1.Knock Rating 2.Volatility 3.Calorific Value 4.Gum Content 5.Sulphur Content 6.Aromatic Content

2. Properties of fuels
 1.Knock Rating
 2.Volatility
 3.Calorific Value
 4.Gum Content
 5.Sulphur Content
 6.Aromatic Content

3. 1.Knock Rating
 If the temperature of the unburned mixture exceeds
the self - ignition temperature and remains at or above
this temperature during a period of time during the
ignition lag , spontaneous ignition or auto ignition
occurs at various 'pin point' locations .This
phenomenon is called as knocking.
 One of the best qualities of fuel is that it should be
used with higher compression ratio without knocking
because high compression ratio provides high engine
efficiency and lower fuel consumption.

4. Knock rating
 The fuel should have high anti-knock value to make
use of the higher compression ratios.

5. 2.Volatility
 Volatility indicates the tendency of a fuel to change
from liquid to vapour form.
 A high volatility is desirable from the point of view of
starting ability and good distribution

6. Volatility affects the following engine/vehicle
conditions:(In SI Engines or Petrol Engines):-
1.Less volatility means difficult starting and
stumbling during warm-up . Excessive volatility
would result vapour lock .
2.Less volatility would cause the droplets of liquid
fuel to break down the oil film on the cylinder wall ,
causing scuffing or scoring.
3.Less volatility would also result in uneven
distribution of fuel to various cylinders.

7. 3.Calorific Value
 The calorific value of a fuel is the thermal energy
released per unit quantity of the fuel when the fuel is
burned completely and the products of combustion
are cooled back to the initial temperature of
combustible mixture.
 The fuel should have a high calorific value
 Gasoline has approximately the calorific value about
38-48 MJ/kg.

8. 4.Gum Content
 A good fuel should have the minimum gum content.
 All petroleum products oxidise in the presence of air .
Gum is formed by the polymerization or oxidation
reaction of certain unsaturated hydrocarbons.

9. 5.Sulphur Content
 All hydrocarbon's contain free sulphur and Hydrogen
sulphide.
 The presence of sulphur in the fuel is highly
undesirable because of the formation of sulphur
dioxide in presence of water vapour will have corrosive
action on engine parts
 A high sulphur content is obviously undesirable.

10. 6.Aromatic Content
 Aromatics ,though ,are high knock -rating
hydrocarbons , yet have a corrosive action on rubber of
the fuel system and have high freezing point .
 Therefore, their proportion in the engine fuel should
not exceed beyond a certain limit.

11. 7. Viscosity
 It is the measure of the resistance to flow.
 it affects the atomisation of fuel and operation of high
pressure fuel pump.
 greater the number of carbon atoms ,greater is the
viscosity of the fuel oil .
 the same the number of carbon atoms, a fuel will have
higher viscosity with lower hydrogen content.
 Viscosity should be high enough to permit bulk flow
and high enough to carry out lubrication.

12. 8. Cloud Point
 The temperature below which ,the wax content of the
oil separates out in the form of solid is known as cloud
point.
 This should be as small as possible so that this
difficulty will not be experienced even in cold winter.

13. 9.Anti-Knock Quality
 A best quality of a fuel used in S.I engine is ,it should
be used with higher compression ratio without
knocking because high compression ratio provide
higher compression ratio and low fuel consumption .
 . The anti-knock characteristic of the gasoline is
mostly dependent on the chemical composition and
molecular structure of the fuel.

14. 10.Specific gravity
 For Petrol It lies in the range 0.7 to .78 .
 In diesel, the value of the specific gravity is between
0.82 and 0.92.
 The specific gravity of the fuel should be higher for
efficient combustion
 The specific gravity of fuel can be determined by
dividing the density of the fuel to the density of water.

15. DESIRABLE PROPERTIES OF GOOD
IC ENGINE FUELS:
A Good I.C engine fuel must possess the following properties:-
1. It must have high energy density(KJ/kg).
2.It should be easy to handle.
3.It must possess good combustion qualities.
4.It must have high thermal stability.
5.It must have low deposit forming density.
6.It should be easy to handle and store.
7.It should be free from hazard.
8.It should not have chemical reactions with engine components , through which it flows.
9.It should easily mix with air and evaporate as quickly as possible.
10.Products of combustion should not be corrosive to engine parts.
11.It must possess low toxicity.
12.Its effect on air-pollution should be the minimum.
13.It should be economically available in very large quantities.
The basic requirement of I.C engine fuel is , the combustion should be fast
with maximum amount of heat release without forming any deposits and should not have
destructive effects on the engine parts and atmospheric air by exhaust gases.

16. REQUIREMENTS OF FUELS FOR S.I
ENGINES:-
Gasoline is the major fuel used for S.I engine . It is a mixture of various
hydrocarbons such as paraffin , olefins , napthene and aromatics . The
composition depends upon the nature of crude available and method of
refining used.
A good fuel used in S.I engine must fulfil the following properties:-
1. It must evaporate quickly when injected by carburettor in the current of
air.
2. It should not pre-ignite.
3.It should be easy to handle.
4.It should be easily available at reasonable cost.
5.It should burn clean and should not deposit the residue.
6.Its exhaust should not have any corrosion effect on the engine parts.
7.It must have high Calorific value.
8.It must be knock resistant.

17. Flash Point
 The temperature at which the vapours of oil flash
when subjected to a flame is known as the flash point .
If container is closed ,it is called closed flash point and
if open it is called open flash point.

18. Fire Point
 It is the temperature at which the oil , if once lit with
flame ,will burn steadily at least for 5 seconds
 The flash point and fire points indicate the
temperature below which , oil can be handled without
any danger of fire.

19. References
 Automobile Engineering ,Vol.2 Kirpal Singh
 Internal Combustion Engines ,V.Ganesan
 Internal combustion Engine ,Mathur & Sharma
 I.C Engines,Domkundwar