Diesel fuel is produced from various sources like petroleum, biomass, and natural gas. It is characterized by properties like cetane number, viscosity, density, sulfur content, etc. Diesel fuel specifications include limits for flash point, viscosity, carbon residue, cetane number, distillation characteristics, corrosion properties, and sulfur and water content. Ignition quality is expressed by terms like cetane number, self-ignition temperature, and aniline point. Diesel fuel must burn cleanly and completely while providing sufficient lubrication and ease of ignition.

2. CONTENTS
What is Diesel
Types of Diesel fuel
Important factors or Properties
Ignition quality of fuel expressed by different terms
Characteristics of Diesel fuel
Diesel fuel Specifications

3. DIESEL FUEL
Diesel fuel in general is any liquid fuel specifically designed for use
in diesel engines, whose fuel ignition takes place, without any spark, as a
result of compression of the inlet air mixture and then injection of fuel.
Diesel fuel is a mixture of hydrocarbons obtained by distillation of
crude oil. The important properties which are used to characterize diesel
fuel include cetane number (or cetane index), fuel volatility, density,
viscosity, cold behavior, and sulfur content.

4. Types of Diesel fuels
Petroleum diesel
Synthetic diesel
Biodiesel
Hydrogenated oils and fats
DME(Dimethyl ether)
Diesel fuel is produced from various sources, the most common
being petroleum. Other sources include biomass, animal fat, biogas,
natural gas, and coal liquefaction.

5. Important factors which influence the choice of fuel:
1) Viscosity of fuel
2) Flash and fire point of fuel
3) Water and sediment present
4) Pour point of fuel
5) Ash content of fuel
6) Sulphur content of fuel
7) Boiling range of fuel ie characteristics of fuel
8) Specific gravity of fuel
9) Carbon residue that will be formed
10) Corrosive and acidity
11) Ignition quality of fuel

6. Fuel viscosity
Viscosity is simply a measure of resistance to flow. Viscosity decreases as the
temperature increases.
Low viscosity fuel produces a fine, atomized mist of fuel which improves its mix
with incoming air to encourage a complete combustion for better power and lower
emissions.
High viscosity fuel tends to result in a heavier mist of fuel which can result in hard
starting and white smoke issues.
Flash point
The flash point is a safety-related characteristic and defines the minimum
temperature at ambient pressure at which a vapor-air mixture can be ignited in a
closed space

7. Water and sediment content in fuel can also cause rusting and damage to fuel
system components. Diesel fuel with a high water content can cause iron oxide
particles to form inside the fuel tank. This causes internal rusting of fuel lines,
pumps and injection components when the engine is not in use.
Pour point of diesel fuel is important in engines which are operate to under
extreme cold conditions. High pour point may interfere with starting a cold
engine. Pour point is important in handling fuel between Storage and engine.
Pour point of fuel should be 5.5 to 8.5°C units below the minimum anticipated
temperature. Maximum pour point for diesel is -15.5ºC.
Water and sediment present
Pour point of fuel

8. Ash content of fuel
Ash content in the fuel represents non combustible material, some of which is
abrasive in nature. Ash content in diesel fuel builds up deposits. As such it should
not exceed 0.12 percent by weight for the heaviest fuel and 0.01 percent for light
fuel used in high speed engines.
Sulphur content of fuel
The sulfur content of diesel fuel has recently drawn a great deal of attention because
of increased wear on the following components:
•Pistons
•Rings
•Valves
•Cylinders
This increased wear is promoted by the corrosive effects of hydrogen sulfide in the
fuel combined with sulfur dioxide (or sulfur trioxide), formed during the combustion
process. The wear is less serious under constant loads and during high–temperature
operation.

9. Boiling range of fuel
Boiling range of fuel represents the temperature range corresponding to beginning and
termination of vapourization of fuel and also the quantum of fuel that will vapourize at
different temperatures. Volatility ie vapourization capacity of a fuel is measured by 90%
distillation temperature. This is the temperature at which 90% of the fuel sample has
distilled off. Lower this temperature higher is the volatility.
Specific gravity of fuel
The specific gravity of the fuel has no direct bearing upon the burning qualities of fuel.
However, the above indicated limitations of viscosity more or less confine the limits of
specific gravity to about 0.83 to 0.90 for airless injection engines, down to 0.94 for air
injection engines

10. Carbon residue
Carbon residue is the carbon left after evaporation and burning off of volatile matter
from a sample of oil by heating. It indicates the tendency of the fuel to form carbon
deposits on engine parts. A maximum carbon residue of 0.10 percent is allowable.
Corrosiveness
The fuel must not be corrosive, must not contain free acids. Otherwise it may
damages the metal surfaces with which it comes in contact in storage and in the
engine

11. Ignition quality of fuel/Cetane rating
Cetane rating is a measure of the ignition quality of a fuel. The
ease at which diesel fuel ignites, and the manner in which it burns,
influences engine starting and combustion roughness. Pure cetane is
a colourless liquid hydrocarbon with excellent ignition qualities and
is rated at 100. The higher the cetane rating, the shorter the lag time
between the time the fuel enters the combustion chamber and the
time it begins to burn. A good quality diesel fuel with a high
cetane rating has a lag time of approximately 0.001 seconds.
Cetane rating requirements depend on the engine size, design,
load and atmospheric conditions. For example, engines operating at
higher altitudes or lower temperature demand a higher cetane fuel
to start and operate correctly. Typical cetane ratings for No. 2
diesel would be 46 – 48. No. 1 diesel is usually about 51 – 53.

12. Ignition quality of fuel is expressed by different terms:
Cetane number of fuel
Self ignition temperature of fuel
Critical compression ratio
Diesel index
Aniline point

13. Cetane number
Cetane number (cetane rating) is an indicator of the combustion speed of diesel
fuel and compression needed for ignition. It plays a similar role for diesel as octane
rating does for gasoline. The CN is an important factor in determining the quality of diesel
fuel, but not the only one; other measurements of diesel fuel's quality include (but are not
limited to) energy content, density, lubricity, cold-flow properties and sulphur content.
Self ignition temperature of fuel
The autoignition temperature is the lowest temperature in which it spontaneously
ignites in a normal atmosphere without an external source of ignition, such as a flame or
spark. This temperature is required to supply the activation energy needed for combustion.

14. Critical compression ratio
Diesel engines normally have compression ratios between 14:1 to 25:1. Higher
compression ratios mean a higher thermal efficiency, which means that theoretically
maximum efficiency can be achieved at an infinite compression ratio
Diesel index is an indication of the ignition quality of a diesel fuel. It can be determined
by calculation from the specific gravity and the aniline point of the sample
Diesel index = (Aniline point * °API) / 100.
Diesel index
The aniline point is called the "aniline point temperature," which is the lowest temperature
at which equal volumes of aniline (C6H5NH2) and the oil form a single phase. The aniline
point (AP) correlates roughly with the amount and type of aromatic hydrocarbons in an oil
sample. The aniline point (AP) correlates roughly with the amount and type of aromatic
hydrocarbons in an oil sample. A low AP is indicative of higher aromatics, while a high AP
is indicative of lower aromatics content.
Aniline point

15.  Must be clean, water, grit and all foreign matter must be removed by
filtering or by a similar process
Should be non corrosive, or at least without an corrosive agents as free
acids
Should have sufficient lubricating property so that there will not be undue
wear of the fuel pump and the injector parts
Must ignite easily for easy starting and smooth running of the engine
Must burn progressively and smoothly which will avoid excessive cylinder
pressures and a rough running engine
Must burn completely and leave no carbon or other deposits and practically
no ash in the engine cylinder. High viscosity fuels may cause smoky
exhaust.
Characteristics of Diesel fuel

16. Must have low carbon residue. High carbon residue may produce deposits of
carbon and a gummy substance on pistons and cylinder liners. Deposits may
cause sticking of piston rings and valve stems.
Must have suitable volatility characteristics. Low volatility reduces maximum
power output, increases fuel consumption and gives smoky exhaust. Such a
fuel also makes starting of a cold engine more difficult.
Characteristics of Diesel fuel

17. Characteristics Requirements
A B C
1. Flash point(Pensky martens closed), min 55° 55° 55°
2. Kinematic viscosity centistokes at 37.8°C, max 2 to 7.5 2 to 7.5 15.7 max.
3. Carbon residue (Ramsbottom-percent b weight) 0.2 0.2 1.5
4. Cetane number, min 45 40 --
5. Diesel index 48 43 --
6. Distillation, percent recovery at 360°C, min 90 90 --
7. Copper strip corrosion for 3 hours at 100°C No.1 No.1 No.2
8. Water content percent by volume, max 0.05 0.05 0.25
9. Sediment percent by weight, max 0.05 0.05 0.10
10. Ash, percent by weight, max 0.01 0.01 0.02
11. Acidity (total) mg of KOH/g, max 0.5 0.5 --
12. Sulphur, total percent b weight (max) 1.0 1.0 0.8
13. Pour point, max 6°C 6°C --
DIESEL FUELS BIS (ISI) SPECIFICATIONS 1460-1974