Piotr Wolanski

Finding the Markstein number using the measurements of expanding spherical laminar flames

Abstract Depedencies of the radii of expanding spherical flames on time elapsed after spark ignition have been measured using a high-speed Schlieren technique in a constant volume bomb. These dependencies are analyzed in order to find the Markstein numbers. Various methods of finding different Markstein numbers are considered. Phenomenological Markstein numbers with respect to the combustion products are obtained by means of the comparison between the measurements of the flame radii as a function of time and the results of the analytical integration of the linear relation between the flame speed and either flame stretch rate or flame curvature. The linear equation with respect to the flame stretch rate cannot approximate the experimental data corresponding to high flame curvature, while the linear equation with respect to the flame curvature approximates all the experimental data with a satisfactory accuracy. The correctness of this linear relation for highly curved flames and the effect of different data fitting schemes are briefly discussed.

The shock wave ignition of dusts

Dust explosions pose a serious hazard in many industries. The detonability and flam inability of dust/oxidizer mixtures depend on the ignition delay of the dust particles when suddenly exposed to a high temperature environment. Consequently, the ignition delay time of dust particles behind a shock wave in the Mach number range of 4.0-5.0 has been measured using a photomultiplier tube to determine the onset of ignition. The dusts investigated included Pittsburgh Seam Coal, graphite, diamond, oats, and RDX. The experimental arrangement, consisting of a shock tube and two different dust injection devices, is described in detail, and experimental results for dusts ranging in particle size from 2 to 74 /*m are presented. In the Mach number range considered, ignition delay times varied from 2 to 100 /*s. A detailed analytical model based on a solution of the heat conduction equations for the particle interior coupled with a solution of the particle equation of motion has been developed. Heterogeneous reactions occurring on the particle surface and in the pores within the particle are used to model the chemistry. The results were in reasonable agreement with most of the data. Approximate analyses based on a comparison of characteristi c thermal and chemical times were also developed. A key conclusion is that the ignition delay is determined mainly by the heat-up time of the particle surface.

Numerical study of dust lifting in a channel with vertical obstacles

Abstract In the paper, several results of numerical computation of multiphase flows in a channel with complex geometry are considered. The objective of the research was to study the dust lifting process from a layer behind a shock wave in a rectangular channel with vertical obstacles in the upper part of the tube. It is to be shown that that kind and also any sort of geometry may crucially change the whole phenomena of dust enhancement and of combustion. This is very important for safety in, for example, coal mines where channels are usually of more sophisticated structure than is usually assumed by most researchers.

Detonation of methane-air mixtures

Experimentally, the propagation of detonation waves in methane-air mixtures has been investigated. In a tube having a large length to diameter ratio steady state wave propagation was achieved. The actual propagation velocities were close to the calculated Chapman-Jouguet velocities. The limits of detonation were ascertained to be between 8 and 14.5 percent methane. A minimum initiation energy density of 9.42MJ/m 2 was established for stoichiometric mixtures implying the need for rather substantial charges for the initiation of spherically symmetric systems. In all cases the detonation wave exhibited a spinning structure. The motion compensated and laser schlieren photographs, smoked foil traces, and pressure transducer records strongly support the currently accepted model for the structure of such a wave, which results in the creation of extremely high local overpressures.

A Three-Dimensional Numerical Study of Rotational Detonation in an Annular Chamber

Detonation waves successively rotating in an annular chamber are numerically investigated to understand an overall ∞owfleld structure in the combustion chamber of an engine and its basic operation with a continuous fuel injection. This study leads to further investigation into continuously rotating detonation wave, which is the backbone in developing a rotating detonation-based propulsion system. A computational code developed is based on multi-dimensional Euler equations with source terms due to chemical reactions. Spatial terms in governing equations are discretized with a flnite volume method and a MUSCLbased Roe scheme, while temporal terms are discretized with a second-order, three-step Runge-Kutta method. Source terms are treated with a time-operator splitting method in order to isolate stifiness. The detonation is modeled with the one-step chemical reaction of a hydrogen and air mixture. A detailed ∞owfleld structure including detonation properties is presented in two- and three-dimensional annular chamber. The propulsive parameters of a rotational detonation engine are evaluated and its comparison of one- and two-waved detonation engine is performed in a three-dimensional chamber.

Large scale grain dust explosions-research in Poland

For the last five years grain dust explosion research was carried out in surface and underground facilities of Experimental Mine “Barbara” Research was focused on problems of evaluation critical dust parameters influencing explosion course, explosion development and suppression by both passive and active means. The main conclusions are as follows: nominal dust concentration needed to obtain flame propagation must be higher than 50 g/m3, for nominal concentrations higher than 100 g/m3 flame acceleration is observed and detonation is possible; strong grain dust explosions can be effectively suppressed with passive water barriers whereas for weak ones active barries must be used.

Sensitivity Analysis of Rotating Detonation Engine with a Detailed Reaction Model

D compressible Euler equations are used for hydrogen/oxygen rotating detonation engine (RDE) to perform a sensitivity analysis for rotating detonation conditions. First of all the used program was compared with the experimental data obtained by Kindracki and Wolanski. The computational average pressure just after the injection of mixture is similar to that of experimental one; about 0.2 to 0.4 MPa. Sensitivity analyses show that the inlet pressure, Mach number, and temperature have a significant effect on rotating detonation device performance. The results show a narrow window of the inlet conditions for the stable operation while achieving high performance of rotating detonation engine.

Research on dust explosions at the University of Michigan

Dust explosion research carried out at the University of Michigan during the last two decades has been summarized. Significant results are presented on the smoldering combustion of dust heaps, turbulent combustion of premixed dust clouds, entrainment and combustion of layered dust, and on shock wave ignition of particles and shock wave initiated detonative combustion. Also, information on the detonation of hybrid mixtures and gaseous mixtures containing nonreactive particles is given.

Dust explosion research in Poland

Abstract The review of basic and applied research in dust explosions in Poland is given. The importance of proper evaluation of explosive dust properties is discussed and a general overview of results obtained in the area of ignition, flame propagation and detonation is presented. A brief description of explosive hazard evaluation under industrial conditions is also given, with a short discussion of dust suppression research.

Flame Imaging Using 3D Electrical Capacitance Tomography

Electrical Capacitance Tomography for visualization of combustion process is based on measurement of variation of electrical properties of flame, such as electrical permittivity and conductivity of the reaction the zone. The signal level depends on the concentration of various charged particles in the combustion zone. Possible carriers are electrons and positive and negative ions. These charged particles may be formed as a result of chemical reactions, which are called chemi-ionization and thermal ionization. These properties in a combustion chamber are measured with specially designed electrodes. Distribution of charged particles in the combustion zone is reconstructed from measurements of electrical signal from the electrodes using linear back projection or iterative linear back projection algorithm.