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Fire Detection, in

Aircraft Engine Mac ©lies

by

C. £»• HeCamy and Wm. F. Boeser

1 . Summary

From measurements of the spectral emission in five separate

wavelength bands on a number of different types of ^ as-air flames,

it appears that the flicker characteristics are the same in each

of the selected parts of the spectrum. Wave analyses of the

flicker frequencies between 2,5 arid ?50 cycles per second show a

distinct maximum amplitude between 5 and 20 cycles per second for

each of the flames studied* This maximum amplitude occurred at a

higher frequency for the flames of premixed gas and air* than for

diffusion flames.

Studies of the ionisation properties of flames have been initiated and are being continued.

2. Flame uadi ation pleasure.- rents

The spectral emission in five separate wavelen th bands has

been recorded simultaneously for a number of different flames*

The records show that the variation of the emission in the five

bands with respect to time is in unison. Consequently, the

flicker characteristics appear to occur in all parts of the spectrum

simultaneously. Therefore it seems that wave analyses of the

flicker in any one part of the spectrum should be sufficient for

further studies. Vie have chosen the infrared for this purpose.

The wave analyses of the flicker frequencies between 2,5 and

7%Q cycles per second have been obtained for various flames, Under

ordinary conditions in a large Unventilated room, with no air movement except the convection currents caused by the flame, the

amplitude of the flicker at a given frequency varies with time. The

amplitude varies considerably with frequency, the maximum ordinarily

occurring at a frequency between five and twenty cycles per second.

Diffusion flames in still air may be observed to flicker with very

regular periodicity. The wave analyses of the flicker of such

flames show a fairly sharp maximum at a fundamental frequency and

several lesser peaks at higher harmonics. This type- of flicker has
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not been observed in flames of premixed air and $ as. In general,

these flames have a maximum amplitude of flicker at a somewhat

higher frequency than diffusion flames.

Plans have been made and equipment procured to study the correlation between gas jet velocity and flicker frequency. Equipment

has been constructed with the objective of producing substantial open

gasoline fires at a constant level and constant rate of burning for

use in flicker studies.

A series of experiments is being conducted to determine the conduction and rectification properties of flames. When two parallel

wires are placed a short distance apart in a Bunsen flame and a potential of a few hundred volts b-c is impressed, a current will

flow across the gap, the magnitude of which will fluctuate considerably with time. Peak currents of several microamperes have been

measured. The magnitude of the current increases with applied

voltage and the area of the wires heated* When wires of different

sizes are used, the system acts as a rectifier. The current through

a diffusion flame was found to be about twice that through a flame

resulting from the burning of premixed gas and air. Although no

studies have been made of the correlation between the fluctuations

in the wrrent and the visible flicker, an attempt to do so is being

considered.

3 . Electrical Properties of Flames

I4 . Financial Condition

commitments on this project:

April 25, 1952 through March 3I, 1953

i April 1 through June 30 , 1953

Total through June 39, 1953

§ 15 , 590.614

laii-iiLi

v 20,695.67

With additional qualified personnel available, our rate of

effort on this project was essentially doubled as of June 1, 1953*
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