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Cars mostly make
use of Spark Ignition type Internal Combustion engine.
How the engine
produces power :
The engine is the
powerhouse of the car. It converts the heat produced by
burning fuel into mechanical energy to turn the wheels.
The fuel, normally a mixture of petrol and air, is burnt
in closed cylinders inside the engine hence the term 'internal
combustion'.
Petrol and air are
mixed in the carburetor and drawn into a combustion chamber
at the top of each cylinder. Pistons, inside the cylinders,
compress the mixture, which is then ignited by a spark plug.
As the mixture burns it expands forcing the piston down
on its power stroke.
The up and down movement
of the pistons is transformed into rotary movement of the
crankshaft, which in turn transmits power to the wheels
through the clutch, gearbox and final drive. Connecting
rods link the pistons to the crankshaft.
A camshaft, driven
by the crankshaft, controls inlet and exhaust valves at
the top of each cylinder.
Initial impetus to
set the engine in motion comes from the starter motor. This
is connected to a starter ring, which is fitted around the
edge of the flywheel, a heavy disc bolted to the end of
the crankshaft.
The starter motor,
which is geared to the flywheel, is operated electrically
and turns the flywheel and crankshaft, which starts the
pistons and connecting rods moving up and down.
The flywheel smoothes
out the power impulses of the pistons and gives a relatively
smooth rotation of the crankshaft.
Because of the heat
produced by an internal combustion engine, the metal parts
would seize without a cooling system. In most cars, coolant
is circulated through channels in the engine called a coolant
jacket. The hot coolant then passes through a radiator where
the heat is dispersed to the atmosphere.
To prevent wear and
overheating, the engine has a lubrication system. Oil, kept
in a sump underneath the cylinder block, is pumped around
the engine.
How Heat Becomes
Driving Power : Fuel Burning
Heat energy produced
by the combustion of petrol and air is converted into mechanicalpower
by the pistons, connecting rods and crankshaft of an engine.
The engine's efficiency depends on how much of this energy
becomes useful power.
The more petrol /
air mixture that can be drawn into a cylinder and the more
it can be compressed, the higher will be the specific output
of the engine.
The degree of compression
is measured by the compression ratio, the ratio of the volumes
of gas inside the cylinder before and after compression.
The average family car has a compression ratio of about
9:1, which means gas in the cylinder is compressed to one-ninth
of its original volume.
The compressed mixture,
when ignited by a spark, should burn rapidly but progressively
and smoothly across the top of the piston. It should not
explode.
If the compression
ratio is too high for the grade of petrol being used, the
burning will not be progressive. Some of the mixture furthest
away from the spark plug will explode violently, or detonate.
This is known as knocking or pinking.
Apart from the loss
of power, this detonation can cause overheating and if allowed
to continue will damage the engine.
Loss of efficiency
and overheating can also occur in an engine from pre-ignition
- ignition before the timed sparking occurs at the spark
plug. This can arise from defective or incorrect spark plugs,
or it can be caused by deposits in the combustion chamber
which have grown hot and glow continuously. Pre-ignition,
like knocking can cause extensive damage, as well as reduce
engine power.
The action cycle
in most car engines is the 4-stroke, with the power stroke
of the piston occurring once every four strokes. During
one revolution of the crankshaft, the piston descends on
its induction/ intake stroke and rises on its compression
strokes. During the next revolution of the shaft, the piston
is forced down on its power/expansion stroke, then rises
on its exhaust stroke to expel burnt gases.
Since the inlet and
exhaust valves must open only once in each cycle, the camshaft
operating them is driven at half the speed of the crankshaft
which makes two revolutions during the 4-stroke cycle.
LUBRICATION SYSTEM
Why the engine
needs oil : -
The oil in an engine
does more than simply cut down friction and wear by
lubricating the pistons, bearings and other moving parts.
It also helps to seal hot high-pressure gases; take heat
away from hot areas and disperses it to the air in the sump;
reduces corrosion; and absorbs some of the harmful waste
products of combustion.
Oil is carried in
the sump, at the bottom of the engine, and forced by a pump
through a filter to the main bearings. The pump will normally
deliver several litres of oil a minute, at a pressure controlled
by a relief valve.
From the main bearings,
the oil passes through feed holes or grooves into drilled
passages in the crankshaft and on to the big end bearings
of the connecting rods. In some engines the oil is taken
to the gudgeon pins through passages drilled in the connecting
rods.
The cylinder walls
and gudgeon pin bearings are lubricated by oil fling oil
- oil escaping from the end of the bearings and dispersed
by the rotating crankshaft. The excess is taken off the
cylinders by scraper rings on the pistons and then drops
back to the sump.
A bleed or tributary
from the main supply passage feeds each camshaft bearing;
and in many overhead valve engines there is another bleed
leading to the rocker shaft bearings. The oil then drains
back from the cylinder head to the sump, where excess heat
is dispersed to the surrounding air. Another bleed supplies
the timing chain or gears on the camshaft drive.
CNG / LPG ENGINES
The CNG (Compressed
Natural Gas ) / LPG (Liquefied Petroleum Gas) can be used
in the SI Engines fitted in the passenger cars without making
any modification in the Engines. However, a Gas conversion
kit retrofitted in the vehicle for safe handling of the
gas and to supply the gas to the carburetor will help to
run the engine with either petrol or CNG/LPG . By a mere
click of the switch in the dashboard, the engines are either
supplied petrol or the gas as fuel to engine.
CNG / LPG is a clean
fuel with high octane number and fully burns in the engine
without leaving any unburned carbon deposits in the engine
and this will help to run with less excess air (near stoichiometric
ratio). This leads to higher operating temperature of the
engine and causes severe nitration on the oil, Use of Gas
in the Engine will also lead to non lubrication of the inlet
valve otherwise lubricated by the liquid fuel particles
and exhaust valve which is lubricated by the carbon deposit
from the unburned petrol.
The Oils for
Gas Engines are specially developed to meets the operating
requirement of the conventional petrol engines and also
to take care of the additional demands of higher operating
temperature & nitration of the Oil and lubrication of
the vale seats by using carefully selected additives to
give the right type of ash deposits.
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drives
(axles) of passenger cars, buses, trucks.
Automatic
Transmission Fluids are used in a number of applications
besides passenger cars and commercial vehicles automatic
transmissions. 
