Studies of Premixed Laminar and Turbulent Flames at Microgravity

The work of the Principal Investigator (PI) has encompassed four topics related to the experimental and theoretical study of combustion limits in premixed flames at microgravity, as discussed in the following sections. These topics include: (1) radiation effects on premixed gas flames; (2) flame structure and stability at low Lewis number; (3) flame propagation and extinction is cylindrical tubes; and (4) experimental simulation of combustion processes using autocatalytic chemical reactions

Studies of premixed laminar and turbulent flames at microgravity

A two and one-half year experimental and theoretical research program on the properties of laminar and turbulent premixed gas flames at microgravity was conducted. Progress during this program is identified and avenues for future studies are discussed

Mechanisms of combustion limits in premixed gas flames at microgravity

A three-year experimental and theoretical research program on the mechanisms of combustion limits of premixed gasflames at microgravity was conducted. Progress during this program is identified and avenues for future studies are discussed

Premixed Atmosphere and Convection Influences on Flame Inhibition and Combustion (PACIFIC)

Under NASA-Lewis Grant NAG3-1611, starting date 6/1/94, a three-year experimental and theoretical study of the effects of ambient atmosphere on the properties of flame spread over thin and thick solid fuel beds has been initiated. In particular the effect of the type of inert gas, which affects the Lewis numbers of fuel and oxidant, and the effect of the addition of sub-flammability-limit concentrations of gaseous fuels to the oxidizing atmosphere will be studied. The effect of convection will be studied through one-g and mu g experiments with and without a forced flow. Moreover, the influence of thermal radiation, whose effect is known to be markedly different depending on the convection level, will be addressed

Structure Of Flame Balls At Low Lewis-number (SOFBALL)

The work has encompassed several topics related to the experimental and theoretical study of combustion limits in premixed flames at microgravity. These topics include (1) flame structure and stability at low Lewis number (which is the basis for the SOFBALL space flight experiment), (2) flame propagation and extinction in cylindrical tubes, and (3) experimental simulation of combustion processes using autocatalytic chemical reactions. Progress on each of these topics is outlined

Structure of Flame Balls at Low Lewis-Number

The Structure of Flame Balls at Low Lewis-Number (SOFBALL) experiment explored the behavior of a newly discovered flame phenomena called "flame balls." These spherical, stable, stationary flame structures, observed only in microgravity, provide a unique opportunity to study the interactions of the two most important processes necessary for combustion (chemical reaction and heat and mass transport) in the simplest possible configuration. The previously unobtainable experimental data provided a comparison with models of flame stability and flame propagation limits that are crucial both in assessing fire safety and in designing efficient, clean-burning combustion engines

Lagrangian, Game Theoretic and PDE Methods for Averaging G-equations in Turbulent Combustion: Existence and Beyond

G-equations are popular level set Hamilton-Jacobi nonlinear partial differential equations (PDEs) of first or second order arising in turbulent combustion. Characterizing the effective burning velocity (also known as the turbulent burning velocity) is a fundamental problem there. We review relevant studies of the G-equation models with a focus on both the existence of effective burning velocity (homogenization), and its dependence on physical and geometric parameters (flow intensity and curvature effect) through representative examples. The corresponding physical background is also presented to provide motivations for mathematical problems of interest. The lack of coercivity of Hamiltonian is a hallmark of G-equations. When either the curvature of the level set or the strain effect of fluid flows is accounted for, the Hamiltonian becomes highly non-convex and nonlinear. In the absence of coercivity and convexity, PDE (Eulerian) approach suffers from insufficient compactness to establish averaging (homogenization). We review and illustrate a suite of Lagrangian tools, most notably min-max (max-min) game representations of curvature and strain G-equations, working in tandem with analysis of streamline structures of fluid flows and PDEs. We discuss open problems for future development in this emerging area of dynamic game analysis for averaging non-coercive, non-convex, and nonlinear PDEs such as geometric (curvature-dependent) PDEs with advection.Comment: 69 page

Technical Progress Report

An ignition source was constructed that is capable of producing a pulsed corona discharge for the purpose of igniting mixtures in a test chamber. The corona generator can also be used as the ignition source for one cylinder on a test engine. The first tests were performed in a cylindrical shaped chamber to study the characteristics of the corona and analyze various electrode geometries. Next a test chamber was constructed that closely represented the dimensions of the combustion chamber of the test engine at USC. Combustion tests were performed in this chamber and various electrode diameters and geometries were tested. Higher peak pressures and faster pressure rise times were realized consistently in all test chambers versus standard spark plug ignition. A test engine was purchased for the project that has two spark plug ports per cylinder to The data acquisition and control system hardware for the USC engine lab was updated with new equipment. New software was also developed to perform the engine control and data acquisition functions including cylinder pressure monitoring. A ceramic corona electrode has been designed that fits in the new test engine and is capable of withstanding the pressures and temperatures encountered inside the combustion chamber. The corona ignition system was tested on the engine and an increase in both peak pressure and IMEP were seen in the initial test. There are issues that must be addressed before on-engine testing can continue such as EMF interference from the corona generator and electrical insulation on portions of the piston and cylinder head to prevent arcing. The EMF issue can be solved with proper shielding and grounding and various ceramic coatings are being researched for electrical insulation