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In this paper, the kerosene/air rotating detonation engines(RDE) are numerically investigated, and the emphasis is laid on the effects of total pressures and equivalence ratios on the operation characteristics of RDE including the initiation, instabilities, and propulsive performance. A hybrid MPI + OpenMP parallel computing model is applied and it is proved to be able to obtain a more effective parallel performance on high performance computing(HPC) systems. A series of cases with the total pressure of 1 MPa, 1.5 MPa, 2 MPa, and the equivalence ratio of 0.9, 1, 1.4 are simulated. On one hand, the total pressure shows a significant impact on the instabilities of rotating detonation waves. The instability phenomenon is observed in cases with low total pressure (1 MPa) and weakened with the increase of the total pressure. The total pressure has a small impact on the detonation wave velocity and the specific impulse. On the other hand, the equivalence ratio shows a negligible influence on the instabilities, while it affects the ignition process and accounts for the detonation velocity deficit. It is more difficult to initiate rotating detonation waves directly in the lean fuel operation condition. Little difference was observed in the thrust with different equivalence ratios of 0.9, 1, and 1.4. The highest specific impulse was obtained in the lean fuel cases, which is around 2700 s. The findings could provide insights into the understanding of the operation characteristics of kerosene/air RDE.

The combustion characteristics of the swirl micro combustor with twisted vanes (Swirl-MC-TV) and the conventional micro combustor (Conventional-MC) are investigated and compared under different inlet velocities (8–40 m/s), wall materials (quartz, steel, and SiC), and equivalence ratios (0.6–1.4). The results show that the larger area of recirculation zones and the stronger recirculation intensity are the key factors for Swirl-MC-TV to stable combustion. When the inlet velocity is 40 m/s, compared with the Conventional-MC, the wall heat loss of the Swirl-MC-TV is reduced by 15.9%, and the reaction heat and combustion efficiency of the Swirl-MC-TV are increased by 17.5% and 5.9%, respectively. When the wall materials of steel and SiC, combustors have a better preheating effect and higher combustion intensity. When the equivalence ratio is greater than 0.6, the wall heat loss of Swirl-MC-TV is larger but the combustion efficiency and the reaction intensity are still higher than Conventional-MC.

The propagation modes of rotating detonation waves supplied with liquid kerosene and oxygen-enriched air were experimentally investigated. Experiments were conducted while maintaining the equivalence ratio at approximately 0.7 and varying the mass flow rate of the oxidizer from 585.3 to 1493.8 g/s. Three propagation modes were obtained, and the propagation characteristics of rotating detonation waves in each mode were extensively analyzed. The results reveal that for the test model with an equivalence ratio of 0.7, the rotating detonation waves exhibit three types of modes in sequence as the mass flow rate of the oxidizer increases, namely, single-wave mode, single/dual-wave hybrid mode, and dual-wave mode. The propagation modes of rotating detonation waves vary randomly in the single/dual-wave hybrid mode, and the mode transition processes are more likely to be accompanied by transient detonation wave extinction due to the lower activity of liquid kerosene. For the single/dual-wave hybrid mode, the pressure feedback of rotating detonation waves to oxidizer plenum in the single-wave mode is greater than that in the dual-wave mode, which is related to the higher pressure peaks of rotating detonation waves in the single-wave mode. Moreover, the relative standard deviation of the propagation frequency is calculated to evaluate the propagation stability of the rotating detonation wave. It was found that the rotating detonation waves possess higher propagation stability in the dual-wave mode than in the single-wave mode.

In this study, we report the explosion characteristics of H2/N2O mixtures at fuel-lean side and stoichiometric condition in a 113 L cylindrical vessel. Experiments were performed at different sub-atmospherical pressures ( P 0 =10 kPa–40 kPa). Explosion pressure traces were obtained by a pressure transducer mounted on the wall. Meanwhile, the flame morphology was recorded using schlieren visualization. The maximum explosion pressure ( P max ) and maximum pressure rise rate ( ( d p / d t ) max ) were derived and discussed. Results show that two competitive effects (i.e., the adiabatic flame temperature and the molecular number) make the maximum P max occurring at φ =0.5—0.6. Linear correlations were found between P max and P 0 . Except the adiabatic flame temperature and flame propagation speed, the flame instability was found to participate in dominating the maximum pressure rise rate. For increased initial pressure, the equivalence ratio of the maximum ( d p / d t ) max switches to the lean side due to the enhanced flame instability. Depending on different equivalence ratios, both linear and quadratic correlations were found between ( d p / d t ) max and P 0 .

Numerical simulation has shown that replacing a part of methane by carbon monoxide in a rich mixture while maintaining the equivalence ratio leads to a decrease in the superadiabatic temperature effect due to the competition of chemical reactions. This is explained by a decrease in the H content in the combustible mixture and a decrease in the superequilibrium concentration of water in combustion products. Using numerical tracer simulation and a comparative analysis of the rates of consumption of CH4 and CO, it has been found that the consumption of both fuels in the CH4/CO/air flame is a competitive reaction path and CO monoxide does not act as an inert component in the low-temperature region of the front (contrary to the statements of a number of authors). Furthermore, the rate of consumption of CH4 is much higher than that of CO due to the larger number of consumption reactions of CH4 and their higher rates. The main contribution to the increase in the concentration of H atoms in the flame in passing from a methane–air mixture to a CH4/CO/air mixture is due to the same reactions that increase the heat release rate: O + CH3 = H + CH2O and CO + OH = CO2 + H. The results obtained and their comparison with literature data lead to the conclusion that the increase in the heat release rate and, hence, the flame propagation rate should be greater in rich mixtures since there the thermophysical effect is higher.

In this study, Al–CuO nanocomposites were fabricated by sol-gel method. As a contrast, the thermite was prepared by physical mixing at the equivalence ratio of 0.5, 1, 2, respectively. The intermediates and samples as prepared were characterized by SEM and XRD. The exothermic properties of the two samples prepared at different equivalence ratios were tested and the reaction products were characterized by XRD. The SEM results show that the sample prepared by the sol-gel method demonstrates a micron-sized agglomerated sphere formed by a mutual wrapping of Al NPs and CuO NPs, and the particles are evenly distributed in the agglomerate. In addition, when the content of Al powder is seriously insufficient, the heat release of the sample prepared by physical mixing is 1.6 times that of by sol-gel method. With the increase of Al powder content, the exothermic properties of Al/CuO NPs prepared by sol-gel method began to increase significantly compared with physical mixing and the difference is 1.5 times when the equivalence ratio increases to 2. It can be concluded that the reason for this result may be attributed to the different mass transfer modes of components due to the different morphologies of samples.

Typical injection schemes of rotating detonation combustors inject fuel locally into the combustion channel, creating stratified fuel-rich and fuel-lean mixing regions. In this study, premixed hydrogen and air rotating detonations are explored in a rotating detonation combustor through premixing part of the fuel into the oxidizer flow. The objective is to investigate the effect of premixing on the operation of the combustor. Three premixing schemes are examined where the detonation wave speeds are analyzed. The results show that in premixing, the fuel-lean regions became more favorable for continuous detonation propagation when premixed with the bypass fuel, resulting in higher detonation wave speeds. This phenomenon is shown to be independent of the global fuel-air equivalence ratio and the amount of fuel premixed into the oxidizer. As such, combustor performance and the operational regime could be improved with lean hydrogen premixing amounts in the main flow oxidizer.

The generation and turbulent transport of temporal equivalence ratio fluctuations in a swirl combustor are experimentally investigated and compared to a one-dimensional transport model. These fluctuations are generated by acoustic perturbations at the fuel injector and play a crucial role in the feedback loop leading to thermoacoustic instabilities. The focus of this investigation lies on the interplay between fuel fluctuations and coherent vortical structures that are both affected by the acoustic forcing. To this end, optical diagnostics are applied inside the mixing duct and in the combustion chamber, housing a turbulent swirl flame. The flame was acoustically perturbed to obtain phase-averaged spatially resolved flow and equivalence ratio fluctuations, which allow the determination of flux-based local and global mixing transfer functions. Measurements show that the mode-conversion model that predicts the generation of equivalence ratio fluctuations at the injector holds for linear acoustic forcing amplitudes, but it fails for non-linear amplitudes. The global (radially integrated) transport of fuel fluctuations from the injector to the flame is reasonably well approximated by a one-dimensional transport model with an effective diffusivity that accounts for turbulent diffusion and dispersion. This approach however, fails to recover critical details of the mixing transfer function, which is caused by non-local interaction of flow and fuel fluctuations. This effect becomes even more pronounced for non-linear forcing amplitudes where strong coherent fluctuations induce a non-trivial frequency dependence of the mixing process. The mechanisms resolved in this study suggest that non-local interference of fuel fluctuations and coherent flow fluctuations is significant for the transport of global equivalence ratio fluctuations at linear acoustic amplitudes and crucial for non-linear amplitudes. To improve future predictions and facilitate a satisfactory modelling, a non-local, two-dimensional approach is necessary.

Gas turbine operation increasingly relies on lean premixed (LPM) combustion to reduce harmful emissions, which is susceptible to thermoacoustic instabilities. Most combustion systems are technically premixed and exhibit a degree of equivalence ratio inhomogeneity. Thermoacoustic pressure oscillations can couple with the heat release oscillations through the generation of equivalence ratio fluctuations at fuel injection sites, which are then convected to the flame front. Previous experimental studies have shown that porous inert media (PIM) can passively mitigate these instabilities by adding acoustic damping and by reducing the thermoacoustic feedback mechanism. To understand the role of PIM on these equivalence ratio oscillations, spatially resolved, phased averaged equivalence ratio fluctuations are measured using the ratio of OH*/CH* chemiluminescence. Spatial imaging of OH* or CH* radicals produce integrated line of sight intensity values and an Abel transformation is used to obtain spatially resolved values. Phase averaged images are synced with dynamic pressure measurements, and an axisymmetric atmospheric burner is used to study the effects of ring-shaped PIM on the spatially resolved equivalence ratio field with self-excited thermoacoustic instabilities. The results show that PIM significantly reduces these fluctuations, and the effects on the stability of the system are discussed.

Nano γAl2O3 has been one of the nanometal oxides that has improved the characteristics of biodiesel. The effect of γAl2O3 nanoparticles addition on premixed flame combustion is investigated with an experiment on the laminar flame speed of Calophyllum inophyllum methyl ester 30% and 70% petrodiesel mixtures, at atmospheric pressure and preheated temperature T = 473K. The γAl2O3 nanoparticles added to CIME30 biodiesel were 0ppm, 100ppm, 200ppm, and 300ppm. Experiments were carried out on a bunsen burner. The equivalent ratio of the mixture between ϕ = 0.67 to 1.17. Experiments revealed that the addition of nanoparticles to CIME30 biodiesel expands the flammability limit and increases the laminar flame speed. CIME30 without nanoparticles, flame stable between ϕ = 0,76 -1,17. CIME30 with nanoparticles, flame stable between ϕ = 0,67 -1,17. Combustion of CIME30 required a lot of air. The highest laminar flame speed occurred at the equivalent ratio ϕ = 0.83. The highest laminar flame speed of CIME30 0, 100, 200, and 300 ppm were 30.77, 34.50, 35.90, 38.45 cm/s respectively. The higher the nano γAl2O3 concentration the higher the laminar flame speed. This occurs due to the catalytic effect of γAl2O3 on biodiesel and its mixtures.

The Cambridge/Sandia turbulent stratified flame (SwB5) is simulated with the LES and Flamelet-Generated Manifolds (FGM) combustion model. Three 3D FGM manifolds are adopted. With the purpose to examine the influence of transport properties, unity and non-unity Lewis numbers ( L e ) are included in the first two manifolds, respectively. The combined effects of non-unity L e and stretch are investigated in the third manifold. Heat loss to the wall is also modeled. Good agreement is found between the simulation and experiment. The equivalence ratio, temperature and mass fractions of CO and H 2 are all well reproduced in contrast with previous simulations. It is found that using non-unity L e can even deteriorate the near-wall temperature modeling. Non-unity L e is proposed to be crucial for the CO prediction as well, besides H 2 . The equivalence ratio modeling is observed to be very important, which accounts for several non-unity L e effects. Flame stretch shows almost no impact on the velocity fields, whereas its effects on the species, equivalence ratio and temperature are identified, although to a limited extent for the Cambridge/Sandia flame.

A numerical investigation of the rapid turbulent filtration combustion within a packed pebble bed is conducted at a fixed superficial velocity of 0.5 m/s, equivalence ratio of 1.0 (methane/air) und...

The influence of the gasification temperature and Equivalence Ratio (ER) on the behavior of an industrial low-grade Solid Recovered Fuel (SRF) was investigated in an air bubbling fluidized bed. The studied SRF exhibits an intermediate composition between biomass-rich SRF and plastic-rich SRF. Its Lower Heating Value (14 MJ/kg) is low since its ash content is very high (35 wt%). But surprisingly, the Cold Gas Efficiency and the Carbon Conversion were relatively high with this type of low-grade SRF. As a result, the syngas produced is quite rich (LHV > 8 MJ/m3 STP) and it may be valorized in gas engines. H2S, HCl, HCN and NH3 in the syngas were analyzed. These results confirm that inorganic gases are an important issue for the valorization of SRF as fuel in gasification processes, even if significant parts of S, N and Cl are not converted into inorganic gases.

Purpose The lean blowout (LBO) limit of the combustor is one of the important performance parameters for any gas turbine combustor design. This study aims to predict the LBO limits of an in-house designed swirl stabilized 3kW can-type micro gas turbine combustor. Design/methodology/approach The experimental prediction of LBO limits was performed on 3kW swirl stabilized combustor fueled with methane for the combustor inlet velocity ranging from 1.70 m/s to 6.80 m/s. The numerical prediction of LBO limits of combustor was performed on two-dimensional axisymmetric model. The blowout limits of combustor were predicted through calculated average exit gas temperature (AEGT) method and compared with experimental predictions. Findings The results show that the predicted LBO equivalence ratio decreases gradually with an increase in combustor inlet velocity. Practical implications This LBO limits predictions will use to fix the operating boundary conditions of 3kW can-type micro gas turbine combustor. This methodology will be used in design stage as well as in the testing stage of the combustor. Originality/value This is a first effort to predict the LBO limits on micro gas turbine combustor through AEGT method. The maximum uncertainty in LBO limit prediction with AEGT is 6 % in comparison with experimental results.

Ammonia is a carbon-free fuel that has the potential to meet increasing energy demand and to reduce CO2 emissions. In the present work, the characteristics of pollutant emissions in ammonia premixed laminar flames are investigated using one-dimensional simulations, and heat release rate (HRR) surrogates for ammonia combustion are proposed. Both atmospheric and high-pressure conditions were considered, and four representative mechanisms for ammonia combustion were employed. It is shown that the total emission of NO and NH3 achieves a minimum around an equivalence ratio (ϕ) of 1.1 under atmospheric conditions, and there is no noticeable emission of NO and NH3 for ϕ = 1.1 ~ 1.5 under high-pressure conditions. Three HRR surrogates, [NH3][OH], [NH2][O], and [NH2][H], were proposed based on the analysis of HRR and elementary reaction profiles. The performance of HRR surrogates was found to vary with equivalence ratios. For example, with the Miller mechanism, [NH3][OH], [NH2][O], and [NH2][H] have the best performance under atmospheric conditions at ϕ = 1.15, 0.95 and 1.05, respectively, and under high-pressure conditions at ϕ = 1.11, 0.87 and 0.96, respectively. Similar conclusions can also be drawn with other mechanisms. These findings provide valuable insights into emission control and flame identification of ammonia combustion.

To pinpoint the relationship between high frequency tangential instability(HFTI) and continuous rotating detonation (CRD), series of H2/Air rotating detonations are experimentally achieved in the hollow chamber with Laval nozzle. The contraction ratio of the nozzle has a significant effect on the detonation. The detonation waves number increases with the increasing of equivalence ratio (ER) or nozzle contraction ratio. Based on its character, a new type of detonation is defined as two dominant peak one wave mode (TDPO). The velocities of detonation waves propagating in this new mode are larger than the Chapman-Jouguet (CJ) theoretic value. On the assumption that the reflection wave is rotated with the detonation wave, this mode is well illustrated. The forming process of two waves is also given. The results show that the appearance of combustion mode is relative to the reflection wave generated at the contraction section of the nozzle. The inner mechanism of the refection wave is illustrated. These works make a foundation to investigate the relationship between rotating detonation and tangential instability.

Flame propagation in Hele-Shaw cells with a micro-sized gap was experimentally investigated. The evolution of flame front morphology was recorded via Schlieren photographs as the hydrogen-oxygen (H2–O2) mixture was ignited at ambient temperature and pressure. By varying gap size, two different regimes of flame propagation are identified: 1) the non-accelerating flame in narrow gaps; 2) the self-accelerating flame in relatively wide gaps. For the former, the initial flame front is globally circular, and subsequently evolves into branches separated from the surface, exhibiting dendritic-growth and fingering shapes. In the latter regimes, the flame front exhibits a cellular structure and accelerates nearly sonic speed due to hydrodynamic instabilities. It is found that the flame acceleration depends non-monotonically on the gap size due to the competing mechanisms of viscosity friction and heat loss through the walls. The effect of equivalence ratio on the non-accelerating flame is studied to identify the mechanism controlling the local extinction flame.

The experience is observed for fourstrokes petrol engine for revolution 1000 rpm - 4000 rpm, with used of power air screw oncarburator and cyclone on outlet intakemanifold. Air – fuel mixture have passed ofcyclone to combustion chamber to becometurbulent flow and homogen. Then theexperience of step by step used power screwand cyclone. The first investigation on standarcondition, the second put of power air screwon carburator, the third put of cyclone on outletintake manifold, the fourth put of combinationof power air screw and cyclone. It wasobserving for increasing air – fuel equivalenceratio and reduction of exhaust COconcentration. Actually, used combination ofpower air screw and cyclone are resulted ofcarbon monoxide concentration drop ofenough significant for 2500 rpm and 4000 rpm,respectively 51% and 67%. The carbonmonoxide least concentration is 1,14% oncondition 4000 rpm.

Aircraft engines must always maintain a margin between the operating equivalence ratio and the lean blowout boundary because flame-out presents a significant risk to the safety of the aircraft. It ...

A three-dimensional Direct Numerical Simulation (DNS) database of statistically spherical flames propagating into the mono-sized droplet-laden mixtures for an overall (i.e. gaseous + liquid phases) equivalence ratio of unity has been considered to investigate the distribution of flame topologies associated with flame self-interaction events. The analysis has been carried out for different values of initial droplet diameters and turbulence intensities to demonstrate their influences on the statistics of flame self-interactions. Spherically expanding stoichiometric premixed gaseous flames have also been additionally considered for the same initial burned gas radius and turbulence intensities for the purpose of comparison with the cases propagating into droplet-laden mixtures. It has been found that the topologies associated with flame self-interaction predominantly occur close to burned gas side of the flame front for turbulent premixed flames and also for droplet cases with small turbulence intensities, although tunnel closure/formation topologies are prevalent in premixed flames in contrast to unburned mixture pocket type topologies in the droplet cases. The distribution of the flame topologies has been observed to be influenced by both turbulence intensity and droplet diameter. The flame self-interaction events have mostly been found in the preheat zone for highly turbulent spray flames. It has been found that the occurrence of tunnel formation and closure topologies dominates over the availability of the unburned and burned mixture pockets in all cases except for the droplet cases under low turbulence intensities. The frequency of flame self-interaction events increases with increasing turbulence intensity and droplet diameter. The differences in the nature and distributions of flame self-interaction events between turbulent premixed and droplet cases are likely to have important implications on the possible extension of flame surface based modelling methodologies for simulating turbulent combustion in droplet-laden mixtures.

In the present study, we investigate the effect of preheating of the reactants on the dynamics of a turbulent bluff-body-stabilized dump combustor during the onset of thermoacoustic instability. As we decrease the equivalence ratio towards a low fuel-lean value, we observe the dynamical transition of the combustor from the state of combustion noise to thermoacoustic instability via intermittency. Such an intermittency route to thermoacoustic instability is preserved for the range of preheat temperatures considered in this study. Further, we notice that an increase in the temperature of the reactants advances the point of the onset of thermoacoustic instability in the system. During the state of combustion noise, high temperature preheating of the reactants shifts the anchoring point of the flame from the shaft to the tip of the bluff-body and suppresses the oscillatory behavior of the global heat release rate in the system. We also observe a change in the multifractal characteristics of the heat release rate fluctuations such that the signal properties change from short-range to long-range correlations. On the other hand, preheating of the reactants to high temperatures during the state of thermoacoustic instability engenders a shift in the frequency of the acoustic field from the third unstable mode to the first unstable mode. Moreover, such preheating expanses the flame surface from one half of the combustor (lower) to both halves and, hence, increases the Pearson’s correlation between the local heat release rate fluctuations measured on both halves of the combustor. Thus, we report that the preheating of the reactants significantly alters the dynamical characteristics of a turbulent combustor during the transition to thermoacoustic instability from that observed in the absence of preheating.

In this study, we investigate the flame stabilization behavior in hydrogen-enriched stratified swirl flames after the flame flashes back into an annular mixing tube with an axial swirler of swirl number 0.9. Two different modes of flame stabilization, namely intermediate stabilization and flameholding, are identified. For 80% or higher hydrogen enrichment of the fuel, the flashback is found to result in flameholding. Acetone-PLIF measurements are used to assess the equivalence ratio distribution in the mixing tube. It is shown that the flow inside the mixing tube has intermittent presence of fuel-rich pockets. Furthermore, high speed laser diagnostic and simultaneous chemiluminescence imaging was carried out to understand the transition of flame propagation from the center-body boundary layer to the outer wall boundary layer. With the help of time-resolved images and simultaneous velocity fields, four different stages of flashback-to-flameholding transition were identified. It was noted that the bright flame kernels formed due to the flame's interaction with fuel-rich pockets, impose significant deflection on the approach flow in the vicinity of the outer wall boundary layer. Acute-tipped narrow flame structures were found to anchor the flame on the outer wall. These flame structures were found to accelerate upstream upon reaching the fuel-rich regions in the outer wall boundary layer.

The most commonly used for gasification of village-level solid waste is the fixed-bed gasifier, but there is no reasonable method to evaluate the gasification process. This paper attempts to find a gasifier that is most suitable for gasification of village-level solid wastes through exergy analysis method. Based on experimental data from literature, the exergy efficiencies and LHV(Low Heat Value) of product gas from updraft and downdraft fixed bed gasifier are studied in this paper. The results show that the updraft fixed bed gasifier has higher exergy efficiency, and the gas produced by the downdraft fixed bed gasifier has a higher heating value. Air gasification has higher exergy efficiency than steam gasification and pure oxygen gasification. The highest exergy efficiency at a gasification temperature of about 1000 °C and ER (Equivalence Ratio) value in the range of 0.33–0.36. The volatile content of gasification raw materials is higher, and the gasification efficiency is higher. Through the research of this paper, a new path to reasonably evaluate the gasification process is obtained.

Recent studies have demonstrated that ammonia could be one of the most promising hydrogen carrier candidates which can be used in large-scale power plants. However, it is challenging to burn ammonia in gas turbines due to its narrow flame stabilization limits. This study investigates the blow-off characteristics and flame macrostructure transition behavior of ammonia/air flame (i.e. NH3 flame) and ammonia/methane/air flame (i.e. 50%NH3 flame) in a swirl combustor. Methane/air flame (i.e. CH4 flame) is also demonstrated for comparative purposes. The flow field and instantaneous OH profile are measured with PIV and OH-PLIF technique, respectively. Large eddy simulation (LES) is conducted to extend understandings of the experimental findings. The results show that the NH3 flame possesses a poor lean flame stability limit which can be largely extended by adding CH4 in the fuel. Moreover, changing swirl number (S) shows no apparent effect on the lean blow-off limit (ϕb) for the NH3 flame. On the contrary, a clear extension on ϕb is found for the 50%NH3 flame when increasing S. Four flame macrostructure modes can be identified when decreasing equivalence ratio (ϕ). The transition from flame II to flame III (ϕt describes the transition equivalence ratio) can be considered as the early warning of blow-off for a swirl stabilized flame. It is found that for the NH3 flame, there is no clear flame macrostructure transition at small inlet velocities (U

In this work, the flame structures of the recent Darmstadt turbulent premixed/stratified flame series with 20% volume fraction H2 addition (Schneider et al., PCI, 2019) are analyzed using flamelet tabulated manifolds. Three different methane/hydrogen flames (MHFs) with increasing complexity are studied. The effects of differential diffusion, stretch and stratification on the applicability of the flamelet model are investigated in detail. Specifically, to investigate the differential diffusion effects, three different modeling approaches are considered, in which the diffusion fluxes are calculated using the multi-component (MC), mixture-averaged (MA) and unity Lewis number (Le1) approaches. To investigate stretch effects, a strained premixed flamelet (SPF) model is proposed, in which the flame’s internal response to stretch is characterized with an additional tabulation coordinate. A double-conditioning analysis is conducted for different flame series. The dataset is conditioned on both the local equivalence ratio and local stratification to analyze the coupling effects of stratification and differential diffusion on the flame structure. Overall, the flamelet predictions are consistent with the experimental findings for all flames.

A counterflow two-phase diffusion flame with polydisperse spray is numerically studied in a 2D configuration, using a Lagrangian formalism for the liquid phase and accurate combustion chemistry. Results exhibit a very complex double flame structure with diffusion and premixed flames, as well as group and individual droplet burning. Monodisperse two-phase counterflow flames are also computed to help analyse the polydisperse flame, and confirm the strong link between droplet diameter and flame regime. For small droplet diameters, the flame has the same structure than a gaseous flame at a different equivalence ratio, and the total heat release of the flame increases with the droplet size. For larger droplets, the premixed mode becomes dominant and the total heat release of the flame exceeds the maximum gaseous diffusion one.

Dependence of flame suppression concentration on the equivalence ratio was analyzed using modeling premixed propane/air flame inhibited by 2-BTP, Novec 1230, CF3Br, H2O, CO2, and N2. It was obtaine...

Central airflow has been widely used to improve the performance of swirl burners in engineering applications. This paper reports an experimental investigation on the effects of such airflow on the combustion stability and shape of swirl flames. The results show that, for a low equivalence ratio, central airflow changes the flame shape from an “inverted cone” to a “rectangle” and significantly increases the flame height. Raising the speed of the central airflow increases the maximum temperature on the central axis of the swirl flame because the airflow enhances the upward momentum of the fuel. By contrast, for a high equivalence ratio, the swirl flame is prone to liftoff owing to the influence of the central airflow on the axial momentum of the fuel. In this case, increasing the fuel flow causes the swirl-flame blowout limit to increase and then decrease. This limit for different equivalence ratios is well described by dimensionless function. These findings will provide an important reference for the design of safe and high-performance swirl burners.

Using a combustion synthesis, the range of achievable textures is broader than using conventional synthesis methods and can be controlled more successfully. As a tool allowing the achievement and control of desired textures, here we bring about wet chemistry synthesis using aluminium nitrate nonahydrate (ANN) precursor systematically combined with different fuels (amino acids). The amino acids ; glycine (G), alanine (A) and asparagine (N) have been specifically selected in order to show the role of gradual increase in their: (1) molar mass, (2) enthalpy of combustion, (3) amine groups content and (4) ratio to ANN. Detailed (micro) structural and thermal characterisations confirm that the nanocrystalline character and thermomechanical stability were not diminished in the course of this synthesis. The conditions leading to development of different morphologies from gels to powders were found to be heavily under the influence of fuel/oxygen ratio, i.e. of the smouldering versus flaming mechanism of the combustion. Higher content of nitrates (predominately from amino-rich amino acids) strongly promoted auto-combustion behaviour. As- derived alumina precursors have been thermally treated at various temperatures (quenched and soaked), to monitor γ- and α-alumina crystallisation, with respect to the development of morphology. Different texture types have been observed, such as porous wormhole, porous and porous expanded flakes. Higher fuel levels promote specific surface increase. This combustion synthesis allows facile tailoring of nanocrystalline γ-alumina with different morphological features, whereas samples having optimal parameters were suitable for catalyst support application on behalf of rapid sorption performance.

Integration of gasification with CO 2 capture using CaO sorbent is proposed as an alternative treatment to convert municipal solid waste (MSW) into energy. Aspen Plus process simulator was employed to study the process. Two models were built to represent the non-sorbent and the sorbent-enabled MSW gasification. The model validation against available experimental data shows high accuracy of the simulation result. The effect of CO 2 capture using CaO sorbent on the syngas composition and lower heating value (LHV) was observed by comparing the two models, and sensitivity analysis was performed on both models. Several process parameters affecting the syngas composition and LHV were investigated, including CaO/MSW ratio, temperature, equivalence ratio, and steam/MSW ratio. The addition of CaO sorbent for CO 2 capture was found to successfully reduce the CO 2 content in the syngas, increase the H 2 composition, and improve the syngas LHV at the temperature below 750 o C. The maximum H 2 composition of 56.67% was obtained from the sorbent-enabled gasification. It was found that increasing equivalence ratio leads to a higher H 2 concentration and syngas LHV. Raising steam/MSW ratio also increases the H 2 production, but also reduces the LHV of the syngas. Observation of the temperature effect found the highest H 2 production at 650 o C for both non-sorbent and sorbent-enabled gasification.

The self-similar propagation of expanding spherical flames in lean hydrogen–air mixtures at elevated pressure was experimentally investigated using a dual-chamber apparatus with the quartz windows that enabled observing a flame radius of up to 110 mm. The flame images of the fully developed cellular structure were recorded, and the largest values of r/rc and Pe for the dual-chamber apparatus were estimated. The acceleration exponent, α, corresponding to the fractal dimension in lean hydrogen–air mixtures at elevated pressure was evaluated by plotting the experimental flame radius as a function of time. In this study, the experimental values of α (α = 1.25–1.43) occur within a wide range of r/rc (r/rc = 2–15). The observed trend of α to increase with a decrease in equivalence ratio, φ, and an increase in initial pressure, Pi, is owing to the effects of the diffusional–thermal and Darrieus–Landau instabilities. The value of α increased with an increase in r/rc and saturated at α = 1.43 at r/rc > 10, and the saturated values of the hydrogen–air flame are within α = 1.4–1.5. The results demonstrated that the flame propagation in lean hydrogen–air mixtures was classified as laminar (r/rc 1), transition (1 10) regimes. Consequently, the practical three-dimensional fractal dimensions for accidental hydrogen–air explosions are D3 = 2.24–2.33.

an invasive weed species, is widely available in different agro-climatic zones of India and has a huge potential in the gasification process. In the present investigation, the fuel properties of ...

Gasification is a process of converting carbon-enriched materials like phytomass, biowaste, etc. into a volatile gas popularly termed as “Producer gas” by providing a limited amount of gasifying ag...

Aviation heavy-fuel spark ignition (SI) piston engines have been paid more and more attention in the area of small aviation. Aviation heavy-fuel refers to aviation kerosene or light diesel fuel, which is safer to use and store compared to gasoline fuel. And diesel fuel is more suitable for small aviation application on land. In this study, numerical simulation was performed to evaluate the possibility of switching from gasoline direct injection spark ignition (DISI) to diesel DISI combustion. Diesel was injected into the cylinder by original DI system and ignited by spark. In the simulation, computational models were calibrated by test data from a DI engine. Based on the calibrated models, furthermore, the behavior of diesel DISI combustion was investigated. The results indicate that diesel DISI combustion is slower compared to gasoline, and the knock tendency of diesel in SI combustion is higher. For a diesel/air mixture with an equivalence ratio of 0.6 to 1.4, higher combustion pressure and faster burning rate occur when the equivalence ratios are 1.2 and 1.0, but the latter has a higher possibility of knock. In summary, the SI combustion of diesel fuel with a rich mixture can achieve better combustion performance in the engine.

espanolEl objetivo del presente trabajo de investigacion ha sido determinar la velocidad de llama del gas natural de Camisea-Peru en un rango amplio de razon de equivalencia mediante un estudio experimental. Se ha implementado los calculos matematicos utilizando el metodo de la teoria termica mediante MathCad y simulando en un mecanismo cinetico actual utilizando el programa CHEMKIN. Se ha conseguido experimentalmente valores de velocidad de llama entre 5% al 10% mayor al metano 100% puro comparado con otros autores en un amplio rango de razon de equivalencia. Esto valida los resultados debido a que el gas ensayado es gas natural con 88.54% de metano y 10.32% de etano, mejorando de esta manera el banco de ensayo experimental del laboratorio de combustion y control de emisiones gaseosas. En conclusion, la metodologia empleada proporciona una adecuada base de datos de velocidad de llama para el gas natural de Camisea-Peru. EnglishThe objective of the present research study was to determine the flame speed of Camisea-Peru natural gas in a wide range of equivalence ratio through an experimental study. Mathematical calculations were implemented using the method of thermal theory in MathCad. Simulations in a current kinetic mechanism were performed using the CHEMKIN program. Values of flame velocity were 5% to 10% higher than 100% pure methane when compared to other authors in a wide range of equivalence ratio. This validated the results since the gas tested was natural gas with 88.54% methane and 10.32% ethane, thus improving the experimental test bench of the laboratory for the combustion and control of gaseous emissions. In conclusion, the methodology presented here provides an adequate database of gas flame velocity for natural gas of Camisea-Peru.

Productions of mono-/di-cyclic aromatic hydrocarbons as well as smaller stable species from extremely fuel-rich CH4/air mixtures (equivalence ratio of 1.7–6.0 and fuel-to-mixture ratio of 15–38 mol...

The effects of droplet diameter, overall (i.e. liquid and gaseous phases) equivalence ratio, and turbulence intensity on the variation of the Minimum Ignition Energy (MIE) for localized forced igni...

A comprehensive experimental and kinetic modeling study of the ignition delay time (IDT) characteristics of some binary blends of C1–C2 gaseous hydrocarbons such as methane/ethylene, methane/ethane, and ethane/ethylene was performed over a wide range of composition (90/10, 70/30, 50/50%), temperature (∼800–2000 K), pressure (∼1–40 bar), equivalence ratio (∼0.5–2.0), and dilution (∼75–90%). An extensive literature review was conducted, and available data were extracted to create a comprehensive database for our simulations. Based on the existing literature data, an experimental matrix was designed using the Taguchi approach (L9) in order to identify and complete the experimental matrix required to generate a comprehensive experimental IDT set necessary for the validation of a chemical kinetic model. The required high- and low-temperature IDTs were collected using low-/high-pressure shock tubes and rapid compression machines, respectively. The predictions of NUIGMech1.0 are examined versus all of the available experimental data, including those taken in the current study using the IDT simulations and a correlation technique. Moreover, the individual effect of the studied parameters, including mixture composition, pressure, equivalence ratio, and dilution on IDT, is investigated over the studied temperature range. Correlations that were developed based on NUIGMech1.0 are presented for each specific blended fuel over the conditions studied. These correlations show an acceptable performance versus the experimental data. The authors would like to express their gratitude to Shell Research Ltd. and Science Foundation Ireland (SFI) for funding via project numbers 15/IA/3177 and 16/SP/3829. The authors from PCFC, RWTH Aachen University, would like to recognize the funding support from the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) through the project number – 322460823 (HE7599/2-1). peer-reviewed 2021-06-03

The oxidation of CH4/diethyl ether mixtures was studied with laser absorption-based time-resolved temperature and CO concentration measurements behind reflected shock waves. Fuel-rich (equivalence ratio ϕ = 2.0) mixtures were studied because of their relevance for mechanism development for partial oxidation reactions in the context of polygeneration processes and measurements at ϕ = 0.5 and 1.0 were used to verify the mechanism performance in an extended range of equivalence ratios. Temperature and CO concentration were measured via absorption using two fundamental vibrations of CO (ν" = 0, P20 and ν" = 1, R21) with two mid-IR quantum-cascade lasers near 4.8546 and 4.5631 µm. Interference from broadband absorption of CO2 in the region near 4.56 µm was quantified based on measured temperature-dependent CO2 absorption cross-sections and mechanism-based prediction of CO2 concentrations. The measured temporal CO-concentration and temperature profiles were compared with simulations based on two mechanisms (Fikri et al., 2017; Yasunaga et al., 2010). For mixtures with ϕ = 0.5, the two mechanisms show similar results, and well reproduce the experimental data. At ϕ = 1.0 and 2.0, the Fikri et al. mechanism shows very good agreement with the experiments whereas the Yasunaga et al. mechanism predicts a too fast CO-concentration and temperature rise.

The control of PM emission is a rather complicated problem to be solved both for diesel engine and GDI engines. There are vast factors affecting PM emission, the fuel, A/F, combustion temperature and so on. But undoubtedly, most efforts are paid to exhaust aftertreatment, rather than the control of generation. This paper is to investigate the effect of dimethyl ether (DME, CH3OCH3) on soot generation in flame. Therefore, a laser induced incandescence (LII) measurement system for soot volume concentration measurements in flame is used. Two DME gaseous mixtures were prepared with equivalence ratios 1 and 2. To highlight its effect on soot formation, acetylene known as the precursor of soot, is added in different ratios. Similarly, CO2 is mixed to simulate exhaust gas recycling (EGR) effect in engines. The experimental results indicate that the fuel property and A/F ratio are the dominating factors for the generation of soot during combustion. The combustion of DME doesn't emit soot obviously even under rich mixture condition. When burning the mixture of DME and acetylene (C2H2) in different proportion, there is barely soot emission at equivalence ratio of 1. The soot emission increases as the proportion of C2H2 increases at equivalence ratio 2, and the DME addition reduces the soot emission of C2H2 flame. CO2 dilution doesn't lead to the increase of soot when burning DME at equivalence 1 and 2. Soot emission is lower when the mixture of DME and acetylene is diluted by CO2, though soot volume concentration increases slightly as the proportion of C2H2 increases. The kinetic analysis indicates that the combustion of DME does not produce the precursor of soot. Under fuel-rich combustion conditions, C2H2 reacts with H radical to form C2H3, which leads to soot. When DME is added, it competes for H radical, which reduces the formation of C2H3 and thus reduces soot formation. The research carried out in this paper indicates that DME fuel has obviously power to reduce soot formation during combustion, no matter whether it is diluted by CO2 or mixed with soot precursor substance C2H2.

Palm kernel shell (PKS) biomass has great potential for power generation via gasification as it contains high energy content. However, abundant it may be, the source of PKS is scattered throughout the country, thus the consistency of feedstock supply may be hard to maintain. Co-gasifying with another source, such as plastics, can be seen as one of a solution to mitigate the supply chain problem. Polystyrene (PS) plastics have potential as a plastic feedstock because of its high domestic and industrial usage. As PS is also hard to recycle, using PS as a co feedstock for gasification is a way for PS waste management. However, the study on the performance of air co-gasification of PKS and PS has not been done before. It is essential to investigate the performance before it is utilized in the real world. In this work, the performance co-gasification of PKS and PS with different operating conditions was investigated. The gasification experiment was done in an electrically heated downdraft gasifier with a diameter of 8 cm. The reaction temperature was varied from 700 to 900 °C, with the equivalence ratio varied from 0.07 to 0.27. The PS weight percentage of the total feedstock was varied from 0 to 30 wt%. It was found that the vol% of CO and H2 on the producer gas increased with temperature while reducing the vol% of CO2 and CH4. HHV and the amount of gas produced were also increasing with increasing temperature. Increasing ER reduced the HHV of the gas but increased the amount of gas produced. Adding more PS to the feedstock blend increased the percentage of the produced gas at 900 °C, however, at the lower temperature of 800 °C, the percentage of gas produced decreased with increasing PS wt%.

This study uses a port-injection spark-ignition four-cylinder natural gas engine to achieve TFR (Thermochemical fuel reforming) mode. To study the effects of fuel reactivity on combustion, reforming process, emissions and fuel economy, chemicals including n-heptane, PRF50 and isooctane are respectively used as enriched fuel. The results show that the higher the reactivity of the enriched fuel, the better the combustion and cycle stability of the reforming cylinder. However, n-heptane enrichment with high reactivity has the problem of knocking at large equivalence ratio. The enrichment limit of PRF50 is the highest, which combines the properties of n-heptane and isooctane. The H2 production abilities of three enriched fuels are similar, but that of isooctane is slightly lower under large equivalence ratios. In terms of fuel economy, the three perform similarly at small equivalence ratios. Whereas it’s lower with isooctane enrichment at large equivalence ratios, which is at the expense of increased NOx emission.

The synergistic effects of chain length, functional group position, and equivalence ratio on the combustion and emission characteristics of lower alcohols were investigated in a constant volume ves...

The response of laminar methane/air counterflow premixed flames under sinusoidal equivalence ratio oscillation was investigated numerically. The timescales of the oscillation were chosen to be sufficiently longer than the flame timescale so that the flame responds quasi-steadily. The response of periodically stratified flame (SF) with a detailed reaction mechanism exhibited the “back-support” effect, in that the consumption speed Sc response deviated increasingly from Sc of steady homogeneous flames (HFs) at higher oscillation frequencies. It was shown that even when the imposed oscillation timescale is much longer than the flame timescale, the flame response can still be delayed under a sufficiently large equivalence ratio gradient. Subsequently, the above results were compared with those obtained with a global four-step mechanism that omits back-diffusion radicals into the reaction zone. As a result, SFs with the global mechanism displayed a much smaller back-support effect in both lean and rich mixtures. Further analysis with modified diffusion coefficients revealed the dominant roles of H2 and radical species diffusion in inducing the back-support effect. Contrary to the previous findings, variations in burned gas temperature were found to play a negligible role in modifying Sc. Additionally, the hysteresis of the back-support effect under periodical stratification was found to be more prominent on the richer side because of the presence of a larger H2 pool.

This study investigated the formation and emission characteristics of nitric oxide (NO) from flameless MILD (moderate or intensive low-oxygen dilution) combustion (MILDC) versus traditional visible-flame combustion (TC) in a 30-kW furnace. Both combustion processes were experimentally operated successively in the same furnace, burning natural gas at a fixed rate of 19 kW and the equivalence ratio of 0.86. Numerical simulations of TC and MILDC were carried out to explain their distinction in the measured furnace temperature and exhaust NO emissions. Present measurements of the NO emission (XNO) versus a varying furnace wall temperature (Tw) have revealed, at the first time, that the relationship of XNO ∼ Tw was exponential in both TC and MILDC. By analyzing the simulated results, the average temperature over the reaction zone was identified to be the common characteristic temperature for scaling NO emissions of both cases. Moreover, relative to TC, MILDC had a fairly uniform temperature distribution and low peak temperature, thus reducing the NO emission by over 90%. The thermal-NO formation was found to contribute more than 70%–80% to the total XNO from TC while the N2O-intermediate route dominated the NO emission from MILDC.

This research work depicts the results obtained during the experiment performed for walnut shell gasification process. In order to carry out the gasification process, a downdraft gasifier h...

Low-order ignition models are important tools in the design of aviation gas turbines. In this paper, a stochastic model that predicts the ignition probability in a combustor based on a timeaveraged cold- ow solution is extended to include local fuel concentration uctuations due to the polydisperse nature of the spray. For this, a stochastic approach to modelling such uctuations is considered, and the e ects of the ow and mixture parameters on the resulting equivalence ratio pdfs are investigated. The concentration of fuel in large droplets results in a high variation of the local equivalence ratio, hence a ecting the local ammability factor at the model's cell scale. The extinction criterion of the ignition model based on a critical Karlovitz number is calibrated based on ignition probability data from canonical experiments using jet fuel, suggesting critical Karlovitz values of spray ames between 0.2-0.6, which is to be contrasted with values of 1.5 for gaseous fuels.