The document discusses different units used to measure heat energy including calories, kilocalories, and British thermal units. It defines higher calorific value and lower calorific value when measuring a fuel's energy content. Various methods for determining calorific values from experimental data are also presented, along with examples of calculating gross calorific value and net calorific value. Octane number and cetane number are introduced as measures of gasoline and diesel fuels' resistance to knocking in spark-ignition and compression-ignition engines respectively.

1. .

2. 1. Calorie:
It is the amount of heat required to increase the temperature
of 1 gram or water through one degree centigrade.
2. Kilocalorie:
This is the unit of heat in metric system, and is defined as “the
quantity of heat required to raise the temperature of one
kilogram of water through one degree centigrade”. 1 k.cal =
1000 cal
3. British thermal unit (B.Th.U.):
This is the unit of heat in English system. It is defined as “the
quantity of heat required to increase the temperature of one
pound of water through one degree Fahrenheit

3. 4. Centigrade heat unit (C.H.U.): It is the quantity of heat required
to raise the temperature of one pound of water through one degree
centigrade.
Inter conversion of various units:
1 k.cal = 1000 cal = 3.968 B.T.U. = 2.2 C.H.U.
Units of calorific value:
The calorific value is generally, expressed in “calorie / gram (cal/g)”
or “kilocalorie / kg (kcal/kg)” or “British thermal unit / lb (B.T.U/lb)”
in case of solid or liquid fuels.
In case of gaseous fuels the units used are “kilocalorie / cubic metre
(kcal/m3)”
or
“B.T.U/ft3

4.  HIGHER CALORIFIC VALUE (HCV)
Higher calorific value of a fuel portion is defined as the amount of
heat evolved when a unit weight (or volume in the case of gaseous
fuels) of the fuel is completely burnt and the products of
combustion cooled to the normal conditions (with water vapor
condensed as a result). The heat contained in the water vapor must
be recovered in the condensation process. it is also called Gross
Calorific Value (GCV), and Higher Heating Value (HHV)
 LOWER CALORIFIC VALUE (LCV)
Lower calorific value of a fuel portion is defined as the amount of
heat evolved when a unit weight (or volume in the case of gaseous
fuels) of the fuel is completely burnt and water vapor leaves with
the combustion products without being condensed. It is also called
Net Calorific Value (NCV), and Lower Heating Value (LHV).

5. Determination of Calorific Value
Mass of the fuel = M Kg.
Initial temp of the water = t₁ C⁰
Final temp of the water = t₂ C⁰
Change in temp =∆ t = (t₂ – t₁) C⁰
Specific heat of water = S
Water equivalent of calorimeter = W Kg.
GCV = ( W x S x ∆t )/M J/Kg
or
GCV = (W + w) x S x ∆t)/M J /Kg
NCV = GCV – 0.09 x %H2 x 587 cal/g

6. Numerical on Calorific Value
Example 1: Calculate calorific value coal samples from the following data.
Mass of the coal = 1g.
Water equivalent of calorimeter = 2 Kg.
Specific heat of water = 4.187 J/Kg/c.
Rise of temperature = 4.80C.
Example2: A coal sample with 93% carbon, 5% of Hydrogen and 2% Ash is
subjected to combustion in a bomb calorimeter. Calculate GCV and NCV
Given that;
Mass of the coal sample = 0.95g
Mass of water in copper calorimeter = 2000g.
Water equivalent wt of calorimeter = 700g.
Rise in temp = 2.8 0C Latent heat of = 587 cal/g.
Specific heat of water = 1 cal/g/0C

7. Numerical on Calorific Value
Example3: When 0.84g of coal was burnt completely in Bomb calorimeter the increase
in temp of 2655 grams of water was 1.850C if the water equivalent calorimeter is
156g Calculate GCV.
Example4: Calculate GCV and NCV of a fuel from the following data.
Mass of fuel=0.75g,
W=350g t =3.020C,
Mass of water = 1150, %
H2=2.8
Example5: Calculate calorific value of a fuel sample of a coal form the following data.
Mass of the coal is 0.6g.
Water equivalent wt of calorimeter is 2200g.
Specific value 4.187 Kg/KJ/C
rise in temperature = 6.520C.
Example7: Calculate GCV and NCV of a fuel from the following data.
Mass of fuel =0.83g, W=3500g. , W = 385 g, t1 =29.20C, t2 = 26.50C,
% H2 = 0.7 and S = 4.2 kj/kg/c

8. Knocking
In an internal combustion engine, a mixture of gasoline vapour and air is
used as a fuel. After the initiation of the combustion reaction, by spark in
the cylinder, the flame should spread rapidly and smoothly through the
gaseous mixture, thereby the expanding gas drives the piston down the
cylinder. The ratio of the gaseous volume in the cylinder at the end of the
suction-stoke to the volume at the end of compression-stroke of the
piston, is known as the ‘compression ratio’. The efficiency of an internal
combustion engine increases with the increase in compression ratio, which
is dependent on the nature of the constituents present in the gasoline
used. In certain circumstances (due to the presence of some constituents
in the gasoline used), 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”. The knocking results in loss of
efficiently.

9. Antiknocking Agents
Following are the substances added to petrol in order to
prevent knocking in I.C. Engines.
 Tetra Ethyl led (TEL)
Pb(CH2CH3)4, was put into petrol, particles of lead and lead oxide
PbO are formed on combustion. This helps the petrol to burn more
slowly and smoothly, preventing knocking.
 TML Tetra Methyl led.
 MTBE Methyl Tertiary Butyl Ether

10. Octane number
 The octane rating of fuel is defined as percentage by volume of iso-
octane in the mixture of iso-octane and normal heptane, which
exactly matches the intensity of fuel in standard engine under a set
of standard operating conditions. It is the ability of resistance of a
fuel to knocking in comparison to Iso-octane, which has octane
number 100 and has high anti-knock quality. Better anti-knock
quality allows us to compress the air-fuel mixture to a larger extent
before it gets ignited by itself. Every fuel is rated between 0 to 100.
(0 is for n-heptane).
 Higher octane number fuels lets you use higher compression ratio in
the engine, which can provide better performance.
 This was all for spark-ignition engine, in which mixture of fuel and
air is compressed. If you use a lower octane no. fuel in your engine,
then there are chances of engine knocking in your engine, which in
severe cases, damage your engine.

11. Cetane number
 The cetane rating of fuel is defined as percentage by volume of normal
cetane in the mixture of normal cetane and α -methyl napthalene which
has same ignition characteristics(ignition delay) as test fuel when
combustion is carried out in standard engine under specified operating
condition. only air is compressed and fuel is injected into the cylinder. So
you can go on compressing as much as you want. But, when you inject the
fuel, it must burn satisfactorily efficiently in the available time.
 This means that this time we need a fuel which burns with minimum delay
when injected into the cylinder.
 Now what is this delay?
 When the fuel enters the cylinder, it needs to be atomized, then mixed
with air then it’s temperature must be raised, then the chemical reaction
of combustion takes it’s time. All these times added, is the ignition delay.
 So Cetane number is a rating that indicates how low it the ignition delay of
the fuel as compared to that of Cetane.