Hot Gas Jet Research Articles

220203 エタノール噴霧の既燃ガスジェット着火現象(OS12 燃焼工学の新展開,オーガナイズド・セッション)

In this study, we experimentally investigated the effects of burnt gas jet ignition on ethanol spray combustion using a constant volume combustion vessel with a sub chamber. The ignition and combustion phenomena were observed by using a high-speed video camera, and combustion pressure history was measured as well. In case of burnt gas jet ignition, compared with a conventional spark plug ignition, stronger luminous flames were observed, and rate of pressure rise and maximum overpressure much increased. Moreover, it was confirmed that measured HCHO concentration of the burnt gas in the combustion vessel remained at low level although the amount of ethanol related to combustion reaction increased. It is mainly due to the strong turbulent mixing effects of the hot burnt gas jet and the spray flows.

Hot-Gas Side Jet in a Supersonic Freestream

The present paper reports on the interaction of a hot side jet in a supersonic freestream and compares the effects with results from cold-gas jet investigations. With high-speed schlieren videos, a significant enlargement of the separation area has been ascertained upstream from the hot-gas jet and quantitatively confirmed with wall pressure measurements. The schlieren videos also show a strong oscillation of the separation and bow shock. By using an algorithm that analyzes the similarity of neighboring images, the oscillation frequency of the separation and bow shock has been measured to be 11.3 kHz. As a consequence of the dominant shocks in the area in front of the jet, the hot jet plume is screened off strongly from the freestream, thus resulting in an upstream inclination. Finally, high-speed videos have revealed large-scale structures in the hot-gas jet and their convection velocities have been analyzed. According to the shocks, the large-scale structures oscillate at 11.3 kHz. Jet oscillation is thus excited by the interaction of the hot-gas jet with the freestream and not by resonances from the combustion chamber.

2D Mixture Fraction Studies in a Hot-Jet Ignition Configuration Using NO-LIF and Correlation Analysis

The problem of measuring mixture fraction (defined here as the fractional part of mass originating from the exhaust gas jet) during the mixing of an unsteady hot exhaust gas jet impinging into a quiescent premixed hydrogen/air mixture is addressed. The diagnostic method is based on planar Laser-Induced Fluorescence of nitric oxide (NO) that is seeded to the hot jet and used as a tag for mixture fraction. The research work presented in this paper focusses on the analytical and experimental data employed for the estimation of mixture fraction using NO as a tracer. Since the NO LIF-signal does not solely depend on the amount of NO, but also on temperature and overall chemical composition, additional information is normally required to transform LIF-signals into mixture fraction values. To provide this additional information, the concept of reduced state spaces is applied: Correlations between state variables (temperature and species) are exploited to establish relationships between the measured signal and the mixture fraction. Simple numerical model simulations are used in combination with spectroscopic calculations to check for correlations between NO-LIF signal and mixture fraction. The result is that sharp correlations between NO-LIF signals and mixture fraction exist, provided that chemical reactions have not yet significantly influenced the flow. These correlations display only little sensitivity with respect to changes of the jet temperature, amount of NO seeded to the jet, and jet velocity. Measurements of NO-LIF were then performed for a non-reacting case before ignition, and mixture fraction maps were obtained from the measured LIF-signals by exploiting the correlations. The resulting data reveal the different driving forces behind mixing at regions near to the jet tip and at the radial shear layers.

Experimental investigation of hot and cold side jet interaction with a supersonic cross-flow

This paper reports on experimental aerodynamic investigations on a high-speed missile with side jet control especially with regard to the interaction of cold and hot side jets with supersonic cross-flow. The hot jets were generated with solid propellants. To analyze the effect of the hot jet in relation to side jet control, wall pressure distributions were measured in the area of jet interaction. As a test parameter, the jet pressure ratio was varied and schlieren images were taken to visualize the shocks. In addition, the development of large-scale vortex structures on hot gas jets was detected with high-speed videos. The frame sequences show periodical turbulent jet structures and permit the manual evaluation of their spatial distribution. Analyzing the images, the convection velocities of the large-scale structures and their convection angles were determined. The convection velocities reach the magnitude of cross-flow velocity shortly behind the hot jet exit.

Influence of rarefaction on the flow dynamics of a stationary supersonic hot-gas expansion

The gas dynamics of a stationary hot-gas jet supersonically expanding into a low pressure environment is studied through numerical simulations. A hybrid coupled continuum-molecular approach is used to model the flow field. Due to the low pressure and high thermodynamic gradients, continuum mechanics results are doubtful, while, because of its excessive time expenses, a full molecular method is not feasible. The results of the hybrid coupled continuum-molecular approach proposed have been successfully validated against experimental data by R. Engeln [Plasma Sources Sci. Technol. 10, 595 (2001)] obtained by means of laser induced fluorescence. Two main questions are addressed: the necessity of applying a molecular approach where rarefaction effects are present in order to correctly model the flow and the demonstration of an invasion of the supersonic part of the flow by background particles. A comparison between the hybrid method and full continuum simulations demonstrates the inadequacy of the latter, due to the influence of rarefaction effects on both velocity and temperature fields. An analysis of the particle velocity distribution in the expansion-shock region shows clear departure from thermodynamic equilibrium and confirms the invasion of the supersonic part of the flow by background particles. A study made through particles and collisions tracking in the supersonic region further proves the presence of background particles in this region and explains how they cause thermodynamic nonequilibrium by colliding and interacting with the local particles.

Detailed investigation of ignition by hot gas jets

Experimental and numerical investigations of the ignition of hydrogen/air mixtures by jets of hot exhaust gases are reported. An experimental realisation of such an ignition process, where a jet of hot exhaust gas impinges through a narrow nozzle into a quiescent hydrogen/air mixture, possibly initiating ignition and combustion, is studied. High-speed laser-induced fluorescence (LIF) image sequences of the hydroxyl radical (OH) and laser Schlieren methods are used to gain information about the spatial and temporal evolution of the ignition process. Recording temporally resolved pressure traces yields information about ambient conditions for the process. Numerical experiments are performed that allow linking these observables to certain characteristic states of the gas mixture. The outcome of numerical modelling and experiments indicates the important influence of the hot jet temperature and speed of mixing between the hot and cold gases on the ignition process. The results show the quenching of the flame inside the nozzle and the subsequent ignition of the mixture by the hot exhaust jet. These detailed examinations of the ignition process improve the knowledge concerning flame transmission out of electrical equipment of the type of protection flameproof enclosure.

Investigation of high-speed combustible gas ignited by a hot gas jetproduced in the shock tube

The high-speed combustible gas ignited by a hot gas jet, which is induced by shock focusing, was experimentally investigated. By use of the separation mode of shock tube, the test section of a single shock tube is split into two parts, which provide the high-speed flow of combustible gas and pilot flame of hot gas jet, respectively. In the interface of two parts of test sections the flame of jet was formed and spread to the high-speed combustible gas. Two kinds of the ignitions, 3-D “line-flame ignition” and 2-D “plane-flame ignition”, were investigated. In the condition of 3-D “line-flame ignition” of combustion, thicker hot gas jet than pure air jet, was observed in schlieren photos. In the condition of 2-D “plane-flame ignition” of combustion, the delay time of ignition and the angle of flame front in schlieren photos were measured, from which the velocity of flame propagation in the high-speed combustible gas is estimated in the range of 30–90m/s and the delay time of ignition is estimated in the range of 0.12–0.29ms.

Fronts in high-temperature laminar gas jets

This paper addresses the slender laminar flow resulting from the discharge of a low-Mach-number hot gas jet of radius a and moderately large Reynolds number Rj into a cold atmosphere of the same gas. We give the boundary-layer solution for plane and round jets with very small values of the ambient-to-jet temperature ratio e accounting for the temperature dependence of the viscosity and conductivity typical of real gases. It is seen that the leading-order description of the jet in the limit e → 0 exhibits a front-like structure, including a precisely defined separating boundary at which heat conduction and viscous shear stresses vanish in the first approximation, so that the temperature and axial velocity remain unperturbed outside the jet. Separate analyses are given for the jet discharging into a stagnant atmosphere, when the jet boundary is a conductive front, and for the jet discharging into a coflowing stream, when the jet boundary appears as a contact surface. We provide in particular the numerical description of the jet development region corresponding to axial distances of order Rja for buoyant and non-buoyant jets, as well as the self-similar solutions that emerge both in the near field and in the far field. In all cases considered, comparisons with numerical integrations of the boundary-layer problem for moderately small values of e indicate that these front descriptions give excellent predictions for the temperature and velocity fields in the near-axis region.

High‐Resolution Finite Volume Methods for Dusty Gas Jets and Plumes

We consider a model for dusty gas flow that consists of the compressible Euler equations for the gas coupled to a similar (but pressureless) system of equations for the mass, momentum, and energy of the dust. These sets of equations are coupled via drag terms and heat transfer. A high-resolution wave-propagation algorithm is used to solve the equations numerically. The one-dimensional algorithm is shown to give agreement with a shock tube test problem in the literature. The two-dimensional algorithm has been applied to model explosive volcanic eruptions in which an axisymmetric jet of hot dusty gas is injected into the atmosphere and the expected behavior is observed at two different vent velocities. The methodology described here, with extensions to three dimensions and adaptive mesh refinement, is being used for more detailed studies of volcanic jet processes.

Establishment of Analytical Model for Peak Temperature Within a Sodium-Water Reaction Jet, (I) Axial Temperature Profile Within an Inert Hot Gas Jet Injected into a Cold Liquid

In order to establish an analytical model for the peak temperature within a sodium-water reaction jet, an analytical and theoretical investigation of an inert-hot-gas jet injected into a bath of cold liquid was performed as the first step. The laboratory study involved measurement of the centerline temperatures within hot N2-gas jets in water and in volatile refrigerant Suva-123. An integral two-fluid (gas+entrained drops) model of the submerged jet was developed in which a single, representative droplet size was employed to treat droplet-to-gas heat and mass exchange. Encouraging agreement with the measured centerline temperatures was obtained by using available information on jet entrainment coefficients. The centerline temperature measurements revealed that fine scale atomization of the entrained liquid occurs in the very near field of the jet and the mist so produced is entirely responsible for the downstream cooling of the submerged jet. The temperature measurements also revealed that water entered and penetrated the injector passage by a distance of about two injector diameters against an essentially sonic gas discharge flow (360 ms−1).

Numerical study of the pusher-type slab reheating furnace

In the present work, a commercial computational fluid dynamics (CFD) software package, PHOENICS, was used in order to develop three-dimensional model of pusher-type slab reheating furnace. The purpose was to gain knowledge of gas flows and temperature distribution in the furnace. The burners were first modelled as hot gas jets, and later the accuracy of the model was improved with the implementation of the eddy-break-up (EBU) reaction model. In the model with the reactions, the flow velocities were slightly slower through the whole furnace area, and the temperature in the charge end of the furnace was considerably higher. The differences between the two cases were compared and the reason for their occurrence was discussed. Furthermore, two turbulence models, k-ε and RNG (renormalization group), were tested. The biggest differences appear in the lower heating zone, where the recirculation zones have different shapes, and the kinetic energy of turbulence is much lower with the RNG model than with the k-ε model.

Advanced Diagnostics and Modeling of Spray Processes

The microstructure and properties of thermally sprayed deposits depend critically on the thermal- and kinetic-energy histories of the particles entrained in the hot-gas jet. At impact, the particle temperature, molten fraction, size, velocity, and chemistry, along with substrate temperature and surface characteristics, control the morphology of individual particle splats. These factors control the adhesion, strength, microstructure, and porosity of a coating and influence the residual-stress state. In order to produce higher-quality coatings and expand the use of this versatile family of technologies, the ability to model and measure particle behavior is essential.

Microstructural evolution in thermally sprayed WC–Co coatings: comparison between nanocomposite and conventional starting powders

WC–Co coatings have been deposited by high velocity oxy-fuel thermal spraying of conventional and nanocomposite powders which contain WC grains in the size range 2–5 μm and 70–250 nm, respectively. The coatings differed not only in microstructural scale, but also in the nature and proportion of the phases present and in the overall degree of decarburization. A model describing the evolution of microstructure has been developed. As a WC–Co particle is heated in the hot gas jet, the cobalt phase melts and the WC grains begin to dissolve in it. The periphery of the semi-molten particle becomes decarburized by oxidation, promoting further WC dissolution in this region. Particle quenching on impact with the substrate results in precipitation from the melt of W 2C and possibly W depending on the local melt composition. The larger surface to volume ratio of the WC in the nanocomposite material promotes more rapid dissolution and thus decarburization. Consequently, W 2C is observed in both coatings, whereas W is found only in the nanocomposite deposit.

Laser-induced ignition using a conical cavity in CH 4–air mixtures

A method that confines all the available energy in the vicinity of the ignition point during a laser-induced ignition process is proposed. It utilizes multiple reflection by a conical cavity surface when a small-diameter laser beam is directed into the cavity. Shadowgraphs of the early stages of the combustion process for quiescent methane/air mixtures show a hot gas jet to emerge from the cavity. During subsequent flame propagation, both similarities with and differences from conventional spark ignition processes are observed, depending on the cavity size and the concentration of mixtures. With laser cavity ignition, the chamber pressure increases relatively rapidly and higher maximum pressure can be achieved. As a result, the combustion duration for laser cavity ignition is decreased relative to laser-induced spark ignition. A model, which simulates flame kernel development and the subsequent combustion process, is tested numerically using the KIVA-II code. The associated flow, pressure, and temperature profiles are evaluated and satisfactory agreement achieved between the experiment and calculated results.

Heat transfer between an impinging air jet and an impinged water surface

Impingement of producer gas obtained from rice-husk gasification onto a water surface has been found to be very effective in removing tar and ash from the gas. Correlations to estimate tar- and dust-removal efficiencies have been developed. An advantage of impingement is that the hot gas jet is cooled. Here, we describe experiments to study heat transfer when heated ambient air impinges on the water surface. An equation to estimate the overall heat-transfer coefficient has been derived. This coefficient is expressed in terms of Nu and is correlated with the following dimensionless groups: v a/ v w, H n/ D n, D c/ D n, and Re. The correlation obtained by minimizing the absolute error is Nu=0.0148 ( v a/ v w) −0.16 × ( H n/ D n) −1.3 ( D c/ D n) −1/2 Re 1.2.

5492621 Sewage water and solids treatment and disposal system

The ash melting furnace (1) disposes the combustion ash (A) resulted from incineration of municipal or other sorts of waste by melting it utilizing as the main fuel the unburnt carbon (C) contained in the ash itself. The ash melting furnace (3) includes a stationary plasma torch (1) which uses air for the working gas, and which is so placed facing the combustion ash (As) heaped up within the furnace (3) as to project its hot gas jet (B) thereon. The furnace (3) further includes a torch unit controller (2) that actuates the plasma torch (1) to secondarily heat and melt the ash (As).

An experimental investigation of thermal mixing and combustion in supersonic flows

A radially lobed nozzle (petal nozzle) is being increasingly recognised as a potential candidate for promoting mixing in compressible flows. An experimental investigation has been conducted to study its effectiveness in improving thermal mixing and combustion in supersonic flow. A hot gas jet issuing supersonically from a lobed nozzle mixes with a cold supersonic jet in a circular mixing tube. The two jets issue coaxially. A detailed survey of the flow field inside the mixing duct reveals that nearly complete thermal mixing (as exemplified by the nearly uniform temperature distribution) could be achieved in a short distance when a lobed nozzle is employed. The results also indicate the presence of large-scale vortices in the flow field downstream of the lobed nozzle. Having thus created a field in which mixing is good, supersonic combustion was then attempted. Kerosene was introduced into the hot stream issuing from the lobed nozzle and it burned mainly in the mixing tube, which served as a supersonic combustor. Resulting temperature and pressure rises were measured and the supersonic combustion efficiency was found to be of the order of 60%. The performance of a conventional conical nozzle was found to be much inferior to that of the petal nozzle under identical conditions.

Risk-based spacecraft fire safety experiments

This paper utilizes the scenario approach of risk assessment to identify modeling needs and, in turn, experiments that would aid in the development of models that would meet these needs. Due to the closed environment of a spacecraft and the lack of egress, fire on-board may pose a severe problem. There are many differences between a fire on-board the spacecraft and one in a terrestrial facility and they must be accounted for in the assessment of risk. Both the risk assessment methodology and the phenomena-based models must be modified. This paper discusses some of the methodology modifications, as well as special experimental results. Multiple experiments have been conducted in terrestrial and microgravity environments in order to construct and validate models required for the assessment and management of risk on-board spacecraft. A logic diagram analyzing the ways in which the crew may be injured and/or the spacecraft may be damaged, as well as operating experience, have identified wire overheating events as being potentially significant accident initiators. As a result, the experiments have concentrated on quantifying the pyrolysis event of a wire being overheated with excessive current. A preliminary set of experiments at the 2·2-second NASA Lewis Drop Tower has led to several observations. The event is violent due to the high heating rates. At these high heating rates, a jet of hot gases and smoke was observed. Frequently the conductor would melt down, sometimes ejecting molten pieces of the copper conductor. The event poses a threat to targets in the near vicinity and further away. Also, the smoke particle size distribution is shifted towards larger sizes in a microgravity environment. This may prove very important in designing a smoke detector. While significant results were obtained from these tests, longer durations of microgravity are required for further quantification to be possible.

Thermal fatigue behaviour of nickel-base superailoy 263 sheets

Abstract An experimental study of the thermal fatigue behaviour of polycrystalline nickel-base superalloy 263 sheets was conducted using a laboratory combustor system. Tests were done on 0.91 mm and 1.2 mm thick sheets. Square specimens (100 × 100 mm) with a 14.85 mm diameter electrodischarge-machined hole at the centre were cycled between a hot combustor gas jet and a cold jet. The maximum specimen temperature was 900 °C, and the minimum temperature was 50 °C during a 2 min fatigue cycle. The number of cycles to crack initiation was determined. It was found that this change in sheet thickness did not significantly alter thermal fatigue life. Scanning electron micrographs revealed that out-of-phase non-isothermal fatigue (resulting from thermal stresses) assisted by grain boundary oxidation is the main mechanism of failure in these tests.

Ignition of a Combustible Mixture by a Hot Unsteady Gas Jet

ABSTRACT The study of the ignition of a combustible mixture induced by means of an unsteady gas jet, at an initial temperature ranging from 700 to 3000 K, requires the construction of an original test facility which consists of a shock tube connected to a combustion chamber via an injector. With this new experimental setup, the ignition conditions of hydrogen-air ( + carbondioxide) mixtures, induced by a hot hydrogen-argon mixture, have been extensively studied, resulting in the determination of the ignition limits of these combustible mixtures, at an initial pressure and temperature of 100 kPa and 403 K respectively.