Unburned Gas Research Articles

Enhanced DDT mechanism from shock-flame interactions in thin channels

We show experimentally and numerically that when a weak shock interacts with a finger flame in a narrow channel, an extremely efficient mechanism for deflagration to detonation transition occurs. This is demonstrated in a 19-mm-thick channel in hydrogen-air mixtures at pressures below 0.2 atm and weak shocks of Mach numbers 1.5 to 2. The mechanism relies primarily on the straining of the flame shape into an elongated alligator flame maintained by the anchoring mechanism of Gamezo in a bifurcated lambda shock due to boundary layers. The mechanism can increase the flame surface area by more than two orders of magnitude without any turbulence on the flame time scale. The resulting alligator-shaped flame is shown to saturate near the Chapman–Jouguet condition and further slowly accelerate until its burning velocity reaches the sound speed in the shocked unburned gas. At this state, the lead shock and further adiabatic compression of the gas in the induction zone gives rise to auto-ignition and very rapid transition to detonation through merging of numerous spontaneous flames from ignition spots. The entire acceleration can occur on a time scale comparable to the laminar flame time.

Two-dimensional laboratory-scale DNS for knocking experiment using n-heptane at engine-like condition

A two-dimensional laboratory-scale DNS of a knocking experiment using a stoichiometric n-C7H16/O2/Ar mixture at engine-like condition with the latest reduced SIP isooctane kinetics was conducted. A compressible reactive flow solver PeleC combined with an in-house efficient chemical kinetics solver MACKS was used. The results of DNS were compared with a “knocking experiment by Kyushu University” conducted in a 14 × 14 × 80 mm rectangular constant volume chamber for the same mixture at an initial temperature of 480 K and pressure of 0.33 MPa. The comparisons showed the present DNS with the latest, validated reduced chemical kinetics successfully reproduced the knock onset timing within an error of 2% as well as the overall features of the experimental observations seen in the Schlieren images such as flame shape transitions, pressure history, and the characteristic faint increase in pressure due to the flame front attachment with the chamber wall. In addition, the present DNS captured that the cool flame ignition occurred homogeneously but accompanied by the rapid formation of density gradients vertical to the side walls in the unburned gas region.

Performance, emissions and end-gas autoignition characteristics of PREMIER combustion in a pilot fuel-ignited dual-fuel biogas engine with various CO2 ratios

Biogas, a renewable and alternative energy, has recently gained attention as an environmentally friendly fuel for power generation in internal combustion (IC) engines. This study aimed to investigate the effect of the carbon dioxide (CO2) to methane (CH4) ratio in a dual-fuel gas engine. It is known that gaseous fuel combustion at high loads is accompanied by knocking if an appropriate combustion controlling strategy is not applied. Therefore, premixed mixture ignition in the end-gas region (PREMIER) combustion was proposed under high load conditions. Experiments were carried out using a dual-fuel gas engine under supercharged conditions, with an intake pressure of 200 kPa. Simulated biogas consisting of CH4 and CO2 was used as a primary fuel and diesel was used as a pilot fuel. The pilot fuel injection timing was varied during the experiments. The indicated mean effective pressure (IMEP) and thermal efficiency increased as injection timing was advanced. With the addition of CO2, the thermal efficiency of PREMIER combustion was slightly increased, although the IMEP was slightly decreased. The unburned gas temperature for PREMIER combustion increases as a function of the CO2 content of the mixture. Due to compression by flame propagation, high unburned gas temperatures in dual-fuel gas engines are important for achieving autoignition inside the end-gas region under PREMIER combustion conditions.

Numerical simulation of the influence of pipe length on explosion flame propagation in open-ended and close-ended pipes.

The pipeline length exerts great influence on flame propagation characteristics, Realizable model and Premixed combustion model were used to study the influence of pipe length on propane-air explosion flame in open-ended and close-ended pipes. Using the numerical model verified by experiments, the changes of flame structure and flame propagation speed are studied. The result showed that the Realizable model was in good agreement with the experimental results. It also proved that the reflected wave produced a strong interference on the flame front, which promoted the formation of tulip flame. Besides, some obvious vortices were usually generated in the burned gas after the tulip flame formed, which will affect the flow field around the flame front and thus exert influence on the flame structure. The formation mechanism of tulip flame as well as the flame self-acceleration is different in open-ended and close-ended pipes. In close-ended pipes, the reflection wave at the pipe end and the reflection-induced countercurrent both promote the formation of tulip flame. As the flame propagates to the pipe end, the flame propagation is inhibited by the compression wave formed by the rapid expansion of combustion products under high temperature. While, in open-ended pipes, the turbulence induced by the opening at the pipe end is the main cause of tulip flame formation. The flame acceleration depends on the combustion reaction of unburned gas, so the velocity of flame propagation continues to increase. Generally, the maximum flame propagation velocity in the open-ended pipe is larger than that in the close-ended pipe.

Performance improvement of turbocharged SI engine by post-oxidation enhancement in exhaust gas in-homogeneity

In this research, the improvement of mixing and pulsation in exhaust manifold with a design and implementation of bypass adapter at exhaust port were deeply investigated. This in-turn can improve the post-oxidation phenomena and hence emissions and engine performance could be enhanced. This research investigation includes 1-D, 3-D simulations and experimental validation on a 4-cylinder turbocharged spark ignition (SI) engine. Firstly, the 1-D and 3-D simulation models were developed and calibrated with the experimental results. Then, the simulations were used for the detailed investigation of mixing and pulsation in exhaust manifold with and without bypass adapter. Thereafter, experimental test for the post-oxidation were conducted with and without consideration of the bypass adapter and results were compared. From the simulation and experimental results, it was proven that by using bypass adapter at the exhaust port, the mixing of exhaust gas species was observed to be significantly improved to some extent. Also, the unbalance between exhaust port and turbocharger upstream gas species were reduced. This also reduced the exhaust gas pulsation. By the improvement of mixing between scavenged O2 and unburned gas species, the post-oxidation reaction was also noted to have improved and consequently the emissions and turbo-speed were found to be better that led to an improved IMEP and thermal efficiency of the engine.

A computational analysis of strained laminar flame propagation in a stratified CH4/H2/air mixture

Propagation of a H2-added strained laminar CH4/air flame in a rich-to-lean stratified mixture is numerically studied. The back-support effect, which is known to enhance the consumption speed of a flame propagating into a leaner mixture compared to that into a homogeneous mixture, is evaluated. A new method is devised to characterize unsteady reactant-to-reactant counterflow flames under transiently decreasing equivalence ratio, in order to elucidate the influence of flow strain on the back-support effect. In contrast to the conventional reactant-to-product configurations, the current configuration is more relevant to unsteady stratified flames back-supported by their own combustion products. Moreover, since H2 distribution downstream of the flame is known to play a crucial role in back-supported CH4/air flames, the influence of H2 addition in the upstream mixture is examined. The results suggest that a larger strain rate leads to a larger equivalence ratio gradient at the reaction zone through increased flow divergence, which amplifies the back-support. Meanwhile, since H2 addition in the upstream mixture does not affect the downstream H2 content, the relative increase in the consumption speed, i.e. the back-support, is suppressed with larger H2 addition. Especially, when the upstream H2 content decreases with the equivalence ratio, the H2 preferentially diffuses toward the unburned gas, which mitigates H2 accumulation in the preheat zone and further weakens the back-support.

Combined isochoric and isobaric acquisition methodology for accurate flame speed measurements from ambient to high pressures and temperatures

The present paper addresses measurement techniques of the most important fundamental property of a combustible mixture, the laminar flame speed. The accurate determination of this parameter has been investigated carefully using two different approaches: the constant pressure method based on the flame front trajectory obtained by means of a Schlieren optical technique, and the constant volume method based only on the pressure-time history recorded during the combustion process. Methane/air flames are selected, because they are relevant for many technical applications and believed to be well understood. Measurements were performed using two high-pressure, high-temperature constant volume vessels at RWTH and ICARE. First, uncertainties stemming from experiments are quantified, and the different sources of errors are identified. Second, the assumption that the unburned gas is compressed isentropically due to the burned gas expansion is verified experimentally for the first time to the authors’ knowledge. More importantly, it was found that combining the two approaches can provide high-fidelity data w.r.t. stretch, radiative heat loss, and instabilities. The data will be very helpful for mechanism development and combustion modeling. Ideally, both approaches are applied simultaneously in the same vessel to obtain a high confidence level in the measured data. Finally, a methodology is proposed to provide flame speeds over a wide range of pressures and temperatures up to 14 bars and 620 K, close to engine-relevant conditions.

A comprehensive experimental and improved kinetic modeling study on the pyrolysis and oxidation of propyne

To improve our understanding of the combustion characteristics of propyne, new experimental data for ignition delay times (IDTs), pyrolysis speciation profiles and flame speed measurements are presented in this study. IDTs for propyne ignition were obtained at equivalence ratios of 0.5, 1.0, and 2.0 in ‘air’ at pressures of 10 and 30 bar, over a wide range of temperatures (690–1460 K) using a rapid compression machine and a high-pressure shock tube. Moreover, experiments were performed in a single-pulse shock tube to study propyne pyrolysis at 2 bar pressure and in the temperature range 1000–1600 K. In addition, laminar flame speeds of propyne were studied at an unburned gas temperature of 373 K and at 1 and 2 bar for a range of equivalence ratios. A detailed chemical kinetic model is provided to describe the pyrolytic and combustion characteristics of propyne across this wide-ranging set of experimental data. This new mechanism shows significant improvements in the predictions for the IDTs, fuel pyrolysis and flame speeds for propyne compared to AramcoMech3.0. The improvement in fuel reactivity predictions in the new mechanism is due to the inclusion of the propyne + HȮ2 reaction system along with ȮH radical addition to the triple bonds of propyne and subsequent reactions.

A direct numerical simulation analysis of turbulent V-shaped flames propagating into droplet-laden mixtures

Three-dimensional Direct Numerical Simulations (DNS) data has been used to analyse the gaseous phase combustion behaviour in a V-shaped flame configuration where fuel is supplied in the form of droplets such that an overall (i.e. liquid+gaseous) equivalence ratio of unity is maintained in the unburned gas. The analysis has been carried out for different initially mono-sized droplet diameters. A gaseous premixed V-shaped flame with the same flow conditions has been utilised to compare the flame propagation in V-shaped spray flames with a corresponding gaseous premixed flame case. It has been found that combustion in the gaseous phase mainly takes place under fuel-lean mode and the probability of finding fuel-lean burning increases with increasing droplet diameter. However, the mean equivalence ratio of the predominantly fuel-lean mixture increases with increasing axial distance from the flame holder. The presence of droplets has been found to give rise to dimples on the reaction progress variable isosurfaces, and the effects of droplet–induced flame wrinkling are reflected by the widening of the curvature probability density functions for large droplets. The heat release has been found to arise mainly from the premixed mode of combustion. Detailed analysis of reaction progress variable transport has been used to explain the mean variations of consumption speed and density-weighted displacement speed with the axial distance from the flame holder. The mean values of consumption speed, density-weighted displacement speed and turbulent burning velocity have been found to decrease with increasing droplet diameter. The flame speed statistics have been utilised to explain that the enhancement of the burning rate cannot be equated to the enhancement of the flame surface area in turbulent droplet-laden V-shaped flames.

A projection procedure to obtain adiabatic flames from non-adiabatic flames using heat flux method

Laminar burning velocity SL at elevated temperature Tu and its temperature dependence coefficient α in SLSL0=(TuTu0)α are important parameters for industrial applications. However, experimental systems with high unburned gas temperatures may encounter pre-dissociation, leading to significant data scattering in the measurements. To negate this, the present work proposes a projection procedure to obtain adiabatic flame parameters at various unburned gas temperatures using non-adiabatic flames on a heat flux burner, by which the preheating can be achieved within much shorter time scale than, e.g., in conventional spherical flame methods, and the advantage of good data consistency in the heat flux method is kept. Burning velocity experiments were carried out with CH4+air atmospheric flames covering Tu = 298–473 K, and the results show good agreement with the proposed projection equations. OH* spontaneous emission profiles were measured, indicating that the projection may extend to other flame characteristics. Uncertainty of the projection process was evaluated and comparisons were made with six popular kinetic mechanisms: GRI-Mech, FFCM-1 mech, Konnov mechanism, Glarborg mechanism, San Diego mechanism and Aramco mechanism. It is found that the simulated coefficients α are higher than experimental data especially at rich conditions; this is also found for literature values of high unburned gas temperature experiments. Possible reasons for this divergence are discussed.

Kinetic modelling of combustion in a spark ignition engine with water injection

This work models the impact of direct water injection on the combustion process in a spark ignition engine. It uses a two-zone kinetic model coupled with detailed combustion chemistry to highlight the thermodynamic and chemical-kinetic interactions between gasoline combustion and water injection. The modelling results agree closely with measurements from a highly boosted, direct injection gasoline engine.This study first proposes an approach to model the mass fraction burned (MFB) profile using a representative in-cylinder pressure trace. The derived MFB profile is then used as the input for a two-zone kinetic model. Within this model, predictive kinetic modelling is used to estimate the knock limited spark advance (KLSA) for a baseline engine operating condition without water injection and subsequently, for several conditions with water injection. Predicted KLSA values obtained using this method agree closely with measured results.Utilising the approach developed in this study, the modelled MFB profile at the baseline operating condition was found to be similar to that obtained at the condition with a water/fuel ratio (WFR) of 60%. This result is likely due to the competing and contrasting effects of reduced in-cylinder temperature versus more advanced combustion phasing at conditions with water injection. Further thermodynamic analysis shows that the charge cooling effect afforded by direct water injection is much greater than the dilution effect in terms of advancing the knock limited combustion phasing. Water injection also affects the kinetic processes that take place in the unburned gas zone, but mainly by altering the in-cylinder thermodynamic conditions – the injected water is not directly involved in the low temperature chemistry in the unburned gas zone, it simply acts as a collision partner.

Dynamics of explosion venting in a compartment with methane-air mixtures

A series of experiments on explosion venting of methane-air mixtures are performed to scrutinize the pressure evolution as well as the flame dynamics and morphology at various vent conditions. Specifically, a premixed flame is ignited at the center of a polycarbonate cylindrical compartment, with three various vent areas considered (with negligible vent relief pressure). As expected, the highest maximum pressure is observed in the case of the smallest vent area. For all three cases, the pressure evolution experiences two major peaks, associated with the instants (i) when the maximum flame front surface area in the chamber is reached and (ii) when an external explosion occurs due to venting of unburned gases, respectively. For the fuel-rich mixtures, a flashback is observed subsequent to the external explosion, constituting the key outcome of the present work. The flame tip velocities show two general trends, namely, exponential acceleration towards the vent, while a flame propagates towards the blocked side of the compartment with no acceleration, which is important to know in the fire/explosion safety applications.

Numerical simulation of hydrogen-air flame acceleration and detonation initiation in tubes equipped with arc obstacles of different chord lengths

Numerical simulation of hydrogen-air detonation characteristics in tubes equipped with arc obstacles of different chord lengths is carried out by using OpenFoam package. The results show the optimal chord length is half the diameter, in which the detonation wave propagates at a high velocity while maintaining small deflagration-to-detonation transition distance. Three different regimes were found in the flame acceleration and detonation initiation for different chord length: (1) For the small chord length, the flame experienced the transition from fingertip to tulip flame, then recovered to fingertip flame again until initiation. The detonation is caused by the hot spot formed by the spontaneous combustion of unburned premixed gas. (2) For the intermediate chord length, the tulip flame quenched by reverse flow will turn into fingertip flame under the jet effect of obstacles. Then, the fingertip flame is transformed into tulip flame again under the action of flow instability. The detonation is initiated by the fusion of two local hot spots produced by the coupling of tulip flame and diffraction wave. (3) For the large chord length, the flame propagates as a fingertip flame. The detonation is initiated by the explosion of the flame surface compressed by reflected wave and shock wave.

Evaluation of autoignition models for production control of a spark-assisted compression ignition engine

The drive to improve performance and efficiency of internal combustion engines has greatly expanded the degrees of freedom of engine systems. As efficiency objectives exceed the capability of traditional combustion strategies, advanced combustion modes are more attractive for production. These advanced combustion strategies typically add sensors, actuators, and degrees of freedom to the combustion process itself. Spark-assisted compression ignition is an efficient production-viable advanced combustion mode characterized by a spark-ignited flame propagation that triggers autoignition in the remaining unburned gas. This research focuses on autoignition modeling for spark-assisted compression ignition combustion phasing control. This work comprehensively evaluates several autoignition model structures and identifies the real-time production control implications of each. The candidate models include four ignition delay correlations, an ignition delay lookup, three polynomial regressions, and an artificial neural network. All are computationally feasible using production controllers, but the artificial neural network model represents autoignition phasing significantly better than the other options evaluated. The polynomial regressions were similar in error and exceeded the accuracy of ignition delay models. The low performance of the induction time integral–based models stems primarily from the exclusion of low-temperature heat release. The regression models are also exercised on an experimental engine dataset to identify the impact of engine phenomenon such as charge stratification on the performance of each model structure. The trends in the model performance as well as the magnitude of the error were similar when evaluated on both spark-assisted compression ignition simulation data and homogeneous charge compression ignition experimental data.

High-Momentum Jet Flames at Elevated Pressure, C: Statistical Distribution of Thermochemical States Obtained From Laser-Raman Measurements

Abstract A detailed investigation on flame structures and stabilization mechanisms of confined high momentum jet flames by one-dimensional (1D)-laser Raman measurements is presented. The flames were operated with natural gas (NG) at gas turbine relevant conditions in an optically accessible high-pressure test rig. The generic burner represents a full scale single nozzle of a high temperature FLOX® gas turbine combustor including a pilot stage. 1D-laser Raman measurements were performed on both an unpiloted and a piloted flame and evaluated on a single shot basis revealing the thermochemical states from unburned inflow conditions to burned hot gas in terms of average and statistical values of the major species concentrations, the mixture fraction and the temperature. The results show a distinct difference in the flame stabilization mechanism between the unpiloted and the piloted case. The former is apparently driven by strong mixing of fresh unburned gas and recirculated hot burned gas that eventually causes autoignition. The piloted flame is stabilized by the pilot stage followed by turbulent flame propagation. The findings help to understand the underlying combustion mechanisms and to further develop gas turbine burners following the FLOX concept.

Evolution of Surface Density Function in an Open Turbulent Jet Spray Flame

A three-dimensional Direct Numerical Simulation of an open turbulent jet spray flame representing a laboratory-scale burner configuration has been used to analyse the statistical behaviours of the magnitude of reaction progress variable gradient left| {nabla c} right| [alternatively known as the Surface Density Function (SDF)] and the strain rates, which affect its evolution. The flame has been found to exhibit fuel-lean combustion close to the jet exit, but fuel-rich conditions have been obtained further downstream due to the evaporation of fuel droplets, which leads to the reduction in the mean value of the SDF in the downstream direction. This change in mixture composition in the axial direction has implications on the statistical behaviours of the SDF and the strain rates affecting its evolution. The mean value of dilatation rate remains positive, whereas the mean normal strain rate assumes positive values where the effects of heat release are strong but becomes negative towards both unburned and burned gas sides. The mean values of dilatation rate, normal strain rate and tangential strain rate decrease downstream of the jet exit. However, the mean behaviours of displacement speed and its components do not change significantly away from the jet exit. The mean values of normal strain rate arising from flame propagation remain positive and thus act to thicken the flame. The mean tangential strain rate due to flame propagation (alternatively the curvature stretch rate) remains negative throughout the flame at all axial locations investigated. The mean effective normal strain rate assumes positive values throughout the flame and it increases in the downstream direction for the present case, which is consistent with the reduction in the peak mean value of the SDF in the axial direction. The mean effective tangential strain rate (alternatively stretch rate) assumes negative values throughout the flame at all axial locations.

Scaling of Second-Order Structure Functions in Turbulent Premixed Flames in the Flamelet Combustion Regime

The second-order velocity structure function statistics have been analysed using a DNS database of statistically planar turbulent premixed flames subjected to unburned gas forcing. The flames considered here represent combustion for moderate values of Karlovitz number from the wrinkled flamelets to the thin reaction zones regimes of turbulent premixed combustion. It has been found that the second-order structure functions exhibit the theoretical asymptotic scalings in the dissipative and (relatively short) inertial ranges. However, the constant of proportionality for the theoretical asymptotic variation for the inertial range changes from one case to another, and this value also changes with structure function orientation. The variation of the structure functions for small length scale separation remains proportional to the square of the separation distance. However, the constant of proportionality for the limiting behaviour according to the separation distance square remains significantly different from the theoretical value obtained in isotropic turbulence. The disagreement increases with increasing turbulence intensity. It has been found that turbulent velocity fluctuations within the flame brush remain anisotropic for all cases considered here and this tendency strengthens towards the trailing edge of the flame brush. It indicates that the turbulence models derived based on the assumptions of homogeneous isotropic turbulence may not be fully valid for turbulent premixed flames.

An analytical model for the transversely forced flame transfer functions of conical and V-flame dynamics

Heat release rate perturbations of two-dimensional asymmetric premixed slot flames subjected to transverse perturbations, so called flame transfer functions (FTFs), are theoretically studied in this paper. The proposed models of both the two-dimensional conical flame and V-flame are studied based upon the linear analysis. The flame front dynamic response under the transverse disturbance is captured and solved using the G-equation model. The analytical solution of the FTF is derived using different oncoming velocity perturbation models, in order to reveal the flame heat release rate response mechanism to the transverse disturbances. In the two-dimensional conical flame model, the flame front tip moves with the transverse perturbations, which in turn also affects the FTF. In the two-dimensional V-flame model, the flame front tips are intersected by the flame branches and the unburned gas boundaries; this also contributes to the different behaviours of the FTF. The linear flame tip dynamics and the explicit analytical models of the FTFs of both the conical flame model and the V-flame model are proposed and validated. Results show that the transverse disturbance propagation velocity model has a significant effect on the FTF. The movement of the flame tip is also affected by the transverse convection models.

Experimental Study on the Effect of Air Pollution Caused by Methane-Air Deflagration Characteristics

In order to study the effect of combustible gas cloud releasing from FPSO upper deck facilities deflagration characteristics on air pollution, a semi-open open test pipe system was built. By changing the initial conditions such as the obstacles length, distance between obstacles, section shape of obstacles and pipe system structure, the flame propagation mechanism and overpressure changing rules of methane / air deflagration were analyzed. As a result of that, the degree of sufficiency of methane combustion was analyzed, which could be seen as air pollution level. With the increase of the length of obstacle and decrease of the distance between obstacles, the induced turbulence increased, the compression effect of unburned gas became stronger, the combustion of combustible gas became more intense and sufficient, and the flame propagation speed and the maximum overpressure increased. The effect of square cross section was more obvious on inducing turbulence than that of rectangular cross section and circular cross section. The flame front was divided into many small flames by the pipe structure obstacle, and the flame front showed as a `spiny` shape. Under the effect of �spiny� flame, the methane combustion was more sufficient, and the maximum overpressure value was 3.1 times of the circular section obstacle condition. In conclusion, as the methane-air deflagration becoming more serious, although the overpressure and flame speed would be higher and the extent of damage to the surrounding facilities would be more serious, the air pollution causing by unburned gas would abate.

Effects of Acoustic Excitation on the Combustion Instability of Hydrogen-Methane Lean Premixed Swirling Flames.

Lean premixed flames are useful for low nitrogen oxide (NOx) emissions but more prone to induce combustion instability in gas turbines. Combustion instability of a lean premixed swirling flame (LPSF) with hydrogen–methane was investigated experimentally. The effects of hydrogen addition on combustion instability with equivalence ratios 0.75–1 were investigated with acoustic frequencies (90–240 Hz) and acoustic amplitudes (the ratio of velocity fluctuation to an average velocity of 0–0.5), respectively, which are characterized by the gain and phase of the flame describing function (FDF). The evolution of vortex and the flame morphologies were observed by the particle image velocimetry (PIV), intensified charge-coupled device (ICCD), photomultiplier tube (PMT), and Cassegrain optical systems. The global and local heat release fluctuations of the LPSF were shown by CH*/OH* chemiluminescence and temperature measurements. Results show that the FDF features maximum and minimum gain values in the acoustic frequency range of 90–240 Hz and reaches local maximum peaks at 110 and 180 Hz and local minimum peaks at 160 Hz. It can also be observed that varying velocity amplitudes (0–0.5) have greater effects on the gain and phase of FDF than changing equivalence ratios (0.75–1) for lean swirling flames. Higher velocity amplitudes more effectively intensified the compression of the flame length, which enhanced the mixing of the high-burning gas and the unburned gas, and then heat release fluctuations increased. However, it is more interesting that the effects of hydrogen addition on the combustion instability of the LPSF show a completely opposite phenomenon due to acoustic frequency under all experimental conditions. The FDFs were compared at typical frequencies of 140 and 180 Hz, and it was found that combustion instability enhanced with increasing hydrogen content at 140 Hz while weakened at 180 Hz. The flow field of PIV images shows that it is related to the location and development of vortices in the flame with varying acoustic frequencies. The intensity of OH*/CH* chemiluminescence, local temperature, and heat release rate show the same changing trend with the flame morphology for two acoustic parameters with the increasing hydrogen content in the LPSF. This directly affects the compression and curvature of the LPSF and thereby changes the mixture and temperature of the combustible gas, which influence the heat release fluctuation of the LPSF.