Flash Point by Abel’s Apparatus
Objective
To determine flash point of a combustible liquid (oil) by Abel’s flash point apparatus.
Introduction
The flash point is defined as the lowest temperature at which a liquid generates flammable
vapours which can be ignited in the air by a flame above its surface. The flash point is
determined experimentally by heating a vessel containing the tested liquid. A flame is
presented at regular intervals to the liquid surface. If a flash occurs in the vessel, it indicates
that the temperature of the tested liquid has reached (or exceeded) the flash point. The test
vessel can be open or close. The flash point is then measured respectively in "open-cup" or in
"closed-cup".
However, it should be noted that the flash point is not sufficient to assess the risk associated
with the use or the storage of a flammable liquid in conditions of liquid-vapour equilibrium.
Indeed, in a closed container, liquid-vapour equilibrium can be established. In this case, the
atmosphere in the container consists of a homogeneous mixture of vapour and air and, if the
vapour concentration is included in the flammability range, comprised between the lower
flammability limit (LFL) and the upper flammability limit (UFL), an explosive atmosphere is
present in the closed container. The bottom point of explosion (LPE) of a liquid is defined as
the temperature at which the concentration of vapours emitted by this fluid, in thermodynamic
liquid-vapour equilibrium conditions and when mixing with air at atmospheric pressure, is
equal to the lower flammability limit (LFL).
Because flash-point values are dependent on the apparatus and experimental method, it is often
difficult to determine the “best” or most probable value when more than one measured value
is available for a given compound. For safety purposes, many fire hazard data compilations
have adopted the policy of publishing the lowest reported value. This practice results in
unnecessary and costly process restrictions, ignores fuel design as an application of flash-point
data and disregards the significant relationships between the flash point and several other
properties. To aid researchers and engineers in flash-point data evaluation, we suggest several
guidelines for selecting the most probable flashpoint.
The flash point of a volatile material is the lowest temperature at which vapors of a fluid will
ignite. Measuring a flash point requires an ignition source. At the flash point, the vapor may
cease to burn when the ignition source is removed. Neither the flash point nor the fire point is
dependent on the temperature of the ignition source, which is much higher.
Theory
Every liquid has a vapor pressure, which is a function of that liquid's temperature. As the
temperature increases, the vapor pressure increases. As the vapor pressure increases, the
concentration of the vapor of the flammable liquid in the air increases. Hence, temperature
determines the concentration of the vapor of the flammable liquid in the air.
A particular concentration of vapor in the air is necessary to sustain combustion, and that
concentration is different for each flammable fluid. The flash point of a flammable liquid is the
lowest temperature at which there will be enough flammable vapour to ignite when an ignition
source is applied.
Gasoline (petrol) is a fuel for use in a spark-ignition engine. The fuel is mixed with air within
its flammable limits and heated above its flash point, then ignited by the spark plug. To ignite
the fuel must have a low flash point, but to avoid preignition caused by residual heat in a hot
combustion chamber, the fuel must have a high autoignition temperature.
Diesel fuel flash points vary between 52 and 96 °C (126 and 205 °F). Diesel is suitable for use
in a compression-ignition engine. Air is compressed until it has been heated above the
autoignition temperature of the
fuel, which is then injected as a
high-pressure spray, keeping
the fuel-air mix within
flammable limits. In a diesel-
fuelled engine, there is no
ignition source (such as the
spark plugs in a gasoline
engine). Consequently, diesel
fuel must have a high flash
point and a low autoignition
temperature.
Procedure
1) Fill the given sample in such a way that the sample level is exactly up to the mark in
the cup.
2) Fix the cup into the apparatus and cover with lid.
3) Insert thermometer in the thermometer holder given in the cup in such a manner that it
will not directly touch the lower bottom of the cup and the paddle stirrer inside the
cup.
4) Fill the water bath with the cold water.
5) Close the sliding shutter and light the standard flame.
6) Adjust the size of flame (4mm diameter) on the metal bead.
7) Stir the oil using paddle stirrer. Introduce the flame by opening the shutter and check
the appearance of the flash.
8) Now heat the apparatus and set the rate of temperature increase at the rate of 1 to 20C
per minute.
9) Verify the flash point of given sample at the interval of 30C rise in the temperature.
10) Discontinue the stirring the sample during the introduction of the test flame.
11) On observing a flash, stop the heating process and allow the temperature to decrease.
12) Check the occurrence of a flash at every 10 C drop in temperature at which the flash
is observed as the flash point of the sample.
Experimental Setup
References
1) www.aidic.it/cet/13/31/158.pdf
2) http://ggnindia.dronacharya.info/apsdept/downloads/labmanuals/chemistry/experimen
t6-18052012.pdf
3) http://dippr.byu.edu/publications/P117%202010%20Flash%20Point%20Evaluation%20an
d%20Experiment.pdf
4) http://rknec.edu/FirstYearContents2012/Applied%20Chemistry%20Practical%20Manual
%20Session%2012-13.pdf
