Department of Mechanical Engineering
Indian Institute of Technology New Delhi
II Semester -- 2017 – 2018
MCL 241 Energy systems and Technologies
TESTING OF FUELS : FLASH AND FIRE POINT
1. Introduction
The flash and fire points of a liquid fuel specimen are the indicators of its flammability.
In general, flash point is the lowest temperature of the test specimen, corrected to a
barometric pressure of 101.3 kPa, at which the application of an ignition source causes
the vapor of the test specimen to ignite momentarily and the flame to propagate across
the surface of the liquid under the specified conditions of test. It is important to realize
that the value of the flash point is not a physical constant but is the result of a flash
point test and is dependent on the apparatus and procedure used. Fire point may be
considered as the lowest temperature of the liquid at which vapor combustion and
burning commences. A fire point happens when an ignition source is applied and the
heat produced is self-sustaining, as it supplies enough vapors to combine with air and
burn even after the removal of the ignition source.
2. Flash and fire point in engine perspective
Gasoline has a flash point around -43⁰ C whereas diesel has flash points higher than
52⁰ C. Lower flash points are the indicators of good flammability and volatility.
Therefore, gasoline makes faster vapour formation than diesel and instantly catches
fire when spark, an external flame source, is provided. However, as its autoignition
temperature is high (in low compression ratio gasoline engine perspective), which is
in the order of 247-280⁰ C, it does not ignite prematurely due to the residual heat
generated during compression stroke and heat transfer from wall. On the contrary, the
higher flash point of diesel indicates poor vaporization tendencies and lesser tendency
to ignite subjected to external flame source. However, as the autoignition temperature
of diesel is low (in high compression ratio diesel engine perspective), which is in the
order of 210⁰ C, diesel autoignites easily with the residual heating during compression
stroke and heat transfer from wall without the need of an external flame source such
as spark plug. Poor vaporization tendency of diesel is dealt with in-cylinder swirl and
high pressure injection.
Vegetable oils have significantly high flash points which are in the order of diesel fuels
and higher. Hence their vaporization and mixing are a huge challenge for direct engine
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, applications. Therefore, vegetable oils are transesterified to produce fatty acid methyl
esters or biodiesel which has comparable flash point for direct compression ignited
diesel engine application. In the alcohol category, methanol has a flash point of around
12⁰ C and autoignition temperature of 470⁰ C. Similarly, ethanol has 16⁰ C flash point
and autoignition temperature around 365⁰ C indicating their close proximity to gasoline
fuel and potential alternative fuel application in spark ignited engines.
3. Penskey Martens Flash Point Apparatus Laboratory test
3.1 Objective: To determine the flash and fire point of a given sample using Pensky-
Martens flash point apparatus and determination of experimental repeatability.
3.2 Apparatus and consumables required:
a) A Pensky-Martens flash point apparatus.
b) Thermometer of suitable range.
c) Test samples.
3.3 Methodology and procedure
3.3.1 Preparation of samples
a) Samples should be in reasonably fluid state before testing. For asphalts and other
viscous materials, preheating should be done to ensure fluidity before testing.
b) Samples may be warmed with constant heating rate. However, under no
circumstances, should be heated above a temperature that lies 16⁰ C below the
expected flash point.
c) Samples containing dissolved water may be dehydrated with calcium chloride or
by filtering through a suitable filter paper. If the same is not done, its consequence
on experimental results and repeatability should be duly inferred.
3.3.2 Generalized procedure
a) Clean and dry all parts of the cup thoroughly.
b) Fill the cup with the sample to be tested to the level indicated by the filling mark.
c) Place the lid on the cup and set the latter on the stove.
d) Insert the thermometer and supply heat with the help of the rheostat switch to
ensure temperature rise rate not more than 5 to 6⁰ C per minute.
e) Turn the stirrer with 90 to 120 rpm in a downward direction.
f) Provide the test flame time to time and start nearly 17⁰ C below the expected flash
point of the sample with 0.5 to 1⁰ C gap.
g) Lower the test flame to the vapour space of the cup for 5s and allow it to be there
for 1s. After that move the test flame up as quickly as possible and shut down the
lid for vapour build up.
h) Do not stir the sample while providing the test flame.
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Indian Institute of Technology New Delhi
II Semester -- 2017 – 2018
MCL 241 Energy systems and Technologies
TESTING OF FUELS : FLASH AND FIRE POINT
1. Introduction
The flash and fire points of a liquid fuel specimen are the indicators of its flammability.
In general, flash point is the lowest temperature of the test specimen, corrected to a
barometric pressure of 101.3 kPa, at which the application of an ignition source causes
the vapor of the test specimen to ignite momentarily and the flame to propagate across
the surface of the liquid under the specified conditions of test. It is important to realize
that the value of the flash point is not a physical constant but is the result of a flash
point test and is dependent on the apparatus and procedure used. Fire point may be
considered as the lowest temperature of the liquid at which vapor combustion and
burning commences. A fire point happens when an ignition source is applied and the
heat produced is self-sustaining, as it supplies enough vapors to combine with air and
burn even after the removal of the ignition source.
2. Flash and fire point in engine perspective
Gasoline has a flash point around -43⁰ C whereas diesel has flash points higher than
52⁰ C. Lower flash points are the indicators of good flammability and volatility.
Therefore, gasoline makes faster vapour formation than diesel and instantly catches
fire when spark, an external flame source, is provided. However, as its autoignition
temperature is high (in low compression ratio gasoline engine perspective), which is
in the order of 247-280⁰ C, it does not ignite prematurely due to the residual heat
generated during compression stroke and heat transfer from wall. On the contrary, the
higher flash point of diesel indicates poor vaporization tendencies and lesser tendency
to ignite subjected to external flame source. However, as the autoignition temperature
of diesel is low (in high compression ratio diesel engine perspective), which is in the
order of 210⁰ C, diesel autoignites easily with the residual heating during compression
stroke and heat transfer from wall without the need of an external flame source such
as spark plug. Poor vaporization tendency of diesel is dealt with in-cylinder swirl and
high pressure injection.
Vegetable oils have significantly high flash points which are in the order of diesel fuels
and higher. Hence their vaporization and mixing are a huge challenge for direct engine
1|Page
, applications. Therefore, vegetable oils are transesterified to produce fatty acid methyl
esters or biodiesel which has comparable flash point for direct compression ignited
diesel engine application. In the alcohol category, methanol has a flash point of around
12⁰ C and autoignition temperature of 470⁰ C. Similarly, ethanol has 16⁰ C flash point
and autoignition temperature around 365⁰ C indicating their close proximity to gasoline
fuel and potential alternative fuel application in spark ignited engines.
3. Penskey Martens Flash Point Apparatus Laboratory test
3.1 Objective: To determine the flash and fire point of a given sample using Pensky-
Martens flash point apparatus and determination of experimental repeatability.
3.2 Apparatus and consumables required:
a) A Pensky-Martens flash point apparatus.
b) Thermometer of suitable range.
c) Test samples.
3.3 Methodology and procedure
3.3.1 Preparation of samples
a) Samples should be in reasonably fluid state before testing. For asphalts and other
viscous materials, preheating should be done to ensure fluidity before testing.
b) Samples may be warmed with constant heating rate. However, under no
circumstances, should be heated above a temperature that lies 16⁰ C below the
expected flash point.
c) Samples containing dissolved water may be dehydrated with calcium chloride or
by filtering through a suitable filter paper. If the same is not done, its consequence
on experimental results and repeatability should be duly inferred.
3.3.2 Generalized procedure
a) Clean and dry all parts of the cup thoroughly.
b) Fill the cup with the sample to be tested to the level indicated by the filling mark.
c) Place the lid on the cup and set the latter on the stove.
d) Insert the thermometer and supply heat with the help of the rheostat switch to
ensure temperature rise rate not more than 5 to 6⁰ C per minute.
e) Turn the stirrer with 90 to 120 rpm in a downward direction.
f) Provide the test flame time to time and start nearly 17⁰ C below the expected flash
point of the sample with 0.5 to 1⁰ C gap.
g) Lower the test flame to the vapour space of the cup for 5s and allow it to be there
for 1s. After that move the test flame up as quickly as possible and shut down the
lid for vapour build up.
h) Do not stir the sample while providing the test flame.
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