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DIESEL FUEL Middle Distillate Fuel

Diesel fuel

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Page 1: Diesel fuel

DIESEL FUEL

Middle Distillate Fuel

Page 2: Diesel fuel

Use of Diesel FuelIn Mobile Applications

• Trucks• Locomotives• And now passenger cars• Ships

Stationary Applications• Power generation• Pump sets in agriculture

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Refinery CapacityIncreased 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.

Page 4: Diesel fuel

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.

Page 5: Diesel fuel

Properties of diesel fuelIt 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 fuel’s 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

Page 6: Diesel fuel

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.

Page 7: Diesel fuel

Octane versus Cetane Rating

• 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

Page 8: Diesel fuel

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.

Page 9: Diesel fuel

Important Characteristics of diesel fuel

1. Knock characteristics-requires high cetane number2. Starting characteristics-requires high volatility but will

give lower power3. Smoking and Odor-high volatility will give better

mixing and lower smoke but also lower power4. 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.

Page 10: Diesel fuel

Important Properties1. Relative density or specific gravity2. 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

6060

5.141

FFatgravityspecific

gravityAPIo

o

Page 11: Diesel fuel

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.

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Aniline PointThis 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.

Page 16: Diesel fuel

Diesel IndexThe 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 FgravityAPIDegreesxFpoanilineIndexDieseloo

Page 17: Diesel fuel

Other Properties

1. Pour point – mainly for low temperature applications

2. Calorific value – mainly for those fuels which come under the category of fuel oils and residual oils which have very high molecular weight and viscosity

Page 18: Diesel fuel

Diesel Fuel Additives

1. Cetane Improvers,2. Detergents,3. Diesel Smoke Suppressants,4. Flow Improver Additives, and5. Other Additives like Anti-rust and Anti-

corrosion.

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Cetane ImproversThese 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.

Page 21: Diesel fuel