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1002-12- 10^+21 July 21, I960 6906

Eighth

Progress Report

on the

Mechanisms of Fire ignition and Extinguishment

hy

To G « Lee

Covering the period 1 January to 30 June I960

for

Bureau of Ships

Department of the Navy

Code 638

Index Numher NS-I83 -OOI

HATiOl^AL BUREAU OF STA

intended for use within the C to additionai evaluation and re listing of this Report, either ii the Office of the Director, Nal however, by the Government : to reproduce additionai copie.

IMPORTANT NOTICE

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015.

•ogress accounting documents

nally published it is subjected

eprcduction, or open-literature on is obtained in writing from

Such permission is not needed,

jrepared if that agency wishes

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MECHANISMS OF FIRE IGNITION AND EXTINGUISHMENT

By

T. G. Lee

1 . Summary

Ion concentrations in a number of flames have been

measured using a symmetrical double Longmuir probe method

in an attempt to determine the effect of temperature differences on the ion concentration. The ionic concentrations

seemed to depend more on the nature of the inert gas than on

the adiabatic flame temperature. A paper is being prepared

on the results of the investigation, copies of which will

be forwarded when available.

2. Ionization Studies

Calcote has shown that the ionic concentration of flames

varies in much the same manner as flame temperature when

plotted as a function of the air- fuel ratio as a fraction

of the stoichiometric value. However, since this ratio is a

dimensionless number, no information was available from his

results, on the rate of fuel supplied to the flame. It seems

reasonable to assume that the rate of positive ion production

is a function of, among other things, the rate of fuel supply,

and the steady state concentration should be related to the

rate of formation of ions. It was, therefore, decided to

measure the ionic concentration in flames of fuel supplied at

a constant rate, and to which various inert gases were added

to change the adiabatic flame temperature.

Argon, nitrogen and carbon dioxide were used as diluents.

It was found that ionic concentrations were greatest with the

use of argon, and lowest when carbon dioxide was used as the

diluent. ’ Addition of inhibitors to the fuel greatly increased the ion

concentrations , the increase being proportional to the amount

of inhibitor added up to a certain concentration and remained

almost constant as the inhibitor concentration was increased

beyond this point. The concentrations of inhibitor used were

considerably below those required for extinction of the flame.

These results are not inconsistent with a mechanism proposed

by Creitz in v/hich the inhibitor is considered to be a stronger

oxidizing agent than oxygen. Reduction of the inhibitor

(decrease in valence) may be accomplished by capture of free

electrons followed by dissociation to give negative halogen

ions, which should result in an increase in the ionic concentration in the reaction zone.
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