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1.1 Spark Ignition Engines
1.2 Compression Ignition Engines
1.3 Two stroke & Four stroke Engines
1.4 Engine Types – Vertical, Horizontal, Inline , V
1.5 OHC and DOHC Engines
1 Spark Ignition (SI) Engines
enters into the combustion chamber together. ignition
takes place with the help of an electric spark by spark
Ø Usually petrol engines are SI engines.
1.4 Four Stroke Engine
In Four Stroke Engine -
Ø First is Intake Stroke: Inlet valve is open and the fuel air mixture is drawn in while the piston goes down.
1. Vertical Engine –
Piston movies vertically up
& down. Crankshaft is
below the cylinder.
Convenient to orient cylinder vertically since they are
taller. Space around cannot be used.
2. Horizontal Engine –
Cylinder is placed
Less Power loss, Better
handling. Packing size is more since very wide.
3. Inline Engine –
Banks of cylinder are placed one behind the other. Mainly six cylinder in one bank are used.
Simpler, Lighter. Longer & Skinny , Hard to pack.
4. V Engine –
Mainly Two rows of cylinder at 90 deg angle (or any other angle making V) to each other are placed.
Short length , easier to fir. But , separate cam shafts for each side of the V makes it complex.
1.6 OHC and DOHC Engines
A camshaft rotates and its lobes open and close the
valves in time with the piston to allow air in and
exhaust outdown to enable combustion cycle of an
engine. Commonly ,there are two type of Camshaft
SOHC = Single Overhead Camshaft
DOHC = Double Overhead Camshaft
In a SOHC engine , the
camshaft is installed in the
cylinder head. Valves are operated either by the rocker
arms or directly through the lobe lifters of rotating
DOHC engine normally has two
camshafts and 4 valves per cylinder.
One side camshaft operates intake
valves, while opposite side camshaft
controls exhaust valves.
SOHC engines are less complicated in design & cheaper.
DOHC engines rev much higher and develop more
power at mid to top rpms for the same displacement
engine. DOHC engines are ideal for performance or
Sports racing new bikes , while these are cooler ,runs more
smoothly, quietly, and efficiently.
Engine – Technical Terms and Parts
2.Engine Technical Terms & Parts-
2.1 Engine – Bore & Stroke
2.2 Engine – Compression Ratio
2.3 Engine – Maximum Power and Torque
2.4 Capacitor Discharged Ignition (CDI)
2.5 Spark plug
2.7 Engine- Cooling System
Engine – Bore & Stroke
Bore : It is the diameter of the cylinder.
Stroke: It is the distance to which piston travels.
What is cc (Cubic Centimetre) ?
Volume of Cylinder : Normally more the Volume of Cylinder of an Engine,
more Power it can produce.
Volume of an engine (V) =
pi * S * B^2 / 4
Engine – Compression Ratio
Compression Ratio –
Engine – Maximum Power and Torque
Torque :Twisting or turning force
Power: How fast can engine do work
I Ps = 735.5 newton·m/s ~= 735.5 W ~= 0.7355 kW
~= 0.98632 hp
Capacitor Discharged Ignition
1.It allows mixture into the cylinder is the inlet valve.
2.The one through which the spent gases escape is the exhaust valve.
An OHC (or DOHC) Engine cylinder
head will have at least two valves per
cylinder (1 inlet and 1 exhaust), but
multi-valve engines may have three (2 inlet and 1
exhaust), or four (2 inlet and 2 exhaust), five (3 inlet
and 2 exhaust) or even more . Multi-valve engines rev
higher and make more , while have more components
resulting higher cost.
Engine- Cooling System
Cooling System – It prevents engine breakdown due to overheating.
1. Air cooled Engines –
Engine of the motorcycle is cooled naturally by the outside atmosphere air.
Engine is surrounded by the liquid cooling system. It uses a coolant to keep the temperature of the engine at an optimum level.
3. Oil Cooled Engines -
In Oil Cooled Engines the oil is circulated between the radiator and the engine case, the radiator takes off the heat from the oil, thus bringing down the temperature, hence helping in maintaining the viscosity of the oil.
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