Detonation Limits Research Articles

Study on detonation characteristics of pulverized coal and evolution law of detonation residue

This study explores the detonation characteristics and compositional changes of pulverized coal, focusing on its use in Rotary Detonation Wave (RDW) technologies. While pulverized coal has shown high fuel efficiency in RDW settings, transitioning from theory to practical detonation engineering presents substantial scientific and technical hurdles. A key issue is the reprocessing of detonation byproducts for in-situ coal mine gob filling, a topic that has received little attention. Utilizing advanced methods like X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), this paper investigates the micro-morphology, composition, and aromatic structures of gas–solid products pre and post-detonation at the Tashan Coal Mine's 2305 working face. Results indicate that coal dust from the underground mining face has enhanced detonation characteristics, with the addition of coal powder fuel extending the gas detonation limits. This benefits economic aspects by reducing reliance on gas fuel and lowering detonation fuel costs. The highest recorded detonation wave velocity was 2450 m/s, 14.8% greater than that of coal dust from external sources, suggesting more effective energy release and pressure gain. Furthermore, the study links detonation combustion intensity to coal's aromatic properties, noting a post-detonation aromaticity index (I) of 0.4941. This indicates an improvement in the aromatic structure under high-temperature conditions, vital for coal's reactivity and energy efficiency in RDW applications. This research not only deepens the understanding of coal dust combustion mechanisms but also advances clean coal utilization and deep coal fluidization mining, addressing significant RDW technological challenges.

Effect of Porous Wall on Detonation Propagation Velocity in Hydrogen-Oxygen Mixtures

ABSTRACT In this paper, the effect of flexible and rigid porous wall on the detonation propagation velocity in hydrogen-oxygen mixtures is investigated systematically. The roles of hydrogen concentration, initial pressure, porous wall geometry and porosity are considered in detail. Pressure sensors are used to record the time-of-arrival of the detonation wave, and the average velocity of the detonation wave can be obtained. The results indicate that the detonation propagation limit in a tube filled with porous materials is shorter than the value obtained in a smooth tube, and the velocity deficits increase obviously with the increase of the porosity and thickness. In the detonation limit, the velocity of detonation wave decreases firstly and then rises after passing through the absorption wall, which is due to the reflection of the shock wave on the surface of the wall. The reaction rate is increased quickly by introducing the local disturbance in the reaction zone, compensating the adverse effects of the porous wall. Compared with changing porosity, increasing thickness has a more significant effect on detonation attenuation. This phenomenon can be due to the excessive bending of the wave front and the heat loss increases.

Flame acceleration, detonation limit and heat loss for hydrogen-oxygen mixture at cryogenic temperature of 77 K

Experimental investigations have been conducted in hydrogen-oxygen mixtures with equivalence ratio of 1.5 at cryogenic temperature (77 K) and initial pressure (P0) from 0.2 to 0.5 atm. The pressure sensors and optical fibers are used to measure the overpressure and flame velocity, respectively. The precursor shock wave is formed by the combination of the 1st and 2nd shock waves. When flame catches up with the precursor shock wave, detonation occurs. Strong flame acceleration was observed in all tested conditions, which can be well characterized and predicted by the Zel'dovich number and expansion ratio. The stuttering and galloping modes were observed at 0.5 and 0.3 atm, respectively. With the decrease of the initial pressure to 0.20–0.25 atm, detonation could not occur, only the deflagration mode was observed. The stability of the mixture can be indicated by the parameter χ, and the improvement of stability of mixture will shorten the initial pressure range where the galloping mode occurs. The heat loss effect on detonation limit has subsequently been examined for the present experiments as well as those with equivalence ratio of 2.6 reported in our previous study [Shen, X. et al., Proceedings of the Combustion Institute 2022]. For equivalence ratio of 2.6, the heat loss is found to have dominant effect on the appearance of detonation limit. Its influence can be quantitatively characterized by critical ratio of heat loss to heat release. However, for equivalence ratio of 1.5, the heat loss effect is found to have only relatively small effect on detonation limit.

Transition to detonation in hydrogen-air mixtures due to shock focusing in a 3-wall 90-deg corner

This work presents an experimental investigation on the transition to detonation due to shock-wave focusing in a 3-wall 90-deg corner in hydrogen-air mixtures (17.5 – 60% H2) initially at 298 K and 1 bara. The reflector was placed at one side of 2 – m long, 0.14 m internal diameter tube. The other side of the tube was equipped with an ignition source and a flame acceleration section. The shock wave approached the reflector with a velocity in the range of 580 – 970 m/s. The reflector was placed symmetrically to the tube axis. The research proved that transition to detonation due to shock focusing highly depends on the shock wave strength and can be triggered in a stoichiometric mixture at shock speed VS = 605 m/s which corresponds to M = 1.485 or 59.9% of the speed of sound in combustion products. The ignition delay time recorded for transition to detonation was at the order of few microseconds. The detonability range observed with the 3-wall 90-deg reflector proved to be 15 - 70 % H2 in air compared to 18 - 59% H2 observed in work performed for a 90-deg wedge reflector configuration at the same initial conditions. Additionally, the scaling factor between critical shock velocity between both types of reflectors is almost constant and equal to 0.84 throughout the investigated mixtures. The high focusing ability of the 3-wall corner has also proved the minimum transition pressure recorded in the corner tip at the level of 8.95 MPa in a stoichiometric mixture. This value corresponds to a nearly 17-fold increase in pressure compared to normal shock post-reflection conditions. Considering the shock focusing as the major trigger for detonation the presented results may explain the differences between the detonability limits observed in obstacle-laden ducts and large-scale experimental setups.

Detonation decomposition of hydrocarbons to produce hydrogen

Detonation decomposition of methane, ethane, propane, butane, propylene and ethylene in their mixtures with oxygen was conducted in a pulsed gas detonation device (PGDD) with a goal of obtaining gaseous hydrogen, H2. Chemical reactions occurring behind the detonation front were elaborated for mixtures differing in the oxygen content. The upper concentration limits of detonation corresponding to minimal oxygen contents (maximal fuel contents), at which detonation is still possible, were determined. It was shown that, in order to maximize the hydrogen yield, 15% of acetylene, C2H2, should be added to methane. The productivity of a PGDD device with a barrel of a diameter of 26 mm and a length of 2 m is 3.60, 3.67, 4.25, 4.39, 4.61 and 5.76 kg h−1 of hydrogen when processing methane, ethylene, ethane, propylene, propane and butane, respectively. Upon detonation of mixtures based on ethylene, propylene and butane, along with hydrogen, nanoscale detonation carbon (NDC) is generated at a rate of 6.9, 6.5 and 5.2 kg h−1, respectively. NDC can be used as an additive to metals and polymers to modify their properties. The obtained results are discussed together with data on the production of hydrogen and NDC by detonation decomposition of acetylene previously obtained by the authors.

Experimental investigation of detonation decay in rough narrow channels

The conditions for detonation propagation in narrow channels are of great interest for ensuring explosion safety in industrial facilities using hydrogen. The roughness of the channel walls can lead to either flame acceleration or to the detonation decay. In this work the propagation of detonation of hydrogen–air mixtures in smooth and rough narrow channels was experimentally studied. The experimental setup consisted of a 3000 mm long driver section and a 1200 mm long diagnostic section with a 7×7mm cross-section. One or two walls of the diagnostic channel were covered with sandpaper which had a grain size of 500–600μm and 80–100μm. Lean, stoichiometric and rich mixtures were used for hydrogen with air. Based on the flame velocity graphs and shock wave pressure in the diagnostic section, several flame propagation regimes were recorded, depending on the fuel concentration and channel roughness. Non-linear effect of the roughness on the detonation propagation was observed. When two pieces of sandpaper were placed on the opposite sides of the narrow channel, a drop in flame velocity to the sound speed of the combustion products was registered for hydrogen mixtures with air. However, covering one wall with small grain sandpaper could lead to expanding of the detonation limits compared to the smooth channel.

Fast Deflagration-to-Detonation Transition in Helical Tubes

When designing a new type of power plants operating on pulsed detonations of gaseous or liquid fuels, the concept of fast deflagration-to-detonation transition (FDDT) is used. According to the concept, a flame arising from a weak ignition source must accelerate so fast as to form an intense shock wave at a minimum distance from the ignition source so that the intensity of the shock wave is sufficient for fast shock-to-detonation transition by some additional arrangements. Hence, the FDDT concept implies the use of special means for flame acceleration and shock wave amplification. In this work, we study the FDDT using a pulsed detonation tube comprising a Shchelkin spiral and a helical tube section with ten coils as the means for flame acceleration and shock amplification (focusing), respectively. To attain the FDDT at the shortest distances for fuels of significantly different detonability, the diameter of the pulsed detonation tube is taken close to the limiting diameter of detonation propagation for air mixtures of regular hydrocarbon fuels (50 mm). Experiments are conducted with air mixtures of individual gaseous fuels (hydrogen, methane, propane, and ethylene) and binary fuel compositions (methane–hydrogen, propane–hydrogen, and ethylene–hydrogen) at normal pressure and temperature conditions. The use of a helical tube with ten coils is shown to considerably extend the fuel-lean concentration limits of detonation as compared to the straight tube and the tube with a helical section with two coils.

Detonation behaviors in stoichiometric CH4-H2-O2 under different initial pressures conditions

In this study, the detonation behaviors (i.e., detonation limit, detonation overpressure, mean velocity, velocity deficit, and cell sizes) of CH4-H2-O2 mixtures in a small-bore tube at different initial pressures (ranging from 6 kPa to 300 kPa) were investigated. Mixtures with different proportions of H2 in the total fuel (0, 10%, 20%, 25%, 30%, 50%, 75%, 100%) were tested. Steady one-dimensional ZND calculations are used to obtain detonation parameters such as induction zone length, stability parameters, and cell sizes. Results indicate that increasing the hydrogen fraction decreases the detonation limit. The addition of hydrogen can reduce velocity deficit, especially near the detonation limit pressure. Velocity deficits were found to be within 3.5% when the initial pressure higher than 50 kPa. Higher initial pressure may result in the mean detonation velocity surpassing the theoretical CJ velocity. The detonation overpressure increases with the initial pressure and decreases with hydrogen fraction. The influence of initial pressure on cell sizes weakens as hydrogen fraction increases. Besides, the induction zone length and stability parameter decrease as hydrogen fraction increases Notably, the stability parameter of mixtures with different hydrogen fractions shows different trends as the initial pressure increases. A linear relationship between actual measured cell sizes and induction zone length is given as λ = 24.56Δi for hydrogen-methane-oxygen mixtures with the initial pressure range of 100 to 300 kPa. If experimental measurement error is considered, the prediction of the Ng model has reasonable accuracy.

Experimental assessment of hydrogen removal rate for passive auto catalytic recombiners

Generation and accumulation of hydrogen in containment atmosphere could pose a potential threat to the integrity of containment as hydrogen can form flammable mixture with air in the containment during postulated severe accident scenario involving multiple failures. Studies on hydrogen generation and distribution for various accident scenarios in reactor containment of Indian pressurized heavy water reactors (PHWRs) indicate that during severe accident with core damage, the possibility of global deflagration in absence of mitigating features is high and may challenge the integrity of containment. Therefore, it is essential to incorporate mitigating provisions inside the containment to prevent the hydrogen reaching deflagration/ detonation limits during such a scenario.Out of several options available for hydrogen mitigation, Passive Auto-catalytic Recombiner (PAR) is one of the most effective and recommended (IAEA -TECDOC-1661(2011)) technology for the removal of hydrogen inside the containment. The testing and evaluation of the performance of PAR for different conditions envisaged in the containment (such as pressure, temperature, steam concentration and poison) is a vital requirement for the deployment of these devices in the nuclear power plants (NPPs). The behavior of catalytic recombiners in terms of hydrogen removal rate with varying hydrogen concentrations is required to be evaluated essentially to work out the numbers and location of recombiners inside the containment. Hence, for testing of catalytic recombiners, an instrumented test facility simulating different reactor containment environment under controlled conditions, has been commissioned. Recombiner Test Facility (RTF) is a test rig for testing of full scale prototypes of catalytic recombiners.Results of Hydrogen Removal Rates (HRR) for varying hydrogen concentration, method for the calculation of HRR and its validation, model equation developed for Corrected Hydrogen Removal Rates (CHRR) usable in numerical simulations are presented in this article. With the proposed method for CHRR, it was established that the Recombiner performance can be evaluated.

Numerical Simulation of Plane and Cellular Detonation Wave Suppression in Hydrogen-Air Mixture by Inert Porous Filters

ABSTRACT Calculations of the interaction of plane (one-dimensional) and cellular (two-dimensional) detonation waves in hydrogen-air mixture with inert filters were carried out on the basis of the proposed physical and mathematical models, based on the detailed and reduced kinetics, describing such processes. The realized detonation regimes of attenuation and suppression of detonation were revealed. Comparison of results obtained by detailed and reduced kinetics showed that reduced kinetics gives overestimated detonation velocities compared to the detailed kinetics. But the obtained concentration limits of detonation practically equal to each other for both kinetics models. Comparison of processes of attenuation and suppression of plane and cellular detonation showed that the suppression of cellular detonation is more difficult to achieve compared to a plane detonation wave. Detonation failure criterion that shows that at the increasing the filter particles diameter, it is necessary to increase the volume concentration proportionally in order to successfully suppress detonation both in the case of a plane detonation wave and in the case of cellular detonation, was obtained.

Математическое моделирование детонации в двигателях с искровым зажиганием

Adjusting engines with a high compression ratio operating on traditional gasoline grades is simplified by the application of mathematical models of the operating cycle that predict the self-ignition of the fuel-air mixture. Mathematical simulation of detonation based on the analysis of a computational model of the thermodynamic cycle of a spark-ignited piston engine, which is close to the actual cycle, can be used to determine with sufficient accuracy in time the change in the current cycle pressure and the temperature of the unburned part of the charge. The model takes into account the heat exchange between the combustion zones of the charge and the walls of the combustion chamber. The onset of detonation is associated with the point of self-ignition of the unburned part of the charge and is determined depending on the thermodynamic parameters of the unburned part of the charge and the kinetic mechanism of pre-ignition chemical processes in the fuel-air mixture. It is shown that mathematical modeling of the self-ignition of the unburned part of the charge in a spark-ignition piston-type internal combustion engine can be performed in the same way as the modeling of self-ignition of the fuel-air mixture under continuing compression in units with a free-sliding piston. The accuracy of the self-ignition calculation using the cycle model has been experimentally verified by indicating it at different speeds and at different excess air and charge volume ratios, as well as different mixture temperatures in the intake manifold. The simulation results were verified experimentally on isooctane and octane blends (60% isooctane) and on commercial gasoline. It was found that at low compression ratios (up to 5 to 7), the low-temperature mechanism of self-ignition prevails, while at higher compression ratios, the high-temperature mechanism prevails. The detonation limit of an internal combustion engine can be determined by the point of self-ignition (explosion) in the unburned part of the charge at a residual cycle fraction of unburned fuel of at least 10%.

Effect of ozone addition on curved detonations

The influence of ozone on quasi-steady curved detonations was numerically studied in stoichiometric H2-air and DME-O2(-CO2) mixtures with 0%, 0.1% and 1% O3 addition. Detonation speed - curvature (D-κ) relations were determined for both fuels. The H2-air mixture has one critical point related to high-temperature chemistry whereas the DME-O2(-CO2) mixture has two critical points, one sustained by high-temperature chemistry, and the other supported by low-temperature chemistry. O3 addition significantly increases the curvature at all the critical points by speeding up both high- and low-temperature chemistry. Two mechanisms were found to be responsible for the results. First, O3 addition increases the rate of reaction initiation by fast decomposition to provide O radical via O3 (+M) = O2 + O (+M). The dominant reaction with fuel therefore changes from a fuel + OH/CH3 radical chain propagation reaction to a fuel + O radical chain branching reaction during the initial stage, which establishes the radical pool more rapidly. Second, O3 influences the reaction pathways. For H2-air with 1% O3, H + O3 = O2 + OH becomes the most important reaction for OH radical and heat generation during the initial stage. For DME-O2-CO2, O3 changes the respective contributions of competing low-temperature chemistry reactions, i.e. CH3OCH2 = CH2O + CH3 vs. CH3OCH2 + O2 = CH3OCH2O2 and CH2OCH2O2H = 2CH2O + OH vs. CH2OCH2O2H + O2 = O2CH2OCH2O2H. The change of dominant reactions either enhances (0.1% of O3) or eliminates (1% O3) the negative temperature coefficient behavior. Our study contributes to the detailed understanding of the thermo-chemical impact of ozone on detonation limits.

Effects of cavity length on operating characteristics of a ramjet rotating detonation engine fueled by liquid kerosene

Our very recent work has experimentally demonstrated the successful operation of a liquid-kerosene-fueled ramjet/air-breathing rotating detonation engine with a cavity-based annular combustor. As a follow-up study, the present work aims to further reveal the effects of cavities on the initiation and propagation characteristics of detonation, and various cavity lengths ranging from 30 mm to 90 mm were employed in the combustor. An air-heater was designed to provide an incoming flow at a total temperature of 860 K, which resembles the specific flight Mach number of 4 at an altitude of 20 km. The total mass flow rate of the incoming air flow was kept at 1.0 kg/s. The results indicate that a sufficient cavity length, which is found to be around 45 mm in minimum, is necessary to achieve the successful initiation of the rotating detonation waves. By increasing the cavity length to 75 mm and 90 mm, the fuel-lean detonation limits in terms of equivalence ratios (ER) can be extended from 0.8 to 0.7. The maximum propagation stability and minimum velocity deficit of 39.1 % (with respect to the ideal Chapman-Jouguet velocity) were achieved when the cavity length was 75 mm with the ER of 0.95. The optical observation indicates that detonation mainly occurs downstream of the cavity. The detonability of the kerosene/air mixture can be enhanced by the preheating of the permanent flame, and better enhancement is provided by larger cavity lengths. However, when the cavity length reaches 90 mm, part of the mixture is pre-ignited and consumed by deflagration. Therefore, the propagation velocity and stability of the rotating detonation wave increase as the cavity is lengthened from 45 mm to 75 mm, while showing a decrease when the cavity length reaches 90 mm. It is suggested that better detonation performance can be achieved by placing the permanent flame in a proper axial position through changing the cavity length. In addition, the increase of the cavity length is beneficial to alleviate the disturbance of the upstream oblique shock wave on the incoming flow in the isolator.

Transition to detonation in inhomogeneous hydrogen-air mixtures: The importance of gradients in detonation cell size

This paper presents a numerical study of flame acceleration and deflagration-to-detonation transition (DDT) of hydrogen-air mixtures in a channel with obstacles, where the mixture composition has a spatial gradient perpendicular to the wave propagation direction. The mixture composition gradient corresponds to a detonation cell size gradient, which characterizes the detonability or the detonation sensitivity. We use a recently developed chemical-diffusive model (CDM) to investigate the influence of the cell size gradient on the detonability of an inhomogeneous mixture and examine characteristic behaviors of flame acceleration and DDT. The CDM is a parametric model for chemical reaction and diffusive transport processes in compressible Navier-Stokes simulations. When optimized, the CDM can reproduce the correct flame and detonation properties, particularly the detonation cell size. The simulation results show that the ease with which an inhomogeneous mixture can detonate is bounded by the detonation limits of the most and least detonable homogeneous mixture. That is, the run-up distance to DDT of inhomogeneous mixtures with 0.8<ϕ<1.0 is found to be greater and less than the most and the least detonable mixtures with ϕ=1.0 and ϕ=0.8, respectively. Other macroscopic observables in the inhomogeneous mixture such as the average combustion wave speed and the total flame surface area are also in between those in these two homogeneous mixtures. The simulation data showed that pressure waves generated by a deflagration play an important role to re-distribute the prescribed mixture composition. The combustion process occurs preferentially in mixtures that initially concentrate along the unobstructed channel centerline. The numerical results agree with prior experimental findings that the averaged equivalence ratio cannot adequately estimate the detonability of an inhomogeneous mixture.

Improving Detonability in a Small-Scale Rotating Detonation Engine Using Partial Premixing

Small-scale rotating detonation engines (RDEs) with low mass flows and high frequency have potential as small thrusters, robust flame holders, and research tools that can be quickly and cheaply modified. However, the necessarily small channel geometry and low mass flow force the detonation wave to propagate near the limits of detonability. Previous success in a small-scale, 28-mm-diameter micro-RDE, operating on nitrous oxide () and ethylene (), exhibited unstable wave behavior with propagation velocities between 47 and 56% the Chapman–Jouguet speed. These results were observed at mass flows from 25 to using an in-chamber jets-in-crossflow (JIC) injection scheme with spark plug initiation. Building upon this work, the current investigation looked to improve the detonation behavior in the micro-RDE without changing the channel geometry or resultant operability and better understand the nature of mechanisms governing the design limitations in RDEs. To improve the wave behavior, a new partially premixed JIC injection scheme was used along with a predetonator ignition device. With these changes, tighter windows of operable mass flows () and equivalence ratios () were observed, between 35 and and 0.6 and 1.3, respectively. Maps of versus before and after detonation showed that the space of conditions conducive to ignition was not isomorphic with the space of conditions that sustained operation. Increases to the injection pressure to chamber pressure ratios improved the probability of detonation but resulted in greater pressure losses than were seen in the original JIC injection scheme. Single wave detonation was achieved for the first time in this RDE and had a peak frequency of 16.6 kHz, or 66% Chapman–Jouguet speed. Increases in fill height drove increases in wave frequency. Decreased fill height estimates compared to the previous design showed that partial premixing decreased the required fill time. These results support that the limits of detonability in small RDEs can be expanded without significantly compromising the characteristic low-mass-flow and high-frequency operation inherent to their geometry.

SIMULATION OF HOMOGENEOUS HYDROGEN-AIR DETONATION INTERACTION WITH POROUS FILTER

Calculations of the interaction of a cellular detonation wave (DW) with an inert porous filter were carried out based on the developed physical and mathematical model of the mechanics of heterogeneous medium which takes into account the detailed chemical kinetics of chemical reactions in the gas phase. Under an inert porous filter, a motionless lattice of inert particles is considered. The following flow regimes were revealed: propagation of attenuated cellular DW at velocities less than the Chapman-Jouguet velocity and detonation failure with the destruction of the cellular structure. Critical volume concentrations of filter particles corresponding to the detonation failure regime were calculated. Dependences of the normalized DW velocity and detonation cell size on the volume concentration of particles in filters were calculated. The concentration limits of detonation (critical volume concentrations of particles lead to detonation failure) in filters with diameters of 50, 100, and 200 µm were determined. The dependences of the normalized DW velocity and size of detonation cell on the volume concentration and diameter of particles in filters were calculated.

Strong flame acceleration and detonation limit of hydrogen-oxygen mixture at cryogenic temperature

A series of experiments were carried out in a closed tube at cryogenic temperature (77 K) for hydrogen-oxygen mixtures. Flame propagation speed and overpressure were measured by optical fibers and pressure sensors, respectively. The first and second shock waves were captured in the cryogenic experiments, although the shock waves always precede the flames in all cases indicating the absence of stable detonation. However, strong flame acceleration was observed for all situations, which is consistent with the prediction by expansion ratio and Zeldovich number. Besides, the tube diameter and length are also critical for flame acceleration to supersonic. All the flames in this work accelerate drastically reaching the C-J deflagration state. But at 0.4 atm, only fast flame is formed, while at higher initial pressures, the flame further accelerates to a galloping mode manifesting a near-limit detonation, which could be indicated by the stability parameter χ.

Numerical modeling of suppression of detonation waves in hydrogen-air mixture by system of inert particles clouds

The interaction of a detonation wave in a hydrogen-air mixture with a series of clouds of inert particles with diameters of 1, 10, and 100 μm is calculated. The concentration and geometric limits of detonation are determined. It was found that an increase in the particle diameter leads to an increase in the concentration limit and to decrease in the geometric limit of detonation. It has been found that an increase in the number of clouds in a series of clouds makes it possible to increase the length of the gaps between them for the successful failure of detonation. In addition, the longer the clouds of inert particles, the greater the maximum distance between them and the smaller their number is necessary to quench the detonation.

Effects of concentration gradient on pulsating and cellular detonations

In the field of explosion accidents and the combustion chamber of propulsion systems, gaseous mixtures are more likely to be highly non-uniform and a detonation usually propagates in a non-homogeneous medium. In this paper, one-dimensional (1D) pulsating detonations propagating in non-homogeneous medium with concentration gradient are studied by direct numerical simulation with a detailed chemistry. It is found that a periodically pulsating detonation can adjust to adapt to the environment with concentration gradient. The superficial concentration gradient can improve survivability of 1D detonation under highly unstable case, widening detonability limit corresponding to equivalence ratio; while the steep concentration gradient will quickly extinguish the detonation. The extend of detonability limit led by the inhomogeneity is reinforced by the presence of transverse wave in 2D detonations. The 2D detonation in the gradient has better viability compared with the 1D due to the coupling interaction of leading shock and transverse wave with the gradient and the transportation of H2 and H along the gradient. This study also demonstrates that the simulations of detonations in the gradient requires detailed chemical mechanism.

Natural gas versus methane: Ignition kinetics and detonation limit behavior in small tubes

Detonation properties of methane and natural gas were studied using ZND simulations and detonation limit experiments. The experiments were performed in two tube sizes, 32 mm and 6.4 mm in inner diameter over a range of initial pressures (between 3.4 kPa and 35 kPa) and with stoichiometric fuel-oxygen compositions. The fuels considered are high purity methane, high purity methane with dopant ozone, a real natural gas, and a family of natural gas surrogates. The natural gas surrogates were developed based on North American natural gas composition variations and designed to capture the expected mean and variance of fundamental combustion properties of natural gases. All natural gases tested in this work show a substantially smaller detonation induction length (about 40%) and lower detonation pressure limit (30% in terms of limiting pressure) than high purity methane. The ozonated methane at 3000 PPMv of ozone doping performed similarly to the natural gases. Overall, the results suggest that in methane-based mixtures, a smaller induction length correlates with a more predictable detonation behavior as evidenced by a lower detonation pressure limit. As such, natural gases are expected to have a wider operating range when used as a fuel for detonation-based engines. As importantly, induction length calculation results reveal that the variability in detonation and combustion behaviors resultant from composition variability is expected to be similar between natural gases and commercial methane. Finally, the results suggest that for safety-related studies, neat methane is a poor surrogate for studying natural gas explosions.