Cetane number

Efficiency of diesel
                               
The cetane number of diesel oil may be defined as the percentage of cetane in a mixture of cetane and Alpha methyl naphathalene which will have the same ignition characteristics as the fuel under test, under the set of conditions

n-alkane>naphathalene>alkene>branched alkanes>aromatics.
Cetane number can be increased by adding ethyl nitrate,isoamyl nitrate,acetone etc.

Induction Lag
The internal between the start of fuel injection and its ignition is termed as ignition delay or induction lag.
Greater is the induction lag,higher is the diesel knock.

Anti knocking Agents

The Octane number of Internal combustion fuel can be raised by the addition of such extremely poisonous materials as tetraethyl lead(C₂H₅)₄Pb) and diethyl telluride

Knocking is the outcome of an early ignition of fuel (in gasoline engines) before the timed ignition spark occurs. It drastically increases the pressure inside the engine cylinder. which results in destructive effects to the engine

Adverse effect of using leaded petrol
Lead oxide vapours are formed on using leaded petrol as a fuel.These vapours are poisonous and may contaiminate the atmosphere. This can be stopped to some extent by adding ethylene dibromide to the leaded petrol.
Pb + Br--CH2---Br  --------- PbBr2 + CH2=CH2

Other anti-knocking agents which can be used are teriary butyl acetate,diethyl telluride,benzol,alcohol.
Factors reducing the Knock
Using high Octane fuel
Using Lower compression ratio
Designing suitable compression chamber

Pollution Reduce way

Lead is poisonous and is extremely toxic.Increasing use of automobile increase the harmful substances in the atmosphere.To improve the pollution problem following methods are used.

Many devices such as, Catalyst converters are used to oxidize the un-burnt hydrocarbons and carbon monoxide to carbon dioxide and to decompose nitrogen oxide into nitrogen and oxygen.

Tetraethyl lead in gasoline is replaced by certain aromatics and branched -chain hydrocarbons. The gasoline is free from tetraethyl lead is termed as leaded free gasoline.

Octane Number or Rating

Iso-Octane / 2,2,4 trimethyl pentane(Upper)  Octane no. 100 and  n-heptane (Lower) Octane no. O

 

 

 

 

 Octane number rating of a gasoline is the percentage of iso-octane in a mixture of iso-octane and n-heptane, which matches the fuel under test in knocking characteristics.
Greater the octane number , greater the anti-knocking property of fuel.

Short notes on Knocking

A four stroke ,spark ignition engine

 Firstly, the fuel vapours with air in carburetter is drawn into the cylinder during the induction part and this step is known as suction stroke.
then, the fuel air mixture is compressed it is known as compression stroke
The mixture is then ignited by an electric spark during combustion the hot gases are produced and increase the pressure and push the piston down is known as power stroke.
In last stroke, the piston expels the exhaust gases from cylinder, it is known as exhaust stroke.

Compression Ratio

     Volume of the gas at the end of the   suction  stroke     (V1)
    Volume of the gas at the end of the compression stroke(V2)

Greater the compression ratio more is the efficiency.
The rate of Oxidation becomes so great that the last portion of the fuel-air mixture gets ignited instantaneously,producing an explosive violence, known as knocking.

Straight chain paraffin>branched chain paraffins>Olefins>cyclo paraffin>naphathalene>Aromatics.

Thus,Olefins of the same carbon-chain length possess better anti-knocking properties than the corresponding paraffins and so on








 Knocking is sharp metallic sound similar to rattling of a hammer produced in internal combustion engines due to uneven of unsteady or uncontrolled combustion of air gasoline mixture.

  

Operation of four strokes engine

Refining of crude petrol

Liquid fuel

Diagram of solid and liquid fuel by vidhi and Shweta class note book

Solid fuel question R T U based pattern question and answer

Moving bed catalytic cracking

Fixed new catalytic cracking.

V

Cracking (gasoline)

Cracking is defined as "the decomposition of bigger hydrocarbon molecules into simpler low boiling hydrocarbons of lower molecular weight"

C₁₀ H₂₂-------Cracking----------- C₅H₁₂        +        C₅H₁₀

Decane                                      n-pentane          Pentene

B.Pt. 174^oC                            B.Pt. 36^oC

Thermal cracking 

Heavy oil ------------------High Temp------Olefins + Parafins

Higher Hydrocarbons                                Lower Hydrocarbons

Liquids Phase thermal cracking 

Heavy oil (gas Oil) -------475-53^oC (100Kg/Cm² Pressure) ------- Products----- Fractionating Column

then we get 50-60% gasoline.

Vapour phase thermal Cracking

Heavy oil ---------vaporised -----------600-650 ^oC (cracked 10-20Kg/ Cm² Pressure------readily vaporised------ Product

Petrol obtained from vapour phase cracking has better anti knocking properties but poor stability than petrol from liquid –phase cracking.

 

Fischer Tropsch Method

It is exothermic process.

Heavy oil ---------Cracking-------Gasoline

Water gas (CO+H₂) produced by passing steam over heated coke.

Mixed with Hydrogen.

Gas purified by passing through Fe₂O₃ ( to remove H₂S),then Fe₂O₃ +Na₂CO₃ ( to remove organic sulphur compounds).

Purified gas compressed to (5-25 atm.) and then led through a convertor, maintained at about 200-300^oC

Polymerization process of synthetic petrol

Labelled Diagram of Bergius Process

synthesis of Gasoline by Bergius process

The low ash coal is finely powdered and made into a paste with heavy oil and then a catalyst is incorporated .
Heated with hydrogen at 450 degree Celsius ,pressure 200-250 atm. for about 1.5 hours

2nH₂ + nC--------- C_nH_2n-- --Cracking----Low boiling liquids hydrocarbons

The gases led to condenser ,crude oil is obtained, which is then fractionated  to get Gasoline, Middle oil and heavy oil.