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2004-28-0078
Significance Of Flash Point in Diesel Fuel Specification A.R.
Arankatle, V.G. Kenjale, tfi.K- Chaudharl and B. Bhanot
The Automotive Research Association of India, Pune
INTRODUCTION
Consequences of ambient air quality on human health is the major
driving force to implement stringent vehicular emission norms and
the related fuel quality specifications. In addition, engine
technology & after-treatment devices, vehicle maintenance
practices, driving pattern and road conditions also contribute to
ambient air quality and emissions of toxic hydrocarbons & gases
that affect human health. The diesel fuel quality in this regard is
of the major concern than gasoline as it constitutes about 38% of
the total consumption of petroleum products in automobiles in our
country. Diesel demand is thus higher by about SVi times than
gasoline whereas in other countries gasoline demand is higher than
diesel.
To improve fuel quality, the Govt, of India constituted a
committee of experts of National repute to formulate an Auto Fuel
Policy for the country together with a road map for its
implementation. Investment of about Rs. 10,000 crores has been made
in last decade for gasoline and diesel quality improvements. The
major milestones achieved in diesel quality improvements from 1994
are as follows:
Sulphur content has been reduced by 75% from 1% max. in 1996 to
0.25% max. in entire country from 1.1.2000. In addition, in the
four metro town sulphur content has been reduced by 95% to 0.05%
max.
To improve ignition performan9e of diesel engines and lower
pollutant emissions, Cetane number, has been increased from 45 to
48 from 1.4.2000.
Improvement have been done in the distillation specification by
1.4.2000 thereby improving performance, life of. diesel engines and
emission reduction
Irrespective of these improvements, many milestones have yet to
be achieved in fuel quality to further meet Euro-Ill and Euro-IV
emission norms which will be implemented in 10 major metropolitan
cities by year 2005 and by 2010 respectively. For the rest of the
country Euro-Ill norms will be implemented by year 2010. To achieve
these targets, the Indian standard IS: 1460-2000 on diesel fuel
needs to be stream-lined with the Euro / EPA fuel quality
specifications ancf follow World Wide Fuel Charter (WWFC)
guide-lines. Some of the major fuel characteristics that need to be
addressed
to achieve demands of vehicle manufactures to meet Euro-Hl and
Euro-IV norms are: Control on density and viscosity within
narrow
range Raise the Flash Point of Fuel with respect tc
tropical conditions in India Control aromatics and in particular
the Poly
Aromatic Hydrocarbons (PAH) in fuel. Bring down the sulphur
contents Mandate on Multi Fuel Additives to improve
lubricity, Cetane number, storage stability, engine cleanliness,
etc.
One of the fuel parameter that is of concern is Flash point of
diesel fuel which is 35C minimum as per IS: 1460-2000. To
demonstrate its importance and significance from safety, engine
performance and emission point of view in Indian context, The
Automotive Research Association of India, Pune (ARAI), did
experimental study. The present paper discusses on results,
observations and provides guidelines on concern subject to improve
fuel quality.
WORLD-WIDE SCENARIO OF FLASH POINT SPECIFICATIONS
By definition, Flash Point is the lowest temperature at which
vapours above liquid will ignite when exposed to a flame or any
other ignition source with sufficient energy. It is a measure of
both volatility and flammability. In case of diesel fuel it is set
by its distillation parameters.
Internationally, the petroleum products are classified for flash
point according to CCE and NFPA norms based on their volatility and
flammability nature (Table-1).
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The Flash point of Indian commercial diesel fuel is categorized
based on CCE classification and falls under Class B, which is
equivalent to Category I as per NFPA norms. The regulations in the
Federal Republic of Germany (FRG) follow DIN 51755 for flash point
of diesel and thus define its importance for storage and
transportation with respect to combustibility of liquid fuels. It
distinguishes between Danger Class Al (Flash point below 21 C),
which includes Spark Ignition Engine Fuels, Danger Class All (Flash
point 21 to 55C), to which kerosene belongs and Danger Class AIM
(Flash point over 55 to 100C) which includes diesel fuels.
Worldwide Fuel Charter and European countries specify the flash
point of 55C minimum. The Australian and New Zealand standard
limits are 61 C min. The Japan specify 45 or 50C depending upon the
climatic conditions. Other European and Asian countries also
specify higher flash points as shown in Table-2.
EXPERIMENTS ON DIFFERENT FLASH POINT DIESELS AND CO-RELATION
WITH OTHER IMPORTANT FUEL PARAMETERS
To signify the importance of flash point of diesel fuel
primarily from safety point of view and secondarily from the
associated emissions The Automotive Research Association of India,
Pune conducted experiments on diesel fuels having flash points from
40 to 80C. In the experimental work the fuel parameters that are
related with flash point were studied along with fuel chemistry,
air-fuel ratio and oxygen content. It also includes analysis of
fuel for density, viscosity, distillation recovery, pour point,
cold filter plugging point (CFPP) and lubricity - the parameters
that are specified in the Indian standard.
The diesel fuel is a complex mixture of hundreds of individual
compounds with carbon number between C10 to C22. These hydrocarbon
compounds makes difficult to separate out the naphtha, kerosene,
diesel and heavy oil fractions that makes the diesel fuel.
According to the literature, based on carbon numbers the naphtha,
kerosene, diesel and heavy oil fractions in the petroleum products
are classified as shown in Fig. 1. It can be seen that they overlap
each other.
Hence, in the ARAI experimental work, the hydrocarbons were
splitted into fractions based on carbon number as follows :
The High Resolution Gas Chromatograph (HRGC) was used to analyze
these fractions in fuel using Detailed Hydrocarbon Analysis (DHA)
software.
However, the Indian standard (13:1460-2000) is an exception and
recommends 35C minimum flash point value due to the economic yield
associated with fuel quality available in the country. Moreover,
Auto Fuel Policy document also states that the property has no
impact on engine performance because the auto-ignition temperature
of the fuel-air mixture is not affected by variations in flash
point.
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An experimental set up (Fig.2) was designed to determine the
effect of diesel fuel flash point on air to fuel vapour ratio and
oxygen content when the fuel
tank is filled with 10, 25, 50, lb % by volume of tank capacity
and heated from room temperature to 55C. The aim and objective of
this experiment was to ascertain the effect of variable ambient
temperature conditions on volatility and flammability of diesel
fuel having different flash point values.
The experimental results are summarized in Table-3 and Fig.3 to
5.
OBSERVATIONS AND COMMENTS ON TEST RESULTS
Density, viscosity, distillation recovery at 350C and 370C meet
the Indian specification for all flash point diesel fuel samples.
However, experimental results show following observations on diesel
fuels with different flash point values.
As per the literature, for combustion to take place at room
temperature and propagate the flame for hydrocarbon-air mixture,
the relative air to fuel ratio (actual fuel-air ratio divided by
stoichiometric or chemically correct fuel-air ratio) should lie
between 0.5 to 2.1. This ratio is known as "lambda value". In
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with low flash point are more prone to catch fire and propagate
the flame in presence of external ignition source when compared
with high flash point fuels (e.g. FP 68C & 80C).
the experiment, it is found that fuels having 43C and 48C flash
point are in the vicinity of lambda value 2.1 (rich end of the
scale) as fuel tank temperature is raised (Fig.3). It means that
fuels
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Based on these observations, 35C min. flash point diesel fuel
may be more dangerous to lead to tank explosion and propagate the
flame for the typical tropical conditions as seen in India.
Particularly this phenomenon occurs where two vehicles collide with
each other or when propeller-shaft fails and rams into fuel tank.
Many of such accidental cases are reported in past in newspapers
where occupants in the vehicle burned to char within no time to
escape out of the vehicle. Such accidental cases lacked in the
systematic investigation and analysis of flash point of fuel with
respect to air to fuel vapour ratio that exists in the fuel tank
and surrounding ambient temperature conditions to support our
observations.
The distillation recovery curve (Fig.4) shows that with increase
in flash point of diesel fuel, the Initial Boiling point (IBP) also
increases
from 137C to 201 C. According to available literature, increase
in IBP from 175C to 210C reduces NOx by 12%, HC by 40% and PM by
24% (see Table-4). The results are thus indicative that flash point
affects distillation curve and especially the IBP and in turn has
significant effect in meeting the emission norms.
The Fig.5 is indicative that fuel constituents also affect the
flash point and IBP of diesel fuel. Decrease in Naphtha fractions
and increase in diesel & kerosene fractions in diesel fuel
increases the flash point of fuel. As per Bosch Automotive
Handbook, less than 3% gasoline (in present discussions referred to
as Naphtha) in diesel fuel is sufficient to lower the flash point
to such an extent that ignition becomes possible at room
temperature. In reality, thus, naphtha fractions should be absent
in the diesel fuel. The presence of naphtha also increases the
static electricity associated with the fuel and can act as source
of ignition.
In neat diesel, the literature survey also shows that kerosene
(C9 to C15) content vary between
35 to 42% and balance should be diesel fractions.
CONCLUSIONS
Indian diesel fuel needs control on naphtha fractions (< C9)
to 5% max.
To reduce the reported accidental cases where occupants are
burnt to char due to explosion of fuel tank when vehicles collide
with each other it is essential to increase flash point of diesel
from 35C to 55C minimum irrespective of loss in economic yield from
safety point of view.
Raising of flash point also increases the IBP of fuel and
significantly reduces the CO, NOx and PM in vehicle exhaust to meet
the emission norms that auto industry has to meet in the
future.
Increase in flash point will reduce menace of adulteration
practices with abuse of solvent/spent naphtha, used oils, spent
solvents, low grade kerosene and diesels, etc. Thus, monitoring of
flash point is a better tool than filter paper test and density
measurement in the field.
With the world trend to move towards low sulphur fuels, there
are some concerns about conductivity. Low flash point diesel fuel
with higher naphtha fractions (light distillate) could become an
increasing concern.
Gas chromatography techniques if adapted in the specification
can help in adulteration studies.
Thus, the overall conclusion is that Indian specification on
Diesel fuel should be revised for the flash point value considering
its relative impact on safety and consequently on CO, NOx and PM
emissions from vehicle exhaust to be in line with International
specifications. Probably, to our knowledge the flash point may act
as a fuel parameter to identify adulteration practices along with
density measurement.