Structure of petroleum, Properties of fuels, Octane number requirement

1. CONVENTIONAL FUELS
.
 Structure of petroleum
 Refining processes
 Properties of fuels
 Fuels for SI engines
 Knock rating of SI engine fuels
 Octane number requirement
 Diesel fuels

2. CONVENTIONAL FUELS
.
 Containing carbon as main
constituent.
 Proper burning gives a large
amount of heat.
 Fuel + O2  products + heat.
 It may be primary or
secondary.
 It may solid, liquid and gas.

5. CONVENTIONAL FUELS
.
Distillation temperature
 Petrol 65 C- 220 C
 Kerosene or paraffin 220 C- 345C
 Heavy fuel oils 345 C -470 C

6. STRUCTURE OF PETROLEUM
.
 Complex mixtures of
hydrocarbons
Contains small amounts of
 Sulphur
 Oxygen
 Nitrogen
Impurities such as
 Water
 Sand

7. Depending upon the number of
carbon and hydrogen atoms .
1. Paraffin series CnH2n + 2
2. Olefin series CnH2n
3. Naphthene series CnH2n
4. Aromatic series CnH2n-6
5. NSO compounds

8. Paraffin series
.
 Paraffin hydrocarbons are
straight chain structure.
 Chemical formula C n H 2n+ 2 ,
 n= number of carbon atoms .
 Carbon atoms is fully utilized by
single bonds with hydrogen
atoms.
 Paraffin are saturated
compounds and very stable .
 Methane CH4- Decane C10H22
 Paraffin= Alkanes => CnH2n+2

10. Olefin series CnH2n
Unsaturated Alkanes
.
Naphthene series CnH2n
Aromatic series CnH2n-6
 Aromatic compounds are ring structured.
 Double bonds indicates that they are
unsaturated.
 But more stable than the other
unsaturated compounds.

11. .
Hydrocarbons Chemical
Formula
Structure saturation Stability
paraffin CnH2n+2 Chain Saturated stable
Olefin C2H2n Chain unsaturate
d
unstable
Naphthene C2H2n Ring Saturated stable
Aromatic CnH2n-6 Ring Highly uns Most unst
.

12. .
Characteristics of hydrocarbon due to
the molecular structure
Paraffin exhibit poor antiknock quality SI engine.
Antiknock quality improves with the increasing
number of carbon atoms and the compactness of
the molecular structure.
Aromatics offer the best resistance to knocking in SI
engines.
CI engines, the order is reversed.
Paraffin’s have the highest heating value and the
aromatics the least.
.

13. REFINING OF PETROLEUM
.
Step 1: separation of water (cottrell’s process)
 Extremely stable emulsion of oil and salt water.
Step2: removal of harmful sulphur compounds
 Treating oil with copper oxide which results copper
sulphide
Step3:fractional distillation
 Separated into gasoline, kerosene, fuel oil etc
 In first step natural gasoline is obtained
 Petroleum is vaporized at temperatures of 6000C
 Compounds with higher boiling points get
condensed at lower levels while those with lower
boiling points move up.

14. MAIN REFINERY PROCESSES
.
 Breaking complex hydrocarbon
molecules into simpler compounds.
 Thermal cracking and high
temperature and pressure
decomposed into smaller, lower
boiling point molecules.
 Catalytic cracking is relatively lower
pressure and temperature.
Due to catalysis, the naphthenes are
cracked to
 Olefins
 Paraffins
=> Olefins to isoparaffins needed for
gasoline.

15. MAIN REFINERY PROCESSES
.
 Hydrogenation addition of hydrogen atoms
to convert unstable compound to stable
ones.
 Polymerization is the process of converting
olefins, into heavier and stable compounds.
 Alkylation to produce a branched chain iso-
paraffin from olefin.
Example: isobutylene + iso-butane alkylation
iso-octane.
 Isomerization changes the position of the
atoms with molecule of a hydrocarbon
without changing its molecular formula.
Example
n-butane into Iso-butane for alkylation.
n- pentane and n-hexane into iso-paraffins to
improve knock rating.

16. MAIN REFINERY PROCESSES
.
 Cyclization joins together the ends of a
straight chain molecule to form a ring
compound of the naphthene family.
 Aromatization is similar to cyclization
 Reformation is used to convert the low
antiknock quality into gasoline of higher
octane rating.
 Blending is a process of obtaining
quality by mixing certain products in
some suitable proportion.

17. Reason of Knock
.
 Too Low Octane
 Bad Timing=> burn time is long
 Lean Air/Fuel Mixture
 Bad Knock Sensor
Rating of Fuels
 Octane number & Cetane
Number.
their antiknock characteristic.