showed that when the concentration of NH3 was low, the NO generated in lean flame was less than that in rich flame, which was more than that in rich flame when the concentration of NH3 was high. NH3 also promoted the formation of H2O in flames. The image spectral intensity of CN* had a significant linear relationship with the CN concentration obtained by simulation, indicating that CN* was mainly generated by CN thermal excitation. The results of sensitivity and path analysis indicated that rich flame contributed to the reaction of N-species with H and that high NH3 concentration promoted the conversion of NH2 to HNO. With increasing NH3 concentration and equivalence ratio, the proportion of CH3 conversion to C2H6 was enhanced, while the proportion of CH3 oxidized decreased. This work reveals the mechanism of volatile nitrogen (NH3) conversion and the influence of equivalence ratio and NH3 concentration on it, which provides theoretical guidance for NOx emission reduction.

Intrinsic instabilities of hydrogen and hydrogen/ammonia premixed flames: Influence of equivalence ratio, fuel composition and pressure

Premixed lean hydrogen-air flames exhibit instabilities due to hydrodynamic instabilities but also thermo-diffusive instabilities. However, in the case of ammonia/hydrogen blends, the effect of ammonia addition on instabilities is still unclear. To investigate intrinsic instabilities in premixed ammonia/hydrogen-air flames, a parametric study of laminar premixed flames is performed for different fuel contents, from pure hydrogen (H2) to a blend of 40% of H2 and 60% of ammonia (NH3) in volume, equivalence ratios (0.4 to 1.0) and pressures (1 and 10 bar) to investigate thermo-diffusive instabilities. Numerical simulations using detailed chemistry are performed where an initial perturbation is set to disturb the planar flame front and to compute its growth rate. During the initial linear phase, the perturbation’s amplitude grows or decreases depending on the flame’s mixture propensity to be unstable or stable, respectively. At small times, the linear growth rate of the perturbation can be estimated and compared to theory. As expected, the maximum growth rate obtained in the linear phase depends on the mixture’s equivalence ratio, fuel ratio, and pressure. Ammonia addition leads to a reduced peak growth rate, likely due to lower reactivity leading to a higher Zel’dovich number. Very lean mixtures (equivalence ratios of 0.4 and 0.5) are thermo-diffusively unstable, regardless of the ammonia content, due to hydrogen’s preferential diffusion.

Investigation on geometric throat matching characteristics of variable geometry rocket-based combined cycle combustor

One of the most effective ways to realize multi-mode and high-performance matching operation of rocket-based combined cycle (RBCC) engine is to adopt a variable geometry combustor. In this study, direct-connect experiments and three-dimensional numerical simulations were used to investigate the matching characteristics between the isolator and the geometric throat of the variable geometry rocket-based combined cycle combustor under Ma 6 condition. The influences of equivalence ratio and geometric throat height variations on the combustor matching characteristics were obtained. The study results show that: (1) The pressure in the combustor and the outlet pressure of the isolator increase gradually with the increase of equivalence ratio, which causes the pre-combustion shock train position in the isolator to move forward gradually. Meanwhile, the combined injection of secondary fuel with the isolator and the pylon is beneficial to the improvement of combustor pressure, thus further improving the engine performance. (2) Different geometric throat heights have a substantial impact on the isolator and combustor matching when the equivalent ratio of the combustor is fixed. Under the conditions of Ma 6 operating at an altitude of 24 km inflow, the starting position of the pre-combustion shock train in the isolator is precisely at the isolator entrance, and the corresponding geometric throat height is 2.10H. The isolator and the combustor can complete matching operation at this point which the geometric throat height is the minimal throat height for Equivalent ratio = 1.0. (3) The reduction in geometric throat height can result in an increase in combustor pressure but a loss in combustor heat release and combustion efficiency of fuel combustion, which are reduced by 21.1% and 7.2% respectively. (4) The heat release and combustion efficiency in the combustor will decrease with a decrease in equivalent ratio at the minimal throat height condition where the isolator and the combustor can complete matching operation. This happens when the equivalent ratio and the geometric throat height change synergistically.

Influence of equivalence ratio and H2 blended ratio on explosion propagation characteristics of DME/H2 blended gas in closed narrow space

To reveal the explosion risk and propagation law of dimethyl ether (DME)/hydrogen (H2) blended gas, the explosion propagation characteristics of DME/H2 blended gas under different equivalence ratio (Φ) and hydrogen blended ratio (λ) was investigated based on experimental research and theoretical analysis. The results show that the peak overpressure (Pp), the peak pressure rise rate (dP/dt)p and the peak shock wave propagation velocity (Vp) show an increasing and then decreasing trend with the increase of Φ, and reach the maximum at Φ = 1.0. The effect of a little addition of H2 on the explosion hazards of blended gas is small, but when λ > 10%, the explosion hazards increase significantly. The magnitude of increase of Pp, (dP/dt)p and Vp is different with the increase of λ. Compared with the enhancement effect on Pp and (dP/dt)p, the enhancement effect on Vp is more obvious with the continuous blend of H2. Comprehensive analysis of the thermodynamic and chemical kinetic parameters of H2, the chemical kinetic parameters of H2 play a dominant role in the explosion risk of hydrogen-blended gases.

Lift-off behaviors of the partially-premixed jet flame in a supersonic vitiated coflow

Achieving fast and efficient combustion is considered as the primary difficulty in overcoming the high-Mach-number scramjet. A novel injection strategy with coflows has been proposed to improve the combustion efficiency, however, the inherent dynamics that drives the partially-premixed combustion is still not very clear. Numerical simulation is adopted to investigate the supersonic partially-premixed flame formed by the coflows of inner jet and annular vitiated air. Validation of numerical results has been conducted by comparing with the experimental data, and the predicted values show a reasonably good agreement with that in the experiments. Numerical results indicate that the supersonic jet flame is stabilized with a certain of lift-off height, with the dynamics balance of flow transport and flame propagation in the autoignition-dominated flame base. According to the flame index, the supersonic reactive flow fields are divided into three stages, including the no reaction region, premixed flame region and diffusion flame region. On this basis, the influence of equivalence ratio and injecting velocity of inner jet on the lift-off behaviors of jet flame, is explored by a series of contrastive analysis.

Influence of equivalence ratio on turbulent burning velocity and extreme fuel consumption rate in lean hydrogen-air turbulent flames

• The extreme fuel consumption rate (FCR) exhibits a high degree of universality. • The time-averaged extreme values are very close to the peak critically strained laminar flames. • This work supports a corner-stone hypothesis of the leading point concept of premixed turbulent burning. Unsteady three-dimensional Direct Numerical Simulations of seven statistically one-dimensional, planar, highly turbulent, complex-chemistry, lean H 2 -air flames are performed using either mixture averaged or equidiffusive model of molecular transport. The equivalence ratio is varied from 0.35 to 0.70 and the Karlovitz number Ka is varied from 3 to 565. Normalized turbulent burning velocities U T /S L are strongly increased when using the mixture-averaged model, with an increase by a factor of 4.1 being documented even at Ka as high as 565. Here, S L is the laminar flame speed. Moreover, the increase in U T /S L is significantly more pronounced in leaner flames, which are characterized by a thinner reaction zone and a larger Zel’dovich number. Furthermore, U T /S L is increased by the turbulence length scale. The extreme (maximum over the computational domain at a single instant) local values of fuel consumption rate (FCR) exhibit a high degree of universality, i.e., in all studied cases and at all instants, these rates are close to the peak values of FCR obtained from the counterpart critically strained, twin, counter-flow laminar premixed flames. This finding appears to directly support a corner-stone hypothesis of the leading point concept of premixed turbulent burning, thus, suggesting the use of characteristics of the critically strained laminar premixed flames as input parameters for models of turbulent combustion of lean H 2 /air mixtures.

Experimental Studies on the Explosion Behaviors of Premixed Hydrogen-Air Mixtures in a Narrow Channel.

Premixed hydrogen–air explosion experiments were carried out in a 1000 mm × 50 mm × 10 mm half-open narrow channel, concerning with the influences of equivalence ratio and ignition position on explosion behaviors. Experimental phenomena were different from explosion in large space. The results indicated that when ignited at the closed end of the channel, three overpressure peaks appeared, caused by the rupture of the film, Helmholtz Oscillation, and the flame-acoustic interaction, respectively. As the equivalence ratio of the hydrogen–air mixtures varied from 0.6 to 1.6, the peak overpressure first increased and then decreased. The maximum peak overpressure occurred at ϕ = 1.2. The hydrogen flame would develop into the plane tulip structure without the influence of the end wall. With the ignition position moved to the open end, overpressure wave and flame oscillated significantly. Compared with other ignition positions, the minimum value of Pmax was obtained at IP950. Based on the explosion behaviors in the narrow channel, it was concluded that the closer the ignition was to the open end, the easier the oscillation was to be formed, the smaller the explosion hazard was.

Process modelling and thermodynamic performance optimization of biomass air gasification fuelled with waste poultry litter pellet by integrating Aspen plus with RSM

This present study investigates the processing of waste poultry litter pellet biomass for the generation of enriched hydrogen syngas using biomass gasifier. Modelling of biomass gasifier was performed in Aspen Plus and Model validation was done using four different agricultural waste biomass with the experimental result and, a good agreement was attained. Sensitivity analysis was performed in which the influence of equivalence ratio (ER), gasification temperature, and moisture content on the producer gas (PG) composition, gas yield, H2/CO ratio, cold gas efficiency (CGE), and the higher heating value (HHV) were investigated. Furthermore, RSM has been employed for the multi-objectives optimization of the variable gasification parameters. R2 value obtained from ANOVA for H2, CGE, and HHV are 92.26%, 93.2%, and 92.4% respectively. The optimized values of H2, CGE, and HHV are 0.21, 57.67%, and 5.71 MJ/Nm3 respectively corresponding to temperature at 830.30 °C, equivalence ratio 0.2, and moisture content 16.36%. The desirability value obtained was around 0.87.

Potential of Semi-Empirical Heat Transfer Models in Predicting the Effects of Equivalence Ratio on Low Temperature Reaction and High Temperature Reaction Heat Release of an HCCI Engine

In this paper, the influence of equivalence ratio on the low-temperature reaction heat release (LTR-HR) and high-temperature reaction heat release (HTR-HR) of homogeneous charge compression ignition engine has been experimentally and numerically examined. The numerical study was performed using zero-dimensional (0D) single-zone model by considering the chemical kinetic of fuel combustion. Annand, Woschni, Hohenberg, Chang (Assanis), and Hensel semi-empirical heat transfer models were employed in the 0D single-zone simulations. In this study, the in-cylinder pressure, rate of heat release, LTR-HR and HTR-HR were investigated. The Hensel heat transfer model was the only model that predicted the combustion in all of the operating conditions. The Hohenberg model properly recognized the effects of equivalence ratio changes on the HTR-HR.

Air-steam gasification of biomass based on a multi-composition multi-step kinetic model: A clean strategy for hydrogen-enriched syngas production

Biomass, as a renewable energy source, has high potential for supplying the energy needs of modern societies. Gasification is a thermochemical route for converting biomass into combustible gas at high temperatures. The main purpose of the present study was to develop an Aspen Plus model of air-steam gasification of biomass (sawdust) to predict the gasification characteristics and performances. The prediction capability of the model was evaluated by comparison with experimental data obtained in a fluidized bed biomass gasifier. First, the influence of gasification temperature on gas composition, product yields and gasifier performances was investigated. The biomass feeding rate and air flow rate were set at~0.445 kg/h and 0.5 Nm3/h, respectively, while the gasifier temperature was varied between 700 °C to 800 °C. With the increase of temperature, the gas yield (DGY) increased steadily from 1.72 to 2.0 Nm3/kg, while the HHV of the produced syngas (HHVgas) increased initially from 5.38 to 5.73 MJ/Nm3 and then decreased to 5.69 MJ/Nm3. After determining optimal temperature (800 °C), the influence of equivalence ratio (ER) and steam/biomass ratio (S/B) on gasification characteristics, dry gas yield (DGY) and tar yield (TRY) was studied. As ER increased from 0.19 to 0.23, TRY decreased from 9.13 g/Nm3 to 8.45 g/Nm3. In contrast, DGY initially increased from 2.02 Nm3/kg to 2.43 Nm3/kg as ER increased from 0.19 to 0.21 and then dropped to 2.24 Nm3/kg at ER of 0.23. An increase in S/B from 0.61 to 2.7 also resulted in a slight increase in HHVgas; however, TRY showed a decreasing trend (from 9.65 g/Nm3 to 8.95 g/Nm3). The results showed that the model developed in this paper is a promising tool for simulating the biomass gasification at various operating conditions.

Experimental and numerical study on the influence of equivalence ratio on key intermediates and silica nanoparticles in flame synthesis

Tetramethylsilane is a precursor often used for the production of flame-synthesized silica nanoparticles or coatings. This study investigates the chemical reaction mechanism of tetramethylsilane in a series of H2/O2/Ar low-pressure (p = 30 mbar) flames from fuel-lean to slightly fuel-rich flame conditions (φ=0.8, 1.0 and 1.2). Mole fraction profiles are obtained by molecular-beam mass spectrometry. The experimental data are compared to simulations using a recently published reaction mechanism. The present study reveals the influence of the flame composition on the depletion of the precursor TMS, the formation of its main carbon-containing products (e.g. CO2 and CO) and the main silicon-containing intermediates (e.g. Si(CH3)3(CH2)OO), Si(OH)4, SiO2, Si4O10H4) appearing along the routes of particle formation. TEM images of synthesized particles reveal that the nanoparticles obtained from the gas-phase synthesis are spheres with a low degree of agglomeration. The particle size distribution appears to be dependent on the equivalence ratio of the synthesis flames and the changes can tentatively be traced to different particle formation pathways. The data set provided in this work can serve a basis for improvements to the reaction mechanisms of the Si/C/H/O system that are urgently needed to improve particle synthesis processes.

Kinetic modeling of biomass gasification and tar formation in a fluidized bed gasifier using equivalent reactor network (ERN)

A chemical kinetic based simulation model of a bubbling fluidized bed biomass gasifier has been developed using an Equivalent Reactor Network (ERN). The pyrolysis zone is modeled using a thermodynamic equilibrium model and a kinetic-controlled perfectly stirred reactor (PSR) placed in succession. The gasification zone and the freeboard are simulated as perfectly stirred reactor (PSR) and plug flow reactor (PFR), respectively. A detailed chemical reaction mechanism is used to describe the chemistry of reaction during devolatilization and gasification stages. The formation and evolution of gaseous and tar species in different zones of the gasifier are estimated and the major reaction paths have been identified. The influence of equivalence ratio (ER) on the gasifier performance and tar species formation has been studied. Out of the three ERs considered (0.27, 0.24 and 0.19), the best performance of the gasifier is exhibited at ER = 0.24 in terms of cold gas efficiency.

Experimental and numerical study on combustion characteristics of super lean H2–O2 premixed laminar flame in argon atmosphere

This paper presents an experimental and numerical research on super lean premixed H2–O2 flames under argon atmosphere in a combustion bomb with constant volume, and applied CHEMKIN to perform simulation for the flames. The high-speed schlieren photography is employed to record the development process of expanding spherical flame, and laminar burning velocities of super lean premixed H2–O2–Ar flames with different back pressures under argon atmosphere are calculated, and the influence of equivalence ratio and initial pressure on flame instability is analyzed, and the mass burning fluxes are calculated by simulation and flame structure and rate of elementary reactions is analyzed. The results show that, with equivalence ratio decrease, laminar flame velocity and mass burning flux will decline; with initial pressure increase, laminar flame speed will decline and mass burning flux will increase. For flame stability, when initial pressure rises, the hydrodynamic instability on hydrogen flame surface is enhanced, more easily resulting in cellular instability. As pressure rises, Lewis number and density ratio under each pressure will approximate to constant values, therefore, flame thickness is the main factor influencing flame instability when initial pressure rises. When equivalence ratio decreases, unequal diffusion instability often occurs easily under leaner conditions during flame development. According to simulation results, the laminar flame velocity is the result of interaction between the chain branching reaction and the chain termination reaction and the changes of equivalence ratio will affect above two reactions. For flame structure, the results show that when equivalence ratio is small, chemical reaction velocity of hydrogen gas burning will decline and reaction zone will enlarge, besides, H and OH concentration will also decline. As equivalence ratio decreases, the maximum H mole fraction constantly declines, which is consistent with the changing trend of laminar flame velocity with equivalence ratio.

Investigation of the impact of the reactants temperature and equivalence ratio on the outlet mixture temperature, velocity and mole fraction for the combustion of the carbon monoxide and nitrous

In the present study, a numerical code is used for three-dimensional simulation of non-premixed form of the combustion of nitrous-carbon monoxide mixture. This code includes standard K-ε as turbulent model and Probability Density Function (PDF) as thermo-chemistry approach. Ten species i.e. nitrous, carbon monoxide, carbon dioxide, nitrogen, nitrogen monoxide, atomic oxygen, oxygen, ozone, cyanate and atomic carbon are assumed contributing in this reaction. For the validation of model, experimental measurement of previous studies are applied. The influence of equivalence ratio and inlet gases temperature, on outlet mixture velocity, temperature and outlet species mole fraction are obtained in the form of charts for wide ranges, which was not clearly obtained in previous works. These charts are useful for designer of these systems. Results indicate, when Ø ≥ 0.15 N2O is decomposed completely and the maximum mole fractions for O2(approximately 0.27), N2 (approximately 0.77) and O3 (depending on the temperature) are obtained. Furthermore, it was found the mole fraction of the outlet carbon dioxide and dimensionless temperature of the outlet mixture are maximum at equivalence ratio equal to unity and if the temperature of the inlet gases is kept constant and the equivalence ratio reduces, the outlet carbon monoxide mole fraction decreases.

Partition of Cu and Pb in a Two-Stage Fluidized-Bed Waste Gasification System

In this study, a two-stage fluidized-bed gasification system was used to determine the distribution of heavy metal contaminants in simulative waste and evaluate the effect of the bed operating temperature, Equivalence ratio (ER), and Steam/Biomass ratio (S/B) in stage 1. The heavy metal concentrations in bed materials and fly ash were measured in two stages. The results show that as the operating temperature of stage 1 increased, the quantity of heavy metals entrapped by stage 1 bed material decreased, while that captured by stage 2 bed material increased. The less volatile Cu was mostly entrapped in stage 1 bed material. The ER and S/B results show that increasing the ER and S/B caused a slight increase in the concentrations of heavy metals entrapped in stage 1 and stage 2 bed materials. However, the influences of ER and S/B were less than that of temperature. The major factors affecting the heavy metal distribution were the operating temperature and the heavy metal volatility. Stage 2 bed material was able to entrap gaseous heavy metals or particles containing heavy metals by particle filtration and chemical adsorption. Thus, the heavy metals (Cu and Pb) had a downward trend after passing through stage 2.

A novel two-stage enriched air biomass gasification for producing low-tar high heating value fuel gas: Pilot verification and performance analysis

A novel two-stage gasifier, consisting of a fluidized bed gasifier and a swirl-melting furnace, was proposed and built to gasify biomass with low ash melting temperatures into clean fuel gas. Improvements of the two-stage gasification in gas upgrading, tar removal and ash separation were confirmed by characteristic analysis of gas, tar, ash and slag. Influence of equivalence ratio (ER), oxygen distribution and gasifying agent were assessed for process optimization. Refined gas with a LHV up to 11.1 MJ/Nm3 and a tar content lower than 1 g/Nm3 was produced. Ash was completely vitrified with a high conversion of fixed carbon and volatile, resulting in a cold gas energy fraction of approximately 80%. Increasing ER promoted gas production but limited energy conversion efficiency and gas LHV. Proper oxygen distribution among the two stages was beneficial to decrease energy loss and increase gas quality. Increasing oxygen percentage of gasifying agent enhanced combustible gas content and improved overall gasification efficiency.

Experimental study on the pre-evaporation pulse combustion of liquid fuel within a porous medium burner

Experimental studies are conducted to investigate the behaviors of pre-evaporation pulse combustion of liquid fuel within a porous medium burner. A controllable electric preheating system is developed to enhance the evaporation of droplet spray and auto-ignite the flammable vapor without second ignition. Base on the stability analysis of the preheating temperature and the calibration of the fuel flow, the characteristics of the pulse flame in a single injection duration are observed in detail. The thermal characters in terms of the temperature distribution are investigated, and the influences of equivalenceratio and the air flow on the temperature are discussed in the present work. Experimental results show that the pulse flame propagates in the manner of four-phases,i.e., the quasi-steady flame, the transient flame, the free flame and the preheating flame. While the quasi-steady flame keepsin a moving state with speed around 0.1 mm/s magnitude order, the propagation of transient flame is similarto a deflagration process with a significant speed of 1.2 m/s magnitude order. The minimum preheating temperature for full evaporation and sustainable combustion is necessary about 1023 K, and the maximum flame temperature achieves up to around 1300 K. As the equivalence ratio increases, an evident temperature improvement and a larger high temperature zone appear, however the propagation speed of the quasi-steady flame almost keeps constant. An increasing air flow plays a limited effect on the maximum temperature while it actually leads toa faster speed of the high temperature zone.