Reciprocating and rotary motion (Fig 1).
FUEL must mix readily with air. The fuel will be easily ignited when broken down in a form of vapourised spray in order to help the fuel enough air to burn fully.
Combustion is the actual igniting and burning fuel mixture. It is the oxygen in the air that combines with the fuel for combustion.
What is important is how fast the fuel burns for the force must be ‘explosive’ to get full power from the engine.
Reciprocating and Rotary Motion Refer (Fig 1)
The engine has two forms of motion to transmit energy: Reciprocating Motion – up and down or back and forth motion. The engine converts reciprocating motion into rotary motion.
Engine cycles
Most engines have one of the 2 types of cycles – 2 Stroke Cycle and 4 Stroke Cycle.
In the 2 strokes cycle engines, there are 2 strokes of the piston, one up and one down, during each cycle. Then it starts over again on another cycle of the same 2 strokes. The whole cycle occurs during one revolution of the crank shaft. In the 4 stroke cycle the pistons move 2 up and 2 down during each cycle. Then it starts over again on another cycle of the same 4 strokes .These cycles occur during 2 revolution of the crankshaft. Most engines today operate with the 4 stroke cycle.
Mixture
For an engine to operate a definite series of events must occur in sequence.
1. Fill the cylinder with combustible mixture.
2. Compress these mixture into the combustion chamber (Top of piston)
3. Ignite the mixture and explosion will occur, pushing the piston to produce power.
4. Removal of the burned gases from the cylinder.
The sequence generally called:
1) Intake
2) Compression
3) Power
4) Exhaust
Four stroke cycle
In 4 Stroke Cycle Engine the same 4 operations occur – Intake, Compression, Power and Exhaust.
However, 4 strokes of the piston – 2 up and 2 down – are needed to complete the cycle. As a result, the crankshaft will rotate 2 complete turns before 1 cycle is completed.
Intake Stroke (Fig 2).
Intake Stroke Refer (Fig 2)
Intake
Fuel Air Mixture is drawn into cylinder from carburetor through open Intake by downstroke of Piston.
The Intake stroke starts with the piston near the top and end shortly after the bottom of its stroke. The intake valve is opened allowing the cylinder as the piston moves down to receive the fuel-air mixture. The valve is then closed, sealing the cylinder.
Compression Stroke (Fig 3).
Compression Stroke (Fig 3)
Compression
Mixture is compressed By Up – Stroke Of Piston. Both Intake and Exhaust Valves Are Closed.
The compression stroke begins with the piston at bottom and rising up to compress the fuel-air mixture. Since the intake and valves are closed, there is no escape for the fuel air and it is compressed to a fraction of its original volume
Power Stroke (Fig 4).
Power Stroke (Fig 4)
Power
Compressed mixture is ignited by spark plug and the expanding gases force piston to bottom of cylinder. Valves remain close.
The power begins when the piston reaches the top of the stroke and the fuel air mixture is ignited. As the mixture burns and expands, it forces the piston down on its power stroke. The valves remain closed so all the force is exerted on the piston.
Exhaust Stroke (Fig 5).
Exhaust Stroke (Fig 5)
Exhaust
Piston on up-stroke forces the burned gases from cylinder through open exhaust valves.
The exhaust stroke begins when the piston nears the end of its power stroke The exhaust valve is opened and the piston rises pushing out the burned gases. When the piston reaches the top the exhaust valve closed and is ready for a new 4 stroke cycle of intake, compression, power and exhaust.
As it completes the cycle, the crankshaft has gone all the way around twice
Now you have completed the topic on How Engine Works Part One and shall be able to:
1) Understand the process of engine cycles: Intake ,Compression, Power and Exhaust in the combustion chamber. Hence you will have better understanding of how important engine tuning is.
2) Knowledge on technical terms like combustion, cylinder, connecting rod, intake, compression, power and exhaust cycles, 2 stroke cycle, 4 stroke cycle.