Prof. Dr. F.
NAWAZ KHAN, VIT UNIVERSITY
Prof. Dr. F. NAWAZ KHAN
Prof. Dr. F. NAWAZ KHAN
Fuels
o Major ingredient carbon, when combusted large amount of heat.
o During the process of combustion of a fuel,
carbon, hydrogen etc. will combine with oxygen to liberate heat at a rapid
rate.
Fuel + O2 Products + heat exothermic
Prof. Dr. F. NAWAZ KHAN
used for various domestic and industrial purposes.
The term combustion refers to the exothermal
oxidation of a fuel, by air or oxygen occurring at a
sufficiently rapid rate to produce a high
temperature, usually with the appearance of a flame.
As most of the fuels contain carbon or carbon and
hydrogen, the combustion involves the oxidation
of carbon to carbon dioxide and hydrogen to
water. Sulphur, if present, is oxidised to
sulphur dioxide while the mineral matter forms
the ash. Prof. Dr. F. NAWAZ KHAN
Prof. Dr. F. NAWAZ KHAN
Fuels Classification
Chemical Fuels
Secondary fuels
Primary fuels Or
Or Artificial fuels
Natural fuels
Solid fuels Solid fuels
Wood, coal Coke Liquid fuels
Liquid fuels charcoal Petrol, diesel,
Petroleum kerosene
Crude oil
Gaseous fuels
Gaseous fuels Bio gas,
Natural gas Water gas,
Producer gas
Prof. Dr. F. NAWAZ KHAN
Characteristics of a good fuel
o High calorific value
o Low cost
o Low moisture content
o Low non-combustible matter
o Moderate ignition temperature
o Moderate velocity of combustion
o Controllable combustion
o Should not undergo spontaneous combustion
o Pollution free combustion products
o Should burn in air easily without much smoke
o Easy to transport
o Storage should be cheap and easy
Prof. Dr. F. NAWAZ KHAN
Property Solid fuels Liquid fuels Gaseous fuels
combustion Slow combustion Quick combustion Combustion is rapid
not easy to control it it can be controlled burning can be
controlled
transport Transportation Transportation is easy Transportation is easy
is difficult through pipelines and through pipelines and
containers containers
storage Storage is safe Risk involved High risk involved in
in storage storage
Calorific Calorific value Calorific value Calorific value
value is relatively low is relatively high is higher that liquid
fuels
Engines Cannot be used in Can be used in IC Can be used in IC
used Internal Combustion engines engines but to a lesser
engines extent
products Ash and smoke are No ash is produced but No ash and no smoke
produced during the some flue gases are are produced
process of combustion produced
Prof. Dr. F. NAWAZ KHAN
Prof. Dr. F. NAWAZ KHAN
oUnits of heat are
Calories, k.calories
B.Th.U (British thermal unit) or C.H.U
(Centrigrade heat unit)
1 B.Th.U = 252 cal =
0.252 k.Cal
1 k.Cal = 3.968
B.Th.U = 2.2 C.H.U
Prof. Dr. F. NAWAZ KHAN
Prof. Dr. F. NAWAZ KHAN
Calorific value of a fuel
Higher or Gross Calorific Value (HCV or GCV):
“ The amount of heat liberated when unit weight or volume of
a fuel is completely burnt and the products of combustion
are cooled to room temperature”
Prof. Dr. F. NAWAZ KHAN
Low or Net Calorific Value (LCV or NCV):
“ The amount of heat liberated when unit weight or
volume of a fuel is completely burnt and the products
of combustion are allowed to escape”
Prof. Dr. F. NAWAZ KHAN
The calorific value of a fuel depends upon the nature of the
fuel and the relative proportions of the elements present,
increasing with increasing amounts of hydrogen. Moisture
if present, considerably reduces the calorific value of a fuel.
The calorific value may be theoretically calculated from the
chemical composition of the fuel.
If both hydrogen and oxygen are present, it may be assumed that
all the oxygen are already combined with 1/8 of its weight of
hydrogen to form water. This fraction is then deducted from the
hydrogen content of the fuel in the calculation. Thus for a fuel
containing carbon, hydrogen, oxygen and sulphur, the calorific
value of the fuel is given by DULONG FORMULA
Prof. Dr. F. NAWAZ KHAN
Prof. Dr. F. NAWAZ KHAN
Determination of Calorific Value
Prof. Dr. F. NAWAZ KHAN
Calculation
m = mass of fuel pellet (g)
W = mass of water in the calorimeter (g)
w = water equivalent of calorimeter, stirrer and thermometer (g)
t1 = initial temperature of calorimeter.
t2 = final temperature of calorimeter.
Heat liberated by the fuel = mL
Heat absorbed by water and apparatus = (W+w)(t2-t1)
Prof. Dr. F. NAWAZ KHAN
Prof. Dr. F. NAWAZ KHAN
1. 0.72 gram of a fuel containing 80% carbon, when burnt in a
bomb calorimeter, increased the temperature of water from 27.3o
to 29.1oC. If the calorimeter contains 250 grams of water and its
water equivalents is 150 grams, calculate the HCV of the fuel. Give
your answer in kJ/kg.
Solution. Here x = 0.72 g ,
W = 250g,
t1 = 27.3oC,
t2 = 29.1oC.
HCV of fuel (L) = (W + w) (t2 – t1) kcal/kg
x
= [(250 + 150) × (29.1-27.3)] kcal/kg
0.72
= 1,000 × 4.2 kJ/g = 4,200 kJ/kg
Prof. Dr. F. NAWAZ KHAN
2. On burning 0.83g of a solid fuel in a bomb calorimeter, the
temperature of 3,500g of water increased from 26.5oC to 29.2oC.
Water equivalent of calorimeter and latent heat of steam are
385.0g of and 587.0 cal/g respectively. If the fuel contains 0.7%
hydrogen, calculate its gross and net calorific value.
Solution. Here wt. of fuel (x) = 0.83 g of ; wt of water (W) = 3,500
g; water equivalent of calorimeter (w) = 385 g; (t2 - t) = (29.2 oC -
26.5 oC) = 2.7oC ; percentage of hydrogen (H) = 0.7% ; latent
heat of steam = 587 cal/g
Gross calorific value = (W + w) (t1 - t2) cal/g
x
= (3,500 +385) × 2.7 = 12,638 cal/g
0.83
NCV = [GCV – 0.09 H × 587]
= (12,63 8– 0.09 × 0.7 × 587) cal/g
= (12,638 – 37) cal/g = 12,601 cal/g
Prof. Dr. F. NAWAZ KHAN
Corrections
Fuse wire correction.
Heat liberated during sparking should be subtracted from heat
liberated.
Acid correction. Fuels containing Sulphur and Nitrogen if oxidized,
the heats of formation of H2SO4 and HNO3 should be subtracted (as
the acid formations are exothermic reactions).
Prof. Dr. F. NAWAZ KHAN
Cooling correction.
As the temperature rises above room temperature, the loss of heat does occur due to
radiation, and the highest temperature recorded will be slightly less than that
obtained. Therefore a correction is necessary to get the correct rise in the temperature
The rate of cooling of the calorimeter from maximum temperature to room
temperature is noted.
From this rate of cooling (i.e., dt°/min)
and the actual time taken for cooling (t min)
then
correction (dt × t) is called cooling correction and is added to the t2, t1 term.
Prof. Dr. F. NAWAZ KHAN
GCV = (W + w) (t1 - t2) –[acid+fuse corrections]
x
= (550+2,200) × 2.42 – [50+10] cal
0.92g
= 7,168.5 cal/g.
NCV = [GCV – 0.09 H × latent heat steam]
= (7168.5 – 0.09 × 6 × 580) cal/g
= 6855.3 cal/g
Prof. Dr. F. NAWAZ KHAN
Prof. Dr. F. NAWAZ KHAN
Prof. Dr. F. NAWAZ KHAN
Prof. Dr. F. NAWAZ KHAN
Heat liberated by the combustion of fuel = VL
Heat absorbed by the circulating water = W (T2-T1)
HCV or GCV = L = W (T2-T1)/V
Let the mass of water condensed per m3 gas = m/V
Then LHS per m3 of gas = m x 587/V
Therefore LCV or NCV = L – mx587/V kcal/m3
Prof. Dr. F. NAWAZ KHAN
1. The following data were obtained in a body’s gas calorimeter experiment:
Volume of the gas used = 0.1 m3 at STP
Wt. Of water heated = 25kg
Temperature of inlet water = 20oC
Temperature of outlet water = 33oC
Wt. of steam condensed = 0.025 kg
Calculate the higher and lower calorific value per m3 at STP. Take the heat liberated in
condensing vapour cooling the condensed as 580 kcal/kg.
Solution: Here V = 0.1 m3; W = 25 kg; T1 = 20oC; T2 = 33 oC; m = 0.025kg
HCV = L= W (T2-T1)/V
= 25(33-20)/0.1 = 3,250 kcal/m3
LCV = HCV- (m/V) × 580
= 3,250 kcal/m3–[(0.025kg/0.1m3) × 580 kcal/kg
= 3,250 kcal/m3 – 145kcal/m3 = 3105 kcal/m3.
Prof. Dr. F. NAWAZ KHAN
Dulong’s Formula
The approximate calorific value of a fuel can be determined by knowing the
amount of constituents present:
Gross or higher calorific value (HCV) from elemental constituents of a fuel.
H = 34500 kcal/kg; C = 8080 kcal/kg; S = 2240 kcal/kg
Oxygen present in the fuel is assumed to be present as water
(fixed hydrogen).
Available Hydrogen = Total hydrogen - Fixed hydrogen
= Total hydrogen - 1/8 mass of oxygen in fuel.
Dulongs formula for calorific value from the chemical composition of fuel
is,
Prof. Dr. F. NAWAZ KHAN
Prof. Dr. F. NAWAZ KHAN
