/Q ^

Copy of 25

NATIONAL BUREAU OF STANDARDS REPORT

DETERMINATION

OF

THE SELF- IGNITION TEMPERATURE

OF

COMBUSTIBLE LIQUIDS

by

N. P. Setchkin

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

2100
U. S. DEPARTMENT OF COMMERCE

Charles Sawyer, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

ms PROJECT NBS REPORT

1002-10-1030 December 9» 1952 2100

DETERMINATION

OF

THE SELF- IGNITION TEMPERATURE

OF

COMBUSTIBLE LIQUIDS

by

N. P. Setchkin

The publication, repi ApprOVCd fOT public rclcaSC by the In part, Is prohibited

unless permission Is

( DireCtOT of tllC National Institute of tandards, Washington 25 , D. c. Such pern Standards and Teehnology (N 1ST)

cally prepared If tha /-v ^ i r port for Its own use on Oetober 9, 2015.

This report has been prepared for record

purposes and is not to be referenced in

published material.

CONTENTS

Page

1. Introduction 1

1.1 Purpose and scope 1

1.2 Criterion for self-ignition temperature. . 2

(a) Early methods and apparatus. ...... 2

(b) Adopted concept and definition of S.I.T. 8

1.3 Governing conditions 9

(a) Thermal characteristics of the apparatus 9

(b) Dimensional characteristics of the

ignition chamber . 10

(c) Pressure and uniformity of temperature . 10

(d) Combustible mixture. 11

(e) Effective temperature for ignition ... 11

(f) Evidence of ignition 11

(g) Effect of extraneous stimuli of ignition 12

2. Test apparatus and procedure 1^

2.1 Construction of apparatus l4

2.2 Test procedure 15

(a) Preheating of the apparatus 15

(b) Admission of charge 15

(c) Observation of temperature changes 17

(d) Observation of evidence l8

3. Test results l8

3.1 Low ignition temperature liquids 18

(a) Carbon disulfide 19

(b) Ethyl ether 19

3.2 Petroleum products ^. . . 21

(a) Motor gasoline (65 octane) . . . . ^ . 21

(b) Other gasolines and varsol 2k

(c) Kerosene and cleaner's solvent 25

(d) Crude oil 25

(e) Diesel fuels 25

(f) Furnace oil No. 2 27

(g) Lubricating oils 27

(h) Benzene . . 28

(i) Toluene 29

3o3 Pure petroleum fractions o . . . o o . . . 29

(a) Normal fractions of the chain type o . . 3l

(b) Normal fractions of ring type. . . . . . 3l

(c) Isomers 3l

3.^ Reference fuels . 33

(a) Primary reference fuels 33

(b) Secondary reference fuels 3V
CONTENTS - cont.

Page

3.5 High Ignition temperature liquids .... 36

(a) Acetone ..... o 38

(b) Acetic acid 38

(c) Ethyl alcohol . » . . o 39

(d) Ethylene glycol o . . 39

(e) Methyl formate ^-0

(f) Methyl alcohol . . ^0

(g) Glycerine, o . . . . o . hO

(h) Paint, varnishes, oil, and miscellaneous

materials 4l

4. Conclusions 43

5 . References 46
DETERMINATION OF THE SELF- IGNITION TEMPERATURE

OF COMBUSTIBLE LIQUIDS

ABSTRACT

A review is presented of methods which

have been used to measure ignition temperatures

of liquids o The fact is mentioned that many of

the previous investigations in this field have

not been conducted in apparatus and under thermal conditions likely to exhibit very low

ignition temperatures. A description is presented of the various stages of development of

an insulated spherical flask type of ignition

apparatus o Using this apparatus, an extensive

study has been performed on the ignition

characteristics of combustible liquids o The

results are presented in narrative graphical

and tabular formo

lo INTRODUCTION

lol Purpose and Scope

The ignition of combustible materials by contact with

flame and other ignition sources is a common yet most complex natural phenomenono The research reported here was

concerned only with self-ignition resulting from reaction

with oxygen of airo Such ignition may be started by

initial heating of normally stable materials to an elevated

temperature o While the results are mainly of interest from

the standpoint of fire and explosion hazards, the study of

various phases of ignition phenomenon may also be of interest

to workers in other fields o Each substance is usually characterized by physical and chemical properties such as density,

viscosity, conductivity, solubility, molecular weight, etco
2

Most of these properties are either of such a basic or fundamental nature or the arbitrary conditions for their measurement have been so well established that consistently reproducible results can be obtained in their measurement by

different workers. However, one thermo chemical property of a

substance pertaining to ignition remains undefined in spite

of its great importance not only for the evaluation of fire

hazards but also for many other practical considerations o The

self-ignition temperature (SIT) defines only general ignition

characteristics of material comparable in type with others and

this characteristic is a function of many governing conditions

which are not yet standardized

o

The scope of this work comprises a general study of the

ignition phenomenon of combustible liquids and the conditions

which control its measurement o A study was first made of the

various test methods and experimental apparatus that had been

previously applied for determination of ignition temperature.

This was important since widely different results are obtained,

depending upon the test method and the assumed definition of

self-ignition temperature.

Having arrived at a concept or definition of selfignition temperature that appeared logical, the next step

was concerned with development of apparatus and test methods.

Requirements for such a test include the elimination of all

extraneous sources of ignition or accelerators of the ignition

reaction. The effect of these can be studied separately.. No

external heat must be applied to the reacting mixture after a

degree of self-heating has set in that of itself will result

in ignition. The combustible mixture must also be isolated as

far as possible against loss of heat to the surroundings so

that the reacting portions of it can follow their natural

thermal processes.

The work reported also includes the presentation of

ignition characteristics of many commonly known combustible

liquids in apparatus designed to measure an exceptionally low

value of ignition temperature.

1.2 Criterion for Self-Ignition Temperature

(a) Early Methods and Apparatus

The ignition behavior of various substances has been

studied by many investigators with various test methods and

equipment constructed to obtain information on ignition under
- 3

-

some specific set of conditions or in conformity with a given

requirement 0 Many of the conditions which have been used were

not advantageous for obtaining a low ignition temperature

o

There also has been no unanimity in views as to the definition

of ignition temperature. A large number of terms have been

used by different investigators to define different stages

of the ignition reaction. For example, the following terms

designate early stages of reaction: "Temperature of Thermal

Reaction (T.ToRo)" (1); "Temperature Initial Combustion

(ToIoC,)" (2); "Critical Inflection Temperature (CdoTo)" (3);

and tepms designating the stage from which the reaction is

defini|:ely accelerated to ignition; "Spontaneous Ignition

Temperature" (^,5); "Autogeneous Ignition Temperature" (6).

Many other terms are indicated by Dro C. R, Brown in his thesis

"The Determination of the Ignition Temperature of Solid

Materials" (7)o

In the study of early methods and apparatus, the

following two basic methods of test procedure were considered:

the "Rising Temperature Method" and the "Constant Temperature

Method". In the first method the temperatures of the

ignition apparatus and the specimen being tested are continually increased until ignition occurs. Dro C. R. Brown, on

page 23 (7) gives references for l6 different methods which

have been used to define ignition temperature when the rising

temperature method is used. However, recently the selfignition temperature has been considered as that temperature

at which self-heating, leading to ignition, is initiated.

This temperature is usually indicated either by the point at

which the time-temperature line for the material departs from

a straight line or by itp point of intersection with the timetemperature curve of the air in the testing device (8). The

rising temperature method has been applied more frequently

for solids than for liquids because slowly heated combustible

mixtures of vapor and air often form relatively stable compounds at comparatively low temperatures which are ignitible

only at higher temperatures than occur with the constant

temperature method. Moreover, this method is subject to certain

experimental difficulties in maintaining a small thermal gradient within the speciman and between it and its surroundings.

Ignition temperatures determined with this method vary with the

rate of temperature rise and therefore are not reproduceable

without elaborate control equipment to maintain a fixed rate

of heating.
- 4 -

With the "Constant Temperature Method" the temperature

of the apparatus is kept constant during the test. The test

is repeated at different initial temperatures and with

different samples of the same substance until self-ignition

occurs. All initial temperatures can be precisely adjusted

and recorded before the test. With a few exceptions, the

initial temperature of a heating bath of the wall of the ignition vessel, or of the air inside the vessel necessary to

promote ignition is generally recognized as the "Ignition

Temperature .

Several test methods may be briefly described as follows :

(1) Oil drop method. Early determinations of ignition

temperature with the so-called "oil drop method" were made

by Holm (9) in 1913 with a heated porcelain surface, Moore

(10) used a platinum crucible submerged in molten metal or

embedded in a steel block, Sortman and Beatty (11) made a

small cylindrical cavity of ^3 ml capacity in a stainless

steel block and provided for circulation of preheated air.

Jentzsch and Von Zerbe (12) also used a steel block with

four cylinders (-7»1 ml) and circulation of oxygen or air.

A modified type of Moore apparatus, heated electrically,

has been widely used by many Investigators (13), The initial

temperature of the bath or wall of the ignition vessel leading to ignition is usually considered as the self-ignition

temperature. The values of ignition temperatures given in

table 1, which is reproduced from reference 13, show appreciable variations fo|* any given liquid because of differences in details of test procedures and apparatus,

(2) Dynamic tube method. In this method, a pyrex tube

is heated in a conventional electric furnace to the desired

temperature indicated by a thermocouple in contact with the

outside surface of the tube, A combustible substance, being

preheated separately. or together with air or oxygen, is allowed to pass through the tube. The tests are repeated at

different temperatures of the tube until evidence of ignition

is observed. Apparatus of this type has been used by Dixon

in 1909 and 1934 (l4, 15)? also by Masson and Wheeler (I 6 ),

Coward (17), and by many others. Coward limited his test

to 15 seconds. Callendar (2) and Moureu (I 8 ) made a study

of slow combustion and determined the "Temperature of Initial

Combustion" (T.I.C.) in an improved apparatus. This
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temperature was defined as the tube temperature necessary

to provide the first appearance of products of combustion

(steam, carbon dioxide, aldehyde, etc.), or was determined

by chemical analysis of samples taken periodically during

various phases of the reaction.

This temperature has some relation to the "Temperature

of Thermal Reaction" (T.T.R) introduced by Estrad^re (1)

and "Critical Inflection Temperature" (C.I.T.) introduced

by Lewis (3). All these temperatures are related to the

"Temperature of Initial Oxidation" (19) or in other words

to the temperature of incipient self-heating. Prettre defined the ignition temperature by appearance of "cold flame"

(T.C.F.) and by normal flame at "Minimum Ignition Temperature"

(M. I.T.). A tabulation of ignition temperatures measured by

this method is included in table 2, which is reproduced from

reference 19»

(3) Evacuated vessel method. In this method a combustible mixture is suddenly admitted into an evacuated vessel

which was preheated to the desired temperature. This method

was originated by Mallard and Le Chatelier in l880 and was

used subsequently by Masson and Wheeler (16) and Townend

(20). Ignition was indicated by rapid rise in pressure.

Lewis and also Pldgeon and Ejigerton (21) modified this

method by admission of the cold combustible mixture into

an evacuated vessel heated at a steady rate (rising temperature method).

(4) Bomb method. The bomb method was used by Neuman

(22) and other investigators for determination of the ignition temperature of combustible mixtures at elevated pressures.

(5) Adiabatic compression method. Heating of a combustible mixture to the ignition point by adiabatic compression was used by Tizard and Pye (23) and Pignot (24). It

is hardly likely that ignition temperatures measured by this

method, which involves the use of rising temperature and

pressure, are directly comparable to those measured at constant pressure,

(6) ASTM standard method. Committee D-2 on Petroleum

Products and Lubricants of ASTM in 1930 adopted the standard

method and apparatus (D286-30) (6) for the determination of

the "Autogeneous Ignition Temperature." The standard apparatus consists of a conical pyrex flask of 160 ml capacity.
- 7 - 1

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(A)

Callendar;

(B)

Lewis;

(C)

Estraddre;

(D)

Prettre;

(E)

Townend

and

Cohen;

(F)

Dumanois

and

others;

(G)

Tizard

and

Pye»
submerged in a molten alloy heated by a gas burner. A few

drops of the liquid to be tested are allowed to fall into

the flask, heated to different initial temperatures until

ignition is observed. The ignition temperature is defined

as the temperature of the solder bath, indicated by a

thermocouple placed in a silica protection tube submerged

in the bath near the flask necessary to cause ignition of

the specimen. This thermocouple has an appreciable time lag

in response to sudden changes in the bath temperature.

(b) Adopted Concept and Definition of Self- Ignition Temperature

The ignition reaction is a thermo chemical process in

which the thermal phase has a predominant effect upon the

direction and intensity of chemical developments because

not only does heat generated from the exothermic reaction

lead to ignition, but also heat dissipation to the surroundings determines whether acceleration to ignition will

occur. This important fact has frequently been overlooked

in studying the problem of ignition. The above criteria

can be illustrated by the time-temperature curves shown on

figure 1, representing the thermal effects of ignition and

nonignition reactions of a combustible substance with

oxygen of air. After the injection of a dispersed charge

of combustible liquid into a closed vessel, the temperature

of the mixture of vapor and air at first falls below the

initial temperature because of heat absorption. If the

initial temperature (to) of air in the vessel is below the

temperature of incipient self-heating (tx), then after a

certain time lag, the temperature recovers mainly by means

of heat supplied from the walls. At a higher initial temperature (tq), the temperature of the combustible mixture

after an initial drop gradually rises due to combined effects of the heated wall and the exothermic reaction until

the temperature (tq) is reached. At the point (a) no heat

is supplied by the wall and the rate of temperature rise

represents the rate of heat generation by the exothermic

reaction. During further increase in temperature of the gas

mixture, the generated heat is partly absorbed by the wall,

partly carried away through the wall to a medium surrounding

the ignition vessel, and a very small part of the heat is

used to raise the temperature of the gas mixture. The rise

in temperature of the mixture continues only in cases where

the rate of heat generation increases faster than the rate

of heat dissipation. Otherwise, both rates become equal and

the temperature of the combustible mixture for a time will
- 9

”

be constant and equal to (ti'), before falling to the initial level at (ti)» A similar phenomenon has been observed

at other higher initial temperatures (t2, t3 , tl+)

,

However,

at certain initial temperatures (t^) the inducing reaction

is continually accelerated and at the point (t^*) evidence of

ignition is observed in the form of flame or explosiono

Temperature (tf) is sometimes called "the Ignition point."

This temperature has no definite and reproducible value due

to its rapid rate of change and often it is below the maximum temperature (t4) observed at lower initial temperatures.

Self-ignition at still higher initial temperatures (t6, etc.)

usually occurs with shorter ignition time lag and with more

violent evidence of ignition.

The initial temperature of air (t^) is taken as the

self-ignition temperature (SIT) of the material tested. This

results in the following definition:

As used in this paper the self-ignition temperature (SIT) of a liquid is the minimum initial

temperature of any combustible mixture with air

at or above which it will pass into a condition

of observable combustion under specific conditions o

1.3 Governing Conditions

(a) Thermal Characteristics of the Apparatus

The influence of the heating bath and ignition chamber

wall on the trend of the ignition reaction and thus the

measured ignition temperature has often beai ignored. During

the preliminary stage of the test, the bath supplie-s heat to

the wall of the ignition chamber and maintains constant

temperature in the apparatus. As soon as the temperature of

the reacting mixture increases above the wall temperature,

due to an exothermic reaction, the direction of heat flow

is reversed and the observed rate of the ignition reaction

is appreciably affected by the rate of heat loss to the

surroundings or by the heat capacity and conductivity of

wall and bath. The higher the rate of heat loss, the higher

is the initial temperature required to accelerate the reaction to ignition.
-10 -

(b) Dimensional Characteristics of the Ignition Chamber

The size, shape and material of the ignition chamber

also have an effect on the observed rate of the ignition

reaction and the value of the self-ignition temperature

because the dimensional characteristics of the ignition

chamber are interrelated with their thermal characteristics.

(c) Pressure and Uniformity of Temperature

The observed self-ignition temperature of a combustible

gas mixture is probably affected by pressure in the ignition

chamber. The tests reported here were conducted under atmospheric pressure without correction for barometric pressure

changes

.

Undoubtedly, ignition develops from molecular interaction of the combustible substance with oxidation agents.

Ignition probably initiates in the most highly energized

molecules of the mixture and propagates throughout the

whole mass (Mareck and Hahn (25) » Not all the molecules

present are in the same energy state. However, the more

uniform the temperature distribution in this mass, the more

favorable conditions will be for rapid propagation of the

Ignition reaction. Because of this, special attention was

given to control of the temperature in the Ignition vessel.

The control of the uniformity of the temperature within

the flask was studied over the range of temperatures from

200° C to 600° C by means of tests conducted in the 1000 ml

ignition apparatus provided with a number of thermocouples.

This made it possible to measure the temperature at various

points of the flask surface and air space and to control the

heat input in different coils in such a manner that the

uniformity of the temperature can be brought to within

2 degrees C.

As Indicated below, the exploration tests clearly demonstrated the effect of heat loss through the exposed neck

of the flask on the uniformity of temperature. With a noninsulated neck the variation of temperature in the flask

reached 13 degrees C. These variations were reduced to

9 degrees C with asbestos insulation and to about 2 degrees C

with the heating coils extended around the neck (Fig. 2).

However, an additional exploration test with single or triple

thermocouples in various parts of the air space showed that
- 11 -

variations in the temperature throughout the flask could be

reduced to even one degree C.

The temperature of the combustible mixture varies more

or less uniformly during the ignition reaction as is indicated by the time-temperature curves observed simultaneously

in different zones of the flasko These curves exhibited

substantially the same pattern, as will be shown later on

Figures 20 and U-2o

(d) Combustible Mixture

The ratio of combustible to air of the combustible

mixture has an appreciable effect upon the minimum ignition

temperature o Excessively rich or lean mixtures usually

increase the ignition temperature o Carbon and soot deposits

also affect the value of the minimum ignition temperature

o

Therefore, the effects of these factors should be considered

in the determination of the lowest self-ignition temperature.,

(e) Effective Temperature for Ignition

The method of determination of the effective temperature

for ignition has an influence on the value of the observed

ignition temperature o The initial temperature of the solder

bath or the temperature of a metal block is often considered

as the effective temperature for ignitiono These temperatures differ appreciably from the initial temperature of air

or the combustible mixture inside the ignition chamber o This

fact has been recognized in the present method for measurement of ignition temperature o This temperature is measured

by a thermocouple inserted in the lower portion of the

ignition chamber, which is also extensively used during the

test for observation of temperature changes during reaction

and for the study of other thermal effects of the ignition

phenomena

o

(f) Evidence of Ignition

Ignition is generally indicated by visual evidence, the

intensity of which varies with the initial temperature o At

high initial temperatures, self-ignition usually occurs in

a more or less violent form such as a bright flash of flame

and audible expulsion of gases (explosion). In the medium

range of temperature a mild flame is often observed, while

at the lowest ignition temperatures a very dull violet or

blue flame is visible, often only under dark room conditions.
12

These latter can be easily confused with cold flame or

chemiluminescence which is not generally recognized as

evidence of ignition in spite of the rapid rise in

temperature of the reacting mixture. Therefore, test

conditions should make observation of the lowest value

of the ignition temperature possible.

Some investigators have limited their tests to 10

or 15 seconds only. In such cases it should be remembered that ignition lag is an inverse function of the

ignition temperature. At high temperatures, the lag may

be only a fraction of a second, while the lag at the

lowest temperature may amount to minutes, depending upon

test conditions. For example, the ignition lag of methyl

cyclohexane at 275° C was found in the 1000 ml flask to be

30 seconds; at 248°C the lag was as long as 20 min 10 sec.

The occurrence of ignition for many liquids can also

be determined by comparison of the time-temperature curves

observed for the ignition and nonignition reactions. It is

intereseing to note that two adjacent typical ignition and

nonignition reactions, illustrated by curves 5 and 4 on

Figure 1, proceeded substantially with the same rate up to

a certain transition point, after which one reaction rapidly

accelerated to ignition and the other changed its course to

a certain maximum temperature (ti^') and eventually cooled

down. These typical curves are usually reproducible to

within a few degrees C of the initial temperature in the

same apparatus under identical conditions. Moreover, the

thermal effect of the reaction observed under different

controllable conditions is also reproducible with the same

accuracy. Therefore, observed effects can be correlated

with the factors representing the test conditions. Because

of this, particular attention was given to observation of

not only visible and audible evidences of ignition but also

to the thermal effects of different reactions in terms of

time-temperature curves.

(g) Effect of Extraneous Stimuli of Ignition

As stated in the introduction, the effect of all

extraneous stimuli of ignition such as flame, spark, detonators, overheated surface or catalytic agents should be

eliminated from the first phase of this study and the

ignition reaction allowed to take its natural course within

the combustible mixture. The effects of the above stimuli

should be studied separately in relation to naturally
- 13

developed ignition, because of the complexity of the superimposed effects 0 For example, the catalytic effect of

certain metals used in construction of the ignition chamber

is usually superimposed by an additional thermal effect of

metal masses c The relative effect of the thermal conductivity of the wall is considerably greater than the effect

of heat capacity^ therefore, the elimination of the first

effect in the experiments makes the catalytic effect

relatively more noticeable

»

In the present study an investigation was made of the

catalytic effect of the thermocouples placed inside the

ignition chambero Heat losses by conduction were practically

eliminated and only the small effect of heat capacity of

wires was left together with the possible catalytic actiono

This action of the thermocouple wires was not detected in

comparative tests conducted with the thermocouple placed

inside the ignition chamber and removed just before injection

of the charge of different liquids. Neither was it detected

with an additional 10 gr of wire placed in the chamber.

Only a slight retarding effect on the ignition reaction was

noticed because part of the heat generated by the exothermic

reaction was absorbed by the mass of wires in increasing their

temperature. As a result, the ignition temperature was found

to be slightly higher with longer wires than with short

thermocouple wires or without wires or thermocouples of any

kind. For example, the minimum self-ignition temperatures of

furnace oil No, 2 were obtained with 10 gr of bare thermocouple wires at 240°C; with three thermocouples in porcelain

tubes at 236° C; with a single thermocouple in the tube at

23^°C; with a bare single thermocouple at 233°C and without

a thermocouple at 232°C, Similar results were found with

other liquids,

Callendar (26) experimented with different metals

placed in a test tube in a manner similar to that mentioned.

His results did not show any catalytic action of these metals

with the exception of platinum black. On the other hand,

different values of ignition temperatures obtained by

Thompson (27) and especially by Matson and Dufour (28) in

chambers made of different metals definitely varied with the

heat conductivity of the metal which has a predominant effect

on the ignition temperature.
- -

2. TEST APPARATUS AND PROCEDURE

2.1 Construction of Apparatus

Having arrived at a concept and definition of selfignition temperature that appears logical, the next step was

concerned with the development of equipment and an experimental method capable of furnishing ignition data with the

desired degree of accuracy.

Initial experiments were conducted with the ASTM

standard ignition apparatus (6) with solder bath and gas

burner. Because of difficulties in controlling temperatures

and poor reproducibility of the results, this apparatus was

modified to include electrical heating elements, a 200 ml

spherical pyrex flask, a starring arrangement in the bath,

and direct measurement of temperature in the flask. In

order to eliminate large heat loss , to the solder bath and

to improve uniformity of temperature control in the flask,

the solder bath was later replaced with two sets of heating

elements made of nichrome wire in an asbestos sleeve wound

around the upper and lower halves of the spherical flask

and protected with alundum cement. The final design of the

ignition apparatus consisted of a 1000 ml spherical pyrex

flask, as shown in Figure 3, placed concentrically inside

a refractory casing so that a 1/2-in. air space was provided

between the flask and the casing for further reduction of

heat loss during tests. The heating wires in the asbestos sleeve were wound around the upper and lower halves of

the casing and the neck with independent control of electric

current. Temperatures of the three heaters were indicated by

three thermocouples made of chromel alumel (26 B & S gage)

wire, placed behind each group of heating coils. Two

additional thermocouples were placed in contact with the

upper and lower surfaces of the flask. The sixth thermocouple, insulated by glass sleeves and also of 26 (B & S

gage) wire, was placed in the lower part of the flask for

indicating the temperature inside the flask. The flask neck

was closed with a cement-asbestos stopper having two passages,

one for the thermocouple wires and the other for injection of

the charge.

Most of the tests reported in this paper were performed

in the 1000 ml capacity apparatus shown in Figure 3. A few

additional determinations were made in the 200 and 12,000 ml

apparatus of similar construction.
The effect of different sizes of apparatus on the

observed self-ignition temperature was studied in the

200, 1000, 12,000 and 15,000 ml capacity spherical pyrex

flasks o These were constructed substantially in the same

manner as shown in Figure 3 with the exception of the 15,000

ml flask which wan made of vitreosel about 3/8 inc thick and

without an air space between the flask and heating coils

o

The heat-absorbing capacity of this flask was higher than

that of the 12,000 ml flask, the thickness of which was only

3/32 incho Results of tests of two liquids in these various

ignition apparatus are presented in table 3« From these data

it is evident that flask size as well as other factors influence the measured ignition temperature

»

The effect of the thermal properties of the apparatus

on the measured self-ignition temperature was studied with

three apparatus equipped with spherical pyrex flasks of the

same capacity (1000 ml) and having the following types of

casings; (1) 5/8 inch thick copper casing directly connected

with the pyrex flask (2) a refractory casing with 1/2 inch

air space, as shown in Figure 3, and (3) a refractory casing

with mirrored inner surface for reflection of radiant heat

back to the flask through 5/8~lnch air space o The results

of this study are given in table 9 of Section 3o6=

2o2 Test Procedure

(a) Preheating of the Apparatus

The ignition apparatus was preheated to the required

temperature by electric current passing through a rheostat

or variac connected with the heating coils wound around the

various portions of the flasko The current was adjusted in

such a manner that a constant temperature was maintained in

the flask within limits of about t 2°Co

(b) Admission of Charge

A constant amount of liquid charge (about 0o2 ml per

1000 ml of air) was usually injected « This was done by use

of a hypodermic syringe and a fine needle providing good

dispersion of liquid droplets essential for rapid evaporation

and uniform Initiation of the reaction throughout the whole

of the spherical flask* The tests were usually repeated with

the same charge until the minimum self-ignition temperature

was obtained* Then a few additional tests were made with

smaller and larger charges, in order to determine the most

favorable combustible-air mixture for the lowest selfignition temperature*
Table

3.

Ignition

characteristics

of

low

ignition

temperature

liquids

obtained

in

apparatus

of

different

sizes - 16 -

<D 1 o

•H> CD MD NO 1—1 o1 B

tkO CD \’ o 00 w1 CM o O cd 1 o •ri o H E

IfN rH EH CM M O MD NO

CO1 O

•H j:!*| o ON iH > CD W Td NO 1—1 o| a CD o o

tuO to1 CM o cd o d1 o •iH O rH

vs

a 1 CM

iH EH o o M o NO * CO o OS rH 1 o

•H £U* > CD m ^

lr\

rH CJ a CD IfN to to iH CM o cd o a o •H o O rH

EH s o o M cu iH cv

CO o rH rH 1 o

•H

C > CD* &q -Cd ro 1—1 o|

CD CX)

O

a W) to| o CM

cd o PI pf| o *nl o O

CM

H - - o O CM OO

CO o 1 rH 1—1 0

Td•H1—1

cd Ph 1 1 to CD

cd •H Xi

•H Td -P u O

<Dd

-P o rHS

Ph Xi

cd

p o tx|

ao

•H

-P•Hd

bO M

do o •H d to CD o o O •H 1—1 d to Ph

CD

O

X

Td

H dtij

•H 0( o

f§

|X{ -H H>

pq to

d

CD

O CD

Ua Td

H

H

O cd

H Pi o

rH 2d ^

Pci s pq >

CD w*

roJ" ItnnO
- 17 -

In order to eliminate the effect of carbon or soot

deposits on the measurements, the products of decomposition

were blown out by a jet of air after each test and the

interior flask surface cleaned regularlyo The final determinations were made with a thoroughly cleaned surface

»

Liquids producing sooty residues (oils, lacquer, paints,

etCo) or solids with low melting temperatures (gum, wax,

tar, etCo) were usually placed in a small crucible held by

a thin wire in the lower part of the flasko This arrangement prevents excessive accumulation of deposits; however,

the minimum ignition temperature obtained in this manner

was either corrected for the cooling effect of the additional mass of the crucible or final determinations were

made without this arrangement

»

(c) Observation of Temperature Changes

The temperature of the heating coils, flask surface

and air in the flask were observed in terms of "emf",

prior to admission of the charge, by means of a type "K"

potentiometer and galvanometer and recorded in millivolts

during a sufficient length of time for indication of

stabilization of temperature throughout the apparatus

»

For a convenient and accurate recording of temperature

during important phases of the thermal process in the combustible mixture, special attention is usually given to the

readings of "emf" of the thermocouple located within the

flasko These readings were made every 15 or 20 seconds,

immediately after injection of the charge and continued

until either ignition took place or the trend of the

process or other phenomena of particular interest were

definitely established o The graphical recording of the

temperature on the millivolt and time scale was used for

a consistent visual presentation of the thermal process

taking place within the flasko The temperatures of coils

and flask surface were observed at 3 to 5 minute intervals,

because these temperatures change only slowlyo

For observation of uniform changes of temperature

inside the flask during the ignition reaction, three thermocouples were placed in the upper, central and lower portions

of the flasko Successive readings of these thermocouples

were taken and were graphically recorded as fast as possible,

Chromel alumel wire of 26 (B & S) gage was generally used

in all tests with exceptions made in some cases which required high precision datao In these cases 32 (B & S) gage wire

was used with a small junction for higher sensitivity of the

thermocouple o
- 18 -

(d) Observation of Evidence

Audible or visible evidence of ignition (explosion, flame,

and puff) were usually observed in conjunction with corresponding changes in the time-temperature curves. In the absence of

these, definitely nonignition reactions were also well indicated by the shape of the curves. The mild form of visual and

audible evidence corresponding to the lowest self-ignition

temperature was usually observed under dark room conditions

through a periscope placed above the flask opening. With the

exception of a few liquids, even a very dull flame was

distinctly visible. Ignition of liquids producing dense smoke

was indicated by illumination of the white clouds which was

also distinctly visible through the periscope.

3.

TEST RESULTS

The following ignition characteristics of combustible

liquids were observed under the specified test conditions:

1. Minimum self-ignition temperature.

2. Character and intensity of the evidence of ignition.

3. Favorable fuel-air mixture ratio for minimum

ignition temperature.

4. Time- temperature curves and ignition lags for

different initial temperatures.

5. Character of the ignition and nonignition

reaction.

The following groups of combustible liquids were subjected

to the ignition tests:

1. Low ignition temperature liquids.

2. Petroleum products.

3. Pure petroleum fractions.

4. Reference fuels.

5. High ignition temperature liquids.

6. Paints, varnishes, oils and miscellaneous liquids.

3.1 Low Ignition Temperature Liquids

The characteristics of two liquids Ignitible at comparatively low temperatures are shown in table 3.
- 19 -

The self-ignition temperature of these liquids varies

with the size and thermal properties of the apparatus.

However, the higher heat capacity of the 15,000 ml vitreosol

flask as compared with the 12,000 ml pyrex flask has a more

important effect on the self-ignition temperature than the

effect of size.

(a) Carbon Disulfide

The self-ignition of carbon disulfide is usually

indicated by a violent explosion accompanied by flame and

a very rapid rise in temperature, shown on Figure ho The

pre-ignition reaction of this material, in contrast with

that of other liquids, is of a very mild form indicated by

a gradual rise in temperature, even for temperatures just

below the ignition region. Consistent fluctuations in the

time-temperature curves may result from secondary reactions

caused by rich mixtures or gases evolved from yellow-brownish

deposits on the flask surface left from previous tests.

Both these factors may have a retarding effect on the

ignition reaction. Normally the lowest self-ignition temperatures for combustible liquids were observed when using

charges of 0.2 to 0.25 ml per 1000 ml of air. However,

self-ignition temperatures of carbon disulfide show a

rapid drop as the fuel charge is reduced from 0.2 to 0.05

ml/lOOOml of air and remain almost constant for charges

below 0.03 ml, as shown in Figure 5°

The carbon, disulfide-air mixture has one critical

ratio for each initial temperature above which the mixture

remained nonignitible . For example, the critical charge for

the initial temperature of 150°C is about 0.l8 ml. With a

charge of 0.25 ml, the reaction was not accelerated to

ignition during the 2-1/2 min test period. If at the end

of this nonignition reaction a fresh charge of air was

admitted, then shortly a violent ignition occurred. This

ignition was probably caused by reduction of concentration

of the mixture below the critical value of 0.l8 ml per

1000 ml.

(b) Ethyl Ether

Self-ignition of ethyl either is usually indicated by

a violent explosion accompanied by a large flame and rapid

rise in temperature. Typical time- temperature curves are

shown in Figure 6.
- 20

The nonignition reaction of this liquid, in contrast

to that of carbon disulfide is characterized by a slow rise

of temperature for a considerable time after injection of the

charge. During the first period of the exothermic reaction,

extending from 5 to 10 seconds, the pressure inside the

flask increased slightly and gases were expelled from the

neck with a just barely audible sound. The temperature of

the mixture continued to rise and in about 10 or 15 min

reached its maximum (25 degrees C above the initial temperature), However, at slightly higher initial temperatures

ignition occurred at a time when the thermocouple indicated

a lower temperature of the mixture than the maximum observed

in the preceding test. This fact seems to indicate that

either development of ignition is not a simple function of

gas temperature, or the thermocouple and temperatureindicating system could not accurately follow the rapid

temperature changes at the point within the gas where

ignition actually takes place. On the other hand, the

initial temperature can be accurately measured and defines

the ignition or nonignition state; therefore, the initial

temperature of the mixture is accepted as the representative

temperature for self-ignition.

Self-ignition of combustible liquids usually occurred

at lower temperatures in the larger apparatus. Data obtained

in the 12,000 and 15,000 ml flasks (table 3) do not follow

this general trend; however, the above relationship can be

maintained only in apparatus of similar construction.

Actually the 15,000 ml flask has larger heat capacity and

higher heat loss per unit of volume than the 12,000 ml flask;

therefore, the effects of the thermal characteristics of the

apparatus are superimposed and affect the dimensional characteristics , The effects of various sizes of ignition chamber on the

ignition and nonignition reactions of ethyl ether are shown

by the set of typical time-temperature curves in Figure 7

and the effect of various charges injected at the same initial

temperatures at l60°C in Figure 8. In the determination of

the lowest self-ignition temperature, it is obvious that

ignition chamber size and thermal properties as well as fuelair ratio should be considered.
21

3.2 Petroleum Products

The ignition characteristics of petroleum products,

determined in different ignition apparatus, are given in

Table ho Some liquids were tested in four different

sizes of apparatus and some liquids only in the apparatus

of 1000 ml capacity, which was tentatively selected as

the standard for tests reported here.

(a) Motor Gasoline (65 octane)

The ignition reactions of various gasolines (kerosene,

cleaner’s solvent and a few other refined petroleum products)

usually proceed with characteristically shaped time-temperature curves which are different from those of other combustible liquids of non-petroleum origin. Well reproducible

variations of these curves occur as the initial temperature

is raised o These seem to indicate that both ignition and

nonignition reactions of these liquids progress as a twostage exothermic reaction. This is shown by the set of timetemperature curves in Figure 9? obtained in the 1000 ml

ignition apparatus with constant charges of 0.20 ml. Somewhat similar characteristics were also found for other

charges (0.10, 0.25 and 0.30 ml/1 in the 200 and 12,000 flasks).

Data for charges of 0.25 ml/1 in the 200 and 12,000 flasks

are shown in Figures 10 and 11.

The injection of the charge was usually made into a

flask uniformly preheated to the required temperature.

Immediately after injection of the charge, a considerable

drop in temperature of the gas mixture was observed due to

evaporation of liquid. However, the temperature was shortly

increased by heat supplied from the wall and the exothermic

reaction, which usually continued about one or two minutes

depending on the level of the initial temperature. The

other stage of reaction was indicated by a fall of temperature, which was probably due either to an interrupted

exothermic reaction or to some endothermic process. The

next stage of the exothermic reaction was initiated after a

certain time interval and continued either until the temperature of the reacting mixture reached its maximum, at which

time the rate of heat generation and heat dissipation to the

surroundings were equal, or to a transition point from which

the rate of heat generation accelerated faster than the rate

of heat dissipation. Therefore, ignition resulted.
Table

4.

Ignltloii-characterlstics.-

of

petroleum

products

obtained

In

flasks

of

dif.ferent

sizes

22

CO0

N

•H

CO

CO

Cti

I—

I

a

o

o

o•N

I—

I

a

o

o

o

CM

I—

I

O

0 ItnU> 1 1 UMTn I 1 1 1 1 O 1 1 1 00 1 1

Lag

tn HpO 1 1 ir\CM 1 1 1 1 1 PO 1 1 1 J" 1 1 d

•H oopo 1 1 J- 1 1 1 1 1 CM 1 1 1 o 1 1

• a

EH O CM 1 1 ITNITN 1 1 1 1 1 O 1 1 1 o 1 1 • O J-ir\ 1 1 HPO 1 1 1 1 1 rO 1 1 1 CM 1 1 M o CM CM 1 1 CM CM 1 1 1 1 1 CM 1 1 1 no 1 1 CO

•o0 O 1 1 00 itncm I 1 1 1 1 lT\ 1 1 1 UA 1 o w 1 1 J- CM J- 1 1 1 1 1 1 1 1 no 1 ^ txO 0 sij O 1 1 \0 CN-CJN 1 1 1 1 1 CM 1 1 1 O 1 no

•

•H

al

1—i 1 1

EH J" 1 1 U^O 1 1 1 1 1 MD 1 1 1 no 1 CM

• o CM 1 1

1—11—1 CM 1 1 1 1 1 CM 1 1 I rH 1 00 M O CM 1 1 CM CM CM 1 1 1 1 1 CM 1 1 1 no 1 -J" CO

o|

0 O O vO O ICNJ- IfN O O O ITNO UMcn POJ-OO IT\ bO w PO O O O Ir\J- pP) O rO-it* -d" -dh iH iH O O J-lCN

0

ai J-IT\OpOCM cm O POCM CM H CM CM O O O O O

a|

o

o

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EHM

oOCO CM ITN O-ro CM ^ ^PO O lr\\0 rO

nOPOCM CMm

CM CM CM CM CM

I—I I—I J" I—I O'' j- OCM CM

o| O I 0 PO I 0|

Sh •H CM I a

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I I I I lT\ II

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I I I I O II

I I I I CM II

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I I I I CM II

I iTNlfNlTN

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I UMN.PO

I pP)lf>lT\ CO

• • 0 -P • • -P +-> -P CM 0

o o o 0 • 1—

1

o o o > o •H iH

1—1 • • o •H \^PO (N- o 0 O

vO i>-00 0 H 0 0 0 0 1—1 bOO H 'a 0 !Z! cu c! d •H 0 CM 00 0

fH 0 0 0 0 0 O •H • • P •H rH 0 0 0 0 0 •H H 4-> -P -P H -POO 0 Cm •H

OJ c:! d C Ih O 0 0 0 0 0 0 S ^ 0 H O 0 0

•H ‘H *H 1—1 0 0 H O O O O O o •H 0 0 0 1—1

1—1 H O 0 0 0 0 •H ^ 0 0 0 0

O O O 0 O 0 0 t^U^O 00 0 O 0 O N 0

0 CO W fn f-i 0 0 0pMi^\O''O P 0H-P CJ H

nj 0 0 0 0 1—1 (h •H 0 0 O 0 O c^CDC!3>WOoQ O S pq EH
Comparison of two adjacent ignition and nonignition

reactions shows that the rate of formation of stable

compounds in the nonignition reaction seems to be greater

than in the ignition reaction; therefore, in spite of the

fact that the temperature of the reacting mixture increased

above the transition-ignition point, self-ignition did not

occur » Moreover, these stable compounds were not ignitible

either by spark or flame or by additional heating of the

mixture up to about 400°C, unless the mixture was diluted

with fresh airo

It is interesting to note that ignition of gasoline

usually occurred during the last stage of reaction, in

contrast with kerosene and cleaner’s solvent for which, as

will be shown later, ignition occurred at the first stage

The time interval between stages of the exothermic reaction

was gradually diminished with increased initial temperature

and finally in the high temperature region both stages

seemed to proceed simultaneously along one smooth line;

under these conditions, it is difficult to estimate at

which stage ignition occurred

The intensity of the evidence of ignition varied with

the initial temperature. At the lower range of temperatures

with some grades of gasoline (high octane number) ignition

with a very dull blue flame was observed under dark room

conditions or through the periscope attached to the flask

necko Gasoline of low octane number generally ignited with

a mild orange flame accompanied by audible expulsion of

gases ("puff"). Both types of evidence were well correlated

with rapid rise in temperature, as is indicated in Figures

9, 10 and 11, Ignition at a higher initial temperature is

usually indicated by a more violent flash of flame or by

audible expulsion.

It is also interesting to point out that the temperature

of a mixture after ignition or nonignition reaction rapidly

falls close to the initial one with the exception of the

high ignition temperature region, where the temperature of

the mixture remains high for a comparatively long time.

Moreover, the surface of the flask after these tests was

more readily covered by soot and carbon deposits than after

the tests at lower temperatures. These conditions prevailed

for very small charges, 0,05 ml/1, as well as for 0,30 ml/1,
24 -

Ignition lags were found to be well correlated with

the ignition temperature, as shown in Figure 12. The

lowest self-ignition temperature was usually determined

from the tests conducted with different charges, as shown

in Figure 13

o

Analysis of the time-temperature curves obtained at

various initial temperatures and in different ignition

apparatus (Figs. 9, 10, 11) indicates that;

(1) The thermal effects of the ignition and nonignition

reactions, recorded in terms of temperature changes with

time, are well reproducible for the same initial temperature.

(2) Observed changes in each stage of the thermal process

or the patterns of the time-temperature curves are not

accidental but seem to represent a definite part of the

thermal process continuously and orderly progressing with

the time.

(3) These patterns are also related to the composition of

the combustible mixture and the test conditions; therefore,

some mechanisms of chemical reactions may be correlated with

definite patterns obtained with the predetermined compositions.

For example (a) the timing and magnitude of the second

drop in temperature consistently diminished with increased

initial temperature and reduced size of the ignition chamber,

(b) The ignition of gasolines always occurred in the second

stage of the exothermic reaction and the minimum self-ignition

temperature always increased and ignition lag decreased with

smaller sizes of the ignition chamber, (c) Both ignition and

adjacent nonignition reactions proceeded in all three

apparatus substantially in the same pattern to the transition

point, from which one reaction rapidly accelerated to ignition

and the other turned to stabilization without ignition at

certain maximum temperatures.

(b) Other Gasolines and Varsol

The characteristics of other gasolines and varsol are

substantially the same as motor and aviation gasolines

(Supply of 1937) with a two-stage reaction and with ignition

occurring at the second stage of reaction.
- 2 ^

-

(c) Kerosene and Cleaner's Solvent

Kerosene and cleaner's solvent belong to another group

of petroleum products, the ignition of which seems to occur

at the first stage of reaction in spite of the fact that the

nonignition reaction proceeded with a two-stage reaction.

Typical time-temperature curves are shown in Figures l4 and

l5o "After burning" of cleaner's solvent in the region of

high ignition temperatures was more pronounced than with

other fuels and ignition at all temperatures was indicated

by mild flame and hardly audible expulsion of gases.

(d) Crude Oil

Langonillas crude oil of gravity 17 AoP.!., flash point

15° C, and sulphur content 1.91 percent, was tested in

connection with the study of the explosion of an oil tanker.

This oil was tested under various conditions and for the

presence of various agents supposed to stimulate ignition.

However, self-ignition occurred with a violent explosion at

the lowest temperature, 262°C, after 35 seconds in the

absence of any accelerating agents.

The character of the ignition and nonignition reaction

of crude oil is appreciably different from that of the

gasoline and kerosene group of fuels. The reaction proceeds

in a one-stage pattern with considerable self-heating for

the nonignition reaction and a rapid increase of temperature

after violent ignition, as shown in Figure I 6 .

(e) Diesel Fuels

The physical properties and ignition characteristics

of four Diesel fuels determined in the 1000 ml flask are

given in table 5°

The time-temperature curves determined for these fuels

are shown in Figures 17 and I 8 . Both ignition and nonignition

reactions of all four fuels are of single-stage pattern.

However, some reduction of the rate of reaction was observed

before more rapid acceleration to ignition or to maximum

temperature of the stabilized state.
Table

5»

Physical

properties

and

ignition

characteristics

of

Diesel

fuels - 26 - 0G

cd -p o 0 pf 0

CO o CvJ CM 1—1 0 o 0 • iTN GO \0 o 1—! o \D iTN CO

iTN CO CO CO CM CM ph 1 1 CM CM

Td

G 0 •H

ft

a

OQ 1—1 o p 0 G o 0

-p CO

O 1—1 O o si • o o CO

CuO OO CO 1 1 CO o iTN pf

•H fO ph u^ CM CM

G 0 1—1 CO CM •H G a

-pCO CM

JH

O 3 0 G

c^ 0

-P CO CMO

x: • • O CO

lr^ W) (M

O CO lr\ o O IfN

ITN •H CO 1 1 1 1 CO

G 0 CM ph CM •H G a

CO CMO 0 0 P 0 0

TdH Cd\

O 0 CN- IN- CM O

G 1—1 O o • o O -P CO -4- lT\ iTN o CO G 1—1

•H 0 0 CO CO 00 O CO •H -p

Ph *H 1—1

pi" CM

a •H

O Td

G

CO bfl ft 1 1 X» ft ft O ft ft o o o O

*=ij CO 0

!>s o

-P -p

G

•H

G 0

fH > -p 0 Td

0) 0 G -p b£) •H rQ G -p •H G 0 > a bO G O O ft ft

cs •H ft o * n O -p O G 0 G

•H •H ft bfl

G

O o O

CD ft 0 G

G o •H

G ft

G •H

O X! •H x: EH -P 0

Cd 0 o o 0 ft ft 0 •H 0d to -p ft 0 0 0 •H 1—1 HH G •H

CD ft •H ftO

G

O bJO > ft

CO EH CO > ft pq CO CO ft

m * 1

Mild

flame 3

Flame 4

Mild

explosion5

Explosion
- 27 -

The two upper curves shown on Figure l8 were obtained

for the straight-run fuel (55 cetane); the two lower curves

correspond to the same fuel doped with 1 percent of ethyl

nitrate. A small addition of a dope reduces the ignition

temperature from 230° to 226° C, and the ignition lag from

2 1/2 min to 1 3/4 min and the intensity of ignition from

explosion to normal flame

(f) Furnace Oil No. 2

General ignition characteristics of furnace oil No, 2

are substantially the same as Diesel fuels of 4l and 55

cetane number, i.e. single scage reaction with medium selfheating before ignition, which occurred at 233°C with mild

flame after 2 min 40 sec.

(g) Lubricating Oils

Lubricating oils generally represent a complex mixture

of different hydrocarbon components having different affinity

for oxygen. Because of this, the self-ignition of oil vapor

does not always proceed in a definite order and as consistently

as is the case with other combustible liquids. Oils having a

comparatively low ignition temperature such as U,S, Navy No,

2075 and 819O were ignited more or less in a definite and

reproducible manner. However, chlorinated paraffin oils and

motor lubricating oils used for internal combustion engines

usually ignited irregularly in the zone of minimum ignition

temi;e3:atures . Above this zone, ignition can be observed

regularly and below it the oil vapors are definitely not

ignitible. For chlorinated paraffin oil this doubtful zone

covers a range of about 10 degrees C but for motor oil it

amounts to about 35 degrees C,

The causes of the irregularity of ignition of these two

oils were not exactly established; however, some explanation

may be offered on the basis of the studies of the timetemperature curves and observation of smoke clouds through

the neck.

The time-temperature curves obtained in the 1000-ml

flask with motor lubricating oil are shown in Figure 19»

These show a rapid increase of temperature due to exothermic

reaction observed at temperatures far below the ignition

temperature. This increase in temperature was often accompanied by expulsion of smoke, which can be confused with the
- 28 -

"Puff” corresponding to ignition. The appearance of flame

can be observed through the mirror placed above the neck of

the flask only in cases where ignition occurred in the

upper layers of the flask. Observation through the periscope attached to the neck, however, often permits the

observer to see the illumination of clouds by flame in the

lower part of the flask.

Irregularities in ignition usually increase with the

charge. For charges of 0.05 or 0.10 ml per 1000 ml of air,

irregularities are considerably less than for charges over

0,20 ml, for which "double" or "triple" ignitions were

often observed at high temperatures and the time-temperature

curves showed fluctuation especially in the large flask

(Figure 20),

Observation under strong flashlight of the reacting

gasses through the neck covered by the pyrex glass indicated

that oil projected into the flask rapidly evaporates with

formation of dense clouds which are not properly mixed with

air due to the high viscosity of oil vapors. Ignition

usually occurred locally with a flash of flame and locally

the products of combustion become transparent. Other portions of the flask are filled with unburned dense clouds

slightly disturbed by the force of ignition. At higher

initial temperatures, ignition usually occurred with violent

audible flash (explosion), causing turbulence in unburned

clouds and repeated ignition. At minimum ignition temperatures the vapor mixture usually ignited with a very weak

flame, which is difficult to observe through dense clouds

even with the periscope. Moreover, nonuniform mixtures of

oil vapor and air at the region of lowest ignition temperature did not always produce favorable conditions for acceleration of reaction to ignition.

The temperature distribution in the 15,000 ml flask

during the nonignition reaction, shown in Figure 20 by the

three time-temperature curves, was observed at the same

time in the top, center and bottom regions of the flask.

Maximum variation of these temperatures was only about

5 degrees C.

(h) Benzene

Samples of pure benzene (C 5H5 ) were subjected to selfignition tests in 200 and 1000-ml flasks. The time-temperature curves obtained in the 1000-ml flask are shown in
- 29 -

Figure 21 » Appreciable self-heating of the reacting mixture was observed 50 degrees C below the self-ignition

temperature o At the initial temperature of 557° C, the

mixture was self-heated to 690° Co However, at the initial

temperature of 565°0, actual ignition was observed at

603°C or about 87 degrees C below the maximum temperature of

the preceding test* Here again evidence is presented of the

fact that for ignition the initial temperature from which

the exothermic reaction proceeds in a certain order is more

important than the instantaneous temperature of the reacting

mixture o It is interesting to note that the maximum temperatures for each reaction fall on a smooth curve. The shape of

the nonignition reaction time-temperature curve is not quite

that of a single-stage reaction.

In spite of a considerable and rapid increase of temperature during the nonignition reaction, ignition was indicated by a barely audible expulsion of dense smoke and mild

flame which was not always visible without the periscope.

(i) Toluene

The determination of the minimum self-ignition temperature of toluene was also difficult because of the very mild

form of ignition which was hardly visible through the dense

smoke. Moreover, rapid self-heating of the reacting mixture

was observed below the ignition region and an early expulsion

of smoke similar to that observed in previous cases (benzene,

lubricating oil, etc.) caused confusion in correctly judging

the time of actual ignition. Therefore, the illumination of

dense smoke even by dull flame, visible through the periscope,

was considered as evidence of ignition.

The two-stage pattern of the reaction of toluene is not

clearly shown on the time-temperature curves obtained in the

1000-ml apparatus. However, the "slow down" of the nonignition reaction is similar to that observed for benzene.

The two-stage reaction is more definitely indicated in the

12,000-ml apparatus, particularly at lower temperatures

which is gradually transformed into "slow down" reaction at

higher temperatures, as shown in Figure 22.

3.3 Pure Petroleum Fractions

Three groups of pure hydrocarbons, listed in tfebXe 6,

were supplied by the division of thermochemistry. The ignition characteristics of these hydrocarbons were determined

in the Bureau's 1000-ml apparatus.
- 30 -

COo

•H

•Po

ccJ (ha0I—I O

fn -P0P0PPPO

10O

•H-P

to •HP0

-PO0P0

SiQco

•0

•H•0d0

to0

•H

P>P0POPP0o

•H

to>. a.0I—I

rP0

EH *0Od0

CO r) o •H •H >

-P

w CO •HP0

-PO0P hX) 0 0

X3 Si odo

•H

—

—

-P

•H e » S r EH

QJO » M M* • f CO - - - ^

•H P H -H

•H

O o a

pq

nHO 0 W

Ci CO o a

Si o p p> 0 0 o

todo

•H

-PO0P

PlH

iH 1—1

UN no rH Un UN 1 1

OlO o Un UN o IN UN Un o 0 o no -d* CM (—1

iH no rH <H 0|

c!! •H|i

—1 1 1 O 1 1 CM CM CM

N

O

al

H CM 0

ft OlOO

O no 1 1 NO no CM 0 NO 00 0 (UN -1 CM r-i O O O ft d -d* -p CM CM CM CM CM CM CM CM CM

ft

d

•H W) 0 d S •H O 1 1 C>- -d" IN O ITN UN p -dO O o • • O 9 • 'N—>' • • OInO 00 ON O -d" NO N 1—1 no

to o |pO NO NO Un (N

H 00 to 00 NO

d rH rH CM CM

d 1 1 o o

•H •H p ft o o 0 0 p o no OO CM o CN CM p

ft NO no CM CM CM rH 1 1 ft 0 0 • • 9 1—1

no CM CM CM CM CM CM t—1

CM CM 0 0 a a p p o od

UN NO CN^ ON

O CM NO NO

N

—s 1 1 1 1 1 1 0 ft

CM NO d"

CM NO

O JN no CM -d- r—1 . rH . rH in Id in rH 1—1

ts

w in Id o CM NO Id Id un NO IN. (Os —1 H 1—1

NO (N o o O o o o o o o0d0N0

ft 0 o 0 d H 0 0 d 0 o d 0 d 0 0 0 0 X In 0 d 0 d d o d 0 o

-p 0 -p 0 0 0 0 pCj 1—1 d ft d o p ft o In 0 0 0 p 0 o 0 H ft

ft

K Id

d

Q

Q

O

O ft

d

d

d

d 1 dd 1 U.J o S WP0aowMO

CM CM

MD

O

CM CM H O

CM CM J- -dON on • o O CJN 00 ON

CO UN

CM CM • a CM CM

(N- 00

NO OO I—I I—I W K

00 o o 0d0

4-> d

rP

>> xi

p>0 0

tti -po a ;o H O P P

EH HH

The

time

temperature

curves

for

the

above

liquicis

are

given

in

figures

23

to

29,*

Key

for

Evidence

of

Ignition - 1

Mild

flame 2

Blue

flame 3

Flame 5

Explosion
- 31 -

(a) Normal Fractions of the Chain Type

The pattern of the time-temperature curves for nonignition reactions for fractions of the chain type are

substantially the same, with the exception of the curves,

for dodecane (Figo 2h) and cetane (Fig<. 26), the nonignition reaction of which has a "slow down" portion

similar to two-stage reaction^ The rate of the inducing

reaction preceding ignition gradually decreases and the

ignition lag increases with carbon content

o

The self-ignition temperature of liquids of the

chain type consistently diminished with an increasing

number of carbon atoms up to l6 along the curve

shown in Figure 27° The curve for fractions of larger

carbon content was not determined exactly, because of very

limited quantities of rare fractions o However, tests of

very small amounts of dotriacontane (C32 H56 ) indicate that

the self-ignition temperature is somewhere above 300° C.. In other words, the curve seemed to turn upward after

carbon number l6<, Additional tests will be necessary to

confirm the shape of this curve

o

(b) Normal Fractions of Ring Type

The time- temperature curves for the two-ring type

fractions tested have similar shapes for ignition and nonignition reactions (FigSo 28 and 29)° It is interesting

to note that in each case exothermic reactions initiated at

temperatures differing by only one degree C were started with

the first stage of reaction and proceeded further with the

second stage at substantially constant temperatureo After

about 12 or 15 min delay, rapid self-heating initiated,

which in one case accelerated to ignition and in another

case reached equilibrium at the nonignition state <> At higher

initial temperatures, ignition of both cyclohexane and methylocyclohexane occurred at the end of the second stage o This

two-stage pattern of reaction is identical with the pattern

obtained for motor and aviation gasolines at the same

region of initial temperatures as shown in Figure 30o

(c) Isomers

Trimethylbutane (Triptane)o The determination of the

minimum self-ignition temperature of this isomer involved

difficulties due to the very mild form of the evidence of
- 32 -

self-ignition. The shape of the time- temperature curves,

shown in Figure 3l, was substantially the same for the

ignition and nonignition reactions. Ignition in this case

could not be judged by the shape of the time-temperature

curve. The expulsion of gases or ’’puff” in the lower

temperature region was also very weak and did not provide

an indication of ignition. The intensity of visual evidence

of ignition changed with initial temperature. At high

temperatures, a bright orange flame was usually distinctly

visible through the mirror placed above the neck of the

reaction vessel. However, at lower temperatures approaching

421° C a blue-violet flame could be observed. The intensity

of this flame was gradually diminished to approach a cold

flame at 4l9°C and to chemiluminescent light at 4l4°C

which was distinctly visible through the periscope placed

above the open neck of the ignition flask.

Isoodtane" (*8,3,4 - Trimethylpentane ) . The ignition

characteristics of Isooctane obtained in the 1000-ml flask

were substantially the same as for Trimethylbutane . The

exothermic reaction became pronounced at about 150 degrees C

below the self-ignition temperature and the shapesof the

time-temperature curves were also similar for the ignition

and nonignition reactions. The expulsion of gases was so

weak that it could be noticed only by odor. Moreover, the

observed reproducibility of blue and cold flame or chemiluminescent light was very poor and was affected by deposits

on the flask wall, by direction of the charge stream, and

by relative humidity of air. Injection of the charge along

the side of the neck wall usually stimulated ignition at

slightly lower temperatures than injection directly to the

bottom of the flask. Ignition of Isooctane, indicated by

dull blue flame was usually observed under dark room conditions (through a periscope). Minimum self-ignition

temperatures obtained in this manner at different times

during three months varied between 408°C and 42 5° C. It is

likely that these variations were due to the combined effects

of different humidity conditions and barometric pressure

changes. In view of such variations, the more reproducible

value of minimum self-ignition temperature was selected as

420°C with corresponding ignition lag of 1 min 20 sec.

Similar difficulties were encountered when the test was

performed in the 200-and 12,000-ml flasks. The reproducibilities of self-ignition temperature were slightly better and

the band of uncertainty in the 200-ml flask was within 12

degrees C and in the 12,000-ml flask even as low as 4°C.
- 33 -

More or less regular ignition was obtained in the 200-ml

flask at 43l°C after 35 seconds and in the 12,000~ml flask

at 376°C after 1 min 45 sec. The factors affecting such

poor reproducibility of the ignition of Isooctane should be

studied more thoroughly.

3c 4 Reference Fuels

Primary and secondary reference fuels have been used

for the rating of various gasolines o The Primary Reference

Fuels consist of mixtures of Isooctane and n-Heptane in

various concentrations. The Secondary Reference Fuels are

composed of mixtures of three specific gasolines in the

following two groups? mixtures of gasoline with gasoline

Ci2 and gasoline 0^2 with F^.

According to the ASTM standard method, the performance

of a gasoline in the CFR (Cooperative Fuel Research Committee)

engine, operated under arbitrarily selected standard conditions,

is matched with the similar performance of an Isooctane-n- Heptane mixture. The percentage of Isooctane in this mixture is

then taken as the octane number of the fuel in being tested.

Four different ASTM methods (motor, research, aviation, and

supercharging) have been widely used for the rating of

gasolines suitable for different purposes and one method for

Diesel fuels. The octane rating of a particular gasoline may

vary appreciably with the ASTM test method selected; because

of this it is necessary to consider the test method when

comparing ratings of different fuels,

(a) Primary Reference Piiels

The ignition characteristics determined in the 1000-ml

flask of a number of Primary Reference Fuel mixtures are

shown in Figures 32, 33 and 34 , The shape of the timetemperature curves of these mixtures varies with the concentration.

It is interesting to note that the self-ignition

temperatures and ignition lags changed at a gradual rate for

mixtures varying in composition from 0 to 70^ Isooctane

(Fig, 35 )° The intensity of ignition also changed gradually

from explosion to mild flame. Moreover, audible expulsion of

gases ( "puff ") without ^flame was observed for mixtures containing 50 to 70% Isooctane at lower temperatures than in
- 34 -

cases where the "puff" was accompanied by flame (ignition).

The temperature curve, corresponding to the first appearance of the "puff", consistently rose with the Isooctane

concentration and at the same time the intensity of the "puff"

diminished

.

Study of the ignition characteristics of mixtures

containing from 0 to 70^ Isooctane indicates that the predominant effect of the n-Heptane component is gradually

diminished until its concentration becomes 70^, at which

point its effect reached "critical significance," For this

mixture, in the temperature range of 260 to 280° C, the effect

of n-Heptane seems still to predominate. However, at higher

temperatures the effect of the Isooctane component becomes

stronger and ignition in this region is defined by a blue

flame. Moreover, ignition over a considerable range of

temperatures is not well reproducible as was reported for

pure Isooctane, At the intermediate range of temperatures

from 294° C to 343 ° C, the mixture seems to have a peculiar

balance between the effects of both components, as a result

of which ignition of the mixture becomes erratic as it was

observed through the periscope only. Moreover, this instability also spreads to other mixtures of lower concentration

forming a so-called " secondary nonignition zone " as shown in

Figure 35»

The secondary nonignition zone was observed also by

Prettre (19) with pentane and hexane, by Townend (20) with

hexane, by Sortman^ and Beatty (11) with heptane and cetane,

and by many others. Nonignition zones were not observed

for these liquids in the present investigation; therefore,

this zone seems to be affected more by the apparatus and

test conditions than by the nature of the substance in

question.

(b) Secondary Reference Fuels

The first group of secondary reference fuels is composed

of mixtures of gasoline (39»6 octane number) and 0^2 (78,9

octane number). The self-ignition temperatures of these

mixtures varied in direct proportion to the concentration, as

is indicated by line II on Figure 36. The second group of

reference fuels is composed of mixtures of gasolines Cj2

( 78,9 octane number) and F^ (99»1 octane number). With these,

ignition temperatures varied substantially in the same manner

as for the Primary Reference Fuels, (Curve III). It was
„ 35 -

found that self-ignition temperatures of mixtures up to

35^ of fuel (Cp2

) varied linearly with the mixture

Ignition temperatures of mixtures of higher concentration

rapidly increased up to 50^ of fuel (C]_ 2 ) which

concentration the mixture becomes nonignitible from

305° C to 382° Co This apparent secondary nonignition zone

also spread to other mixtures of lower concentration, as

is shown by a dotted line in Figure 36 o The self-ignition

temperature of mixtures containing larger concentrations

of fuel (F3) varied in a linear fashion with concentration,

and ignition in this region was indicated by dull blue

flame c The expulsion of gases ("puff”) without flame was

observed at lower temperatures, as shoim by the dotted

line (between 50^ and 90% concentration)

o

The octane ratings of various mixtures of both groups

of Secondary Reference FUels were calculated from the

concentration of fuels Ac and Cp 2 und fuels Cp2 ^ud F30

The self-ignition temperatures of these mixtures were

plotted against their octane ratings together with the

Self-ignition temperatures of Primary Reference Fuels, as

shown in Figure 37<> Comparison of both self-ignition

temperature curves obtained for the Primary Reference

Fuels and Secondary Reference Fuels mixtures shows the

following important facts;

(1) Both curves indicate that the self-ignition

temperature is a discontinuous function of concentration

of reference mixtures or corresponding cooperative fuel

research committee ratings because of the secondary

nonignition zoneo

(2) Primary and Secondary Reference Fuel mixtures

of the same cooperative fuel research committee ratings

have different self-ignition temperature and ignition

characteristics with the exception of the two end fuels

( and F3

)

o

(3) The ignition characteristics of samples of two

other gasolines are also not well correlated with the

characteristics of corresponding mixtures of Primary and

Secondary Reference Fuels, as shown in Figure 37« For

example, the self-ignition temperatures of samples S^g

(87 octane) and Sp^(73 octane) are far away from the curve

of the Primary Reference Fuels, Only Spy lies within the

blue-flame zone of the rated mixture.
- 36 -

This poor correlation may be due to the fact that the

appearance or intensity of knock and ignition lag, affecting

the cooperative fuel research committee engine ratings, is

dependent not only on the molecular structure, stability and

other characteristics of fuel, but also on the operating

engine conditions, such as compression ratio, air manifold

and water jacket temperatures, speed and other factors which

affect different fuels in different ways.

Poor correlation of the cooperative fuel research

committee engine ratings with the ignition characteristics

determined in other laboratory test apparatus have also been

observed by other investigators (Jentzsch, Eckert, Zerbe and

Carhart )

.

The presence of a combustion accelerator or dope in

gasoline affects not only the octane rating but also the

ignition characteristics and shape of the time-temperature

curves. In the lower part of Figure 38, a typical timetemperature curve for fuel (C12 ) (78.9 octane; is shown.

The upper portion of the same chart contains time-temperature

curves of the same fuel (C12 ) with 1.25 ml tetra-ethyl lead

per gallon of gasoline. The shape of these curves changed

entirely and many additional stages of reaction developed

before the reaction finally accelerated to ignition.

3.5 High Ignition Temperature Liquids

A few liquids ignitible at high temperatures were

subjected to regular ignition tests in apparatus of different

capacities. The ignition characteristics of these liquids are

given in table 7 and the shapes of the time- temperature curves

are shown in Figures 39, ^0, and 4l. The first five liquids

given in table 7 have substantially the same shapes in timetemperature curves and comparatively short ignition lag.

These curves are similar to those for acetone shown in

Figure 39»

Both the ignition and nonignition reactions rapidly

accelerated during the few seconds after injection to ignition

or to maximum temperature. Methyl alcohol has a slightly

different shape in the time-temperature curves shown in

Figure 40, with the nonignition reaction lasting for several

minutes. Glycerine has an extremely violent exothermic

reaction even in the nonignitioniegion, as shown in Figure 4l.
Table

7.

Ignition

characteristics

of

high

ignition

temperature

liquids - 37 - *

o| /'“N

cdI ^ o o 1 o NO 1—1 bp cP| CM m J" 1 1 o no a cd o 1—1

CM 1 1 no

O o rI o e *

CM EH 1 1 • o| J" no 1 1 nO I—1 M o vO vO vD 1 1 00 [>- • J- -J- no 1 1 no no

CO

CJ| CD

O no

O no ITN

O rH

CO bO co| ^ r—1

Ph CM CM no no

cd C\j tH sz|| Ch a *3 ^ o O

O

O rH

O

«H o 1 o . o , • ' o ' EH rH CO iH 00 00 CT\

CD iH • o| o CO ON CTv NO CM CO

tg

M o 1 ph J" no no J- no

•H • CO CO

OI

bO CDI ''O CO 00 1 1 O 1 cd co| CM o CM 1 rH 1

r—1

•StO o O 1 1 rH 1 al o • • ^ o EH

CM • Of CJN lr\ CM 1 1 rH 1 M 0 1 rH O O 1 1 pf 1 • ITN Its J" 1 pI" 1 CO

rHo CD rH rH o -P o

r~\

O >» cd X!

cd XJ rH

a o

•H •H

O bP

u o o o o H CD

CD cd rH <D Ch cd

d

-P CD cdd •H

Cd cn o CD I—1

rH (h S O •H H H >> CD -p 4-> >> >» X! XJ O

CD CD X3 4-> +> >> o O -P 0 CD rH < <d s S cO

CO

cc3 SI Ooors ir\

I—I *
- 3 S -

(a) Acetone

Acetone ignites at the minimum temperature in an

unusual manner observable through the periscope. The

flame is very often either initiated by a small, red,

glowing center of carbonized deposit of acetone on the

flask wall and a blue-violet light spreads from this red

center throughout the whole gas mass or it is initiated

without this glowing center. The light usually appeared

without audible manifestation and continued to be visible

for about 20 seconds at ^91° C and about 15 seconds at

505° Co The intensity of this light gradually increased

from dull blue-violet at ^91^C up to blue-pink at 5l 5°C

and to a regular pink-violet flash with an audible explosion at higher temperatures. The initial blue-violet

light is similar to chemiluminescence, and when first

observed it was questioned whether this could be taken

as an indication of ignition. However, in consideration

of the very sharp increase in the time- temperature curve

(Fig, 39 ) at 491°C, this temperature was accepted as a

minimum self-ignition temperature.

(b) Acetic Acid

Ignition of acetic acid occurred so irregularly that

it was very difficult to define the lowest self-ignition

temperature. One explanation of such irrugularity may

result from the fact that it is possible that acetic acid

may exist in two interchangeable states, "dimer" and

"monomer", which can be expressed by the following relationship:

( CH3 C OOH ) 2 41^2 CH3 COOH

It is possible that uncontrolled variables cause

acetic acid to take either one or the other form, the

ignition temperatures of which may be different.

In contrast to acetone, the glowing center usually

was observed for only 15 seconds with definitely nonignition

reactions. Ignition of acetic acid, in spite of existing

irregularities, was defined by distinctly audible and

visible evidence, which usually occurred about 8 seconds

after injection of the charge. Ignition was initiated with

blue flame which, at the end of the ignition period, changed

to a pink color. Appearance of this color may be connected
- 39 -

with another phenomenon observed during ignition of acetic

acid in the spherical flask of 35-ml capacity. Due to the

very small size of the ignition chamber, the minimum selfignition temperature was found at 517° C, at which temperature

the flask walls were dull red. Normal ignition was indicated

by a blue flame; however, at a temperature slightly below

515° C a pink light was observed without audible evidence.

Study of this light through the periscope indicated that, at

the end of exothermic reaction (nonignition) or about 15 sec

after injection of the charge, clouds or fog formed in the

transparent gas mixture which was illuminated by the reflection

from the dull red walls of the ignition chamber. This phenomenon gave an erroneous impression of pink light or flame.

Ignition in the 1000-ml flask occurred at 491°C, at which

time the wall of the chamber was a very dull red color. The

formation of clouds or fog at the end of the reaction may also

be confused with the appearance of pink flame.

(c) Ethyl Alcohol

The shape of the time-temperature curve for ethyl alcohol

was similar to that of acetone (Fig. 39)* Due to the rapid

increase of temperature (and pressure) at the time of evaporation,

an audible expulsion of gases was observed before ignition.

The actual ignition at 391°C after seconds was accompanied

by blue flame with a second expulsion of gas.

Ethyl alcohol-water mixtures were also found to be

readily ignitible. The self-ignition temperature rapidly

increased from 391° C to as the water content of the

mixture approached 70^. Very weak flame was observed at

467° C even with 80^ water.

(d) Ethylene Glycol

Ethylene glycol was subjected to ignition tests in

connection with a determination of the fire hazard of antifreeze in aircraft installations. The ignition of pure

ethylene glycol in the 1000-ml flask was indicated at 398°C

by orange-blue flame and hardly audible expulsion of gases.

However, the same liquid with 3^ of antirusting ingredient

(triethanolamine phosphate) ignited at 395°C with violent

audible flash. Furthermore, ethylene glycol was tested in

solution with different percentages of water. It is interesting to report that ignition was observed at 460° C in a highly

dilute solution (90^ water )o However, ignition of solutions

with more than 40^ water was so weak that the flame could

be observed only through the periscope.
- ^-0 -

Two antifreezing liquids, R-19 and R-19d, were tested

in the same manner and the results indicate that these

liquids are highly ignitible. Both liquids are a petroleum

distillate (kerosene type). Liquid R-19 is a pure product

and R-19d is a mixture with a special ingredient for prevention of softening of rubber hose in engine installations.

The self-ignition temperature of R-19 is 211°C and ignition

lag 3 min ’fo sec, while R-19d ignites at 223° C after 1 min

30 sec. Ignition of both liquids occurred suddenly without

preliminary self-heating at only 3 degrees C above the

initial temperature and was indicated by violent audible

explosion; therefore, both liquids were considered high

fire hazards,

(e) Methyl Formate

Ignition of methyl formate was indicated regularly by

a mild explosion and rapid rise in temperature similar to

that for acetone (Fig, 39)

»

(f) Methyl Alcohol

The shape of the time- temperature curves for methyl

alcohol, shown in Figure VO, are slightly different from

those of the previously described liquids. The curves for

the ignition reaction are distinctly different from the

nonignition reaction and give supplemental evidence of a

very mild form of ignition, which is usually indicated by

a dull blue flame and weak expulsion of clear gas.

(g) Glycerine

Ignition of glycerine was indicated by a very violent

explosion accompanied by long flame and smoke expelled from

the neck of the ignition apparatus. A very rapid rise in

temperature of the gas mixture was recorded immediately after

injection of the charge for both ignition and nonignition

reactions, as shown in Figure ^1,

Progressive development of the different stages of the

ignition reaction was observed through the mirror and

periscope. Immediately after injection of the charge,

viscous glycerine droplets accumulated on the bottom surface

of the flask and rapidly evaporated with dense white clouds.

These clouds later (about 20 sec) became clear either due to

superheating or partial oxidation. The next stage usually

began about 5 sec later with the appearance of a small blue
- 4l

flame with a pink center. Due to rapid propagation of flame,

gases were expelled from the neck of the flask with considerable force.

The shapes of the time-temperature curves of a nonignition

reaction adjacent to the ignition region were studied simultaneously in different parts of the I5j000-ml flask. In spite

of the comparatively high rate of reaction, the temperature

distribution within the flask was not far from uniform, as

shown in Figure 42. The shapes of the time-temperature curves

are substantially the same in the top, central and bottom

portions of the flask. Continuous recording would probably

show still better uniformity in temperature distribution

through the whole cycle.

(h) Paint, Varnishes, Oil and Miscellaneous Materials

A number of combustible materials of commercial grade

were tested in the 1000-ml ignition apparatus. Ignition

characteristics of these materials are given in table 8.

(1) Black enamel. Noticeable decomposition of synthetic

automobile black enamel (601) was indicated at 270°C by the

appearance of smoke. At a temperature of about 445° C, carbonized residue of the charge was self-heated to the glow state.

However, self-ignition occurred at 478° C with audible expulsion of a large flame and smoke. As a result of ignition,

all the carbon residue was burned out and the flask surface

became clear.

The temperature curves for black enamel are shown in

Figure 43, and are typical of many materials of this class.

(2) Pine tar. Pine tar of commercial grade, due to

its low "fluidity" was preheated in boiling water before

injection by hypodermic syringe. The exothermic reaction

of a mixture of pine tar vapor with air also initiated far

below the ignition temperature. The shape of the timetemperature curves is substantially the same as for black

enamel. Ignition was indicated by flame and mild expulsion

of smoke. The flask surface after ignition was usually

covered by a brownish coating and tar residue cooked to a

hard carbon deposit removable only with a scraper. However,

the residue after ignition of pine oil was soft and easily

removable from the surface.
Table

8„

Ignition

characteristics

of

miscellaneous

liquids - k2 - *

CDO

CJ0

rO ph no no NO no no no IfN no

•H>

o|

01:^

O o- ph P^ CM no UN p|* CM

O

tU) 0| o H o O CM

OO CM rH ' rH pjaj

i-q •HO

O o OO

O

O

O o o O e m

EH o vO lr\ (ON (ON

O CON CM cxo o e O no rH C\J o IfN IfN pf pf" (ON Its M o 1-d- no ph pf ro no no no CM CM CO H 0 O 0

vO oI 1 0 1 1 d rH

H

d

TJ o 0 cS r—1

cd cd 0|

Cti •H *H iH tH •tH •rH •Hi

f-i -p o 1—1

CM 0 o o p;

C5 0 p 1 1 O

pp •H

xi 0 O o o I o o 0 0 d

-p s Td 0:1 TO > > P TO

Q

Q W)

s::! s f 1 -P s g

M o EH EH •H o o

CO o EH EH o o PO0 p o

:s o p

d

o3 •H 0 0 P p P H TO 0 p cd G •H 1 1 1—1 -p o3 TO 0 •H > 0 0 rH d a 0 I—1 •H a •(H 1—1

•rH

w P o p 0

Ph 0 o •H ''

—' d p‘ 0 d p 1—1 o •H o: 0 03 •H or) X! X P P p p P -P o 0 p w w 0 0 0 d • ’ 0 o •rH •rH d d d 0 0 0 0 w -p d d C7^ CT* a t 0,

cc!

d

dd

w

p

p

bOO

pW rH •H •H •rH 0 03 0 cd cd Cd d

pq Oi Oh PI o > PI P P EH *

(Da

aJ

Mild

explosion

Explosion

Violent

Explosion
Table 9 * The values of the self-lgnltlon temperature of

different liquids found in the IQQQ-ml ignition

apparatus of different thermal characteristics

Liquids

1

? Type of casing

, Metal ' Refractory ' Mirror surface

•

, 1C , 1£ . 1C

Acetic acid ' 501 ' 488 1 474

1 Acetone . 505

1 491

1 Ethyl alcohol ' 405 ' 391 ' 385

» Gasoline (motor) 1 24-9 ' 243 ' 238

1 • • Isooctane 420 • 409

f Toluene , J29 ' 519

1 Varsol ' 237 ' 235 ' 234

t Ethyl ether . 172 ' 170

T

1
- 44 -

(3) Linseed oil. Ignition characteristics of linseed

oil are similar to lubricating oils and appreciable selfheating of the vapor-air mixture was observed at temperatures far below the ignition temperature.

(4) Varnish and lacquer. The ignition characteristics

of varnish and lacquers are substantially the same, particularly in the nonignition region. Self-heating of the vaporair mixture was initiated far below the self-ignition

temperature. As the initial flask temperature approached

the ignition temperature, the reaction became almost violent.

A few degrees below self-ignition temperature, self-heating

of the mixture often is 20 or 25 degrees C above the initial

temperature. Ignition of these liquids, with the exception

of interior varnish and lacquer thinner, is very mild; both

the lacquer thinner and interior varnish ignited with an

audible explosion.

(5) Turpentine. The time- temperature curves for

turpentine are very similar to those for kerosene and even

had the same two-stage nonignition reaction with ignition

definitely in the first stage, as shown in Figure

3.6 Effect of Thermal Characteristics of the Apparatus

The effect of thermal characteristics of the ignition

apparatus described in section 2.1 on the observed selfignition temperature of combustible liquids is shown in

table Results of further study and analysis of this

effect are reserved for a future paper.

4, CONCLUSIONS

The following conclusions are presented as a result of

the work reported:

(1) Thermo- chemical processes occurring during the ignition

of combustible liquids can be presented by means of timetemperature curves together- with visual and audible evidence of ignition.

(2) The shape, size, and thermal properties of the ignition

vessel together with the details of the test procedure

have an important effect on the observed ignition

characteristics

.
- ^5 -

( 3 ) Ignition temperatures measured with the new apparatus

described are lower than those observed by most other

workers

.

(^) With the apparatus used in these tests, the experimental

results have proved highly reproducible.

( 5 ) Changes in the observed ignition temperatures of a

given liquid measured in different apparatus are

correlated with changes in size and thermal properties of these apparatus.
- 46 -

5. REFERENCES

(1) S. M. Estradere, Public Techn. Ministry of Air (Paris)

No. 49 (1934)

(2) H. L, Callendar, Eng. page l4? (192?)

(3) J. S. Lewis, Journal Ch. Soc. 1555 (192?) J 58? 2241 (1930)

(4) D. T. A, Townend and J. MacCormack, J.Po Insto, page 473 (1939)

(5) H. Moore, J. Soc. Ch. 36, 109 (1917); J.T.P.T., 6, 186

( 1920 )

(6) ASTM Standard Method, Proc. ASTM vol. 28, Part 1, 9±5 (1928),

vol. 30, Part 1, 776, 788 (1930)

(7) 0. R. Brown, "The Determination of the Ignition Temperature

of Solid ^fe.terials", The Catholic Univ. of Am. page 11 (1934)

(8) T. T. S. Sebastian and M. A. Mayers, Ind. Eng. Ch. 29, 1118

(1937)

(9) H, Holm, Z Ang. Ch. , 26, 273 (1913)

(10) H. Moore, J. Soc. Ch. , 36, 109 (1917) and J. I Pt, 6, 86

( 1920 )

(11) C. W, Sortman and H. A. Beatty, Ind. Eng. Ch. , 33, 357 (1941)

(12) H. Jentzsch, V.D.T. vol. 68, No. 11 and 44 (1924), vol. 69

No. 43 (1925)

(13) D. M. Newitt and D. T. A. Townend, Science of Petroleum,

vol. IV, page 2958 (1938)

(14) H. B. Dixon and H, F. Coward, J. Ch. Soc., 98, 5l4 (1909)

(15) H. B. Dixon, J. Ch. Soc. 1382 (1934)

(16) H. J. Masson and R. V. Wheeler, J. Ch. Soc. 121, 2079 (1922)

and 125, 1869 (1924)

(17) H. F. Coward, J. Ch. Soc. 1382 (1934)

(18) C. Moureu Chim. et Ind. 3 (1927). Comp, zend, l85, 1545 (1927)
- ^7 -

(19) Prettre, Science of Petroleum, vol. IV, page 2951 (1938)

(20) D. T. A. Townend, Proc. Royal Soc. l4l-A, 484 (1933),

143-A, 168 (1933), 146-A, 113 (1934)

(21) L. M. Pidgeon and D. C. Edgerton, J. Ch. S., 66l, 676 (1932)

(22) Z. V. D. Neuman, I, 70, 1071 (1926), NACA, Techn. Mem. 39

( 1926 )

(23) H. T. Tizard and D. R. Pye, Aut. Eng. 13, 136 (1923)

(24) A. Pignot, Comp. Rand., l82, 376 (1926)

(25) Mareck and Hahn, "Catalytic Oxidation of Organic Compounds",

p. 311

(26) H. L. Callendar, Eng. l83 (1927)

(27) N. J. Thompson, Ind. Eng. Ch. 21, 134 (1929)

(28) A. F. l^tson and R. E. Dufour, Underwriters' Laboratories,

Inc., Bui. of Research No. 43, 1950

FP 3199
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' '

w*'" - • ; ' \ \I1 .

*41.