Page 313 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

from the ground. is received. This mineral oil is found in nearby deposits. It is called natural gas because it is used
in the same form in which it is found, without any adulteration or alteration. It is a mixture of hydrocarbon gas
and vapor. Methane (CH ) is compressed and used in vehicles, which is stored in the cylinder by increasing the
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pressure (2000 to 2200 N/cm²). CNG contains 80 to 90% methane, 4.5% ethane, 0.7 to 0.8% butane, 1.7 to 2%
and many other gases in small quantities. The main quantity is methane.
CNG had a slow start but after the Supreme Court issued guidelines, it became famous as a fuel for motor
vehicles. In India, it has been used only in big cities. Because in Delhi, air pollution was increasing day by day due
to the smoke coming out of petrol and diesel vehicles, which was polluting the environment and many diseases
were increasing. But after using CNG in vehicles, the level of air pollution has continuously decreased. There are
many CNG stations in Delhi which are connected to each other through pipelines. This gas is sent by tanks to
the remaining gas stations. The government is making plans to use CNG in many other cities of India, because
pollution due to diesel and petrol smoke is increasing day by day in big cities.
Petrol/gasoline Diesel LPG CNG

Chemical formula CXH2.0X CXH2.0X C3H8 CH4
Octane/cetane 85-95 octane no 45-55 cetain no 94-112 octane no 120-130 octane no
number
Method of ignition Spark ignition Compression Spark ignition Spark ignition
ignition

Molar mass (kg/mol) 109 204 0.4 17.3
Stoichemetric (A/F) 14.7 14.6 17 17.2
s mass

Stoichemetric 1.42 1.46 1.88 1.25
mixture density (kg/
m³)
L.H.V. (MJ/kg) 43.5 42.7 42-47 47.5
L.H.V. of 2.85 2.75 2.61 2.62
stoichemetric
mixture (MJ/kg)
Combustion Energy 42.7 36 42 24.6
(MJ/m³)
Flammability limit in 1.4-7.6 1-6 Approx. 4.8 4.3-15.2
air (vol% in air)
Flame propagation 0.5 _ 2.2-4.7 0.41
speed (m/s)
Adiabatic Flame 2150 2054 1967 1890
Temp. (°C)
Auto-ignition Temp. 258 316 410-580 540
(°C)

Wobbe Index (MJ/ _ _ 39 51-58
m³)

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CITS : Automotive - Mechanic Diesel - Lesson 88 - 93