Ignition Of Mixtures Research Articles

Mixing and flame structure study of inverse swirl diffusion flames

Swirling flames appear in many practical applications to enhance flame stabilization. However, relatively few studies have investigated the inverse swirl diffusion flames (ISDFs) in detail. In ISDFs, a central swirling air jet is surrounded by an annular methane fuel jet. In the first part of this work, the stability map of ISDFs is studied. This map shows two distinctive stability regions: a swirling-jet-like region at low swirl and a compact swirling flame region at high swirl intensity. Regardless of the bulk air jet velocity (U), these two regions are separated by an optimum swirl intensity -leading to the highest flame stability. Then across these two regions, the development of the fuel–air mixing and the flame-flow interaction were investigated via acetone-PLIF and simultaneous PIV/OH-PLIF measurements. At the same U, increasing the swirl intensity leads to different mixing patterns. An annular-rich jet exists in the swirling-jet-like region versus a compact short mixing field in the compact flame stability region. Moreover, the development of the fuel–air mixing field downstream of the burner exit impacts the flame-flow interaction. The fast and early fuel–air mixing enhances the mutual interaction between the lower edge of the flame and the wrinkled flame, and the spots of the high heat released from the downstream regions - hence a highly stable flame is obtained. The lower flame edge is seen to track the instantaneous lower stagnation point of the swirling flow, while the increased heat release spots/flame wrinkling track the shear layer vortices. Beyond the optimum swirl intensity, increasing the swirl intensity retarding the fuel–air mixing and weakens the mixture ignitability, straining the flame in the vicinity of the flame edge or the vortices of the shear layer. These results suggest that suitable modifications of the mixing field close to the burner nozzle of ISDFs may increase flame stability.

Optical and electrical investigation of plasma generated by high-energy self-stabilized spark ignition system

Spark discharge plasma is commonly used for ignition in internal combustion engines. The environmental performance of internal combustion engines with forced ignition is improved when operating under lean mixture conditions. High-energy ignition systems are needed to ensure reliable ignition of lean mixtures. The ignition of a combustible mixture is influenced by several plasma parameters, such as the temperature of its various components, the size of the plasma, and the deposited energy. It is, therefore, beneficial to know these parameters. Here, we present optical and electrical investigation of plasma generated in ambient air by a novel high-energy self-stabilized spark ignition system. The electrical investigation showed two high current pulses, with the current amplitude of ∼40 and ∼150 A. The energy is deposited to the spark gap mainly during the second current pulse, and it is increasing from 213 to 541 mJ with the increasing gap size from 3 to 13 mm. The energy efficiency increases with the gap as well, from around 23% to 58%. Time-resolved emission spectra enabled us to estimate the evolution of the gas temperature, electron excitation temperature, and electron density in the generated plasma. It was found that the highest electron density, 3–4 × 1017 cm−3, correlates with the maximum of the second pulse current. We observed a specific plasma evolution between the two current pulses, with an increase in temperature from 4500 to 7500 K and a contraction of the plasma channel diameter from 3.3 to 0.5 mm.

Formation of products upon ignition, combustion and melting of mixtures of high-entropy alloy FeNiCoCrCu with titanium and carbon

The dependence of the ignition temperature, combustion rate and composition of the resulting products on the concentration of Ti + C in mixtures with powder of a high-entropy alloy (HEA) FeNiCoCrCu and the initial mixture of metals forming it (MIX) has been studied. HEA was obtained by mechanical activation (MA) of a mixture of metal powders in argon. At the melting temperature, the high-entropy FeNiCoCrCu alloy decomposes into several phases, but the basis of the HEA alloy, as well as the alloy obtained by melting and crystallizing MIX, is a 5-component phase with an average formula Cu1.2Fe1.4Ni1.4Co1.4Cr. In addition, 5, 4, and 3-component phases with averaged formulas Cu2Ni2Co2Fe2Cr, Cu3Ni3Co2.9Fe2.5Cr, Cu4.8Ni4.5Co4.6Fe4.2Cr, Cu40Fe2Ni4Co2C, Cr12.5Fe3.2Co2.6Ni and Co3.2 Fe3,5 Cr are present in small amounts in the binder. Experiments on the ignition and combustion of mixtures of MIX and HEA with Ti + C were carried out in argon at atmospheric pressure. The combustion rate, ignition temperature, and maximum temperature reached in the thermal explosion of MIX and HEA mixtures with Ti + C increase with increasing Ti + C concentration. Due to the low exothermicity of the mixtures, the experiments were carried out at an initial temperature of 500 °С. At this initial temperature, the combustion limit of the samples occurs when the Ti + C concentration in the HEA and MIX mixtures is less than 30 %. Based on the results of scanning electron microscopy, the volume concentration of the number of titanium carbide (TiC) particles in molten samples was calculated. In an alloy with a HEA binder, the number of TiC particles per unit volume is 1.5-3.0 times greater than in an alloy with a MIX binder, and their size is correspondingly smaller. With an increase in the concentration of Ti + C from 30 to 40 % in a mixture with HEA, the number of TiC particles per unit volume decreases. In a mixture with MIX, the number of TiC particles per unit volume passes through a minimum. This is due to two opposite processes: on the one hand, the probability of the generation of TiC particles increases, on the other hand, their coagulation occurs.

Laser and pre-chamber ignition, combustion and flame propagation characteristics of CH4/air mixtures in a constant volume combustion chamber

The most important stages determining the qualitative and quantitative characteristics of a combustion process are mixture preparation, ignition, combustion itself and pollutant emissions. Among these, the ignition phenomenon stands out in terms of ensuring a reliable operation under every working condition (which also affects subsequent stages). In this study, the influence of the properties and the type of the ignition source on combustion and flame propagation characteristics of methane/air mixtures were investigated by using a passively Q-switched Nd:YAG crystal laser and a pre-chamber ignitor in a constant volume combustion chamber. The number of consecutive pulses and the air-fuel-equivalence ratio are studied parameters. With the laser ignition system, it was possible to ignite fuel-air mixtures at very lean conditions. However, as flow conditions in the combustion chamber varied due to the protruding part of the pre-chamber ignitor, ignition possibility decreased and combustion metrics worsened. The number of pulses affected combustion parameters such as the ignition delay time, the combustion duration, the rate of pressure rise etc. in a non-monotonic manner. Deteriorations and improvements on such parameters were detected depending on the air–fuel-equivalence ratio λ.

Экспериментальные исследования тепловозного газодизельного двигателя с системой электронного управления топливоподачей

Fuel efficiency and exhaust gases toxicity are the main indicators of the locomotive diesel operation. To increase them, the paper proposes to convert the locomotive diesel to working on natural gas. Expediency of such conversion to operate on the natural gas according to the gas-diesel cycle, where natural gas being the main gaseous fuel is ignited from the dose of petroleum diesel fuel, is demonstrated. This diesel engine operation ensures stable ignition of the air-fuel mixture in a wide range of speed and load conditions. An electronic fuel supply control system for the gas-diesel engine was developed. Experimental studies of the locomotive gas-diesel engine created on the basis of the D50 diesel engine with the electronic fuel supply control system in the diesel characteristic modes were carried out. Substitution of the petroleum diesel fuel with natural gas in these modes was 60.3...94.1 % by weight. For the mode corresponding to the first position of the driver’s controller, opacity of the exhaust gases decreased by 19.6 %, when the diesel engine was switched to the gas-diesel cycle.

Performance Requirements on Laser Ignition System

Abstract: Combustion is one of the most prominent energy conversion processes used in all areas of human life, even though it is being used on a large scale in various fields it has vital drawbacks like emission of greenhouse gases from IC engines majorly affecting the environment on a global level. One of the reasons of this issue being improper or inefficient ignition of the air-fuel mixture. However, this can be reduced to an extent by employing methods like lean combustion and re-circulating the exhaust gases. This is when the need of an alternative ignition system is required, one such concept being LASER IGNITION SYSTEM for internal combustion engines. On comparison laser ignition system provides number of potential benefits over conventional ignition by electric spark plug. Use of laser ignition system comes with advantages like- Reduction of NOx emission by 20% also improved efficiencies are obtained. The thermodynamic requirements of high compression ratios and high power density are fulfilled well by this system. Therefore, laser ignitors could replace conventional spark plugs in automobile industry. This not only provides better performance and fuel economy, but would also create less harmful emissions

Analysis of the Effect of Mathematical Models of Chemical Transformations on the Ignition of Hydrogen-Oxygen Mixtures

Analysis of the Effect of Mathematical Models of Chemical Transformations on the Ignition of Hydrogen-Oxygen Mixtures

Comparative Analysis of Some Mathematical Models Ignition of Hydrogen-Oxygen Mixtures

Comparative Analysis of Some Mathematical Models Ignition of Hydrogen-Oxygen Mixtures

Kinetic Mechanism of Ignition of Propane-Butane Mixtures at Low and High Temperatures: Development and Application

Kinetic Mechanism of Ignition of Propane-Butane Mixtures at Low and High Temperatures: Development and Application

Research of the efficiency using the model of the spatial hinge in an internal combustion engine

An internal combustion engine is a heat system for many kinds of use in the field of engineering. The difficult economic situation around petroleum products, which is associate with their deficit and modern environmental safety standards require switching to alternative energy sources and looking for ways to modernize internal combustion engines to increase their efficiency. A large number of internal combustion engines belong to the crank group. The analysis of the crank group showed their low technical efficiency. When the piston is in the upper position at the time of ignition of the combustible mixture in the cylinder, the maximum pressure occurs. This leads to maximum driving force with a minimum crank angle. Also increases the friction of the piston on the cylinder wall, the wear of the cylinder wall, additional local heating of the surface of the cylinder and over-load of the crankshaft. Thus, a decrease in the net power resulting from the combustion of fuel in the engine occurs. To increase the efficiency of the crank mechanism, it is propose to apply a new design of the torque transmission mechanism in the engine, which will be built based on a spatial hinge. This paper presents a study of the power and kinematic parameters of the spatial hinge of an internal combustion engine.

Pilot diesel-ignited ammonia dual fuel low-speed marine engines: A comparative analysis of ammonia premixed and high-pressure spray combustion modes with CFD simulation

Decarbonization of global shipping plays an important role in avoiding the worst impacts of climate change, and ammonia is a promising sustainable and zero-carbon fuel in the maritime sector. The dual-fuel mode has the potential to compensate for the poor combustion property of ammonia, but the existing studies are mainly focused on automotive medium- and high-speed engines, researches on marine low-speed engines are rarely reported. In this paper, the numerical models of pilot diesel-ignited ammonia dual fuel engine under both the premixed and high-pressure spray combustion modes are established using a commercial low-speed marine diesel engine as the prototype, and verified against the experimental data of the spray mixture formation, ignition delay, in-cylinder pressure and pollutant emissions. Then, the engine performance and emissions of both two modes are studied and optimized. The results show that under the diesel replacement ratio of the commercial methane/diesel dual-fuel marine engine (i.e. around 98%–99%), both two modes can achieve an indicated thermal efficiency (ITE) of over 50%. At the optimized ammonia premixed combustion point, the ITE is increased by 5.1% owing to the significantly reduced cooling loss, but at the expense of 140.6% higher NOx emissions compared to the diesel-only mode. The optimized ammonia high-pressure spray combustion point can achieve a similar ITE and reduce the NOx emissions by around 47% compared to the diesel-only mode. For both the optimum points, the GHG emissions (i.e. CO2 + 300 × N2O) are reduced by around 97%, while the unburned NH3 emissions are negligibly small.

Modeling of spark ignition in gaseous mixtures using adaptive mesh refinement coupled to the thickened flame model

In standard LES of spark ignition using the thickened flame model (TFM) and a static mesh, in other words without the use of adaptive mesh refinement (AMR), a progressive increase of the thickening factor F from unity to the nominal value is a consequence of the progressive increase of the cell size away from the spark plug. If the refined mesh is limited to a small region around the spark plug, the computational cost is limited but F will increase very rapidly as soon as the flame leaves the spark region, leading to an erroneous prediction of the total heat release rate as shown in this study. Conversely, using a large refined mesh region will allow such a progressive increase of F but at the cost of a strongly increased computational cost. To solve this issue, two new spark ignition models called TFM-AMR-I and TFM-AMR-I-Ftrans are proposed for TFM. These models are based on TFM-AMR Mehl et al.(2021) which employs AMR to ensure the desired thickening level and a constant number of grid points across the flame. It also uses a realistic spark plug energy model as in Colin et al.(2019). To avoid the aforementioned issue, a physical criterion is proposed to start the increase of F only when the flame kernel can be considered self-sustained. As this criterion is given by a model transport equation, the possible convection of the kernel outside the spark region doesn’t prevent the model to work properly. Secondly, in both models the increase of F is no more dictated by the cell size of the static mesh but it is given by an additional transport equation that controls the growth rate of F in time.These models are applied to the laminar propane/air ignition experiment presented in Colin et al.(2019). It is first shown that the experimental MIE is correctly recovered when using a DNS type resolution, that is, F=1 at any time. Then both proposed LES ignition models are applied to the same case: they recover correctly the MIE of the DNS provided the stretch correction of Quillatre (2014) is applied, which confirms the need to correct the effect of stretch with TFM. At the same time, TFM-AMR-I under-predicts the total heat release rate, which is attributed to the jump of the thickening factor at each AMR level removal. On the contrary, TFM-AMR-I-Ftrans compares better with the DNS, which is attributed to the continuous evolution of F with this model. Finally, it is shown that both models lead to a computational time reduction of a factor between 2 and 6 compared to static mesh TFM simulations.

Computational Fluid Dynamics Modeling of Low Temperature Ignition Processes From a Nanosecond Pulsed Discharge at Quiescent Conditions

Abstract Recent interest in nonequilibrium plasma discharges as sources of ignition for the automotive industry has not yet been accompanied by the availability of dedicated models to perform this task in computational fluid dynamics (CFD) engine simulations. The need for a low-temperature plasma (LTP) ignition model has motivated much work in simulating these discharges from first principles. Most ignition models assume that an equilibrium plasma comprises the bulk of discharge kernels. LTP discharges, however, exhibit highly nonequilibrium behavior. In this work, a method to determine a consistent initialization of LTP discharge kernels for use in engine CFD codes like converge is proposed. The method utilizes first principles discharge simulations. Such an LTP kernel is introduced in a flammable mixture of air and fuel, and the subsequent plasma expansion and ignition simulation is carried out using a reacting flow solver with detailed chemistry. The proposed numerical approach is shown to produce results that agree with experimental observations regarding the ignitability of methane-air and ethylene-air mixtures by LTP discharges.

Co-milling as a synergy factor for co-firing. A case study of wood/coal blends

It is known that simple adding of wood allows one to accelerate the ignition of powder mixtures compared to the situation when pure coal is used. This study focuses on testing the hypothesis about the effect of co-milling coal and wood on their co-firing: is the case of composite powdered fuels should ensure the maximum possible efficiency of heat and mass transfer? Firstly, we will show that co-milling of coal and wood leads not independent size reduction of two materials but gives composite powder – coal-covered wood. For the composite fuel further reduction of the ignition delay time of air suspension and reduction of the limit volume concentration required for flame propagation have demonstrated. Obtained synergy also manifests in thermogravimetry. Here we propose a simple method for analyzing the mass loss curves. For any coal-to-wood sawdust ratio, combustion of the composites and mixtures both can be viewed as a weighted sum of the curves of individual components. But only in the case of composites calculated sawdust content is higher than the actual one: the mass loss is redistributed towards the stage occurring at lower temperatures due to geometry of wood/coal contact.

Thermoelectric detector application for measuring the ignition delay time in a shock heated combustible mixture

The problem of flight safety of high-speed aircrafts is primarily related to the reliability of engines, which, in turn, depends on the correct understanding of the processes of ignition and combustion of fuel in the combustion chambers of engines during their design. In this work, a new method for registration the ignition of shock heated gaseous fuels using a thermoelectric detector is proposed. The detector well measures the ignition delay time of fuels in the microsecond range, which is characteristic of detonation processes in the combustion chambers of promising aircraft engines operating on detonation combustion. The efficiency of the detector is demonstrated by the ignition of a propane-air mixture behind a reflected shock wave as an example. During the experiments, the thermoelectric detector showed such properties as the ability to register high heat flux values, low inertia, high signal-to-noise ratio, and high temporal resolution. The data obtained are compared with the measurement data of the ignition delay time by optical and piezoelectric methods obtained in this work, as well as in the studies of other authors.

Comparison of thermophysical properties and combustion characteristics of various biodiesels in a non-MILD ultra-low emission swirl burner

All global decarbonization strategies increase the importance of biodiesels in the future. Presently, three representative biodiesels: coconut, oil palm, and waste cooking oil, were studied. The coconut methyl ester is the most volatile, while palm methyl ester is among the least volatile biodiesels. The waste cooking oil-based biodiesel has a highlighted presence in the circular economy. Firstly, the thermophysical properties of the three neat biodiesels and blends with commercial diesel fuel are presented. Density, surface tension, and kinematic viscosity affect atomization, and the distillation curve characterizes fuel evaporation, while the flash point is critical for mixture ignition. The fuels behaved similarly up to 25 V/V% biodiesel-diesel mixture. Secondly, all fuels are tested in a Mixture Temperature-Controlled burner, featuring distributed combustion without any low-oxygen technique. The flame shape was highly affected by fuel volatility and governed pollutant emissions. NO emission was evaluated due to practically complete combustion in all cases, concluding that distributed combustion may lead to nearly a magnitude reduction of this pollutant. The maximum value was below 14 mg/Nm3, fulfilling the current European gas turbine standard with an 80% margin. Our goal is to introduce the Mixture Temperature-Controlled combustion concept in boilers and gas turbines.

Facilitated ignition and detonation initiation of hydrogen-oxygen mixtures by ozone doping

This work computationally studies homogeneous and inhomogeneous ozone addition in hydrogen-oxygen ignition and transition to detonation, with emphasis on the ozone-induced two-stage behaviors in the chemical kinetics and wave dynamics. In 0D homogenous ignitions, ozone addition induces an additional first-stage reaction and substantially reduces the ignition delay time (IDT). At intermediate initial temperatures, e.g. T0 = 600 K, a critical value, αcr, is identified to delineate different regimes for ozone fraction in the total oxidizer, α. Specifically, the first-stage ignition occurs several orders earlier than IDT for α<αcr, while the IDTs for two stages are comparable for α>αcr. Mechanistically, low-to-intermediate temperature HO2 chemistry introduces a quasi-steady intermediate state in the former regime, whereas ozone reactions directly accelerate high-temperature H2O2 reactions in the latter one. Furthermore, according to the Zel'dovich mechanism, ozone concentration non-uniformity can establish reactivity gradient and hence further initiate double spontaneous waves with multiple dynamics. Coherent coupling between the second-stage heat release and pressure (shock) wave can further evolve into detonation, whereas such synchronized enhancement is not observed in the first-stage ignition due to its large excitation time. Corresponding to the multi-timescales in 0D ignition, when the initial α interval are respectively below, across and above αcr, the low- and high- temperature reaction fronts always separate, first separate then merge, and always merge, respectively. It is also noted that at higher initial temperatures αcr decreases, and that the first-stage reaction becomes less concentrated. Consequently, detonation can be initiated with smaller amounts of ozone and is minimally influenced by the first-stage reaction.

Shock-tube study of high-temperature ignition of propane-air mixtures at elevated pressures

Ignition delay time measurements in high-temperature propane-air mixtures have been performed behind reflected shock wave at temperatures T = 1043 ÷ 1778 K, pressures p = 17.7 ÷ 42.8 atm, and equivalence ratios φ = 0.5, 1.0, and 2.0. Simultaneously, the emission characteristics of the flammable mixture associated with the emission of electronically excited OH* radical were recorded. The available detailed kinetic mechanisms of propane ignition were used to describe the obtained experimental data. Sensitivity analyses of the propane-air mixtures with various equivalence ratios was carried out to single out the key reactions proceeded in these mixtures. The data obtained make it possible to specify the available information on the ignition of combustible mixtures and thereby to improve the understanding of the processes occurring in the combustion chambers.

Fundamental Study of Ignition and Combustion Characteristics of Natural Gas Engines Using Pilot Fuel Injection - Effects of Pilot Fuel Injection Strategies on Ignition and Combustion Characteristics of Methane-Air Mixture

Fundamental Study of Ignition and Combustion Characteristics of Natural Gas Engines Using Pilot Fuel Injection - Effects of Pilot Fuel Injection Strategies on Ignition and Combustion Characteristics of Methane-Air Mixture

Maximum reduction in greenhouse gas emissions by complete replacement of natural gas with pure hydrogen as a sole low reactive fuel in a RCCI engine

In order to maximum reduction in hydrocarbon fuels consumption as the largest source of greenhouse gas emissions, the aim of this study is to evaluate a RCCI engine performance fueled with diesel fuel and pure hydrogen as sole low reactive fuel. For this purpose, a single-cylinder heavy-duty diesel engine with bathtub piston bowl profile and compression ratio of 14.88:1 is assessed that operates at its mid-load range from 9.4 to 13.5 bar gross IMEPs. In order to overcome the NOx challenge resulted from using pure hydrogen, the use of suitable amount of EGR and nitrogen addition as air-hydrogen diluents along with the advanced SOI timing were employed. The simulation results show that in a hydrogen-fueled RCCI engine, while reducing the diesel fuel energy share as the only supplier of air-hydrogen mixture ignition energy to about 13%, the HES percentage can be enhanced up to 87%. Although, the SOC will occur with a long delay and the CA50 will take place about 15°CA after the TDC compared to the experimental data, however, the maximum loss of the engine load is less than 6% with the GIE of more than 48% without any exposure to diesel knock. Moreover, not only the EURO VI level of the CO and UHC emissions and the EPA level of Formaldehyde emission can be met, but also, the EURO VI level of NOx emission as the most important challenge of a hydrogen-fueled engine is achievable.