Higher Flame Speed Research Articles

The influence of textile materials on flame resistance ratings of professional uniforms

This study compares the flame speed of different textile materials employed in professional uniforms. Five different garments of aeronauts’ uniforms were analyzed (totaling 200 specimens submitted to flammability tests). Plain weaves and twill weaves composed by 100% CO; 100% PES; 67% PES/33% CO; 50% PES/50% WO; and 55% PES/45%WO were analyzed in the warp and filling directions. The flame speed of each material was determined, and differences in the flame propagation of the fabrics were identified. The lowest flame speed occurred for the material 50% PES/50% WO plain weave and weft direction (0.742 ± 0.140 m/s). The highest flame speed was 3.698 ± 1.806 cm/s for the material 67%PES/33%CO, plain weave and filling direction. Future experiments for reducing the fabric flammability of the uniforms could be related to more closed fabric constructions; mixtures with synthetic fibers to add functionality; changing the direction of the fabric; and changing the weight and torsion of its constituent yarns.

Experimental investigation of the hydrogen-rich offgas spark ignition engine under the various compression ratios

Hydrogen is gaining substantial attention from both public and industries for its promising characteristics as an alternative fuel for internal combustion engines. High flame speed, strong knock resistance, as well as zero carbon dioxide emission put hydrogen ahead of most other alternative fuels. The fast flame and low knock tendency are favorable traits for high compression ratio, which is a key enabler for high efficiency. In this study, engine experiments were conducted to investigate the combustion and emission characteristics of a high-compression ratio, single-cylinder, spark-ignition engine with hydrogen-rich gas mixture. The compression ratio was varied from 10:1 to 17:1 by modifying the piston bowl geometry. The engine load was adjusted through the air fuel ratio by changing the mass flow rate of the fuel gas while the intake throttle valve maintained at wide open position. The consequent excess air to fuel ratio was varied from 3.5 at the lightest to 1.0 at the highest load operation. Spark timing sweep was performed to determine the optimal timings at various load conditions. The highest compression ratio in the present study, 17.0, yielded the highest indicated thermal efficiency, which was 51% at medium load condition. High and low load operations exhibited lower thermal efficiencies, with the estimated excess air to fuel ratio approaching 1.0 and 3.5, respectively. The optimal spark timings of the high load conditions under high compression ratios were retarded to top-dead center or later to avoid backfire and pre-ignition. Results of efficiency loss analysis show that high-temperature combustion is the major contributor to efficiency reduction at high load conditions, whereas the gas exchange process and elongated burn duration were the largest contributors at low load conditions.

Vapour Cloud Explosions - The Evidence for Deflagration to Detonation Transition

Approximately forty years ago, it was realised that the generation of high flame speeds would result in damaging pressures being produced in vapour cloud explosions (VCEs). At the time, however, it was not clear how high flame speeds could be generated in VCE. Research in the 1970s and 1980s showed that if a vapour cloud engulfed a region of congested process pipework, the flame could accelerate to levels where damaging pressures were produced. Since that time, the accepted basis for assessing VCE hazards has been to consider congested process regions as potential locations of deflagrations, with pressure reducing as the explosion propagated away from the region. However, this was not sufficient to explain the evidence found following the Buncefield explosion in the UK (2005). The research conducted following Buncefield, the most extensive for any VCE, led to the conclusion that the incident involved a transition from a deflagration to a detonation (DDT). In reaching this conclusion, several possibilities were considered and dismissed, including a speculative explosion mechanism not previously observed that involved ignition by radiation of dust particles ahead of the flame. Taken in combination with more recent experimental studies, they indicate that DDT was not just an explanation for Buncefield, but likely has a much wider relevance. The evidence obtained from Buncefield and subsequent research supporting DDT will be reviewed.

Hydrogen flame propagation inside an obstructed chamber

Hydrogen is recognized as a most dangerous gas due to high ignition rate and flame speed. In this work, numerical simulations have been performed to simulate the flow pattern and flame deflagration of hydrogen gas inside a confined chamber with different obstacles. This study tries to disclose the transient progress of flame to define the key actual factors affecting flow feature and flame propagation. In order to simulate hydrogen flame deflagration the limited obstacle channel, a three-dimensional model is established and large eddy simulation (LES) method is applied for the simulation of the model. The impacts of obstacle geometry on the pressure distribution are carefully examined. Obtained results show that overpressure inside the confined channel significantly increase within 0.3–0.6 ms. In this work, comprehensive reliable correlation for prediction of the pressure inside the confined channel is present. Our findings clearly demonstrates that velocity-density coefficient plays significant role the pressure distribution inside the model.

Experimental and numerical investigation of performance of an ethanol-gasoline dual-injection engine

Experiments and simulations were performed to investigate the effect of ethanol direct injection plus gasoline port injection (EDI + GPI) on engine performance. Gasoline direct injection plus GPI (GDI + GPI) was also tested as a reference to EDI + GPI. The experimental results showed that volumetric efficiency increased with the raise of direct injection ratio in both EDI + GPI and GDI + GPI conditions. The volumetric efficiency and IMEP of EDI + GPI were greater than that of GDI + GPI, due to the stronger charge cooling effect of EDI. Combustion process was improved by EDI when ethanol energy ratio (EER) was less than 42%, however further increase of EER led to the deterioration of combustion process. Simulation results showed that ethanol's high laminar flame speed played a dominate role to the improvement of combustion process. Although EDI negatively affected the equivalence ratio around spark plug, this disadvantage was offset by the high laminar flame speed of ethanol, resulting in shorter initial and major combustion durations. Simulation results also found that combustion process was deteriorated when EER was greater than 42%, which was mainly due to over-cooling and poor mixing of EDI. Regarding emissions, NO decreased while CO and HC increased with the raise of both EDI and GDI ratios.

Evaluation Dual Fuel Engine Fuelled With Hydrogen and Biogas as Secondary Fuel

The present energy scenario hydrogen fuel plays a dominant role in the power generation. Due to its unique characteristics of an extensive range of flammability, high flame speed, and diffusivity. In this present investigation, the diesel engine is converted into dual-fuel mode devoid of major conversions of the engine. The tests are performed on a dual-fuel mode and investigated the efficiency, emissions, and combustion features of the diesel engine. In the present context, hydrogen and biogas are injected from the inlet manifold as subsidiary fuel and diesel are injected as pilot fuel. The gaseous fuel injected in two different flow rates they are, 3 litres per minute (lpm), and 4lpm. The results from the experimentation revealed that the diesel with 4 lpm of hydrogen shows the 31.11 % enhancement of brake thermal efficiency but it shows 4.14% higher NOX emissions when compared with the pure diesel. But it shows. At the same time diesel with 4 lpm of Biogas exhibits 15.90% enhancement of brake thermal efficiency and 8.96% decrease in the NOX emissions in contrast to that of the single-mode of fuel with diesel.

Effects of late injection on lean combustion characteristics of methane in a high compression ratio optical engine

Energy crisis and environment pollution have made engines fueled with natural gas getting more and more attention, but practical engines fueled with natural gas often suffer from low engine power output and thermal efficiency. In this study, with addressing the role of late high-pressure injection, engine performance and flame propagation were studied in a high compression-ratio optical engine fueled with methane under lean combustion condition. First, the experiments with different excess air coefficients under two representative injection timing conditions were performed. The results show that with the increase of excess air coefficient, the indicated mean effective pressure (IMEP) is decreased. When the excess air coefficient is high, the combustion even becomes unstable under early injection conditions, which is due to the low flame speed. Second, different injection timings were employed under lean condition, and the results show that the combustion process is significantly affected by injection timing. Advanced combustion phase and higher heat release rate are observed under late injection condition. Finally, further analysis of flame images and pressure shows that late injection can increase the air intake quantity but also in-cylinder turbulence intensity. The highest flame speed is obtained under the latest injection condition with an increment above 50%, and flame propagation direction is also changed under different injection timings. Besides the compression pressure before spark is higher for late injection, meaning high volumetric efficiency. Therefore, late injection with high pressure is an effective way to improve the power output and thermal efficiency of natural gas engine.

Experimental based comparative exergy analysis of a multi-cylinder spark ignition engine fuelled with different gaseous (CNG, HCNG, and hydrogen) fuels

The experimental investigation was carried out on a multi-cylinder spark ignition (SI) engine fuelled with compressed natural gas (CNG), hydrogen blended CNG (HCNG) and hydrogen with varying load at 1500 rpm in order to perform comparative exergy analysis. The exergy analysis indicates that work exergy, heat transfer exergy and exhaust exergy were the highest with hydrogen at all loads due to its high flame temperature, low quenching distance, and high flame speed. The engine's exergy efficiency was the highest with hydrogen (34.23%), and it was about 24.23% and 24.08% with CNG and HCNG respectively at high load (20.25 kW). This indicates a higher potential of hydrogen to convert chemical energy input of fuel into heat and then power output. The exergy destruction was observed minimum with hydrogen at all loads, and it was drastically reduced at high loads. The combustion irreversibility which was calculated using species present during combustion, was the main contributor to exergy destruction, and it decreased with hydrogen. The minimum combustion irreversibility was 11.75% with hydrogen, followed by HCNG and CNG with 16.46% and 18.88% respectively at high load. The high quality of heat due to high in-cylinder temperature and low entropy generation during combustion caused by less number of chemical species in hydrogen combustion are the main reasons for lower combustion irreversibility with hydrogen.

Effect of the turbulence intensity on knocking tendency in a SI engine with high compression ratio using biogas and blends with natural gas, propane and hydrogen

This research presents the test results carried out in a diesel engine converted to spark ignition (SI) using gaseous fuels, applying a geometry change of the pistons combustion chamber (GCPCC) to increase the turbulence intensity during the combustion process; with similar compression ratio (CR) of the original diesel engine; the increase in turbulence intensity was planned to rise turbulent flame speed of biogas, to compensate its low laminar flame speed. The research present the test to evaluate the effect of increase turbulence intensity on knocking tendency; using fuel blends of biogas with natural gas, propane and hydrogen; for each fuel blend the maximum output power was measured just into the knocking threshold before and after GCPCC; spark timing (ST) was adjusted for optimum generating efficiency at the knocking threshold. Turbulence intensity with GCPCC was estimated using Fluent 13, with 3D Combustion Fluid Dynamics (CFD) numerical simulations; 12 combustion chamber geometries were simulated in motoring conditions; the selected geometry had the greatest simulated turbulent kinetic energy (TKE) and Reynolds number (Re) during combustion. The increased turbulence intensity was measured indirectly through the periods of combustion duration to mass fraction burn 0–5%, 0–50% and 0–90%; for almost all the fuel blends the increased turbulence intensity of the engine, increased the knocking tendency requiring to reduce the maximum output power to keep engine operation just into the knocking threshold. Biogas was the only fuel without power derating by the conditions of higher pressure and higher turbulence during combustion by GCPCC and improve its generating efficiency. Peak pressure, heat release rate, mean effective pressure and exhaust temperature were lower after GCPCC. Tests results indicated that knocking tendency was increased because of the higher turbulent flame speed; fuel blends with high laminar flame speed and low methane number (MN) had higher knocking tendency and lower output power.

Low-load hydrogen-diesel dual-fuel engine operation – A combustion efficiency improvement approach

Hydrogen-diesel dual-fuel operation can provide significant benefits to the performance and carbon-based emissions formation of compression-ignition engines. The wide flammability range of hydrogen allows engine operation at extremely low equivalence ratios while its high diffusivity and flame speed promote wide range combustion inside the cylinder. Nonetheless, despite the excellent properties of hydrogen for internal combustion, unburned hydrogen emissions and poor combustion efficiency have been previously observed at low-load conditions of compression ignition engines.The focus of the present study is to assess the effects of different engine operation and diesel injection parameters on the combustion efficiency of a heavy-duty dual-fuel engine while observing their interactions with the brake thermal efficiency (BTE) and emissions formation of the engine. In an attempt to reduce the unburned hydrogen rates at the exhaust of the engine, exhaust gas recirculation (EGR) and different diesel injection strategies were implemented. Statistical methods were applied in this study to reduce the experimental time.The results show a strong connection between unburned hydrogen rates, combustion and brake thermal efficiencies with the EGR rate. Higher EGR rates increase the intake charge temperature and provide improved hydrogen combustion and fuel economy. Operation of the dual-fuel engine at low-load with high EGR rate and slightly advanced main diesel injection can deliver simultaneous benefits to most of the harmful emissions and the BTE of the engine. Despite the efforts to achieve optimal engine operation at low loads, the combustion efficiency for most of the tested cases was in the range of 90%. Thus, increased hydrogen rates should be avoided as the benefits of the dual-fuel operation are weak at low-load conditions.

Comparison study of the ignition and combustion characteristics of directly-written Al/PVDF, Al/Viton and Al/THV composites

The aluminum–fluorine reaction is attracting growing interest due to its higher density over aluminum–oxygen. Fluorine rich polymers are particularly interesting for their applications as an energetic binder in advanced additive manufacturing of energetic materials. In this paper, three soluble polymers of PVDF (59 wt% F), Viton (66 wt% F) and THV (73 wt% F) are incorporated with aluminum nanoparticles (Al NPs) and prepared as free-standing films using solvent-based direct writing. The three composite films are compared for their mechanical properties as well as the ignition and combustion performance. Tensile stress was found to order as Al/PVDF > Al/THV > Al/Viton while the elasticity of Al/Viton is much higher than the other two. The burn rate of different composite films increases with Al content, while the flame temperature peaks slightly fuel-rich. The Al/PVDF had the highest burn rate, however, the flame temperature ordered as Al/THV (∼2500 K) > Al/Viton (∼2000 K) > Al/PVDF (∼1500 K), consistent with fluorine content. With higher fluorine and lower hydrogen content, THV releases more CFx gas than HF, which generates higher temperature. However, HF which is predominantly produced from PVDF has the lowest ignition by far and may be responsible for its high flame speed.

Studies of high pressure 1,3-butadiene flame speeds and high temperature kinetics using hydrogen and oxygen sensitization

The high pressure flame speeds and high temperature kinetics of 1,3-butadiene mixtures are studied by using spherical flames at fuel rich and lean conditions at 1–18 atm with H2 and O2 additions. H2 and O2 are added in the mixture to perturb concentrations of H/O radicals and the flame speed sensitivity to 1,3-butadiene + O/H reactions. The presently measured 1,3-butadiene/air flame speeds agree with previous studies at ambient pressure, but are lower at 5 atm. Comparison between the new experimental data and the prediction by the recently developed 1,3-butadiene model (Zhou et al., 2018) shows over-prediction of the flame speeds, especially at high pressure and fuel lean conditions. With H2 and O2 sensitization, the discrepancy between the model prediction and experiments becomes even larger. Sensitivity analysis shows that the flame speed is very sensitive to 1,3-butadiene + O/H reactions, especially to the branching and termination reaction ratio of 1,3-C4H6 + O = C2H3 + CH2CHO (R1) and 1,3-C4H6 + O = CH2O + C3H4-a (R2). The sensitivity of the flame speed to the branching ratio of these two reactions increases with the increase of H2 and O2 enrichment. Due to the lack of accurate theoretical calculations of these two reaction rates, the new flame speed data and previously measured ignition delay time were used to assess the uncertainty of the branching ratio and reaction rates of R1 and R2. It shows that the optimized branching ratio significantly improves the flame speed and ignition delay time predictions, especially at high pressure and fuel lean conditions. The present study reveals that H2 and O2 sensitization in flames provides an important way to identify the uncertainties of fuel + O/H reactions and to improve the model predictability for flames.

Study on the flame development patterns and flame speeds from homogeneous charge to stratified charge by fueling n-heptane in an optical engine

The operation range of some new compression ignition (CI) combustion modes was extended compared to that of HCCI because of fuel stratification. Few researches tried to analyze the mechanism by comparison of flame development patterns and flame speed under different stratified conditions. In this work, high-speed imaging of natural flame luminosity was used to study the combustion process from homogeneous charge to stratified charge with a higher frame rate. Different stratification conditions were formed by adjusting the injection timings. Results show that the proportion of flame propagation increases and combustion reaction rate decreases as fuel distribution in cylinder changes from homogeneous charge to stratified charge. Flame propagation of auto-ignition kernel exists although the combustion is dominated by multipoint auto-ignition in HCCI combustion. The flame spreading speed is much higher than the flame speed because the fictitious reaction front is shorter than the actual reaction front for flame spreading speed calculation. Four principles are proposed for equivalent radius method to get more reasonable results of flame speed. For conditions that do not satisfy these principles, effective front method can be used. Flame speed in CI combustion modes is in the range of 10–50 m/s depending on different stratification conditions in current study. There is a good correlation between the flame speed and the peak heat release rate as SOI is retarded, i.e., high flame speed corresponds to high peak heat release rate. It can be concluded that controlling fuel stratification is an effective method to regulate the ratio between auto-ignition and flame propagation and achieve effective control on combustion reaction rate.

Exploring the potential of reformed-exhaust gas recirculation (R-EGR) for increased efficiency of methanol fueled SI engines

Methanol is a promising fuel for spark ignition engines because of its high octane number, high octane sensitivity, high heat of vaporization and high laminar flame speed. To further boost the efficiency of methanol engines, the use of waste heat for driving fuel reforming was considered. This study explores the possibility of the reformed-exhaust gas recirculation (R-EGR) concept for increased efficiency of methanol engines. A simple Otto cycle calculation and a more detailed gas dynamic engine simulation are used to evaluate that potential. Both methodologies point to an enhancement in engine efficiency with fuel reforming compared to conventional EGR but not as much as the increase in lower heating value of the reforming product would suggest. A gas dynamic engine simulation shows a shortening of the flame development period and the combustion duration in line with the expected behavior with the hydrogen-rich reformer product gas. However, the heat loss increases with the presence of hydrogen in the reactants. The improvement of brake thermal efficiency is mainly attributed to the reduction of pumping work. The R-EGR concept is also evaluated for ethanol and iso-octane. As the reforming fraction increases, the efficiency of ethanol and iso-octane fueled engines rises faster than for the methanol engines due to a higher enhancement of exergy in their reforming products. At high reforming fractions, the efficiency of the ethanol engine becomes higher than with methanol. However, if the impact of optimal compression ratio for different fuels are considered, the methanol engine is able to produce a higher efficiency than the ethanol engine.

Flame development analysis in a diesel optical engine converted to spark ignition natural gas operation

The conversion of heavy-duty diesel engines to spark-ignition natural gas operation has the potential to decrease the use of conventional petroleum-based fuels and reduce greenhouse gas emissions. A better understanding of the fundamentals such as early natural gas flame development in re-entrant bowl combustion chambers can accelerate this conversion. This paper details an optical investigation of flame luminosity inside a conventional heavy-duty diesel engine converted to spark-ignition natural gas operation by replacing the diesel fuel injector with a spark plug and adding a port-fuel gas injector in the intake manifold. Knock-free lean-burn experiments were performed at medium engine load using methane as fuel. Combustion images confirmed that kernel inception played an important role in the subsequent flame propagation. In addition, flame luminosity images of individual engine cycles showed strong flame wrinkling and counterclockwise rotation due to increased turbulence inside the re-entrant bowl. However, the flame front for the mean cycle was relatively circular. Flame luminosity also suggested a thick flame and a high turbulent flame speed for early inside-the-bowl flame propagation, at the operating conditions investigated. Higher surface-to-volume ratio in the squish region increased the heat transfer to the surroundings and reduced flame propagation, which increased the late combustion period. The separation of the combustion process into two distinct zones (i.e., inside and outside the piston bowl) created a secondary peak or “bump” in the heat release of individual cycles. The data suggests that the combustion strategy should optimize the mass of fuel that burns inside the squish region. In addition, the moderate rate of pressure-rise and lack of knocking showed promise for heavy-duty diesel engines converted to spark-ignition natural gas operation.

Idle performance of a hydrogen rotary engine at different excess air ratios

Rotary engine has flat chamber and longs for fuel with high flame speed and small quenching distance. Hydrogen has many excellent characteristics that are suitable for the rotary engine. In this paper, the performance of a rotary engine fueled with pure hydrogen at different excess air ratios was experimentally investigated. The investigation was carried out on a single-rotor hydrogen-fueled rotary engine equipped with port fuel injection system. An online electronic control module was used to govern the hydrogen injection duration and excess air ratio. In this study, the engine was operating at the idle speed of 3000 rpm and different excess air ratios varied from 0.993 to 1.283. The test results demonstrated that the fuel energy flow rate of the hydrogen rotary engine and engine stability were reduced with the increase of excess air ratio. When the excess air ratio increased from 0.993 to 1.283, the hydrogen energy flow rate was decreased from 14.91 to 11.55 MJ/h. Both the flame development and propagation periods were increased with excess air ratio. CO emission was negligible, but HC, CO2 and NOx emissions were still detected due to the evaporation and possible burning of the lubrication-used gasoline, and oxidation reaction of nitrogen of the intake air.

Power generation performance of hydrogen-fueled micro thermophotovoltaic reactor

A tubular platinum reactor with a perforated annular array enables fuel/air mixtures to exchange sides, thus sustaining flames and preventing heat loss. Consequently, the combustion efficiency and operational range can be enhanced. A hydrogen/air mixture was introduced into inner and outer chambers at different equivalence ratios and flow velocities to chemically and physically investigate the interplay between the chambers. The benefits of hydrogen include a high gravimetric heating value, flame speed, and diffusion capacity and short chemical reaction time. The coexistence of heterogeneous (surface) and homogeneous (gas) reactions in the micro TPV reactor was examined and elucidated in terms of aerodynamics, mass and heat transfer, and chemical reactivity. Furthermore, a TPV reactor with TPV cell arrays was assembled, and the corresponding radiant efficiency of the emitter and the overall efficiency of the proposed micro TPV system were determined in this study.

Effect of Hydrogen Addition and Equivalence Ratio on Swirl Motion of Direct Ignition Engine

Objective: Reducing emissions and better quality of combustion are keen research areas in automobile. For better quality of combustion, modifications of engine features and utilizing novel fuels investigated in many researches. Methods: Hydrogen has very low ignition energy, high flame speed and helps to obtain ultra-lean-burn mixture. In this research work, the hydrogen mole fractions were added in the primary diesel fuel in the ranging from 10% to 90% with each interval of 10 % and varied equivalence ratio from 0.6 to 1.4 to examine the effect on velocity magnitude contour of airfuel particles and swirl motion. Results: All the results were obtained through simulations by using ANSYS Fluent 17 for Internal Combustion (IC) Engines. The addition of hydrogen increases the turbulence intensity of the fuel and leads to better quality of combustion. In addition, the swirl motion decreased because of addition of hydrogen addition and increasing the equivalence ratio. Keywords: Contour Velocity Magnitude, Diesel Fuel, Equivalence Ratio, Hydrogen, and Swirl Ratio.

Elongated VCE blast waves and structural response

Elongated congested volumes are common at chemical processing and petroleum refining facilities due to the arrangement of processing units, but there have been relatively few evaluations reported for the blast loads produced by elongated vapor cloud explosions (VCEs). The accidental VCE that occurred at the Buncefield, UK facility in 2005 involved an elongated congested volume formed by the trees and undergrowth along a portion of the site boundary. Some of near‐field damage indicators present at the Buncefield site could not be reasonably explained using existing standard VCE blast load prediction techniques that are based on an assumption that the congested volume filled with flammable gas cloud is hemispherical and located at grade level.This paper summarizes recent work to define the characteristics associated with elongated congested volume VCEs and identify differences relative to standard VCEs involving compact congested volume geometries. The main conclusions from this work with regard to the blast wave shape for an elongated congested volume deflagration are: (1) the blast wave behaves as an acoustic wave along the long axis, (2) the blast wave has a very quick transition from the positive phase peak pressure to the negative phase peak pressure (i.e., quick relative to the positive phase duration), and (3) the magnitude of the pressure drop between the peak positive and negative pressures diminishes quickly with distance outside the congested volume. These observations are not consistent with the behavior of a compact congested volume geometry VCE blast wave.Deflagration and deflagration‐to‐detonation transition (DDT) regimes were also identified for unconfined elongated congested volume VCEs as a function of the normalized flame travel distance and flame speed. These regimes were verified with existing test data, including data from the on‐going RPSEA test program. These observations and the DDT regime identification provide a frame of reference to develop a better understanding of elongated congested volume VCEs.Generic structures, with properties typical of conventional construction, were analyzed to illustrate the effect of the elongated congested volume VCE blast loads on structural response. The results show that, for an elongated congested volume VCE, a high flame speed deflagration may result in more severe structural response in the near‐field than for a detonation (i.e., due to a DDT). These results provide an alternative near‐field damage indicator analysis approach for the investigation of elongated congested volume VCE incidents. © 2017 American Institute of Chemical Engineers Process Saf Prog 37: 283–293, 2018

Flame propagation and flow field measurements in a Hartmann dust explosion tube

In this paper both the flame structure and propagation velocities of zirconium and lycopodium dusts are studied experimentally in air. The measurements were conducted in a Hartmann tube and a high-speed CMOS camera was used to record the images of the flame. The results show that the zirconium flame has a spherical shape, whereas the lycopodium flame has a very complex structure which makes flame speed calculation difficult and the lycopodium flame speed needs to be determined through statistical averaging of multiple measurements. This discrepancy between the flame structure of lycopodium and zirconium is attributed to the flame speed. In case of lycopodium, the flame speed is much lower, which makes the flame structure and propagation very sensitive to turbulent fluctuations of the flow field at the time of ignition. To reveal the structure of the flow field in the Hartmann tube prior to ignition, Time-Resolved Particle Image Velocimetry (TR-PIV) was used. The data of the PIV measurement shows the existence of large turbulent zones, which decay in time. These turbulent structures have a large influence on the flame propagation and therefore, it was concluded that flame speed measurements in a Hartmann tube can only be reliable for powders with a high flame speed.