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To explore the combustion characteristics of ammonia‒hydrogen‒air flame, explosion venting experiments of ammonia‒hydrogen‒air mixtures with different equivalence ratios (ϕ), in the range of 0.6–1.7, are carried out in a 2 m long duct. The results show that the pressure‒time histories inside the duct have a three-peak structure (P b , P out , and P ext), which is caused by the burst of the vent cover, venting of burned mixtures, and counterflow flame generated by the external explosion, respectively. P out evolves into three pressure peak types with increasing ϕ. The pressure peak value P e is generated at the pressure measuring point outside the duct because of the external explosion. The change in P e with ϕ is consistent with P out and P ext , all of which increase first and then decrease with increasing ϕ and reach a maximum value at ϕ = 1.3. This study provides basic theoretical support for the promotion and application of ammonia mixed fuel. • The effects of the equivalence ratio, ϕ , on duct-vented ammonia‒hydrogen‒air deflagration were studied. • Counterflow flame generated by the external explosion was observed in all experiments. • The pressure‒time histories inside the duct under each operating condition present had a three-peak structure. • The maximum overpressure inside and outside duct first increased and thereafter decreased. [ABSTRACT FROM AUTHOR]

Hydrogen, as a clean and promising energy carrier, is considered a viable alternative fuel for the future. However, accidental hydrogen leakages and explosions pose considerable safety concerns in hydrogen energy applications and process industries. This study investigated the flame propagation characteristics of non-uniform premixed hydrogen-air mixtures in a rectangular closed duct with a length-to-diameter ratio of 5.78, taking into account varying equivalence ratios and diffusion times. First, numerical simulations using FLUENT were conducted to model the hydrogen diffusion process in a confined space, determining the hydrogen concentration evolution post-leakage. After approximately 200 s of diffusion, the premixed hydrogen-air mixtures remained in a state of homogeneous mixing, with the hydrogen concentration stabilizing at approximately 1.25 × 10−2 kg/m³. Subsequently, experimental observations were performed using a visual pipeline system, high-speed photography, and flame structure analysis. These experiments examined inhomogeneous hydrogen-air mixtures under seven different equivalence ratios and five different diffusion time conditions. The effects of equivalence ratios and diffusion times on flame propagation characteristics were analyzed. The results revealed that equivalence ratio significantly influenced the flame structure, with higher equivalence ratios producing more pronounced flame surface wrinkles. However, the typical evolution of the tulip flame remained consistent. At a constant equivalence ratio, flame propagation velocity exhibited an initial increase followed by a decrease over time. These findings demonstrate that turbulence intensity accelerated the flame propagation in non-uniform premixed hydrogen-air mixtures. This study underscores the importance of further research on hydrogen safety fundamentals and technologies to develop comprehensive safety standards. • The evolution law of hydrogen concentration field in confined space was determined by FLUENT. • The flame propagation characteristics of the non-uniform premixed hydrogen-air mixtures were investigated. • Effects of equivalence ratios and diffusion times on the flame propagation characteristics of the premixed gas were analyzed. • A detailed comparative analysis was conducted on characteristics such as flame structure and propagation velocity. [ABSTRACT FROM AUTHOR]

In order to reveal the deflagration mechanism of DME/H2-blended gasses, the micro-mechanism was studied based on the constructed UC San Diego 2016 pyrolysis oxidation mechanism model. The results show that adiabatic flame temperature and laminar flame speed increase with the increase in the equivalence ratio (Φ); they first increase and then decrease with the increase in the hydrogen (H2)-blended ratio (λ), and with the increase in λ, the Φ corresponding to the peak laminar flame speed of the blended gas increases. The addition of H2 increases the consumption of O2, and H2 reacts with CO to form H2O and CO2, promoting complete combustion. When Φ = 1.0–1.2, the equilibrium mole fraction of H and OH-activated radicals reach the maximum, and with the addition of H2, the concentration of activating radicals gradually increases, while the number of promoted elementary reactions increases by two, and the number of inhibited elementary reactions does not increase. Meanwhile, the addition of H2 increases the reaction rate of most reactions on the main chemical reaction path CH3OCH3→CH3OCH2→CH2O→HCO→CO→CO2 of DME and increases the risk of the deflagration of DME/H2-blended gas. [ABSTRACT FROM AUTHOR]

In the endeavor to accomplish a fully de-carbonized globe, sparkling interest is growing towards using natural gas (NG) having as vastly major component methane (CH4). This has the lowest carbon/hydrogen atom ratio compared to other conventional fossil fuels used in engines and power-plants hence mitigating carbon dioxide (CO2) emissions. Given that using neat hydrogen (H2) containing nil carbon still possesses several issues, blending CH4 with H2 constitutes a stepping-stone towards the ultimate goal of zero producing CO2. In this context, the current work investigates the exergy terms development in high-speed spark-ignition engine (SI) fueled with various hydrogen/methane blends from neat CH4 to 50% vol. fraction H2, at equivalence ratios (EQR) from stoichiometric into the lean region. Experimental data available for that engine were used for validation from the first-law (energy) perspective plus emissions and cycle-by-cycle variations (CCV), using in-house, comprehensive, two-zone (unburned and burned), quasi-dimensional turbulent combustion model tracking tightly the flame-front pathway, developed and reported recently by authors. The latter is expanded to comprise exergy terms accompanying the energy outcomes, affording extra valuable information on judicious energy usage. The development in each zone, over the engine cycle, of various exergy terms accounting too for the reactive and diffusion components making up the chemical exergy is calculated and assessed. The correct calculation of species and temperature histories inside the burned zone subsequent to entrainment of fresh mixture from the unburned zone contributes to more exact computation, especially considering the H2 percentage in the fuel blend modifying temperature-levels, which is key factor when the irreversibility is calculated from a balance comprising all rest exergy terms. Illustrative diagrams of the exergy terms in every zone and whole charge reveal the influence of H2 and EQR values on exergy terms, furnishing thorough information. Concerning the joint content of both zones normalized exergy values over the engine cycle, the heat loss transfer exergy curves acquire higher values the higher the H2 or EQR, the work transfer exergy curves acquire slightly higher values the higher the H2 and slightly higher values the lower the EQR, and the irreversibility curves acquire lower values the higher the H2 or EQR. This exergy approach can offer new reflection for the prospective research to advancing engines performance along judicious use of fully friendly ecological fuel as H2. This extended and in-depth exergy analysis on the use of hydrogen in engines has not appeared in the literature. It can lead to undertaking corrective actions for the irreversibility, exergy losses, and chemical exergy, eventually increasing the knowledge of the SI engines science and technology for building smarter control devices when fueling the IC engines with H2 fuel, which can prove to be game changer to attaining a clean energy environment transition. [ABSTRACT FROM AUTHOR]

This study examines the impacts of equivalence ratio and temperature for different liquid–gas fuel mixtures such as hydrogen, methane, propane and benzene, ethanol, gasoline, hexane, isooctane, methanol and toluene on the variation of power output, thermal efficiency, efficiency of exergy (second law efficiency) and NO formation were examined. The mixtures consist of 50% of liquid fuels and 50% of gaseous fuels. The results revealed that the equivalence ratios and fuel temperatures remarkably affect the NO and performance of the spark ignition engine. The minimum values of performance characteristics of the fuels are attained at 1.5 of equivalence ratio. Maximum power output values are observed at 1 of the equivalence ratio. Power, thermal and exergy efficiencies decrease with increasing fuel temperatures. However, NO formation has reverse relation with temperature. Maximum and minimum values of power output are 16.21 kW and 1.03 kW which are observed with toluene–hydrogen and methanol–hydrogen mixtures. Maximum and minimum values of thermal efficiency are 45.04% and 3.29% which are observed with benzene–hydrogen and methanol–hydrogen mixture combustion. The same mixture kinds provided maximum and minimum values of exergy efficiency and NO formation as 45.24–3.28% and 1.83E-06 mol/cm3–2.97E-32 mol/cm3, respectively. In the results, the performance characteristics are changed depending on equivalence ratios and fuel temperatures. [ABSTRACT FROM AUTHOR]

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Underground coal gasification is a complex physico-chemical process. UCG thermodynamic equilibrium model was established and validated, and the effects of the steam-to-oxygen ratio (RH2O/O2) and the equivalence ratio (ER) on the gasification temperature and the gaseous products were investigated. At low ER (0.08–0.14), coal is incompletely gasificated when the gasification temperature is less than the corresponding peak temperature. At high ER (0.16–0.30), coal is completely gasificated. With the increase of RH2O/O2, the gasification temperature decreases monotonically and finally tends to approach 850°C at RH2O/O2 = 4.5. H2 reaches high concentration at ER = 0.18–0.24 and RH2O/O2 = 1–3, but the change of CH4 concentration is just the opposite. CO concentration is high at RH2O/O2<1.5. In order to reach high the utilization effectiveness of oxygen, RH2O/O2 has the corresponding optimum value where the utilization effectiveness of oxygen reaches peak value at ER = 0.08–0.2. [ABSTRACT FROM AUTHOR]

This paper systematically studies cladding materials prepared by mixing 316 L and 2Cr13 alloy powders in different ratios. The powder was melted and deposited on a Q235B carbon steel substrate using laser melting deposition with a high Ni transition layer and appropriate laser process parameters. Bimetallic plates with a thickness of 10 mm ±0.5 mm was prepared. The microstructure of different parts of the bimetallic plates and the impact toughness and hardness were observed and tested under different alloy ratios. The results indicate that the Nickel‐Chromium equivalence ratio increased, the hardness and wear resistance of the bimetallic plates increased, and the degree of eutectic segregation in the eutectic structure also increased. When the ratio of 2Cr13 reached 60 %, the impact toughness increased significantly, and the needle‐like second phase appeared in the structure. X‐ray diffractometer analysis determined that this second phase was (Fe, Cr)7C3. After Charpy impact testing, the fracture microstructure showed many dimples, indicating micropore aggregation fracture. This study guides preparing large‐thickness cladding layers on iron and steel parts using laser melting deposition. [ABSTRACT FROM AUTHOR]

This study focuses on the three-dimensional flow and combustion characteristics of a cavitied scramjet engine with multi-position injection. A single-equation large eddy simulation (LES) turbulence model is employed, with a detailed reaction mechanism for hydrogen combustion, as described by Jachimowski. The combustion characteristics of hydrogen in the scramjet combustion chamber are analyzed. Based on the combustion chamber model, the influence of different equivalence ratios, injection timing, injection positions, and injection pressures on the flame formation and propagation process are compared. The results indicate that within a certain range, an increase in the equivalence ratio enhances the combustion intensity and chamber pressure. In the case of multi-position injection, the order of injection from different nozzles has little effect on the final flame stabilization mode and pressure distribution. The opposite-side distribution of nozzles can effectively improve the fuel efficiency and the internal pressure. Furthermore, when the nozzles are closely placed in the opposite-side distribution, the combustion efficiency increases, although this leads to a higher total pressure loss. In scenarios where the fuel injection duration is short, an increase in the injection pressure at the upstream nozzles of the cavity results in a higher local equivalence ratio, as well as reduced fuel mixing and ignition time. [ABSTRACT FROM AUTHOR]

The diffusion porous media combustion is one possible way to eliminate the drawbacks of the existing combustion systems. Inverse diffusion flame (IDF) has features of both premixed and non-premixed flames. To integrate the advantages of porous media combustion with IDF, inverse diffusion porous (IDP) medium burner is tested for change in flame morphology and emissions at different equivalence ratio (ϕ). The porous media located at the exit of IDF burner has potential to deliver minimum flame length with low emissions. Flame appearance, flame height, flame zones etc. and emissions are experimentally investigated. Methane is used as fuel. Visible flame height is captured digitally and evaluated using ImageJ software. Central plane flame temperature is measured experimentally. CO and NOX emissions are recorded with Testo-340 flue gas analyser. The use of porous media at flame base is beneficiary in terms of achieving better air-fuel mixing and radial diffusion of air-fuel mixture. This reduces flame height with porous medium at all range of ϕ. Increase in ϕ reduces CO and enhances NOX emissions. Porous media reduces CO by 75 % and NOX by 60 %. Inverse diffusion porous medium burner emits lowest emissions in rich conditions. [ABSTRACT FROM AUTHOR]

The results of diagnostic tests under steady-state speed conditions of an unloaded engine do not fully reflect the emissivity of vehicles adapted to run on natural gas. Therefore, it is reasonable to pay attention to the emissions performance of these vehicles under dynamic conditions. In this regard, the tests were carried out on a chassis dynamometer with the engine fueled by gasoline and natural gas. Due to the area of operation of natural gas vehicles being usually limited to urban areas, the urban phases of the NEDC (New European Driving Cycle) and WLTC (Worldwide harmonized Light-duty vehicles Test Cycle) were adapted. While CO2 emissions are lower when fueled by natural gas, CH4 emissions can be high, which is related to momentary changes in the composition of the combustible mixture. Although CH4 emissions are higher when the engine runs on natural gas, the CO2eq value is, depending on the driving cycle, about 15–25% lower than when running on petrol. Additionally, studies have shown that in engines adapted to run on CNG (compressed natural gas), it is advisable to consider the use of catalytic converters optimized to run on natural gas, as is the case with vehicles which are factory–adapted to run on CNG. [ABSTRACT FROM AUTHOR]

The investigation of the ignition delay of hydrocarbon fuel is highly valuable for enhancing combustion efficiency, optimizing fuel thermal efficiency, and mitigating pollutant emissions. This paper has developed a BP-MRPSO neural network model for studying hydrocarbon fuel ignition and clarified the novelty of this model compared to the traditional BP and ANN models from the literature. The model integrates the particle swarm optimization (PSO) algorithm with MapReduce-based parallel processing technology. This integration improves the prediction accuracy and processing efficiency of the model. Compared to the traditional BP model, the BP-MRPSO model can increase the average correlation coefficient, from 0.9745 to 0.9896. The R2 value for predicting fire characteristics using this model can exceed 90%. Meanwhile, when the two hidden layers of both the BP and BP-MRPSO models consist of 9 and 8 neurons, respectively, the accuracy of the BP-MRPSO model is increased by 38.89% compared to the BP model. This proved that the new BP-MRPSO model has the capacity to handle large datasets while achieving great precision and efficiency. The findings could provide a new perspective for examining the properties of fuel ignition, which is expected to contribute to the development and assessment of aviation fuel ignition characteristics in the future. [ABSTRACT FROM AUTHOR]

In this work, two-dimensional n -dodecane/air/nitrogen cellular detonations are simulated with various equivalence ratios (ERs). A skeletal mechanism consisting of 54 species and 269 reactions is used. The lower and upper equivalence ratio boundaries for self-sustained detonation are 0.3 and 2.2, respectively. Detonation with different regimes characterized by the detonation cell patterns is observed, which aligns well with the category based on the stability parameter, i.e., weakly and highly unstable detonations, and extinction. In terms of the frontal structure, non-negligible effect of diffusion on the cellular detonation is revealed, especially in the vicinity of the leading shock front. In highly unstable and quenched detonations, the alternation in reaction pathway within the induction zone accounts for the changes of detonation dynamics, such as the absence or extended sequence of important radical formation, e.g., OH. In addition, the composition of the unburned pockets depends on both pocket location from the leading shock front and the ER in the fresh mixture, because the former determines the residence time, whilst the latter affects the pocket reaction rate. • The significance of detonation front on the chemistry explosive mode are revealed through CEMA. • Cellular structure and detonation dynamics in mixtures with various ERs are investigated. • The reaction pathways at various locations behind the leading shock front are compared. [ABSTRACT FROM AUTHOR]

The primary objective of this paper is to study the detonation re-initiation through multiple reflections upon its entry into a confined space containing liquid fuel within a flow system, which holds significant implications for two-phase pulse detonation engines (PDE) and rotating detonation engines (RDE). Utilizing the Eulerian-Lagrangian method, this study investigates the disparities in the diffraction, quenching, and re-initiation processes of liquid n-heptane/air detonation upstream and downstream. Additionally, it explores the interaction between shock waves and droplets as well as determines the lean flammability limit for re-initiation within a flow system. The findings suggest that the incoming flow significantly contributes to the upstream decoupled detonation re-initiation, as it intensifies the leading shock, thereby expediting droplet fragmentation and evaporation. However, the compressive effect of the incoming flow is insufficient to initiate upstream detonation independently. To achieve re-initiation, it is still necessary for the detonation wave to be reflected by the wall. Moreover, the incoming flow expands the re-initiation boundaries, thereby facilitating the re-initiation of upstream detonation. As the equivalence ratio decreases, a higher inflow Mach number is required to achieve upstream re-initiation. • Upstream and downstream detonation re-initiation are compared. • Interaction between droplets and leading shock upstream and downstream are illustrated. • The detonation re-initiation boundaries beneath an incoming flow are found. [ABSTRACT FROM AUTHOR]

A key characteristic of diesel engines is predicting the ignition delay period. This work predicts the ignition delay in diesel engines using combinations of ethanol/diesel fuel blend and pure diesel as fuel replacements. It provides an empirical formula for predicting delay periods. A growing interest in alternative fuel blends, representing a substantial shift from the use of traditional diesel fuel, is reported. Modern study is focused on examining these combinations and how they might affect the dynamics of combustion in diesel engines. Experiments were carried out utilizing five different ethanol/diesel fuel blends, including pure diesel, with ethanol percentages varying from 5% to 20% in 5% quantities. Tests were conducted at a constant engine speed of 1,500 rpm, with various compression ratios of 16, 17, and 18, with torque levels ranging from 0 to 21 N.m. In this study, general formulas for predicting ignition delay are constructed numerically. There was a greater consistency between the experimental outcomes and the expected ignition delay. The findings indicated that the E20 combined fuel continuously exhibited the least igniting delay period across all compression ratio variables. The findings demonstrated that the ignition delay period starts to shorten with increased cetane number, ignition pressure, temperature, and equivalency ratio. A shorter period of ignition delay is the outcome of higher compression ratios. The predictive model created here is a ground-breaking addition to the industry, offering a solid foundation for assessing the efficiency and emissions properties of different ethanol/diesel blends.

Detonation-based engines have a higher thermal efficiency than deflagration-based engines and are therefore widely studied. In this study, the effect of initiation conditions on the detonation wave propagation and the performance of a pulse detonation engine, one type of detonationbased engine, was numerically investigated. Hydrogen-oxygen mixtures with equivalence ratios of φ=0.8, 1.0, and 1.2 were defined as initiation conditions with constant pressure and temperature. The numerical simulations were conducted using the transient explicit density-based solver in the ANSYS Fluent commercial software. The adaptability of the adaptive mesh refinement method in detonation-based engines was explored in the numerical studies, reducing the average total cell count by a factor of 2.617, and obtaining consistent results according to validation studies. The adaptive mesh refinement method was also used in numerical simulations where different equivalence ratios were defined. It was determined that an increase in the equivalence ratio resulted in an increase in the detonation wave velocity. Also, an increase in thrust distribution at the nozzle exit was observed before the blowdown stage, and the calculated thrust values for φ=0.8, φ=1.0, and φ=1.2 were 248.28 N, 264.5 N, and 270.83 N, respectively.

The diffusion porous media combustion is one possible way to eliminate the drawbacks of the existing combustion systems. Inverse diffusion flame (IDF) has features of both premixed and non-premixed flames. To integrate the advantages of porous media combustion with IDF, inverse diffusion porous (IDP) medium burner is tested for change in flame morphology and emissions at different equivalence ratio (ɸ). The porous media located at the exit of IDF burner has potential to deliver minimum flame length with low emissions. Flame appearance, flame height, flame zones etc. and emissions are experimentally investigated. Methane is used as fuel. Visible flame height is captured digitally and evaluated using ImageJ software. Central plane flame temperature is measured experimentally. CO and NOX emissions are recorded with Testo-340 flue gas analyser. The use of porous media at flame base is beneficiary in terms of achieving better air-fuel mixing and radial diffusion of air-fuel mixture. This reduces flame height with porous medium at all range of ɸ. Increase in ɸ reduces CO and enhances NOX emissions. Porous media reduces CO by 75 % and NOX by 60 %. Inverse diffusion porous medium burner emits lowest emissions in rich conditions.

In general, a leaner mixture condition improves combustion efficiency in compression ignition (CI) combustion using diesel. However, in the case of leaner air–fuel mixture conditions, it disturbs flame propagation in spark ignition combustion using gasoline, i.e., low reactivity fuel, causing a decrease in combustion efficiency. Since dual-fuel combustion in a CI engine typically involves the use of high- and low-reactivity fuels together, the differing reactivity conditions in the cylinder become as important as the local equivalence ratio in the cylinder. Thus, there is a need to verify the effect of a leaner mixture condition on combustion efficiency in dual-fuel CI combustion. For this reason, this study experimentally evaluates the effects of varying equivalence ratios on the combustion efficiency of gasoline/diesel dual-fueled CI combustion in a 0.4-L single-cylinder engine under low-speed (1500 rpm) and low-load (total LHV 570 J/str) conditions. To vary the equivalence ratios, intake pressures and exhaust gas recirculation (EGR) rates were, respectively, changed under the part-load condition. The results emphasize that as the equivalence ratio becomes leaner by increasing the intake pressure, combustion efficiency worsens due to the low reactivity properties and certain flame propagation modes of gasoline combustion. On the contrary, increasing the EGR rate did not significantly influence combustion efficiency, but it effectively helped reduce nitrogen oxide (NOx) emissions. Based on these results, it is concluded that optimizing dual-fuel CI combustion to suppress NOx emissions is better achieved using EGR, rather than creating a leaner mixture condition. [ABSTRACT FROM AUTHOR]

Using experimental and LES methods, this paper investigates the effects of equivalence ratio and blockage ratio on hydrogen flame acceleration, explosion overpressure characteristics, and flow field properties in a closed obstructed duct. The study indicates that there is a positive correspondence between the flame acceleration and pressure rise in a closed duct. The continuous flame acceleration is driven by flow compression and turbulent combustion propulsion, corresponding to a rapid pressure rising. After the quasi-plane flame, the explosion overpressure begins to oscillate at a high frequency. As the blockage ratio increases, the turbulent combustion is intensified, consequently leading to a noticeable increase in flame velocity and pressure rising rate. While high obstacles exert an obstructive effect on the initial flame propagation and the pressure oscillations. The vorticity is mainly distributed in the shear flow region and the burned region, and its magnitude and distribution area increase with a higher obstacle ratio. • Correspondence between flame acceleration and overpressure characteristics is revealed. • The adiabatic and isothermal compression are analyzed in a closed obstructed duct. • Vector field and vorticity field at different blockage ratios are investigated. [ABSTRACT FROM AUTHOR]

The increased gasification potential of bulk density agricultural residues such as groundnut shell (GS) and rice husk (RH) could aid in the effective implementation of bioenergy for a wider range of applications. Mixing high-carbon biomass with such feedstocks is an appealing option for improving producer gas (PG) quality. Though spent tea waste (STW) has a high-carbon content due to its small particle size and high-moisture levels, it is not directly used in gasifiers for PG generation. However, it could be a promising secondary biomass in the gasification of GS and RH. To establish this strategy, an appropriate mixing method and a study on the gasification potential of the mixture as feedstock for downdraft gasifiers is essential. In this study, STW was mixed with GS and RH at various mixing ratios and tested in a downdraft gasifier. The experimental results showed that, up to a 40% weight ratio of STW with the primary biomasses, the gasifier could operate continuously without any incomplete gasification. The calorific value, cold gas efficiency and hot gas efficiency improvements for GS/STW blends at the best equivalence ratio (ER) were 19.3%, 19.61% and 18.04%, respectively, whereas for the RH/STW blend, the improvements were 16.2%, 14.5% and 13.81%. The best performance of GS/STW and RH/STW blends was found for ERs of 0.3 and 0.25, respectively, which are different from the optimum ERs for the gasification of primary feedstocks alone. [ABSTRACT FROM AUTHOR]

Hydrogen-rich gas was produced from Citrullus-lanatus in a fixed-bed reactor using a novel Ni/dolomite/MgO/ γ − Al 2 O 3 with air-steam mixture as the gasifying agent. The feed and steam-air flow rates were 3 and 0.8 kg/h with fixed steam-air volume-concentration of 40% v/v. The results displayed a high cracking activity of the hydrocarbons/tar in the biomass by the catalyst with a resultant upgrade in the gas quality/H 2 yield. The highest H 2 yield was 66.1 g/kg biomass, a minimal tar concentration of 2 g/Nm3 with steam-to-biomass ratio of 2 at 1100 °C. The highest H 2 yield (57 vol%) was achieved at 0.28 equivalence ratio. [Display omitted] • Egusi melon seed shells were dehulled and gasified for hydrogen production. • A novel 2 wt% Ni/dolomite/MgO/ γ − Al 2 O 3 catalyst was employed in the gasification process. • The optimum hydrogen gas production was received for ER of 0.28 and a temperature of 1100 °C. • The highest quantity of hydrogen produced was 66.1 g H 2 /kg biomass. [ABSTRACT FROM AUTHOR]

Detonation-based engines have a higher thermal efficiency than deflagration-based engines and are therefore widely studied. In this study, the effect of initiation conditions on the detonation wave propagation and the performance of a pulse detonation engine, one type of detonationbased engine, was numerically investigated. Hydrogen-oxygen mixtures with equivalence ratios of φ=0.8, 1.0, and 1.2 were defined as initiation conditions with constant pressure and temperature. The numerical simulations were conducted using the transient explicit density-based solver in the ANSYS Fluent commercial software. The adaptability of the adaptive mesh refinement method in detonation-based engines was explored in the numerical studies, reducing the average total cell count by a factor of 2.617, and obtaining consistent results according to validation studies. The adaptive mesh refinement method was also used in numerical simulations where different equivalence ratios were defined. It was determined that an increase in the equivalence ratio resulted in an increase in the detonation wave velocity. Also, an increase in thrust distribution at the nozzle exit was observed before the blowdown stage, and the calculated thrust values for φ=0.8, φ=1.0, and φ=1.2 were 248.28 N, 264.5 N, and 270.83 N, respectively. [ABSTRACT FROM AUTHOR]

This paper provides an experimental investigation of a kerosene/air burner (the NexGen burner designed on the FAA's proposed ISO 2685 standard), which is used to generate flame/burnt gases impinging on material samples in the field of fire safety. The purpose of this study is to characterize this burner, and experimental means are implemented to better understand the effects of the equivalence ratio on the spatial distribution of the gas temperature (thermocouples), the heat flux (heat flux gauge), and gas emission species. Hence, the measured flame temperature, heat flux, and heat release rate increase up to a critical value of equivalence ratio equal to 1.03. Furthermore, a pyrolysis test was carried out on composite materials and the results of the comparative analysis of carbon‐phenolic, carbon‐BMI, and carbon‐PEKK materials show that carbon‐PEKK had the lowest mass loss, highest back‐face temperature without significant material delamination, and the lowest concentration of gas emission species. [ABSTRACT FROM AUTHOR]

An experimental study of premixed syngas/air flame explosive characteristics in an obstacle pipe is introduced. Square obstacles with a blocking rate of 0.5 are installed at varying positions from the ignition end inside a closed pipe to conduct syngas-air explosion dynamics experiment with varying equivalence ratios (Φ) and obstacle positions (OP). Results show that compared to OP = 150 mm, the tulip flame will form at OP = 450 mm and OP = 750 mm. The distribution of flame front velocity and overpressure have same trend in the process of flame oscillation. Nevertheless, the overpressure curve will produce oscillation when the flame propagates out of the pipe at OP = 450 mm. As the increase of OP, the maximum flame front velocity first increases and then decreases and the maximum overpressure decreases gradually. Both the maximum flame front velocity and maximum overpressure first increase then decrease with Φ, reaching the maximum at Φ = 1.4. This research can provide some suggestions when syngas-air fuels are applied in the presence of obstacles. • The maximum overpressure and flame front velocity reach the maximum at Φ = 1.4. • The pressure oscillation is most pronounced at OP = 450 mm. • The distribution of flame front velocity and overpressure have same trend. • The maximum flame front velocity reaches the maximum at OP = 450 mm. • The maximum overpressure reaches the maximum at OP = 150 mm. [ABSTRACT FROM AUTHOR]

The rotating detonation rocket engine has certain advantages in propulsion performance and is expected to develop into a new type of attitude/orbit control power device. In this paper, an experimental investigation on the detonation propagation characteristics during the short-time pulse operating process of rotating detonation combustor (RDC) was performed. A 60-mm RDC was employed, and the H 2 and oxygen-rich air were used as the reactant. The results show that the experiment can successfully achieve rotating detonation mode when the RDC is operating with a 10-Hz pulse frequency. With the increase of oxidizer mass flow rate, the velocity and pressure of the detonation wave will increase. The average propagation frequency of the detonation wave shows a trend of first increasing and then slightly decreasing as increasing the equivalence ratio. There is a large velocity fluctuation in the RDC pulse operation, and the stability of the detonation wave is significantly affected by the equivalence ratio. The propagation velocity and stability of the detonation wave can be improved by increasing the supply mass flow rate or equivalence ratio with a certain condition. When the equivalence ratio is larger than 0.7, the establishment time of the detonation wave is less than 1 ms, which can meet the requirement of the fast response when the RDC is applied to attitude control engine. [ABSTRACT FROM AUTHOR]

This study experimentally explored the effects of equivalence ratio settings on ethanol fuel combustion oscillations with a laboratory-scale combustor. A contrary flame equivalence ratio adjusting trend was selected to investigate the dynamic characteristics of an ethanol atomization burner. Research findings denote that optimizing the equivalence ratio settings can prevent the occurrence of combustion instability in ethanol burners. In the combustion chamber, the sound pressure amplitude increased from 138 Pa to 171 Pa and eventually dropped to 38 Pa, as the equivalence ratio increased from 0.45 to 0.90. However, the sound pressure amplitude increased from 35 Pa to 199 Pa and eventually dropped to 162 Pa, as the equivalence ratio decreased from 0.90 to 0.45. The oscillation frequency of the ethanol atomization burner presents a migration characteristic; this is mainly due to thermal effects associated with changes in the equivalence ratio that increase/decrease the speed of sound in burnt gases, leading to increased/decreased oscillation frequencies. The trend of the change in flame heat release rate is basically like that of sound pressure, but the time-series signal of the flame heat release rate is different from that of sound pressure. It can be concluded that the reversible change in equivalence ratio will bring significant changes to the amplitude of combustion oscillations. At the same time, the macroscopic morphology of the flame will also undergo significant changes. The flame front length decreased from 25 cm to 18 cm, and the flame frontal angle increased from 23 to 42 degrees when the equivalence ratio increased. A strange phenomenon has been observed, which is that there is also sound pressure fluctuation inside the atomized air pipeline, and it presents a special square waveform. This study explored the equivalence ratio adjusting trends on ethanol combustion instability, which will provide the theoretical basis for the design of ethanol atomization burners. [ABSTRACT FROM AUTHOR]

To investigate the characteristics of rotating detonation waves fueled by liquid kerosene with increasing equivalence ratios, the experiments were performed through increasing the supply of liquid kerosene under three different mass flow rates of oxidizer. Various mode transitions were realized, including transition from unstable detonation to stable single-wave mode, transition from unstable detonation to stable double-wave mode and transition from double-wave mode to single-wave & double-wave hybrid mode. The results demonstrate that the increase of equivalence ratios leads to the improvement of mixture reactivity under lean-fuel limit, which enhances the propagation stability and pressure peak of rotating detonation waves, and then results in the transition from unstable detonation to a stable propagation mode. In addition, when the mass flow rate of oxidizer is approximately 1100 g/s, the transition from double-wave mode to single-wave & double-wave hybrid mode is observed by increasing the equivalence ratio from 0.6 to 0.93. It is concluded that the mutation of dynamic balance between the RDW and injection plenum caused by the increasing of equivalence ratio is one of the reasons inducing the mode transition. This work illustrates the feasibility of modulating the propagation mode in rotating detonation waves fueled by liquid kerosene, and promotes the application of rotating detonation engine.

Biomass gasification is an attractive technology capable of producing a versatile product gas that can be used for heat and power production as well as used as a feedstock for biofuels and higher-value chemicals synthesis. A fluidized bed gasifier is one of the better choices for an industrial scale operation. However, the specification and performance of different feedstocks must be characterized to use in a specific application with acceptable efficiency. In this article, the authors took two different feedstocks (i.e., wood and grass pellets) for the experimental characterization in a 20-kW pilot-scale bubbling fluidized bed gasifier. Equivalence ratio was varied between 0.1 to 0.2 for the grass pellets and 0.214 to 0.371 for the wood pellets. Frequent agglomerations were observed during the experiment with the grass pellets at a temperature of 800 °C and above. The carbon conversion for the gasification of grass pellets was observed to be lower compared to the gasification of wood pellets. Gasification of wood pellets gave a carbon conversion of around 60% at a temperature of around 850 °C.

The combination of various fuels in an internal combustion engine is a major area of research in the field, aimed at conserving fossil fuels and reducing environmental pollution. This paper examines the performance and pollution emissions of a DA465QE Towner engine using a biogas/gasoline hybrid fuel in a light truck engine. Results show that when the engine runs on methane, the cycle indicator work is reduced by up to 13% compared to gasoline. When running on biogas M6C4, the cycle indicator work decreases the most by 27% compared to gasoline, and when running at high speeds, the engine power increases. The optimal gasoline content blended with M7C3 biogas is 30%, with the cycle indicator work and NOx emission increasing quickly and CO and HC emissions decreasing sharply with less than 30% gasoline content.

[Introduction] As the country has set ambitious targets in carbon peaking and carbon neutrality for the energy sector, there is a growing demand for technology improvements of low-carbon emission for power station gas turbines. It is urgent to explore the path of the key technology for this goal in China. The lean premixed combustion technology of gas turbine can make the air volume for combustion deviate from the theoretical air volume, which is the main technology to reduce NOx emission at present. At the same time, by mixing hydrogen in natural gas when combusting, it can effectively reduce the consumption of fossil energy and reduce carbon emissions. [Method] In this paper, a one-dimensional premixed free propagation flame model was established by Chemkin-Pro software, and the effects of different equivalent ratios, initial temperatures, initial pressures, and hydrogen-blended ratios on combustion temperatures, combustion rates, pollutant generation concentration, combustion free radicals, and chain reactions were compared. The temperature distribution, fuel component change and emission characteristics of combustion process were simulated. [Result] It is found that by mixing hydrogen in natural gas when combusting, fossil energy consumption and carbon emissions can be effectively reduced. However, the higher flame temperature brought by the lean premixed combustion of natural gas mixed with hydrogen will promote the generation of NOx, and at the same time, more CO will be produced at a lower equivalent ratio. [Conclusion] Based on the above research, the key data of hydrogen-blended combustion are obtained, which lays a foundation for the completion of hydrogen-blended combustion technology route.

In order to reveal the deflagration mechanism of DME/H2-blended gasses, the micro-mechanism was studied based on the constructed UC San Diego 2016 pyrolysis oxidation mechanism model. The results show that adiabatic flame temperature and laminar flame speed increase with the increase in the equivalence ratio (Φ); they first increase and then decrease with the increase in the hydrogen (H2)-blended ratio (λ), and with the increase in λ, the Φ corresponding to the peak laminar flame speed of the blended gas increases. The addition of H2 increases the consumption of O2, and H2 reacts with CO to form H2O and CO2, promoting complete combustion. When Φ = 1.0–1.2, the equilibrium mole fraction of H and OH-activated radicals reach the maximum, and with the addition of H2, the concentration of activating radicals gradually increases, while the number of promoted elementary reactions increases by two, and the number of inhibited elementary reactions does not increase. Meanwhile, the addition of H2 increases the reaction rate of most reactions on the main chemical reaction path CH3OCH3→CH3OCH2→CH2O→HCO→CO→CO2 of DME and increases the risk of the deflagration of DME/H2-blended gas.

Ammonia (NH 3) has been gaining popularity as a carbon-free alternative fuel in recent years. OH∗ chemiluminescence is a promising method to study the structure of ammonia flames, but research on this aspect is still lacking. In this study, the OH∗ chemiluminescence distributions and structure characteristics in NH 3 /H 2 and NH 3 /cracked gas swirl flames are experimentally investigated. The OH∗ distributions of NH 3 /H 2 and NH 3 /cracked gas under different addition levels and equivalence ratios are compared. The results show that the increase of equivalence ratio and hydrogen doping level significantly increased the OH∗ chemiluminescence peak of NH 3 /air swirling flame. Especially in fuel-lean flames, the equivalence ratio effect is greater than the NH 3 dilution effect, while the two effects are comparable in equivalence and fuel-rich conditions. The stretching effect of NH 3 /cracked gas is stronger, and the flame width is narrower than that of NH 3 /H 2 flame, but the peak value of OH∗ radiation is higher. • Profiles of OH∗chemiluminescence in NH 3 /H 2 swirling flame are visualized. • The intensity of the OH∗ peak increases as φ and X NH3 increase. • The φ effect dominates the increase of OH∗ intensity during lean combustion. • Partially cracked NH 3 /air flame OH∗ chemiluminescence are investigated. [ABSTRACT FROM AUTHOR]

A mixture of H 2 and CO called syngas is a strategically important intermediate synthetic gas in chemical industries. A common production method of the syngas is catalytic steam reforming of natural gas which is limited due to the environmental and energy consumption subjects. In the current work, as a proper alternative, the ultra-rich thermal partial oxidation (non-catalytic) of natural gas was experimentally investigated to produce syngas with H 2 /CO ratio near two in a zirconia inert porous burner. High equivalence ratio aiming to extend ultra-rich fuel with pure oxygen (oxy-natural gas combustion) was considered at higher thermal loads by modifying the previous facility. The experimental tests were obtained at high thermal powers of 12–20 kW with equivalence ratios of 2.7 up to 3.1 where only pure oxygen was used as the oxidizer. Analyzing the product samples captured from the reactor output showed that a syngas with H 2 /CO of about 1.8 was produced at the equivalence ratio of 3.1 at 20 kW. The more thermal power was applied, the more H 2 /CO was produced with a greater conversion of natural gas within the reactor. • The ultra-rich partial oxidation of natural gas with pure oxygen was investigated. • H 2 and CO were produced in a thermal process at the temperature of up to 1748 K. • The product of the reactions at above 1500 K contains 44.7% of hydrogen. • A zirconia burner with oxygen-natural gas feed produces a H 2 /CO ratio near two. [ABSTRACT FROM AUTHOR]

Three-dimensional simulations are conducted for rotating detonative combustion fueled by n -heptane sprays without any fuel pre-vaporization. Parametric studies are performed to study the influences of equivalence ratio on the rotating detonation wave. The decoupled process of the detonation wave with lean equivalence ratio is also been analyzed. It is found that when the global equivalence ratio is lower than 0.6, a stable propagating detonation wave cannot be observed in the combustion chamber. With the gradual increase of the global equivalence ratio, the detonation wave can stably propagate in the combustion chamber after ignition. When the global equivalence ratio is 0.8–1.5, the propagation mode of the detonation wave in the combustion chamber is one-way propagation mode. When the global equivalence ratio gradually increase from 0.8 to 1.5, the formation time of the detonation wave first decreases and then increases with the increase of the equivalence ratio. Besides, the stability of the detonation wave first increases and then decreases with the increase of the equivalence ratio. Moreover, the thrust of the rotating detonation chamber fueled by n -heptane increases gradually with the increase of the equivalence ratio. The specific impulse of the combustion chamber first increases and then decreases with the increase of the equivalence ratio. • The developing process of detonation wave is obtained. • The extinction process of the detonation wave is described. • Propagation characteristics and stability of detonation wave are analyzed. • The influences of equivalence ratios are studied. [ABSTRACT FROM AUTHOR]

Based on the visualized gas cloud explosion pipeline test platform, the influence of the sudden contraction structure on the deflagration characteristics of the hydrogen-methane-air gas cloud is investigated. The results show that the changes of flame propagation velocity, explosion overpressure, and flame temperature after deflagration of the premixed gas cloud all present three stages: rapid increase, rapid decline, and secondary acceleration caused by the sudden contraction of pipeline structure. The equivalence ratio significantly affects the hydrogen-methane-air detonation process in the sudden contraction of the pipe structure. As the hydrogen content increases, the flame propagation becomes faster and the explosion impact becomes greater. The formation of "Tulip" flame is closely related to the flame propagation speed. During the process of flame propagation, inertia dominates, causing the flame propagation speed to reach its first peak at the abrupt contraction structure. [Display omitted] • The effect of sudden contraction pipeline on premixed gas detonation is examined. • The detonation process of pre-mixed gas clouds undergoes three stages. • The speed of flame propagation is closely related to inertia. • The flame structure of the "tulip" is closely related to the flame speed. • The effect of hydrogen and equivalence ratio on deflagration is examined. [ABSTRACT FROM AUTHOR]

The energy production potential of some common food waste, including cooked rice, “eba,” orange, yam, and potato peels, has been studied through thermodynamic modeling and simulation. The key gasification processes were modeled individually in ASPEN PLUS. The component properties were calculated with Peng-Robinson’s equation of state. The effect of the equivalence ratio (ER), steam-to-biomass ratio (STBR), and gasifier operating temperature on the composition, cold gas efficiency (CGE), and higher heating value (HHV) of the syngas was studied. Results revealed that the production of H2 and CO2 reduces with the increase in ER and increases with STBR. The molar fraction of CO is inversely proportional to that of CO2. Increasing ER causes an increase in oxidizer within the gasifier and a corresponding increase in the molar fraction of N2. Reduction in STBR reduces both the N2 content and heating value of syngas. Syngas from both feedstocks has heating values ranging from 18.48 to 11.04 MJ/kg, with food waste yielding higher HHV than hardwood. The CGE for hardwood ranges from 55.6% to 74.95%, while for food waste, it ranges from 49.3% to 57%. This study demonstrates the production of high-quality syngas from locally sourced food waste. [ABSTRACT FROM AUTHOR]

The industrial torch system is used to handle large amounts of flammable, toxic, and corrosive gases emitted during accidents or normal production processes. It utilizes open flames to burn off the gas pollutants. This study employs computational fluid dynamics (CFD) to investigate the combustion characteristics and efficiency of flames under high-velocity jet, aiming to address the issue of low combustion efficiency under high-velocity jet conditions. A three-dimensional flame model was established using methane and air as fuel, in order to investigate the variations and impact mechanisms of the combustion flame temperature field and carbon dioxide mass fraction distribution under different jet velocities, pilot component temperatures, and equivalence ratios. The reasons for low combustion efficiency under highvelocity jet conditions were analyzed. It was proposed to increase the combustion efficiency of the flame by raising the temperature of the pilot component, which differs from the traditional method of adding combustion-assisting gases. The combustion efficiency of flames under various operating conditions was evaluated. The results showed that as the jet velocity (v) increased from 49.6 m/s to 65 m/s, the height of the combustion flame in the vertical direction decreased continuously. Additionally, the high-temperature region at the center of the flame gradually decreased, leading to a 5.26% decrease in the highest flame temperature and a 3% decrease in combustion efficiency. When v = 70 m/s, the high-velocity fuel flow penetrated the ignition source, causing a large amount of methane to escape into the atmosphere without combustion, resulting in flame extinction. Elevating the temperature (T) of the pilot component can reduce the impact of high-velocity jet on combustion efficiency. When T = 2000 K, the flame reignites with a combustion efficiency of 94.1%. As the mass flow rate of the fuel composition inlet is reduced from 33.45 × 10−5 kg/s to 12.74 × 10−5 kg/s, the highest temperature of the combustion flame drops from 2072 K to 1451 K. As the equivalence ratio (φ) increases from 1.05 to 1.2, the height of the combustion flame in the vertical direction decreases continuously, resulting in a 0.7% decrease in the highest flame temperature and a 10.5% decrease in combustion efficiency [ABSTRACT FROM AUTHOR]

This study reported the development of an advanced shaft furnace, which improved the conventional waste gasification system, and evaluated its performance using operation data and gasification criteria such as cold gas efficiency, carbon conversion ratio, lower heating value, emissions, slag quality, and heavy metal distributions. The coke consumption of the Advance Shaft Furnace was 15.2 kg/t-MSW, which was approximately 1/4 that of the conventional system. The carbon conversion ratio of the Advance Shaft Furnace was 90.7%. Because of higher carbon conversion, the air pollution control residue was reduced from 39.8 kg-t-MSW to 25.3 kg/t-MSW. With the equivalence ratio increasing, carbon monoxide concentration in the syngas decreased and the syngas temperature increased. The other gasification criteria of the advanced shaft furnace were also comparable to the conventional system. The PCDD/DFs emissions from the stack of the advance shaft furnace were 0.0088 ng-TEQ/m3N, which were comparable to that of the conventional system. The total emissions of the PCDD/DFs from the developed system were 3.9 μg-TEQ/t-MSW, indicating that the developed system can contribute to the reduction of the environmental impact. The Advance Shaft Furnace also has the possibility of recovering materials efficiently. Most of the lead, zinc, and chlorine were distributed in the air pollution control residue at rates of 94.9%, 80.4%, and 97.7%, respectively. Most high-boiling-point heavy metals, such as iron and copper, are distributed in metal. These results indicate that the development of the Advance Shaft Furnace can overcome the disadvantages of the conventional system while keeping the advantages, reducing the environmental impact. Furthermore, the application of biomass coke to the advanced shaft furnace can contribute to the decarbonization and carbon neutrality. [ABSTRACT FROM AUTHOR]

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Whisky distillery by-products draff and pot ale (PA) have an energy content that potentially can be used to decarbonize distillery heating. Draff consists of wet grains which are the residue of the first stage of whisky production. PA is the liquid residue that results from the first stage of the distillation at malt distilleries. The yearly production of distillery by-products was estimated to have increased by 27,000 tonnes (dry) in 2014. It is not feasible to store distillery by-products because of their bio-chemical nature and high volumes. Therefore, distillery by-products need to be removed from the site as they are produced. The most economical way to dispose of distillery by-products is by using them as feed stock for bioenergy. Some distilleries send draff and pot ale to AD plants, but to be useful they have to be dried and the use of fossil fuels for this makes the process uneconomical and the carbon emissions have to be deducted from any green biogas that is produced. This work showed for the first time that distillery draff could be air-gasified. The restricted ventilation Cone calorimeter method was used. An FTIR that was calibrated for 60 species was used to carry out the speciation of the product gases. The experimentally determined optimum gasification equivalence ratio (Ø) and gasification thermal efficiency for the gasification of draff were 4.5 and 90% respectively. [ABSTRACT FROM AUTHOR]

Copyright of Power Generation Technology is the property of Power Generation Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Although their ease of transport, storage, and use makes hydrocarbon fuels dominant in commercial energy systems, the emission of harmful gases, including greenhouse gases, is a fatal disadvantage. Despite ongoing research to improve thermal efficiency and reduce the emissions of internal combustion engines using conventional hydrocarbon fuels, achieving net-zero carbon requires decarbonizing fuels rather than reducing the use of internal combustion engines. Hence, transitioning away from hydrocarbon fuels and evolving internal combustion engines into clean engines using carbon-free fuels, such as hydrogen, is necessary. This study designs a 2.0 L research engine and numerically analyzes its combustion characteristics and spray behavior by varying the spray angle and equivalence ratio. When comparing the turbulence kinetic energy at a 45-degree spray angle with that at 30 degrees and 60 degrees, on average, there was a difference of approximately 37.54 m2/s2 and 26.21 m2/s2, respectively. However, misfires occur in the lean condition. Although hydrogen has a wide flammability range, poor mixture formation under lean conditions can result in misfires. The 60-degree spray angle resulted in the highest combustion temperatures and pressures for all equivalence ratio conditions, consequently leading to the highest emissions of nitrogen oxides. Specifically, at a lambda value of 2.5, the 60-degree spray angle emitted approximately 29 ppm, 0 ppm, and 161 ppm of nitrogen oxides for each respective spray angle. [ABSTRACT FROM AUTHOR]

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Hydrogenation of methane (CH4) is an important means of achieving energy savings and large-scale hydrogen (H2) transportation. Explosion venting is considered to be an effective method to reduce the risk of gas explosions. To investigate the parameters of the explosion characteristics of CH4/H2/Air premixed fuel under venting conditions, the explosion characteristics and the dynamic propagation law of venting flame in CH4/Air mixtures with 5% concentration were studied in 20 L and 40 L square explosion venting vessels. The development process of flames inside vessels, the evolution characteristics of explosive venting flames, and the changes in explosion pressure were tested using a high-speed camera and pressure sensors. The maximum explosion pressure, the maximum explosion pressure rise rate, and the maximum flame velocity increased first and then decreased with the addition of H2. However, the maximum flame length increased continuously with the increase of H2. With the increase of hydrogenation, the maximum flame area showed an exponential increase. At equivalence ratio less than 1, the effect of hydrogenation on the flame area was much attenuated than that at equivalence ratio was greater than 1.

This paper provides an experimental investigation of a Kerosene/air flame (produced by the NexGen burner designed by the FAA, and here calibrated for ISO 2685/AC20-135 standards fire tests conditions), which is used to generate flame/burnt gases impinging on material samples in the field of fire safety. The purpose of this study is to characterize this burner, and experimental means are implemented to better understand the effects of the equivalence ratio on the spatial distribution of the gas temperature (thermocouples) and the heat flux (heat flux gauge). A parametric study was carried out by varying the global equivalence ratio (ER); highlighting a flickering phenomenon, a relation between the ER and the heat flux, and determining empirical correlations. Hence, the measured flame temperature, heat flux, and heat release rate increase up to a critical value of equivalence ratio equal to 1.03 (flame temperature (1101.5 °C) and heat flux (140 kW/m2).

In propulsion systems based on oblique detonation waves (ODWs), the airflow compressed by the inlet still has a very high velocity and the complete mixing of fuel and airflow is unattainable, which thus has a huge effect on wave systems of oblique detonations. In this paper, the ODWs in non-uniform inflows were considered as the object. By means of the evolutions of wave angles and displacement distances of wave front, the disturbance characteristics of ODWs were studied using the Euler equations coupled with the hydrogen-air detailed reaction model. The equivalence ratio was chosen as the representation variable of nonuniformity, and a disturbance region with a varying height was introduced into the incoming flow. The symbol φA was defined as the disturbance amplitude and the equivalence ratio distribution in the disturbance region was modeled using the sinusoidal function. It is found that with the decrease of φA, the wave angle decreases and the wave front moves downstream, the opposite trend is observed when the equivalence ratio increases. When φA is negative and small enough, a novel phenomenon characterized by the abrupt change of wave angle can be observed. Further analyses show that this phenomenon is due to ODW re-initiation under the influence of non-uniform equivalent ratio. When φA is posi-tive and large enough, the ODW angle of the disturbance region is in a non-equilibrium state. A larger equivalence ratio gradient results in a higher value than the theoretical wave front angle, while a smaller equivalent ratio gradient has a lower value than the theoretical one. Quantitative analyses of wave front positions show that the displacement distance of the wave front with φA is nonlinear when φA is positive, and linear when φA is negative. Meanwhile, the displacement distance is linear with the height of the disturbance region.