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(searched for: doi:10.2514/8.7472)
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, Li Qiao
Journal of Propulsion and Power, Volume 34, pp 1166-1177; https://doi.org/10.2514/1.b36927

Abstract:
Unstable combustion was observed in a dual-chamber combustor that mimics heavy-duty gas engines utilizing prechamber jet ignition. Prechamber combustion generated a hot turbulent jet that ignited the ultra-lean H2/air mixture in the main chamber. Thermoacoustic combustion instability was initiated for main-chamber equivalence ratio, ϕ<0.5, and grew severe in the lean-burn regime, 0.22<ϕ<0.3. Simultaneous schlieren and OH* chemiluminescence were used to visualize the unstable flame propagation and to characterize the instability. Classical acoustic resonator analysis and pressure spectra showed the longitudinal mode of acoustic disturbance as the primary instability mode for all equivalence ratios. However, a leaner flame was affected more due to stronger coupling between heat release and the pressure field perturbation. Transverse and mixed modes were observed at lean conditions, ϕ<0.4. A phase-resolved measurement of strain rates along flame edge showed an oscillating strain along pressure perturbation cycle. To model the instability, 3D linearized Euler equations were solved in the frequency domain coupled with combustion response models. The physical significance of the instability modes and their behavior were identified using dynamic mode decomposition. Based on the experimental and modeling results, a mechanism for thermoacoustic instability was proposed for ultra-lean premixed H2/air ignition by a hot turbulent jet.
Sayan Biswas
Published: 4 May 2018
The publisher has not yet granted permission to display this abstract.
Sayan Biswas
Published: 4 May 2018
Springer Theses pp 101-127; https://doi.org/10.1007/978-3-319-76243-2_5

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Sayan Biswas
Published: 4 May 2018
Springer Theses pp 129-158; https://doi.org/10.1007/978-3-319-76243-2_6

The publisher has not yet granted permission to display this abstract.
Combustion Science and Technology, Volume 191, pp 296-310; https://doi.org/10.1080/00102202.2018.1459586

Abstract:
In this paper, the ignition of a hydrogen–air mixture by a jet of burned hot gas (often termed reignition in the field of explosion protection) is studied in a two-chamber experimental configuration. This experiment allows systematic creation of hot gas jets emerging from a thin, long nozzle and them to impinge into an unburned, cold hydrogen–air mixture, possibly causing (re)ignition. In an extensive parametric study, hot exhaust gas jets originating from different nozzle diameters (0.6 mm–1.2 mm) and lengths (25 mm and 70 mm), as well as different pressure ratios along the nozzle (up to 5.5) were tested for their ability to reignite the hydrogen–air mixture. It was investigated how often reignition occurred within 10 tests under each condition. Dependencies between the occurrence of reignition and the mentioned nozzle and jet parameters were determined. It was found that the outcome (reignition or no reignition) can differ for nominally identical experimental paramete rs, which demonstrates the parametric sensitivity of the process. The statistical frequency of reignition occurrence depends on the nozzle diameter as well as on its length. For pressure ratios above the critical value, reignition occurred more often for the longer nozzle (l = 70 mm) at a given diameter. Some of these findings, notably the dependence on the nozzle length, pose a challenge to conventional models.
Prasanna Chinnathambi, Bryce Thelen, Michael Naylor, Dave Cook, Elisa Toulson
Published: 3 April 2018
SAE Technical Paper Series; https://doi.org/10.4271/2018-01-1135

Abstract:
An auxiliary fueled prechamber ignition system can be used in an IC engine environment to provide lean limit extension with minimal cyclic variability and low emissions. Geometry and distribution of the prechamber orifices form an important criterion for performance of these systems since they are responsible for transferring and distributing the ignition energy into the main chamber charge. Combustion performance of nozzles with a single jet, dual diverging jets and dual converging jets for a methane fueled prechamber ignition system is evaluated and compared in a rapid compression machine (RCM). Upon entering the main chamber, the dual diverging jets penetrate the main chamber in opposite directions creating two jet tips, while the dual converging jets, after exiting the orifices, converge into a single location within the main chamber. Both these configurations minimize jet-wall impingement compared to the single jet. The total cross-sectional area of the orifice(s) are maintained the same for all the nozzles while for the dual jet configurations, the angle between the nozzle holes are kept constant. High speed color images along with pressure records obtained from the experiments are further processed to extract derived quantities such as burn duration, flame edge and flame area. Experimental results revealed that the single jet and converging jets offer a slightly higher lean limit extension while the dual diverging jets offer overall superior combustion performance.
, Robert Schießl, Detlev Markus
Zeitschrift für Physikalische Chemie, Volume 231, pp 1737-1771; https://doi.org/10.1515/zpch-2016-0914

Abstract:
This paper describes some of our experimental studies on the re-ignition caused by jets of hot gas that interact with unburned fuel/air mixtures. The problem is approached from two complementary sides: On the one hand, phenomenological studies are conducted, which ask for the conditions under which a hot jet may cause ignition. A dedicated experiment is described which allows to create well-controlled exhaust gas jets and ambient conditions. In this experiment, parameters influencing the ignition process are varied, and the dependence of jet behavior on these parameters (i.e. pressure ratio, diameter and length of the gap through which the exhaust gas has to pass before getting into contact with ambient fuel/air) is studied. In particular, the frequency of a jet causing re-ignition in the ambient gas is studied. On the other hand, we also perform studies which are more “analytical” in nature. These attempt a more in-depth understanding, by first decomposing the hot jet ignition phenomenon into the underlying physical processes, and then studying these processes in isolation. This approach is applied to measurements of mixture fraction fields. First, non reacting isothermal variable density jets are studied. Here, the density of the gas mixture varies as to mimic the density of hot exhaust gas at varying temperatures. A laser-based non-intrusive method is introduced that allows to determine quantitative mixture fraction fields; although applied here to cold jets only, the method is also applicable to hot jets. The results show the effect of turbulence on the mixing field in and at the free jet, and allow to derive quantities that describe the statistics of the turbulent jet, like probability density functions (PDFs) and geometrical size of fluctuations.
Abdullah Karimi,
Published: 27 March 2016
Journal of Combustion, Volume 2016, pp 1-13; https://doi.org/10.1155/2016/9565839

Abstract:
Ignition of a combustible mixture by a transient jet of hot reactive gas is important for safety of mines, prechamber ignition in IC engines, detonation initiation, and novel constant-volume combustors. The present work is a numerical study of the hot jet ignition process in a long constant-volume combustor (CVC) that represents a wave rotor channel. The hot jet of combustion products from a prechamber is injected through a converging nozzle into the main CVC chamber containing a premixed fuel-air mixture. Combustion in a two-dimensional analogue of the CVC chamber is modeled using a global reaction mechanism, a skeletal mechanism, or a detailed reaction mechanism for three hydrocarbon fuels: methane, propane, and ethylene. Turbulence is modeled using the two-equation SST -ω model, and each reaction rate is limited by the local turbulent mixing timescale. Hybrid turbulent-kinetic schemes using some skeletal reaction mechanisms and detailed mechanisms are good predictors of the experimental data. Shock wave traverse of the reaction zone is seen to significantly increase the overall reaction rate, likely due to compression heating, as well as baroclinic vorticity generation that stirs and mixes reactants and increases flame area. Less easily ignitable methane mixture is found to show slower initial reaction and greater dependence on shock interaction than propane and ethylene.1. IntroductionIntentional hot jet ignition of premixed combustible mixture finds application in internal combustion engines [1, 2] and pulsed detonation engines [3] and is of particular interest in wave rotor combustors [4–6]. Chemically active radicals and fast turbulent mixing in the jets create an explosion that is more energetic and spatially distributed than a spark [3], allowing rapid ignition of lean and nonuniform mixtures.Hot jet ignition involves complex flow phenomena, including jet stability, vortex evolution, fluid mixing, and turbulence generation. The presence of reactive species in the jet influences the chemical kinetics of fuel combustion. A high-speed compressible transient jet is usually accompanied by shock formation in a confined volume, leading to subsequent reshaping of flame fronts by shock waves and expansion waves. The ignition delay time for a jet-ignited CVC may be defined as the time from jet initiation to the occurrence of rapid, visible, and pressure-generating heat release in the CVC chamber [7, 8]. There are many definitions of ignition delay time used in the literature for varied phenomena. Autoignition delay in shock tube and rapid compression experiments depend only on chemical processes, while jet ignition and spark ignition also include physical processes. Ignition delay following hot jet injection includes time for transient jet vortex development, entrainment and mixing with the gas in the CVC chamber, and chemical evolution. In addition, the ignition process in the confined space is influenced by temperature changes due to traveling pressure waves arising from nearby combustion and distant reflection.A combustible mixture can be ignited by an inert gas jet or reactive gas from another combustion source. Prior experiments mainly addressed mine safety using a steady, relatively low-speed, nonreactive hot gas jet issuing into an unconfined well-mixed stationary or quiescent combustible mixture. In contrast, the hot jet ignition reported here is more similar to turbulent jet ignition systems using prechambers in spark ignition engines, reviewed by Toulson et al. [1]. Such a prechamber mixture is well controlled and reliably spark-ignited and produces a hot jet that acts as a distributed ignition source. The jet allows reliable combustion of the main CVC charge over a broader range of air-fuel ratios and more rapid combustion than direct electric spark in lean mixtures. Chemically reactive radicals and jet-induced turbulence are equivalent to two orders of magnitude higher energy than spark ignition [2]. Using various chemically stable hot gases, Wolfhard [9] observed variations in minimum jet temperature for ignition, possibly due to different heat capacities. Vanpée and Wolfhard [10] developed an overall rate expression for ignition of methane and ethane fuel-air mixtures by low-velocity hot inert gas jets. Cato and Kuchta [11] experimented with laminar hot-air jets and concluded that ignition depends on jet base temperature, jet dimensions, composition of the combustible mixture, and jet velocity. Smirnov and Nikitin [12] performed numerical simulation of turbulent diffusive combustion using only three species: oxidant, fuel, and products.Tarzhanov et al. [13] investigated using hot detonation products to detonate stagnant propane-air mixtures. They found that detonation initiation depends on the initial volume concentrations of the mixture, mass fraction of hot detonation products, and the energy deposited from the detonation products. Using a jet issuing through a circular orifice, Mayinger et al. [14] derived correlations between measured induction time (ignition delay time), the mixing time of the jet, and the adiabatic autoignition time for the fuel-air mixtures.Bilgin [15] developed a constant-volume combustor (CVC) with long aspect ratio and square cross section, representing a wave rotor channel [16]. The CVC is ignited by a jet of hot combustion products from a separately fueled prechamber that could be spun to cause the jet to traverse one end of the CVC. The relative motion reproduces the action of a wave rotor channel, and prechamber may be representative of a previously combusted channel supplying hot gas. Bilgin proposed a correlation between the Damköhler number and ignition of a fuel-air mixture in the CVC. For the geometry of this CVC, Baronia et al. [17] performed numerical simulations for a stationary (nontraversing) torch jet using global reaction mechanisms (one-step and four-step) for a propane-air mixture. Bilgin’s measurements were not well matched by Baronia’s simulations, possibly due to lack of detailed chemistry and matched jet composition. Perera [8] carried out experiments on the same CVC test rig for three fuels, methane, ethylene, and propane, with varying equivalence ratios in the prechamber and the CVC chamber. The ignition delay time variation and the ignitability limits, both lean and rich, were investigated for each fuel under fixed initial temperature and pressure conditions in the CVC chamber. The variation of ignition delay time for fuels with different prechamber equivalence ratios and nozzle geometries were also observed, with nonobvious trends.The ignition of combustible mixture using hot inert jet or combusted products has been rarely studied numerically using global reaction mechanisms, and very few studies that use detailed or skeletal reaction mechanisms are known [18–20]. The present work seeks to use detailed numerical simulations to investigate the ignition by a hot jet and ensuing combustion of three hydrocarbon fuels (methane, propane, and ethylene). Chemical kinetics are modeled using detailed reaction mechanisms for the three fuels after verifying the inadequacy of a four-step global reaction mechanism for propane. The hot jet is modeled as the equilibrium major products of rich ethylene combustion in the prechamber. The role of shock-flame interaction on ignition in the CVC chamber is also studied. The reaction pathways are discussed for the detailed methane mechanism. The predicted ignition delay times have been compared with the published experimental data [5].2. Problem Description and Numerical MethodologyThis work was motivated by the ignition delay studies of Perera et al. [7] in a constant-volume combustor (Figure 1) which is an evolution of the rig initially used by Bilgin et al. [16]. Its main CVC chamber had a square cross section. A converging round nozzle delivers a jet from a cylindrical prechamber to the CVC.Figure 1: Constant-volume combustor rig.In this work, a simple two-dimensional (2D) combustor, prechamber, and jet nozzle are considered to simulate the transient, turbulent, reacting, and compressible flow at reasonable computational cost. For 2D calculations to bear some similarity to the experiment of interest, it was decided to preserve the volume ratio of the prechamber to the CVC. This allows the same volume flow rate between the experiment and numerical calculations, preserving mass and energy realism and the nominal pressure history. The height and length of the channel and nozzle are also matched, and the varying width of the nozzle is taken equal to the corresponding diameter. While this does not preserve the area ratio, it does retain the relative height ratio of the confined jet. In the 2D model, the rectangular CVC is 406.4 mm (16.0 inches) long and 39.88 mm (1.57 inches) tall, with nozzle exit width of 5.99 mm (0.236 inches) centered on end of the CVC. A rectangular prechamber internal cavity has an internal volume of 1.293 times the CVC, not including the small nozzle volume. A leak proof connection between the prechamber and CVC chamber is assumed, as the experiment appears to have negligible gas outflow at low pressure before ignition in the CVC.The simulation uses the velocity-pressure coupled, second-order implicit scheme available in a general-purpose computational fluid dynamics (CFD) program [25]. Turbulence is modeled using the shear-stress-transport (SST) two-equation -ω model [26]. The computational domain is discretized using polyhedral meshes with varying mesh density in the prechamber, nozzle, and CVC chamber (Figure 2). Adiabatic boundary conditions are used for all walls and wall of law is employed for turbulence.Figure 2: Geometry used for simulation.The flow is driven by the initial pressure difference between prechamber and CVC chamber when an intervening diaphragm is suddenly splayed away, similar to a shock tube. Initially, the CVC has a fuel-air mixture at atmospheric pressure and temperature
, Manikanda Rajagopal, Razi Nalim
Journal of Engineering for Gas Turbines and Power, Volume 136; https://doi.org/10.1115/1.4025659

Abstract:
Hot-jet ignition of a combustible mixture has application in internal combustion engines, detonation initiation, and wave rotor combustion. Numerical predictions are made for ignition of combustible mixtures using a traversing jet of chemically active gas at one end of a long constant-volume combustor (CVC) with an aspect ratio similar to a wave rotor channel. The CVC initially contains a stoichiometric mixture of ethylene or methane at atmospheric conditions. The traversing jet issues from a rotating prechamber that generates gaseous combustion products, assumed at chemical equilibrium for estimating major species. Turbulent combustion uses a hybrid eddy-breakup model with detailed finite-rate kinetics and a two-equation k-ω model. The confined jet is observed to behave initially as a wall jet and later as a wall-impinging jet. The jet evolution, vortex structure, and mixing behavior are significantly different for traversing jets, stationary centered jets, and near-wall jets. Pressure waves in the CVC chamber affect ignition through flame vorticity generation and compression. The jet and ignition behavior are compared with high-speed video images from a prior experiment. Production of unstable intermediate species like C2H4 and CH3 appears to depend significantly on the initial jet location while relatively stable species like OH are less sensitive.
Rajesh Sadanandan, Robert Alexander Schießl, Detlef Markus, Ulrich Maas
Published: 30 July 2010
Applied Scientific Research, Volume 86, pp 45-62; https://doi.org/10.1007/s10494-010-9285-0

The publisher has not yet granted permission to display this abstract.
N. Djebaili, R. Lisbet, G. Dupré, C. Paillard
Combustion Science and Technology, Volume 104, pp 273-285; https://doi.org/10.1080/00102209508907724

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.
Y. Ju
Combustion Science and Technology, Volume 108, pp 47-65; https://doi.org/10.1080/00102209508960389

Abstract:
Ignition of a cold fuel injection into a supersonic hot airstream is analyzed both asymptotically and numerically. The present study extends the Liñán and Crespo's analysis of ignition in a mixing layer of parallel streams to the analysis of ignition in a jet flow. The ignition distance is related explicitly to the thermodynamic parameters and the width of jet The asymptotic analysis not only correlates the ignition distance in a fuel jet with that in a mixing layer of parallel streams, but also reveals the difference between them. It is shown that ignition mechanism of a fuel jet in an infinite air stream can be divided into three regimes, ignition regime in a mixing layer of parallel streams, ignition regime determined by jet scale and chemical scale, and ignition regime controlled by chemical scale only, according to the width of jet The present analysis theoretically exhibits the linear dependence of ignition distance on the logarithmic function of jet width. A good agreement is established between the results obtained from the asymptotic analysis and those obtained by numerical simulations.
N. Djebaili, R. Lisbet, G. Dupre, C. Paillard
Symposium (International) on Combustion, Volume 25, pp 1539-1545; https://doi.org/10.1016/s0082-0784(06)80798-8

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Zachary J. Fink, Marcel Vanpee
Combustion Science and Technology, Volume 11, pp 229-238; https://doi.org/10.1080/00102207508946702

Abstract:
Overall rate expressions have been developed to describe the ignition of nearly stagnant fuel-air mixtures in a vertical jet of hot, inert gas. Kinetic parameters, frequency factor A, activation energy E, fuel power C and oxygen power D, were computed to match experimental ignition results in the rate expression where (C + D) = total order of reaction Mf = molecular weight of fuel Mo = molecular weight of oxygen P = total pressure (1.0 atomspheres in this study) R = gas constant T = absolute temperature of hot gas ignition measured at jet base °K Wf = fuel mass rate of consumption gm/cm3 sec Yf = fuel mole fraction Yo = oxygen mole fraction Because the current hot gas ignition system is similar to a dilute batch or plug flow reactor at constant density, a simplifying correlation of where ucl, = center line velocity of hot gas z = ignition distance from jet base at constant composition yielded a straight line with a slope of −E/R. This correlation proved to be valid for all ignition experiments run with five hot gas diameters ranging from 0.476 to 1.588 cm and all computations with reasonable values of the kinetic parameters. Using literature estimates of 1.1, 1.7 and 1.8 for (C + D) yielded E values from this correlation of 50,430, 44,930 and 41,460 cal/mole for methane, ethane and ethylene respectively. A and C were computed on the basis of complete reaction to CO2 and H2O in the preignition zone. To account for the observed maximum rate with a stoichiometric mixture, fits were made with C being positive for lean mixtures and negative for rich ones. An overall fit with a C of zero was made to stoichiometric experiments with A's of 2.9 × 107, 4.7 × 1010 and 1.4 × 1010 for methane, ethane and ethylene respectively.
H. Phillips
Published: 31 October 1972
Combustion and Flame, Volume 19, pp 181-186; https://doi.org/10.1016/s0010-2180(72)80208-6

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H. Phillips
Published: 31 October 1972
Combustion and Flame, Volume 19, pp 187-195; https://doi.org/10.1016/s0010-2180(72)80209-8

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M.E. Morrison, K. Scheller
Published: 29 February 1972
Combustion and Flame, Volume 18, pp 3-12; https://doi.org/10.1016/0010-2180(72)90026-0

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Peter Tolson
Published: 29 February 1972
Combustion and Flame, Volume 18, pp 19-26; https://doi.org/10.1016/0010-2180(72)90028-4

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T. A. Ponizko, A. I. Rozlovskii
Combustion, Explosion, and Shock Waves, Volume 1, pp 5-11; https://doi.org/10.1007/bf00748804

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J.M. Kuchta, R.J. Cato, M.G. Zabetakis
Published: 31 December 1964
Combustion and Flame, Volume 8, pp 348-350; https://doi.org/10.1016/0010-2180(64)90126-9

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