Fuel Equivalence Ratio Research Articles

Experimental study on transpiration cooling with phase change in rotating detonation engine

Transpiration cooling with phase change is an effective method for protecting high heat flux walls from ablation in combustion chambers and spaceflight vehicles. The combustion chamber walls of the rotating detonation engine (RDE) experience high heat flux, which poses significant challenges to thermal protection and limits its development. This study introduces a transpiration cooling thermal protection system for a kerosene/air RDE, where the liquid coolant absorbs heat with phase change, reducing wall temperature by more than 50% under certain conditions. The experiments investigated the effects of coolant flow rate, coolant types (water and kerosene), porosity of porous media, and fuel equivalence ratio on both transpiration cooling and detonation wave dynamics. The results show that water provides superior cooling effectiveness compared to kerosene, particularly with increased flow rates and porosity. During RDE operation, increasing flow rates of both water and kerosene initially enhances cooling efficiency but eventually leads to an overall reduction. Furthermore, higher coolant flow rates of both water and kerosene can disrupt the stability of detonation waves within the combustion chamber. Although enlarging the equivalence ratio improves cooling efficiency, maintaining continuous detonation wave generation remains challenging. The cooling efficiency in the detonation combustion mode is lower than that in deflagration. Additionally, carbon deposition was observed in the transpiration cooling system, particularly during prolonged operation. These findings provide valuable insights for the optimization and technical guidance of RDE design.

Experimental investigation of OH* emission spectrum characteristics and transient ignition dynamics in methane and coal dust mixtures explosions

Combustible gases, dusts and their mixtures are widely present in human production and life，and the fire and explosion disasters caused by them pose a serious threat to the field of energy security applications. Studying the ignition process of mixtures is essential for disaster risk assessment and safety protection. In this work, the explosion characteristics and OH* emission spectra of the mixtures were experimentally tested by varying the fuel equivalence ratio ( ER ≈ 0.79 ~ 1.71), and the evolution of the transient flow field structure during the ignition process was quantitatively analyzed using the schlieren image velocimetry method. The results indicate that the emission spectrum of OH* is closely correlated with the maximum explosion pressure, and the spectral intensity of OH* at 306.4nm is consistent with the maximum rate of explosion pressure rise. The flow field during the ignition process of the mixtures shows that a small amount of coal dust (concentration≤30g/m3) can significantly promote flame acceleration and instability as the methane concentration is in lean combustion or stoichiometric ratio. However, when the concentration of coal dust increases (concentration≥40g/m3), coal dust will suppress flame acceleration and instability. For methane concentration in fuel-rich combustion state, coal dust always suppresses flame acceleration and instability. The experimental results contribute to a further understanding of gas and coal dust mixed explosions and provide a verification database for the construction of chemical kinetic mechanisms.

Simplification and verification of chemical reaction mechanism of RP-3 aviation kerosene

To reveal the combustion and explosion characteristics of RP-3 aviation kerosene, a three-step simplified mechanism involving CO-CO2, H2-H2O equilibrium was constructed. Using a general program based on Cantera and genetic algorithms, the reaction rate parameters were optimized under given conditions, and a relationship between reaction rate parameters and fuel equivalence ratio was developed. The optimized mechanism was compared with multiple flame parameters under multiple operating conditions of RP-3 aviation kerosene. The results showed that the laminar flame speed and adiabatic flame temperature of the three-step simplified mechanism were in good agreement with the experimental data of RP-3 aviation kerosene within the temperature range of 300 ∼ 600 K and pressure range of 1–5 atm, with an error of less than 10 %. The optimized mechanism corrected using a correction function is in good agreement with experimental and numerical results under multiple conditions, verifying the rationality of the simplified program and the accuracy of the three-step simplified mechanism. For practical engineering issues, RP-3 aviation kerosene explosion experiments were conducted, and the pressure and flame data were analyzed and compared. The results indicated that the three-step simplified mechanism had satisfactory calculation time scales and numerical simulation feasibility.

Coupling study of onboard power generation system of Magnetohydrodynamics enhanced Brayton Cycle

Closed cycle power generation systems offer a possible solution to meet the high electricity needs of hypersonic vehicles, but the power generation is limited by the finite cold source and cycle temperature. Introducing two-phase flow liquid metal (LM) MHD power generation based on Closed-Brayton-Cycle (CBC) is a potential solution that can enhance the thermal-electricity conversion process at the system level. However, it is difficult to reflect the complex coupling relationship between the power generation system and the vehicles propulsion system and the limitations of finite cold sources by relying only on ideal system analysis, especially the contradiction between the void fraction and the mass flow of working fluid after the introduction of LMMHD power generation. The study utilizes a multi-dimensional model to evaluate the performance of the CBC enhanced by multi-stage LMMHD generators coupled with hydrocarbon fuel scramjet. The multi-stage mixing-separation LMMHD generator is proposed to decouple the void fraction of the MHD channel and the wall cooling process, and control the void fraction by change number of stages. The calculation result indicate that the void fraction significantly affects the overall power generation performance, including output power, performance boundary, etc. Increasing the void fraction is beneficial, and the optimal void fraction is 0.65. At the same Mach number, the fuel cooling capacity available to the system increases with the fuel equivalence ratio, resulting in higher total power output. The maximum Mach number for thermal protection of the combustor walls alone may surpass 9.5. For gas void fractions of 0.35/0.5/0.65, the maximum power generation reaches 182.8/167.1/156.9 kW, respectively. The novel system is compared with other advanced thermal-electricity conversion cycles under nearly the same conditions and demonstrated clear performance advantages.

Combustion characteristics of premixed ammonia-hydrogen/air swirl flames at elevated pressure

Ammonia (NH3)-hydrogen (H2) blends which are obtainable by NH3 cracking can be an eminent carbon-free fuel. To provide a valuable database for the practical application of cracking-based NH3-H2 fuel, the effects of pressure on the combustion characteristics of premixed NH3-H2(-nitrogen (N2))/air swirl flames are investigated in terms of H2 mole fraction in the NH3-H2 blend and fuel-equivalence ratio. Extinction mechanisms at fuel-lean and rich flames are the same for both normal and elevated pressures, though only the blowoff is observed for elevated pressure. With increasing pressure, fuel-rich limits are generally extended but fuel-lean limits are reduced, NOx emissions decrease and the condition of the maximum NOx emissions moves towards fuel-richer condition. Flame visualization exhibits the shifted main reaction zone upstream, the increased flame wrinkling and the reduced OH and NO intensities with increasing pressure. Dilution effects of N2 at elevated pressure become remarkable compared with those at normal pressure.

Experimental and kinetic modeling study of iso-propylamine oxidation with SVUV-time of flight mass spectrometry

Atmospheric oxidation experiments of iso-propylamine (IPA) were conducted in a jet-stirred reactor over the temperature range from 550 to 870 K at fuel-equivalence ratios of 0.5 and 2.0. A combination of synchrotron vacuum ultraviolet (SVUV) photoionization and time-of-flight mass spectrometry (TOFMS) was utilized to identify and quantify oxidation products and intermediates. Compared to the previous n-propylamine (NPA) low-temperature oxidation [Proc. Combust. Inst., 39 (2023) 295–303.], some intermediates and products were newly observed among the 34 detected species, including nitrosyl hydride, methylamine, acetonitrile, nitrous oxide, ethyl isocyanide, propanenitrile, 2-propanimine, n-methylformamide and 2-methylallylamine. A kinetic model consisting of 815 species and 4402 reactions was developed based on the iso-propanol model [Prog. Energy Combust. Sci. 67 (2018) 31–68.] and an ethylamine model [Prog. Energy Combust. Sci. 44 (2014) 40–102.]. The onset temperature of IPA and O2 consumption is 750 K under both lean and rich conditions. Rate-of-production (ROP) and sensitivity analyses were performed at 800 K to illustrate the reacting paths from parent fuel to major intermediates and products, and identify the most sensitive reactions. H2O2(+M) = 2OH(+M) is the most sensitive reaction with a promoting effect on IPA consumption while 2HO2 = H2O2+O2 is the most inhibiting one. Important N-containing pollutants like NH3, NOx, HCN, CH3NH2 and so on were analyzed with respect to their reaction routes. (CH3)2CNH is abundant due to the H-abstraction reactions between tC3H6NH2 radical with O2. This work was made for gaining a more comprehensive insight into the oxidation of IPA and make a foundation for further exploring amine chemistry.

Numerical Simulation on the Spray Angle of the Dual-layer Hole Nozzle in a Partition Combustion System of the Diesel Engine

To study the effect of the spray angles of the dual-layer hole nozzle on the combustion and emissions performance in the partition combustion system, the in-cylinder spray, mixture formation and combustion processes of the new combustion system were simulated and investigated using AVL FIRE software. The results show that, compared with the variation of the lower-layer spray angles, the change of the upper-layer spray angles has a great influence on the instantaneous heat release rate. The increasing spray angles of the lower-layer holes lead to reduced peak values of the heat release rate in the cylinder. In all the spray angle cases, the first fire area of the cylinder is in the B zone of the combustion chamber. Compared with lower-layer spray angle, the upper-layer spray angle has a greater impact on the airflow disturbance in the combustion chamber. Appropriately increasing the upper-layer spray angle facilitates the mixing of fuel and air in the combustion chamber and reduces the unburnt fuel equivalence ratio. When the spray angles of the upper- and lower-layer holes are 157° and 112°, respectively, the combustion indicates power has the largest value of 12.18 kW. At the same time, the Soot emission is also the smallest, with a value of 0.52 g/kW·h.

Experimental Study on Effects of Different Factors on Continuous Detonation of Superfine Lignite: Particle Size and Fuel Equivalent Ratio

ABSTRACT The Rotating Detonation Engine (RDE) is garnering attention for its high thermal cycle efficiency. In order to explore the detonation evolution of lignite/gas/oxygen gas-solid two-phase fuel in RDE, self-developed RDE(L:1000 mm) was used to study the detonation characteristics of lignite dust with ultra-fine particle size in methane/oxygen atmosphere, and the effects of ultra-fine particle size and equivalent ratio on detonation characteristics were explored, achieving stable propagation of rodtating detonation waves (RDW) with durations between 0.611 and 0.684s. The results indicate that the introduction of lignite dust significantly enhances the detonation effects compared to pure methane fuel. An increase in the overall equivalence ratio boosts the propagation velocity of RDW in methane-solid fuels, while a larger lignite dust particle size slows it down. Among ultrafine lignite powder sizes, a 1 μm particle size achieved the highest detonation wave speed. In terms of RDW propulsion, the impact of particle size and methane-solid fuel equivalence ratio on thrust mirrors their effect on detonation wave velocity. At a global equivalence ratio (GER) of 1.8, the specific impulse under different particle sizes was about 0.6 times that at a GER of 1.0, suggesting that an excess of fuel can reduce detonation effectiveness. The optimal specific impulse results were obtained with a lignite powder addition rate of 6 g/s, particle size of 1 μm, and GER of 1.0, reaching 4.6 kN·s·kg−1. The research results reveal the detonation process and detonation propagation law of lignite in methane/oxygen, especially for the future application of lignite in detonation energy release engineering.

Optimized Emission Analysis in Hydrogen Internal Combustion Engines: Fourier Transform Infrared Spectroscopy Innovations and Exhaust Humidity Analysis

<div>In today’s landscape, environmental protection and nature conservation have become paramount across industries, spurring the ever-increasing aspect of decarbonization. Regulatory measures in transportation have shifted focus away from combustion engines, making way for electric mobility, particularly in smaller engines. However, larger applications like ships and stationary power generation face limitations, not enabling an analogous shift to electrification. Instead, the emphasis shifted to zero-carbon fuel alternatives such as hydrogen and ammonia. In addition to minimal carbon-containing emissions due to incineration of lubricating oil, hydrogen combustion with air results in nitrogen oxide emissions, still necessitating quantification for engine operation compliance with legal regulations. A commonly used multicomponent exhaust gas analyzer on FTIR principle can suffer from higher volumetric water shares in the exhaust gas of the hydrogen engine, influencing the emission analysis. This concern prompted the development of a new evaluation approach for hydrogen operation, analyzing unique wavelength bands for hydrogen operation while considering the higher volumetric water shares in the exhaust gas of a hydrogen engine and its missing carbonaceous emissions. The method’s capability of providing more credible results for hydrogen-powered engines is demonstrated by assessing the newly introduced hydrogen method through variations of the indicated mean effective pressure, the air–fuel equivalence ratio, and the intake air humidity. Presuming minimal CO<sub>2</sub> emissions, the method allows a more realistic allocation of absorption spectra to other emissions. In addition to investigations on the new hydrogen evaluation method, a model for calculating the volumetric water share in the hydrogen engine’s exhaust gas is presented. By comparing the theoretical to the measured water share, the hydrogen emissions of the engine can be calculated without the need for additional hydrogen slip measurement.</div>

Potential Analysis of Defossilized Operation of a Heavy-Duty Dual-Fuel Engine Utilizing Dimethyl Carbonate/Methyl Formate as Primary and Poly Oxymethylene Dimethyl Ether as Pilot Fuel

<div>This study demonstrates the defossilized operation of a heavy-duty port-fuel-injected dual-fuel engine and highlights its potential benefits with minimal retrofitting effort. The investigation focuses on the optical characterization of the in-cylinder processes, ranging from mixture formation, ignition, and combustion, on a fully optically accessible single-cylinder research engine. The article revisits selected operating conditions in a thermodynamic configuration combined with Fourier transform infrared spectroscopy.</div> <div>One approach is to quickly diminish fossil fuel use by retrofitting present engines with decarbonized or defossilized alternatives. As both fuels are oxygenated, a considerable change in the overall ignition limits, air–fuel equivalence ratio, burning rate, and resistance against undesired pre-ignition or knocking is expected, with dire need of characterization.</div> <div>Two simultaneous high-speed recording channels granted cycle-resolved access to the natural flame luminosity, which was recorded in red/green/blue and OH chemiluminescence.</div> <div>Selected conditions were investigated in more detail with the simultaneous application of planar laser-induced fluorescence of OH and HCHO and recording natural flame luminescence in a cycle-averaged manner.</div> <div>Poly oxymethylene dimethyl ether was used as pilot fuel, building on prior investigations. The mixture of 65 vol% Dimethyl Carbonate and 35 vol% Methyl Formate with prior verification on a passenger-car-sized engine substitutes synthetic natural gas in this study.</div> <div>Thermodynamically, the increased compression ratio up to 17.6 resulted in feasible operation and increased indicated efficiency. On the lower compression ratio of 15.48, a more comprehensive range of applicable air–fuel equivalence ratios and increased degrees of freedom regarding the pilot’s total energy share are observed compared to the base configuration with natural gas and EN590 as pilot fuel.</div> <div>The air–fuel equivalence ratio sweep from λ = 1.0–2.0 revealed predominantly premixed and high-temperature heat release via OH*. The temporal and spatial evolution shifts while leaning out the mixture with increasing gradients on the radial distribution and decouples for lean mixtures from the initial spray trajectory.</div>

Investigation of Unsteady Combustion Regimes in a Kerosene-Fueled Scramjet with Air Throttling

This paper describes an experimental study investigating unsteady combustion regimes in a kerosene-fueled scramjet. The results are obtained under inflow conditions of a 2.9 MPa stagnation pressure, 1900 K stagnation temperature, and a Mach number of 3.0. The air throttling position is 240 mm downstream of the combustor entrance, with an air throttling flow rate (ratio of air throttling mass flux to inflow mass flux) of 38% and a fuel equivalence ratio of 0.37. Combustion is relatively stable when air throttling is applied and is dominated by auto-ignition. When air throttling is turned off, the combustion becomes more unsteady and is dominated by flame propagation. At the same time, the combustion mode changes, and the frequency of the combustion mode transition is 286 Hz. Schlieren images and one-dimension analysis show that the effect of air throttling is the coupling of cold throat (aerodynamic throat) and hot throat (thermal throat). The proper orthogonal decomposition and dynamic mode decomposition analysis present that when air throttling is applied or removed, the frequencies of injector–flame feedback are almost the same, while the frequencies of shock–flame feedback exhibit considerable variation, which is caused by the location of the precombustion shock affected by air throttling.

Plasma assisted combustion of different biogas mixtures in low swirl burner

This study explores the impact of plasma driving frequency on diverse biogas compositions, emphasizing flame behaviour by analysing spatial emissions of OH*, C2*, and CH* from plasma-assisted flames. Experimental investigation performed combusting mixtures with 25 % and 60 % CH4 in CO2 under lean combustion conditions with the varying fuel equivalence ratios from 0.71 to 0.83 and plasma discharge frequencies from 60 to 120 kHz resulting in higher energy density.Obtained results indicate that the plasma assistance notably enhances flame stability under lean fuel conditions with increasing frequency from 80 to 120 kHz. The discharge frequency of 60 kHz indicates insufficient energy to enhance combustion of low calorific value mixtures as the flame lift-off height increases approximately by 0.43–1.5 % for the mixture of 25 vol% CH4 in CO2 and by 0.26–7.7 % for the mixture of 60 vol% CH4 in CO2. Changing the plasma frequency from 80 to 120 kHz, the flame position is shifted closer to the burner nozzle for both mixtures and the highest effect is determined at 120 kHz. The flame lift-off height is reduced by 2.43–16.34 % for the mixture with 25 vol% of CH4 and by 3.57–51.28 % for the mixture with 60 % of CH4. The plasma-assisted combustion leads to improved combustion efficiency as CO emissions are reduced from 1550 ppm to 45 ppm for biogas mixture, but in the case of low calorific value gas, the CO emissions increase linearly with the frequency increase even the flame curvature and stability is improved.

Combustion Characteristics and Application Performance of JP-10/Nano-Sized Aluminum Gel-Fueled Scramjet

Using nano-sized energetic materials as fuel additives to hydrocarbon gel fuel has gained in popularity due to the advantages of higher energy density and shorter ignition delay times. Combustion characteristics and application performance of gel fuel containing 16% wt aluminum nanoparticles were investigated on a direct-connect scramjet platform with an inflow Mach number of 2, an inflow total temperature of 1700 K, and a fuel equivalence ratio ranging from 0.6 to 1.0. The gel fuel could be stably injected and atomized efficiently by a nitrogen-assisted injector. The combustion efficiency of JP-10+Al gel fuel was 4.27% higher than that of JP-10 gel fuel, while the addition of aluminum increased the density specific impulse by 6.34%, indicating that the addition of aluminum nanoparticles indeed presented a positive effect on combustion and engine performance. The wall deposition phenomenon of gel fuel was particularly slight as compared to that of slurry fuel cases. Unlike nanoaluminum-blended slurry fuel, nanoaluminum-blended gel fuel controlled the potential risk of increasing thermal load to the least degree within the scope of existing research, with wall heat flux increasing by 7.43% solely as a result of elevated airflow temperature, indicating its advantageous application prospect.

Combustion instability analysis in an ethylene-fueled scramjet combustor under various fuel penetration height conditions using an image-based nonlinear dimensionality reduction method

The present study investigates the effects of fuel penetration height on combustion instabilities in an ethylene-fueled scramjet model combustor with a cavity flameholder. Experiments were performed at the stagnation temperature of 1900 K, the stagnation pressure of 0.37 MPa, and the Mach number of 2. Three fuel injection orifice diameters:2.3, 2.4, and 2.5 mm, were tested to elucidate the effects of ethylene penetration height on combustion instabilities. Furthermore, high-speed measurements of CH* chemiluminescence and shadowgraphs were performed with high-speed video cameras. To examine the dynamics of the combustion instabilities, time-resolved CH* chemiluminescence images and shock parameters, extracted from snapshots of shadowgraphs, were analyzed using a non-linear dimensionality reduction algorithm: Gaussian Process Dynamical Model (GPDM). Thereafter, further analyses on the acquired latent variables were conducted with Recurrence Plot (RP). The experimental results showed that the fuel equivalence ratio (ϕ) range for cavity shear-layer combustion mode expanded as d decreased. Furthermore, for ϕ = 0.18, the instability behavior remarkably changed at around d = 2.4 mm. Therefore, the instability dynamics for ϕ = 0.18 were investigated using GPDM and RP including results from our previous study (d = 2, 3, and 4 mm), revealing differences in the instability behaviors. For d = 3 and 4 mm, jet-wake combustion and ram combustion modes were established alternately with a frequency of about 1600 Hz. In contrast, at d = 2.4 and 2.5 mm, although a similar instability in the d = 4 mm case was present at almost the same oscillation frequency, a different instability behavior was also confirmed. This additional instability exhibited an intermediate state between jet-wake combustion and ram combustion modes. These two instabilities emerged aperiodically. For an unstable combustion in shear layer observed for d = 2 and 2.3 mm, corresponding RPs exhibited black patches, indicating that the oscillation amplitude diminished substantially.

Performance Assessment of Closed-Brayton-Cycle and Thermoelectric Generator Combined Power Generation System Coupled with Hydrocarbon-Fueled Scramjet

Closed-Brayton-cycle (CBC) is a potential scheme to provide high-power electricity for hypersonic vehicles, but finite cold source onboard limits its power level. A thermoelectric generator (TEG) combined with CBC is a feasible power enhancement approach by extending the available temperature range of cold source. In this study, a performance assessment of the CBC-TEG combined power generation system coupled with hydrocarbon-fueled scramjet is performed to exhibit its possible operation characteristics and performance limitations on hypersonic vehicles. Results indicate that, at a fixed flight Mach number, a larger fuel equivalence ratio (φ) leads to a higher total electric power and CBC power but a lower TEG power. There are three limitations on the fuel equivalence ratio, TEG temperature difference, and combustion heat dissipation adjustment for the operation of CBC-TEG. The total power of CBC-TEG can be adjusted by φ, but the adjustable range becomes smaller at higher Ma. The electric quantity at unit fuel mass increases with φ, mainly due to the higher thermoelectric conversion efficiency. Moreover, the maximum value of the electric quantity at unit fuel mass for CBC-TEG reaches 277.0 kJ/kg, which is about 33.4% higher than that of standalone CBC.

Combustion characteristics of premixed ammonia-hydrogen/air flames in a swirl model combustor

Ammonia (NH3)-hydrogen (H2) blends based on the thermal cracking of NH3 are considered as a prominent carbon-free fuel. This study aims to provide the combustion characteristics of premixed NH3-H2(-N2)/air swirl flames under various conditions of fuel-equivalence ratio (ϕ) and H2 content in the fuel blend (xh,f). Results show four representative types of premixed NH3-H2(-N2)/air flames depending on ϕ. Combustion stability limits are extended with increasing xh,f and through the transition from laminar to turbulent combustion condition. With increasing xh,f, NOx emissions are enhanced and their peak values are observed to fuel-leaner condition. The deNOx effect of NH3 is enhanced with increasing xh,f, and different main pathways for the oxidation of NH3 to NO are found depending on ϕ. Flame visualization including the distributions of OH(∗) and NO radicals indicates that OH promotes NO production. No remarkable discrepancies of the combustion characteristics between the premixed NH3-H2/air and NH3-H2-N2/air flames are found.

Correlation of wall heat loss with quenching distance for premixed H2/Air flames during unsteady Flame-Wall interaction

Flame-wall interaction (FWI) of a laminar, premixed hydrogen/air flame perturbed by a pulsating inflow with excitation frequency (f) is investigated using fully resolved simulations employing finite-rate chemistry and detailed molecular diffusion. The setup is a two-dimensional (2D) V-shaped flame interacting with an isothermal wall on one side and a freely propagating flame on the other side, exhibiting a side-wall quenching and a freely-propagating mode. The impact of unsteady flame stretch on flame dynamics is characterized by the Damköhler number (Da), which is defined by the ratio of the turnover time of the oscillating inflow to the flame transit time. Da is found to directly describe the degree of flame deformation during flame propagation. During FWI, flame pocket formation is suppressed at conditions with Da close to unity. The correlation between wall heat flux (WHF) and quenching Peclet number (Peq) shows a time delay that depends on Da. A negative linear correlation can be recovered between time-averaged wall heat flux (WHF¯) with the quenching Peclet number (Peq¯), and its slope depends on the fuel equivalence ratio. For the lean hydrogen flame, the flame stretch near the quenching point leads to a decrease in flame intensity during FWI and therefore different slope of the correlation of WHF vs. Peq.

Gas-Dynamic Interactions between Pre-Chamber and Main Chamber in Passive Pre-Chamber Ignition Gasoline Engines

<div>Pre-chamber turbulent jet ignition (TJI) is a method of generating distributed ignition sites through multiple high-speed turbulent jets in order to achieve an enhanced burn rate in the engine cylinder when compared to conventional spark plug ignition. To study the gas-dynamic interactions between the two chambers in a gasoline engine, a three-dimensional numerical model was developed using the commercial CFD code CONVERGE. The geometry and parameters of the engine used were based on a modified turbocharged GM four-cylinder 2.0 L GDI gasoline engine. Pre-chambers with nozzle diameters of 0.75 mm and 1.5 mm were used to investigate the effect of pre-chamber geometry on pre-chamber charging, combustion, and jet formation. The local developments of gas temperature and velocity were captured by adaptive mesh refinement, while the turbulence was resolved with the k-epsilon model of the Reynolds averaged Navier–Stokes (RANS) equations. The combustion process was modeled with the extended coherent flamelet model (ECFM). Data from engine experiments were compared with the computed main chamber pressures and heat release rates, and the results show good consistency with the model calculations. The scavenging and air–fuel equivalence ratio (λ) distribution of the pre-chambers improved with the larger nozzle, while the smaller nozzle generated jets with higher velocity, greater turbulence kinetic energy, and longer penetration length. Moreover, after the primary jet formation, secondary pre-chamber charging, combustion, and secondary jet formation were observed.</div>

Performance Improvement of Kerosene Fuelled Scramjet Combustor Through Modified Fuel Injection - A Cfd Study

Full scale kerosene fuelled scramjet combustor of a hypersonic air-breathing vehicle is numerically explored for two different fuel injection systems. A commercial software CFXTASCflow has been used for the reacting flow computation within the combustor. Three dimensional Navier-Stokes equations are solved along with k-ε turbulence model to analyse the flow field. Eddy Dissipation Model (EDM) with fast rate chemical kinetics is used for combustion modeling. Lagrangian Particle Tracking Method (LPTM) has been used to simulate the trajectory of the kerosene droplets. Kerosene is injected from the struts. Reacting flow simulations have been carried out for the fuel equivalence ratio of 1.0. The overall flow characteristics in the combustor are presented through the distribution of various thermochemical parameters at different cross sections. Kerosene which is injected in liquid phase completely vaporizes within the combustor. Considerable improvement in the performance in terms of thrust and combustion efficiency is observed with the modified fuel injection system.

Flammability Properties of the Pyrolysis Gas Generated from Willow Wood

Willow wood presents a real interest for biomass pyrolysis due to its fast growth, renewability, and high energy density. Following the pyrolysis of willow wood in an inert atmosphere, a multi-fuel gaseous mixture was obtained, with the following composition (by volume): 38.20% CO/21.87% H2/17.44% CH4/1.15% O2/17.15% CO2/4.19% N2. The propagation of laminar premixed flames in these multifuel mixtures with air was investigated numerically for initial temperatures from 298 to 500 K, initial pressures from 1 to 20 bar, and fuel equivalence ratios between 0.60 and 2.00. The combustion of these gaseous mixtures as free laminar premixed flames was simulated by means of the INSFLA package and an extended reaction mechanism with 592 elementary reactions and 53 species. The modelling of the gas-phase combustion delivered several important parameters: the laminar burning velocities, Su, the maximum flame temperatures, Tfl,max, the flame front thicknesses, dfl, and the peak concentrations of the main reaction intermediates. The obtained parameters, discussed in correlation with the initial pressure and temperature, afforded the determination of the overall activation parameters of multifuel oxidation with air.