High octane number, Iso-octane (C8H18), CALORIFIC VALUE

1. Rating of Spark-
Ignition Engine Fuels
 Resistance to the knocking is
depended on the chemical
composition of the fuel.
Other parameters are
1. Air-fuel ratio
2. Ignition timing
3. Engine speed
4. Dilution
5. The shape of the combustion
chamber
6. compression ratio
7. Ambient conditions

2. Antiknock characteristics
 Two reference fuels for antiknock
characteristics.
 High octane number, and less octane
number.
Example
 Iso-octane (C8H18) is rich in the
octane. It is around 100 as the octane
number
 Normal Heptane (C7H16) has 0 as the
octane number

3. Octane number
A= is the amount of Tetra-
ethyl lead in ml/gal of fuel
 Is defined as the percentage by the
volume of the iso-octane in the mixture
of iso-Octane and normal heptane.
 Tetra ethyl lead to the iso-octane will
result in the fuel with a greater antiknock
property.
 Small change in the octane number
brings grater antiknock property.
Ex. ON increases from 92 to 93 result in the
greater antiknock property than the ON
increasing from the 30 to 31.
 Octane number above 100 and relatively
performance of the engine computed by

4. CALORIFIC VALUE
.
 "The total quantity of heat liberated, when
a unit mass (or volume) of the fuel is burnt
completely.“
 Calorie' is the amount of heat required to
raise the temperature of one gram of water
through one degree centigrade (15-16°c).
 "Kilocalorie" is equal to 1,000 calories. It
may be defined as 'the quantity of heat
required to raise the temperature of one
kilogram of water through one degree
centigrade. 1 kcal = 1,000 calorie.

5. HCV and LCV
• ..
 Gross or higher calorific value (HCV) is "the total
amount of heat produced, when unit
mass/volume of the fuel has been burnt
completely and the products of combustion have
been cooled to room temperature"(i.E., 15°C or
60°F ).
 Net or lower calorific value (LCV) is "the net heat
produced, when unit mass /volume of the fuel is
burnt completely and the products are permitted
to escape".
 Net calorific value= gross calorific value - latent
heat of condensation of water vapour produced =
gcv - mass of hydrogen per unit weight of the fuel
burnt x 9 x latent heat of condensation of water
vapour.

6. Theoretical calculation of calorific value using Dulongs formula
.
 HCV =1/100[8,080 C + 34,500 (H – O/8)+ 2,240 S] kcal/kg
 LCV = [ HCV - 9H/100 x 587] kcal/kg = [HCV - 0.09 H x 587]
kcal/kg
Flame Temperature
 The maximum temperature to which an
object can be heated by the flame.
 Temperature of flame mainly depends upon
calorific value and other properties.
Theoretical flame temperature = (heat of combustion+ sensible heat in fuel and air)
Total quantity of the combustion product)X (their mean specific heats)

7. Bomb Calorimeter of solid
and liquid fuel
.
 If we equate the heat given out by
the fuel to the heat taken up by the
calorimeter and the water, the
calorific value of a fuel can be
determined.

8. Construction and working principle of Bomb calorimeter
.
 It consist of a stainless steel bomb in
which combustion of fuel is made to take
place.
 A known mass of the given fuel is taken
inside the steel bomb which is connected
with two electrodes.
 The bomb lid is tightly screwed and filled
with O2 up to 25 atm.
 The water is stirred with the help of
mechanical stirrer and the initial temp is
recorded.
 The electrodes are then connected to 6
volt battery and the circuit is completed.
 Uniform stirring of water is continued and
the maximum temp is recorded.

9. Calculation of Bomb Calorimeter
.
Heat liberated by the fuel = heat taken up by the
calorimeter
 X * C = (W +w) (t2 - t1 )
 C= (W +w) (t2 - t1 )/ X
 H.C. V = (W +w) (t2 - t1 )/ X
X= mass in gm of the fuel sample
W= mass of water in calorimeter
w= water equivalent of calorimeter, stirrer,
thermometer, bomb etc in gm
t1= initial temp of water in oc
t2= final temp of water in oc
C= calorific value of the fuel

10. Boy’s Calorimeter for determination of calorific value of gases
& volatile Liquid Fuels
.

11. Description of Boy’s or Junkers
.
Description of the apparatus
1. Bunsen Burner: special type of Burner clamped
at the bottom & pushed up in chamber during
the carrying out combustion.
2. Gasometer: to measure the volume of gas
burning per unit time and also pressure and
temperature of the gas before burning can be
read.
3. Pressure governor: It can control the supply of
quantity of gas at give pressure.
4. Gas Calorimeter/ Combustion chamber:
It is a vertical cylinder, which is surrounded by
annular space for heating water and interchange
coils. The entire is covered by an outer jacket in
order to reduce the heat loss by radiation and
convection.

12. Procedure of Determination
• Gaseous fuel burnt (V)
• At given T and p in period of time
(t).
• Quantity of water (w kg) passing
• Rise in temperature (T2 -T1 )
• Steam condensed (in kg)
 Install the equipment on a flat rigid platform near
an uninterrupted continuous water source of ½”
size and a drain pipe.
 Connect the gas source to the pressure regulator,
gas flow meter and the burner respectively in
series.
 Insert the thermometer to measure water inlet
and outlet temperatures.
 Start the water flow through the calorimeter at a
study constant flow rate.
 Start the gas flow slowly and light the burner out
side the calorimeter.
 Then the reading are taken simultaneously.

13. Calculation
.
• Volume of gas burn at STP in certain time (t)= V
• Mass of the cooling water used in time t = W
• Temperature of inlet water = T1,
• Temperature of outlet water = T2
• Mass of steam condensed in time t
in graduated cylinder = m
• Higher calorific value of fuel = L ,
• Specific heat of water = S
• Heat absorbed by circulating water = W(T2 -T1 )×specific heat of water (s) heat
produced by combustion of fuel = VL

14. Ultimate analysis
.
Carbon and hydrogen
 About 1-2 g of accurately weighed coal
sample is burnt in a current of oxygen
in a combustion apparatus.
 C and H of the coal are converted into
CO2 and H2O respectively.
 The gaseous products of combustion
are absorbed respectively in KOH and
CaCl2 tubes of known weights.
 The increase in weights of these are
then determined.