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Dissertation Defense – Akshit Markan – July 13th 2:00PM

Title: Development of a Burning Rate Emulator (BRE) for Study of Condensed Fuel Burning in Microgravity.

Date and Time: Friday, 13th July at 2:00 PM

Location:  FPE Conference Room, 3106 J.M. Patterson Building.

Committee:

Dr. Peter Sunderland (Chair/Advisor),

Dr. James Quintiere,

Dr. Howard Baum,

Dr. Michael Gollner,

Dr. Christopher Cadou (Dean’s Representative).

Abstract:

The Burning Rate Emulator (BRE) is a gas-fueled burner that emulates the burning of real condensed phase fuels. This is accomplished by matching four fundamental properties: heat of gasification, heat of combustion, surface vaporization temperature, and laminar smoke point. Previous research has confirmed the BRE technique in normal gravity. The aim of the current study is to establish immediate sustained burning in a quiescent microgravity environment and analyze the resulting flame shapes and heat transfer to the burner. This study presents 49 BRE tests at NASA Glenn’s 5.18-s Zero Gravity Research Facility for two burner diameters (25 mm and 50 mm) with methane, ethylene and nitrogen-diluted ethylene as fuels. The burner sizes and test parameters are chosen to emulate small laminar pool fires. The experiments show the evolution of an approximately ellipsoidal flame moving away from the burner. The flames are nearly hemispherical at the end of the 5-s experiment, with the flame height still increasing. The heat flux initially falls quickly and then becomes steadier. Steady-state theory correlates the end-of-drop experimental data for the flame heat flux, and therefore the fuel burning rate. The apparent lack of correlation of the burning rate for the larger burner is attributed to gas radiation.

The burner’s perforated copper plate is calibrated as a slug calorimeter in which two heat flux thermopile sensors are embedded. The slug calorimeter provides the average heat flux over the burner surface as a function of time. During the 5-s microgravity experiments, average heat fluxes measured with the calorimeter agree with the locally measured heat fluxes through a theoretical distribution function. The results show that the average slug calorimeter heat flux and the two local heat flux measurements are in harmony over a wide range of microgravity flame fluxes ranging from 5-20 kW/m2, with the edge heat flux much higher.

The transient combustion model formulated in oblate ellipsoidal coordinates is developed to analyze the behavior of the microgravity BRE flames. The model is axially symmetric and considers the burning of gaseous fuel leaving the surface of a porous ellipsoidal burner in microgravity. A composite solution is generated as a product of an exact steady state solution and an asymptotic transient solution that becomes exact far from the burner. The BRE burner geometry is idealized as an axially symmetric porous disc. The 5-s microgravity results are compared to the transient model to help predict the flame behavior beyond the duration of the test.