Internal Combustion Engine
Introduction
Internal Combustion System
The engine consists of a piston and a cylinder which is provided with inlet valves and exhaust valve. The opening and closing of these valves are controlled by the motion of the piston.
There are four steps involved in IC Engines:
- Intake (Suction).
- Compression.
- Power.
- Exhaust.
Suction Stroke (Intake): The combustion starts with the piston at the Top Dead Centre or TDC position. The piston now starts to move down. Just before the piston begins its downward motion, the intake valve opens up. As the piston moves down, it sucks in the fresh air-fuel mixture from the manifold. As the piston reaches Bottom Dead Centre or BDC, the chamber fills up with air-fuel.
Compression Stroke: Once the piston has reached BDC, the compression stroke begins. Just before the piston reaches the lowermost position, the intake valve closes. Now the piston moves upwards. As it moves up, it compresses the sir-fuel mixture as it has no place to escape with the closed valves.
Power Stroke: Just before the piston reaches the topmost position in the compression stroke, the spark plug mounted on the cylinder head lets off a very tiny spark. When this spark comes into contact with the compressed sir-fuel mixture, it ignites the mixture. Once ignited, the flame rapidly expands. Since the valves are still closed, the flame has no place to escape and pushes the piston downwards. This is the power stroke where usable power is generated by the motion of the piston.
Exhaust Stroke: The piston with the momentum gained from the previous stroke starts to move back upwards. As it begins to move, the exhaust valve opens up. The leftover gases from the combustion process are pushed out. With this one 4-stroke cycle is completed. After this, the piston again moves from TDC to BDC and the cycle restarts.
Cooling System in Internal Combustion Engines
Due to the combustion of fuel inside the cylinder very high temperature is produced. Any metal tends to become weak at high temperature. If engine is not cooled, parts such as the cylinder, the cylinder head, the piston, the piston rings and the valves will get over heated resulting in the reduction of strength and distortion of components. Overheating may cause seizure of the piston. Properties of the lubricating oil will change, and it may decompose resulting in carbon deposit in the cylinder. Hence all IC engines are provided with cooling systems.
These are of two types:
- Air Cooling: Fins are provided on the cylinder and cylinder head and air is circulated over them. Heat removal rate depends on the area of fins, amount and velocity of air circulating and the temperature difference with the surrounding.
- Water Cooling: In this case the cylinder and the cylinder heads are provided with jackets in which water is circulated. Hot water coming out of these jackets is cooled by air through a finned radiator and recirculated.