2. Use of Diesel Fuel
In Mobile Applications
โข Trucks
โข Locomotives
โข And now passenger cars
โข Ships
Stationary Applications
โข Power generation
โข Pump sets in agriculture
3. Refinery Capacity
Increased consumption of diesel fuel will increase
crude oil consumption because diesel oil density
is more.
Refinery energy consumption decreases slightly as
diesel production increases (according to one
estimate).
But to cater to increased diesel production,
existing facilities must be expanded and will
increase costs (so lower diesel cost benefit will
be lost).
But there could be a reduced crude oil usage with
increased diesel production.
4. Indian context
In India we have two types of diesel fuels:
1. High speed diesel (HSD) used in automotive
applications and
2. Light diesel oil (LDO) used in stationary
applications.
Diesel fuel properties are influenced by the source
of the crude oil and the method of refining.
5. Properties of diesel fuel
It is found that
Specific gravity, flash point, viscosity, sulfur
content, and carbon residue increase with
increase in service severity.
The cetane number (which measures the fuelโs
ignition quality) decreases with increase in
service severity. There is also a decrease in
volatility with increase in service severity.
Properties are, however, inter-related and it is
difficult to isolate the effect of any single variable
6. Properties of diesel fuel
(Continued)
It is found that the self-ignition temperature of the
normal paraffins decreases as the length of the
chain increases.
Since the cetane rating of the fuel is a measure of
the ignition characteristics of the fuel, it can be
concluded that the heavier members of the
paraffin family have higher cetane ratings.
In fact, cetane, C16H34 (hexadecane) is the primary
reference fuel in the cetane scale with an
arbitrary cetane rating of 100 while other normal
paraffins have cetane ratings that vary almost
linearly with the length of the chain.
7. Octane versus Cetane Rating
โข It is generally observed that there is an
inverse relationship of octane and cetane
ratings. Wilkes, in 1940, gave the following
relationship between the cetane number
[CN] and the motor octane number [MON]:
CN = 60 - 0.5*MON
8. Characteristics of Hydrocarbons
as Diesel Fuels
S.No. General
Formula
Hydrocarbon Characteristics
1. n-paraffins CnH2n+2
(Straight chain)
Low specific gravity &
high cetane number
2 Iso-paraffins CnH2n+2 (Branch
chain)
Same sp.gr. as 1 but
lower cetane no. & B.P.
3 Cyclo-
paraffins
CnH2n Higher sp.gr. than 1 but
lower cetane number
4 Benzenes CnH2n-6 Higher sp.gr & B.P. but
lower cetane no. than 1-3
5 Naphthalenes CnH2n-12 Highest sp.gr & B.P. &
lowest cetane no.
9. Important Characteristics of diesel
fuel
1. Knock characteristics-requires high cetane number
2. Starting characteristics-requires high volatility but will
give lower power
3. Smoking and Odor-high volatility will give better
mixing and lower smoke but also lower power
4. Corrosion and Wear-due to presence of sulfur and
ash
5. Ease of Handling-should have low pour point and
viscosity for ease of handling but high flash and fire
point for safety and fire hazard.
6. Density, heat of combustion and cleanliness.
10. Important Properties
1. Relative density or specific gravity
2. API gravity given by:
3. Flash point (usually above 130 deg.C)
4. Fire point (about 10-15 deg higher)
5. Sulfur content (must be very low)
6. Carbon residue (must be low-deposit problem)
7. Ash (must be low-abrasion problem)
5.131
60
60
5.141
โ=
F
Fatgravityspecific
gravityAPI
o
o
11. Important Properties (Distillation)
Low 50% point to prevent smoke and low
90% point to reduce carbon residue).
End point temperatures less than 370 deg.
C desirable
The 50% temperature is usually regarded as
a better index of the overall mixing
problem than the 90% temperature.
12.
13.
14.
15. Aniline Point
This is an approximate measure of the aromatic content of
a hydrocarbon fuel.
It is defined as the lowest temperature at which a fuel oil is
completely miscible with an equal volume of aniline.
Aniline is an aromatic compound and aromatics are more
miscible in aniline than are paraffins.
Hence, the lower the aniline point, the higher the aromatics
content in the fuel oil.
The higher the aromatics content, the lower the cetane
number of the fuel.
The aniline point can thus be used to indicate the
probable ignition behavior of a diesel fuel.
16. Diesel Index
The Diesel Index indicates the ignition quality of
the fuel. It is found to correlate, approximately, to
the cetane number of commercial fuels. It is
obtained by the following equation
Diesel Index and cetane number are usually about
50. Lower values will result in smoky exhaust
( ) ( )
100
60int FgravityAPIDegreesxFpoaniline
IndexDiesel
oo
=
17. Other Properties
1. Pour point โ mainly for low temperature
applications
2. Calorific value โ mainly for those fuels
which come under the category of fuel
oils and residual oils which have very
high molecular weight and viscosity
18. Diesel Fuel Additives
1. Cetane Improvers,
2. Detergents,
3. Diesel Smoke Suppressants,
4. Flow Improver Additives, and
5. Other Additives like Anti-rust and Anti-
corrosion.
19.
20. Cetane Improvers
These are compounds that readily decompose to give free
radicals and thus enhance the rate of chain initiation in
diesel combustion.
They promote fast oxidation of fuels and thus improve their
ignition characteristics.
Chemical compounds such as alkyl nitrates, ether nitrates,
dinitrates of polyethylene glycols and certain peroxides
are well known cetane improvers.
In general, however, in view of their low cost and ease of
handling, most commercial significance has been
attached to different primary alkyl nitrates.
