Completed Work

Welcome to the PACIFIC project present and completed research front page. This project deals with flame spread over solid thin fuels at earth and microgravity conditions with a sprinkle of some thick fuel work.. It was thought of by professor Paul Ronney and I am the graduate student Linton Honda.

This project is funded by NASA and is conducted on the USC campus in PCE 209 and at the NASA Lewis Research Center's 2.2 second drop tower and 5 second drop tower (Zero-g).

The best way to describe what we do is that we burn stuff. Yes we realize everyone knows how to burn it, but it is an excellent tool to expand our current knowledge to different fuels and environments. We change the oxygen concentration, diluent, buoyancy, pressure, fuel, just about everything you can think of. One of the things that we have found is that flames actually spread faster in space when using carbon dioxide or sulfur hexafluoride as a diluent. Big deal? OH YES! The space shuttle and the future space station use carbon dioxide fire extinguishers. So we are seeing how these things influence flame spread.

Anyway, I'll let you read about it more in some of our older papers on quickie web pages linked below.


	Article in the 27th Symposium on Combustion 98. Understanding Combustion Processes Through Microgravity Research


	Paper in Combustion Science and Technology 98. Effect of Ambient Atmosphere on Flame Spread at Microgravity


	Abstract for Paper in Combustion Science and Technology 98. Effect of Ambient Atmosphere on Flame Spread at Microgravity


	Article in the Fall International Meeting Combustion Workshop 97. Premixed Atmosphere & Convection Influences on Flame Inhibition & Combustion (PACIFIC)


	Article in the Western States Section of the Combustion Institute 96 Article in the Western States Section of the Combustion Institute 96


	Article in the Western States Section of the Combustion Institute 95 Mechanisms of Concurrent-Flow Flame Spread Over Thin Solid Fuels


	You can find PACIFIC related materials at our FTP site: ftp://cpl.usc.edu/pub/pacific


	Or you can read some abstracts below:

Abstract 97

A three year experimental and theoretical research program on the effects of ambient atmosphere on flame spread over solid fuels at 1g and microgravity is proposed. In particular, thick solid fuels will be used while varying the type of inert gas, which affects the Lewis number, and the addition of sub flammability limit gaseous fuels to the oxidizing atmosphere are proposed. To date many thin fuel tests have been performed under these same varying conditions with results that have exceeded expectations. However according to previous analysis, thick fuels should prove even more interesting. Although these experiments
are more difficult to perform due to the many limitations cited within, they are the only next logical step.

Abstract 95

A three year experimental and theoretical research program on the effects of ambient atmosphere on flame spread over solid fuels at 1g and microgravity is proposed. In particular, thick solid fuels will be used while varying the type of inert gas, which affects the Lewis number, and the addition of sub flammability limit gaseous fuels to the oxidizing atmosphere are proposed. To date many thin fuel tests have been performed under these same varying conditions with results that have exceeded expectations. However according to previous analysis, thick fuels should prove even more interesting. Although these experiments are more difficult to perform due to the many limitations cited within, they are the only next logical step.

The study of concurrent-flow flame spread over solid fuel beds has received wide attention in combustion literature because of its application to upward fire spread in buildings, up walls, etc. Despite all of the theoretical and experimental research done on the subject, however, some aspects of this problem are still not well understood. For example, studies reviewed by Fernandez-Pello (1984) have predicted that the spread rate (Sf) increases with time because the convective and diffusive transport are in the same direction and as a result the fuel surface area exposed to the hot combustion products also increases with time, leading to an accelerating flame spread. However, experimentally for thin (Fernandez-Pello and Hirano, 1983) and thick (Fernandez-Pello, 1984) fuels, the flame spread rate is sometimes found to be steady, . It is proposed here that the heat losses by conduction to the sample holders or radiative transport from the fuel surface may limit Sf and lead to steady spread. Equating the time scales for heat transfer to the fuel bed and the time scale for heat loss leads to the following predictions:


	Table 1

Fuel/Stabilization Type	Buoyant Convection	Forced Convection
Thin / Conductive Loss	Sf ~ GrW Sf,opp	Sf ~ Re Sf,opp
Thick / Conductive Loss	Sf ~ GrW2/3 Sf,opp	Sf ~ Sf,opp
Thin / Radiative Loss	Sf ~ GrW PlW3 Sf,opp	Sf ~ Re PlW Sf,opp
Thick / Radiative Loss	Sf ~ GrW2/3 PlW2 Sf,opp	Sf ~ Sf,opp

where GrW g W3/g2 , PlW [g(Tf - Tv)]/[W(Tv4 - T4)] , Re UW / g , Sf,opp is the opposed-flow flame spread rate, the parameters g, W, U, , , T, , are the gravitational acceleration, fuel width, gas velocity, viscosity, conductivity, temperature, fuel bed emissivity, and Stephan-Boltzman constant, and the subscripts g, v, and refer to the gas, fuel surface, and ambient, respectively. Also, note that the transition from convective to radiative stabilization should occur where there respective fluxes are equal, i.e., when Plw 1. Rearranging and plug in typical values of temperatures, etc., gives W 1.3 cm at crossover. This corresponds to a Grw between 104 and 105. Non-dimensionalizing the previous chart and focusing on thin fuels with buoyant flows, both laminar and turbulent, leads to the following predictions:


	Table 2

L/W

Sf(con)/S
f(opp)

Conduction Stabilization

Radiation Stabalization

Laminar	Turbulent	Laminar	Turbulent
Grw	Grw⁴/7	GrwPlw⁴	Grw-2Plw-5
~GrW ~W³~P²	~GrW⁴/7 ~W¹²/7 ~P⁸/7	~GrWP^lW³ ~W⁰~P²	~GrW-2PlW-6 ~W⁰~P-4

A simple set of experiments was performed on upward-spreading flames over narrow samples in various atmospheric conditions (e.g. pressure, oxygen concentration, etc.) to test these predictions. According to table 1, for small widths controlled by the laminar conduction

Figure 1

stabilization mechanism, the non-dimensionalized spread rate should be linearly proportional to the Grashof Number. Indeed, Fig. 1 shows this to be the case for Grashof Numbers from 3000 to 20000. Table 2 predicts that, in this same region, non-dimensionalizing the data should put most of the data onto the same curve, regardless of Oxygen concentration or pressure. Fig. 1 shows that this is indeed the case for more than four orders of magnitude of the Grashof Number. As, shown earlier, the stabilization mechanism should change from laminar conduction stabilization to radiative between 104 and 105. Fig. 1 shows this to be the case, with the slope of the curve shifting at GrW = 2 x 104. For larger Grashof Numbers in this region, different pressures would cause the curve to level off on different levels, and different inert gases would also change the curve because the stabilization mechanism would change from conductive to radiative mechanisms. The agreement between these results and the model predictions provide some justification for the mechanisms proposed herein. Please read further on our ftp sites.