Nitrogen Dilution Ratio Research Articles

Eulerian–Lagrangian modeling of deflagration to detonation transition in n-decane/oxygen/nitrogen mixtures

In this work, to promote deflagration to detonation transition (DDT), a designed hot jet in a pre-detonator is produced to initiate detonations in the main detonation tube. We perform two-dimensional simulations of the DDT process for low-volatile fuel (n-decane) mixed with nitrogen and oxygen based on the Eulerian–Lagrangian approach. The effects of fuel atomization, vaporization, and shock focusing on the flame acceleration and DDT are discussed under different nitrogen dilution ratio and droplet size conditions. The results show that the flame acceleration process can be divided into slow and fast deflagration stages. Additionally, initiation times are mainly determined by the fuel atomization and evaporation in the slow deflagration stage, which dominates the entire DDT time. Furthermore, there are different intensities of hot jets rather than stable detonation waves formed at the pre-detonator exit. Moreover, local decoupling and re-initiation events are detected near the internal wall of the U-bend, inducing the overdriven detonation decaying into stable detonation waves in the smooth tube. The results also demonstrate that the detonation pressure and velocity decrease by 13.56% and 12.55%, respectively, as the nitrogen dilution ratio increases from 0.5 to 2. In particular, as the nitrogen dilution ratio continued to increase to 2.25, the development in DDT is similar, but the jet intensity is significantly weakened. While as the droplet size increases from 10 to 40 μm, the detonation pressure and velocity decrease only by 2.69% and 1.49%, respectively.

Laminar Burning Speeds and Flammability Limits of CH4/O2 Mixtures With Varying N2 Dilution at Sub-Atmospheric Conditions

ABSTRACT This paper presents experimentally determined laminar burning speeds () of premixed methane/oxygen/nitrogen mixtures at sub-atmospheric conditions obtained by using the constant-pressure spherical flame method. The goal of the conducted experiments was to investigate the effects of nitrogen dilution and pressure reduction on the laminar flame speed and flammability limits of methane/oxygen mixtures. Nitrogen content was varied between 3.1 and 79.3 volume percent. at a target pressure of 0.5 bar was investigated. Actual pressure levels ranged between 0.506 and 0.568 bar. Experiments at 1 bar were conducted as a benchmark case of the setup compared to results from literature. The laminar flame speed is found to increase with decreasing nitrogen content and decreasing pressure. The obtained results show good agreement with simulated data using the several chemical reaction mechanisms within 4.8% for near stochiometric mixtures. The upper flammability limit (UFL) is shown to be pressure-sensitive while the lower flammability limit (LFL) remains stationary for both pressure levels compared to reference data at 1 bar. Furthermore, the LFL is shown to stay at 6% vol methane content, independent of nitrogen dilution ratio.

Experimental investigation on the propagation characteristics of detonations in a semi-confined straight channel

In a rotating detonation engine, detonation waves propagate in the combustor chamber with one side unconfined which will introduce lateral relief and, therefore, results in deficits of the propagation velocity and the peak pressure. To study the critical mixture height for detonation propagation, a simple combustor without considering the curvature has been used, which provides a planar semi-confined channel with different channel heights, e.g., 10 mm, 20 mm, and 30 mm. Effects of the nitrogen dilution ratio, the equivalence ratio, and the channel height on the propagation modes, the velocity deficit, and the cellular structure have been investigated when ethylene was utilized. The non-dimensional channel height (h/λa) was also adopted to evaluate the impacts of lateral relief. Experimental results indicated that three different propagation modes existed in the semi-confined channel. Velocity deficits resulted from the lateral relief mechanism were observed and the maximum velocity deficit is around 10–15%. Besides, the cell width increased and became more irregular when reducing the channel height. Successful detonation propagation can be obtained with a minimum normalized channel height of h/λa > 2, which will provide information for practical detonation operations.

The role of reactive PAH dimerization in reducing soot nucleation reversibility

Abstract Nucleation of incipient soot or carbon black nanoparticles has significant scientific and industrial importance because it influences the particle size distribution, morphology and composition, hence its health and environmental impact as well as functional properties. R eversible P olycyclic Aromatic Hydrocarbon (PAH) C lustering (RPC) with van der Waals forces (vdW) was proposed recently as opposed to I rreversible P AH C lustering (IPC) for soot nucleation (Eaves et al., Proc. Combust. Inst, 35 (2015) 1787) to relax the assumption of stable dimer formation with physical bonds at flame temperatures. Here, the necessity of considering chemical bond formation between PAHs in a dimer for reducing soot nucleation reversibility in ethylene coflow diffusion flames with a wide range of nitrogen dilution ratios is demonstrated. An RPC model with C hemical B ond F ormation (RPC CBF) is developed and its performance is compared to those of RPC and IPC models. Only the RPC CBF model with low reversibility for PAH addition on the surface of soot primary particles can predict soot volume fraction, average primary particle diameter, primary particle number density and the bimodal size distribution of soot agglomerates on the flame centerline within experimental uncertainty. While the IPC model overpredicts soot concentrations by a factor of five with increased dilution, the RPC model underpredicts it by more than two orders of magnitude for the flame with 68% nitrogen dilution. The RPC model fails to predict the observed bimodality of agglomerate particle size distribution in flames with low dilution because its predicted nucleation rate is much weaker compared to that of growth. Accounting for chemical bond formation for dimers is essential to form enough nuclei with increasing dilution and temperature. Also, low reversibility for PAH addition is required to predict the balance between nucleation and surface growth, hence the average size of soot primary particles.

Combustion characteristics of syngas on scaled gas turbine combustor in pressurized condition: Pressure, H2/CO ratio, and N2 dilution of fuel

To facilitate fuel interchangeability for industrial gas turbines, various kinds of fossil fuels including syngas from coal gasification and steel mill gases including Blast Furnace Gas (BFG) have been investigated by previous researchers to determine their viability as alternative fuels for power generation. In the present study, various syngas components produced from coal gasification were combined to produce a simulated mixed gas, which was fed into a pressurized gas turbine combustion test rig to determine the combustion characteristics. A scaled model of the 7EA combustor from GE was used to conduct a basic comparative study on the emission trend (NOx), exhaust gas temperature distribution according to the combustor pressure, syngas composition and dilution ratio at the fuel side. The major findings were that modification of the empirical formula for pressure affects NOx emission and nitrogen dilution ratio affects the temperature profile uniformity on the fuel side.

C2 yield enhancement during oxidative coupling of methane in a nonpermselective porous membrane reactor

A systematic comparison between a packed bed membrane reactor (PBMR) and packed bed reactor (PBR) for oxidative coupling of methane (OCM) on Na2WO4-Mn/SiO2 catalyst reveals the utility of distributing the oxygen feed along the catalyst bed length. A sufficiently high transmembrane pressure difference is needed to realize a moderate C2+ yield enhancement (∼30%). The enhancement is attributed to a shift in selectivity towards the desired coupling reaction by maintaining a high methane to oxygen ratio along the bed length. The elevated transmembrane pressure is achieved by adjusting the shell and tube side parameters including catalyst particle size, inert dilution ratio, residence time, and temperature. Under identical reaction conditions, a C2+ yield of 23.6% is obtained for the PBMR compared to 18% for the PBR. The potential detrimental impact of an axial pressure drop in the catalyst bed is compensated by increasing the shell side pressure through an increase in the shell-side nitrogen dilution ratio. Experiments were conducted at lower nitrogen dilution by increasing the catalyst particle size and reducing the tube side pressure. At a dilution ratio of ∼38%, a C2+ yield of 20% compared to 17% in PBR was obtained, which is on the higher end of the C2+ yield reported in literature for a distributed feed membrane reactor at a low dilution. Ways to overcome bypassing of the catalyst bed by shell side O2 as well as back diffusion of methane were also investigated. The results emphasize the crucial role of transmembrane pressure in enhancing the distribution of oxygen feed along the reactor length for improved OCM catalyst performance.

Direct estimation of edge flame speeds of lifted laminar jet flames and a modified stabilization mechanism

The flame stabilization mechanism of a lifted flame in a laminar fuel jet has been explained based on the edge flame concept. Previous studies have employed a similarity solution between velocity and fuel concentration, and showed that a lifted flame can be stabilized when the Schmidt number, Sc, is within a range of either Sc > 1 or Sc < 0.5. However, two unsolved problems remained, and they were mainly answered in this study. First, the edge flame speed could not be determined from the similarity solution using the experimental results of stable lifted flames. To resolve this, the experimental relationship between the fuel flow rate and the liftoff height was measured with a higher resolution, and a new method employing an effective Schmidt number was suggested. As a result, the relationship between the edge flame speed and the fuel concentration gradient could then be directly estimated from the simple experimental values for flow rate and the liftoff height. This new method was validated for various experimental parameters including the tube diameter, air-premixing ratio, and nitrogen-dilution ratio. Second, the reason why a stable lifted flame was not obtained when Sc < 0.5 could not be explained theoretically. Here, the existence of a unique criterion of Sc > 1, for a stable lifted flame was clarified theoretically. This study will advance understanding of the characteristics and stabilization mechanism of lifted edge flames in laminar non-premixed fuel jets.

On the existence and multiplicity of rotating detonations

The operating behavior of a rotating detonation combustor is experimentally explored for stoichiometric H2–O2–N2 mixtures for four combustor geometries to determine the role of cell width (λ) and combustor channel width (wch) on the existence of detonation and number of waves. The ratio of nitrogen dilution ratio (β=N2:O2) of the oxidizer is varied from β=3.76 (air) to β=2, yielding a reduction in the cell width by a factor of two. The regime of successful detonation is bounded by a minimum normalized channel width of wch/λ > 0.5, which agrees with the limit for classical detonation propagation in a rectangular channel. The number of detonation waves within the combustor ranges from n=1–3, and increases in a predictable fashion when the normalized perimeter of a detonation front exceeds p/λ > 7.4. From the present work, it appears feasible to predict the existence and multiplicity of rotating detonations from the combustor geometry and mixture cell width.

Development of NOx response model of H2/CO/CH4 syngases with nitrogen dilution in a gas turbine model combustor

The NOx prediction model was developed by utilizing the NOx emission data obtained from various compositions of H2/CO/CH4 syngases with and without nitrogen dilution at 40 kWth and 50 kWth. The knowledge obtained from the test results of a partially premixed gas turbine model combustor clarified that the Zeldovich mechanism dominated NOx formation in which flame temperature and residence time were the two vital factors. The ANOVA general linear model was applied to obtain the correlation between the input parameters (fuel mole concentration and heat input) and NOx emissions after two facts were verified: 1) the flame temperature could be expressed in terms of only input parameters; 2) the residence time and input parameters were highly correlated with OH∗ chemiluminescence images from which the flame volume could be calculated by depicting the primary combustion zone.The new empirical correlation showed a good match with the experimental data. The correlation coefficient between the measured and the predicted NOx was 89%, and most of the predicted NOx was within the 95% z-confidential interval. Although the developed model was fitted to the tested combustor, the comparison of the results of the developed model with other models indicated that a model developed for only one combustor had better precision than the generalized model. It was also noted that only the fuel composition and the heat input with the diluents ratio, if used, were enough to establish the NOx prediction model in developing the NOx model of a gas turbine combustor for power generation because the air flow rate and the combustor pressure were kept constant during the operation.The developed NOx prediction model could be efficiently utilized in the reduction of NOx emissions during the design and operation of syngas turbines because its application covers a wide range of H2/CO/CH4 syngas compositions with a wide range of nitrogen dilution ratios. Moreover, because it does not need complex computational fluid dynamics simulation or additional experimentation, the developed model could potentially reduce the costs of such tasks.

Performance Characterization and Auto-Ignition Performance of a Rapid Compression Machine

A rapid compression machine (RCM) test bench is developed in this study. The performance characterization and auto-ignition performance tests are conducted at an initial temperature of 293 K, a compression ratio of 9.5 to 16.5, a compressed temperature of 650 K to 850 K, a driving gas pressure range of 0.25 MPa to 0.7 MPa, an initial pressure of 0.04 MPa to 0.09 MPa, and a nitrogen dilution ratio of 35% to 65%. A new type of hydraulic piston is used to address the problem in which the hydraulic buffer adversely affects the rapid compression process. Auto-ignition performance tests of the RCM are then performed using a DME–O2–N2 mixture. The two-stage ignition delay and negative temperature coefficient (NTC) behavior of the mixture are observed. The effects of driving gas pressure, compression ratio, initial pressure, and nitrogen dilution ratio on the two-stage ignition delay are investigated. Results show that both the first-stage and overall ignition delays tend to increase with increasing driving gas pressure. The driving gas pressure within a certain range does not significantly influence the compressed pressure. With increasing compression ratio, the first-stage ignition delay is shortened, whereas the second-stage ignition delay is extended. With increasing initial pressure, both the first-stage and second-stage ignition delays are shortened. The second-stage ignition delay is shortened to a greater extent than that of the first-stage. With increasing nitrogen dilution ratio, the first-stage ignition delay is shortened, whereas the second-stage is extended. Thus, overall ignition delay presents different trends under various compression ratios and compressed pressure conditions.

Experimental and Numerical Study on the Laminar Flame Speed of n-Butane/Dimethyl Ether–Air Mixtures

Laminar flame speeds of n-butane/dimethyl ether (DME)–air mixtures were first measured using the outwardly expanding spherical flame and high-speed schlieren photography over a wide range of equivalence ratios, nitrogen dilution ratios, and DME blending ratios at elevated temperatures and pressures. The measured flame speeds were compared to the calculated flame speeds with some representative chemical kinetic models. Results show that laminar flame speeds of n-butane/DME blends slightly increase with the increase of the DME blending ratio. Reaction pathway analysis was performed, and the effect of the DME blending ratio on the laminar flame speed was interpreted with the latest Aramco Mech 1.3 model. A correlation of the laminar flame speed of n-butane/DME blends as a function of the equivalence ratio, temperature, pressure, and DME blending ratio is provided.

모델 가스터빈 연소기에서 합성가스 연소성능시험 - Part 1 : 화염안정성

This paper describes on the flame stability and combustion instability of coal derived synthetic gas especially for gases of Buggenum IGCC in Netherlands and Taean IGCC in Korea. These combustion characteristics were observed by conducting ambient-pressure elevated-temperature combustion tests in GE7EA model combustor when varying heat input and nitrogen dilution ratio. Flame stability map is plotted according to the flame structure by dividing all regimes into six, and only regime I and II are identified to be stable. Both syngases of Taean and Buggenum with nitrogen integration corresponds to regime II in which syngas burnt stably and flame coupled with outer recirculation flow. Stable regime of Buggenum is larger than that of Taean when considering only /CO ratio due to higher content of hydrogen. However, when considering nitrogen dilution, syngas of Taean is burnt more stably than that of Buggenum since more nitrogen in Buggenum has negative effect on the stability of flame.

모델 가스터빈 연소기에서 합성가스 연소성능시험 - Part 2 : NOx/CO 배출특성, 온도특성, 화염구조

본 논문은 부게넘 및 태안 IGCC플랜트의 연료를 대상으로 석탄으로부터 생성된 합성가스의 NOx/CO배출 특성, 온도특성, 화염의 구조에 대해 기술하였다. GE7EA 모사 가스터빈 연소기를 대상으로 상압 고온 연소시험을 수행하여 입열량 및 질소희석에 따른 연소특성을 관찰하였다. 입열량이 감소하고, 희석제량이 증가할 때 단열화염온도의 감소로 NOx가 감소하였고, 저부하에서는 희석량이 증가할수록 불완전 연소로 인해 CO가 증가하였다. 이러한 NOx 감소 및 CO발생은 각각 <TEX>$1500^{\circ}C$</TEX> 와 <TEX>$1250^{\circ}C$</TEX>의 특정 화염온도에서 관찰되었다. 또한 질소 희석이 증가할수록 단열화염온도 및 연소기 라이너의 온도가 감소했고, 화염 부상과 같은 화염구조의 변화로 인해 특이점이 관찰되었다. 본 연구결과를 통해 질소희석이 NOx/CO배출 및 온도, 화염구조에 미치는 영향이 검토되었으며, 시험 데이터는 향후 태안 IGCC 플랜트의 운전시 최적 조건 선정을 위한 기초자료로 활용될 예정이다. This paper describes on the NOx/CO emission characteristics, temperature characteristics and flame structures when firing coal derived synthetic gas especially for gases of Buggenum and Taean IGCC. These combustion characteristics were observed by conducting ambient-pressure elevated-temperature combustion tests in GE7EA model combustor when varying heat input and nitrogen dilution ratio. Nitrogen addition caused decrement in adiabatic flame temperature, thus resulting in the NOx reduction. At low heat input condition, nitrogen dilution raised the CO emission dramatically due to incomplete combustion. These NOx reduction and CO arising phenomena were observed at certain flame temperature of <TEX>$1500^{\circ}C$</TEX> and <TEX>$1250^{\circ}C$</TEX>, respectively. As increasing nitrogen dilution, adiabatic flame temperature and combustor liner temperature were decreased and singular points were detected due to change in flame structure such as flame lifting. From the results, the effect of nitrogen dilution on the NOx/CO and flame structure was examined, and the test data will be utilized as a reference to achieve optimal operating condition of the Taean IGCC demonstration plant.

Transmission of near-limit detonation wave through a planar sudden expansion in a narrow channel

Transmission of single-cell and spinning detonation waves in C2H4+3(O2+βN2) mixtures through a 2-D sudden expansion experimentally studied using high-speed cinematography and soot film visualization. Nitrogen dilution ratio, β, is utilized to control cell size and detonation mode. Detonation wave of ethylene/oxygen/nitrogen mixture was initiated via DDT in the 1mm×1mm cross-section and 250mm long initiator channel before propagating into the 3mm×1mm receptor channel. Visualizations show that detonation waves were extinct and accompanied with abrupt decrease in visible reaction front propagating velocities right after passing through the sudden expansion. However, re-acceleration of the reaction front and re-initiation of the detonation wave were observed downstream in the expanded receptor section. Two re-initiation modes with large disparity in the re-initiation distance were experimentally characterized. For mixtures with nitrogen dilution ratio equals 0.3 or less, the cellular detonation front propagated with single cell in the initiator section before entering the sudden expansion. The re-initiation distance was less than 50mm and was likely achieved via shock reflection. Velocity characterization shows that steady propagating speed of the detonation wave is ∼100m/s higher in receptor section than in the initiator section. Since the cell size became larger than 1mm for mixtures with β⩾0.3, the detonation wave propagated in spinning detonation mode before transmitting into the expanded section. The reaction front would have to go through another DDT process to reach detonation state in the receptor section, and the re-initiation distance was increased to more than 150mm. Moreover, step height of the sudden expansion was proposed as the characteristic length scale to obtain a unified non-dimensional correlation between re-initiation distance and detonation cell size.

Laminar Burning Characteristics of Diluted n-Butanol/Air Mixtures

Experimental and numerical studies on laminar burning characteristics of diluted n-butanol/air premixed mixtures were conducted. Experiments were conducted using the spherically expanding flames at different dilution ratios of nitrogen at the initial pressure of 0.1 MPa and temperature of 428 K. Both measured and computed results show that with the increase of dilution ratio of nitrogen, the laminar flame speed of n-butanol/air mixtures is decreased. This is attributed to the decrease of adiabatic flame temperature of the mixtures. In addition, effective Lewis numbers of n-butanol/air mixtures at varied dilution ratios were deduced, and flame instability was analyzed. Results show that in the case of equivalence ratio less than 1.4, flame tends to stabilize with nitrogen dilution for the n-butanol/air mixture. In contrast, in the case of equivalence ratio equals to and larger than 1.4, the flame tends to become unstabilized when mixtures are diluted with nitrogen. The measured laminar flame speeds are in good agreement with the computed laminar flame speeds at different nitrogen dilution ratios. Results show a linear relationship between the normalized laminar flame speed and nitrogen dilution ratio. Sensitivity analysis was conducted using the recently developed detailed kinetic mechanism. Results indicate that the three-body reactions are dominant at large dilution ratio.

Numerical study on combustion of diluted methanol-air premixed mixtures

The effect of nitrogen dilution on the premixed combustion characteristics and flame structure of laminar premixed methanol-air-nitrogen mixtures are analyzed numerically based on an extended methanol oxidation mechanism. The laminar burning velocities, the mass burning fluxes, the adiabatic flame temperature, the global activation temperature, the Zeldovich number, the effective Lewis number and the laminar flame structure of the methanol-air-nitrogen mixtures are obtained under different nitrogen dilution ratios. Comparison between experiments and numerical simulations show that the extended methanol oxidation mechanism can well reproduce the laminar burning velocities for lean and near stoichiometric methanol-air-nitrogen mixtures. The laminar burning velocities and the mass burning fluxes decrease with the increase of nitrogen dilution ratio and the effect is more obvious for the lean mixture. The effective Lewis number of the mixture increases with the increase of nitrogen dilution ratio, and the diffusive-thermal instability of the flame front is decreased by the nitrogen addition. Nitrogen addition can suppress the hydrodynamic instability of methanol-air-nitrogen flames. The decrease of the mole fraction of OH and H is mainly responsible for the suppressed effect of nitrogen diluent on the chemical reaction in the methanol-air-nitrogen laminar premixed flames, and the NOx and formaldehyde emissions are decreased by the nitrogen addition. methanol, dilution, premixed combustion, numerical analysis With increasing concern about fuel shortage and air pollution control, researches on improving engine fuel economy and reducing exhaust emissions have become the major topics in combustion and engine studies. Because of limited reserves of crude oil, the development of alternative-fuel engines has attracted more attention in the engine community. Alternative fuels usually are clean fuels compared with traditional diesel fuel and gasoline fuel in the engine combustion process. The introduction of these alternative fuels is beneficial to the solution of the fuel shortage and reduction of engine exhaust emissions. Nowadays, clean alternative fuels mainly include hydrogen, compressed natural gas (CNG), liquid petroleum gas (LPG), dimethyl ether (DME), and alcohols in internal combustion engines application

Study on nitrogen diluted propane–air premixed flames at elevated pressures and temperatures

Using a high pressure constant volume combustion vessel, the propagation and morphology of spark-ignited outwardly expanding nitrogen diluted propane–air flames were imaged and recorded by schlieren photography and high-speed digital camera. The unstretched laminar burning velocities and Markstein lengths were subsequently determined over wide range of initial temperatures, initial pressures and nitrogen dilution ratios. Two recently developed mechanisms were used to predict the reference laminar burning velocity. The results show that the measured unstretched laminar burning velocities agree well with those in the literature and the computationally predicted results. The flame images show that the diffusional–thermal instability is promoted as the mixture becomes richer, and the hydrodynamic instability is increased with the increase of the initial pressure and it is decreased with the increase of dilution ratio. The normalized laminar burning velocities show a linear correlation with respect to the dilution ratio, indicating that the effect of nitrogen dilution is more obvious at higher pressures.

Effects of N2 Dilution on Laminar Burning Characteristics of Propane−Air Premixed Flames

Effects of nitrogen dilution on laminar burning velocities and Markstein lengths of propane-air mixtures were determined at the atmospheric pressure and room temperature based on the spherically expanding flames. The results show that, with the increase of the nitrogen dilution ratio, the burning velocity decreases and, for equivalence ratio less than 1.4, Markstein length increases with the increase of the dilution ratio, indicating that nitrogen addition decreases the preferential diffusion instability. The density ratio decreases, and the laminar flame thickness increases, which indicates the decrease of hydrodynamic instability. The ratio of unstretched laminar burning velocity with and without diluent is only related to the dilution ratio and is not influenced by the equivalence ratio. A linear correlation is found between the ratio of unstretched laminar burning velocity with and without the diluent and the dilution ratio.

Thermal degradation of two liquid fuels and detonation tests for pulse detonation engine studies

The use of liquid fuels such as kerosene is of interest for the pulse detonation engine (PDE). Within this context, the aim of this work, which is a preliminary study, was to show the feasibility to initiate a detonation in air with liquid-fuel pyrolysis products, using energies and dimensions of test facility similars to those of PDEs. Therefore, two liquids fuels have been compared, JP10, which is a synthesis fuel generally used in the field of missile applications, and decane, which is one of the major components of standard kerosenes (F-34, Jet A1, ...). The thermal degradation of these fuels was studied with two pyrolysis processes, a batch reactor and a flow reactor. The temperatures varied from 600°C to 1,000°C and residence times for the batch reactor and the flow reactor were, respectively, between 10–30 s and 0.1–2 s. Subsequently, the detonability of synthetic gaseous mixtures, which was a schematisation of the decomposition state after the pyrolysis process, has been studied. The detonability study, regarding nitrogen dilution and equivalence ratio, was investigated in a 50 mm-diameter, 2.5 m-long detonation tube. These dimensions are compatible with applications in the aircraft industry and, more particularly, in PDEs. Therefore, JP10 and decane were compared to choose the best candidate for liquid-fuel PDE studies.

04/02491 Extension of no. 3 coke oven service life at JFE-Fukuyama works: Maruoka, M. et al. ISSTech Conference Proceedings, 1st, Indianapolis, IN, United States, 27–30 April, 2003, 1197–1206

Using a high pressure constant volume combustion vessel, the propagation and morphology of spark-ignited outwardly expanding nitrogen diluted propane–air flames were imaged and recorded by schlieren photography and high-speed digital camera. The unstretched laminar burning velocities and Markstein lengths were subsequently determined over wide range of initial temperatures, initial pressures and nitrogen dilution ratios. Two recently developed mechanisms were used to predict the reference laminar burning velocity. The results show that the measured unstretched laminar burning velocities agree well with those in the literature and the computationally predicted results. The flame images show that the diffusional–thermal instability is promoted as the mixture becomes richer, and the hydrodynamic instability is increased with the increase of the initial pressure and it is decreased with the increase of dilution ratio. The normalized laminar burning velocities show a linear correlation with respect to the dilution ratio, indicating that the effect of nitrogen dilution is more obvious at higher pressures.