Introduction
Petrol Engine was introduced by the German engineers Gottlieb Daimler and Karl Benz in 1885. It is considered as one of biggest achievement in the automotive field. It uses petrol called as gasoline in USA as a fuel. Within the engine burning of fuel mixed with air causes hot gases to expand against parts of the engine and force them to move. So petrol engines are called internal-combustion engines. Petrol engines are compact and light in weight for the power they produce. The rate at which it produces work is usually measured in horsepower or watts.
Petrol Engine is a complex piece of machinery made up of about 150 moving parts. It is a reciprocating piston engine, in which a number of pistons move up and down in cylinders. A mixture of petrol and air is introduced to the space above the pistons and ignited. The gases produced force the pistons down, generating power. The engine-operating cycle is repeated every four strokes (upward or downward movement) of the piston, this being known as the four-stroke cycle. The motion of the pistons rotate a crankshaft, at the end of which is a heavy flywheel. From the flywheel the power is transferred to the car's driving wheels via the transmission system of clutch, gearbox, and final drive.
Parts of a petrol Engine
The parts of the petrol engine can be subdivided into a number of systems.
a) The fuel system pumps fuel from the petrol tank into the carburettor. There it mixes with air and is sucked into the engine cylinders. With electronic fuel injection, it goes directly from the tank into the cylinders by way of an electronic monitor.
b) The ignition system supplies the sparks to ignite the fuel mixture in the cylinders. By means of an ignition coil and contact breaker, it boosts the 12-volt battery voltage to pulses of 18,000 volts or more. These go via a distributor to the spark plugs in the cylinders, where they create the sparks. Ignition of the fuel in the cylinders produces temperatures of 700°C/1,300°F or more, and the engine must be cooled to prevent overheating.
c) Water-cooling system Most engines have a water-cooling system, in which water circulates through channels in the cylinder block, thus extracting the heat. It flows through pipes in a radiator, which are cooled by fan-blown air. A few cars and most motorcycles are air-cooled, the cylinders being surrounded by many fins to present a large surface area to the air.
d) The lubrication system also reduces some heat, but its main job is to keep the moving parts coated with oil, which is pumped under pressure to the camshaft, crankshaft, and valve-operating gear.
Kinds of petrol engines
Reciprocating petrol engines are distinguished in a number of ways. Some of them are as follows:
(1) Type of compression
(2) Valve arrangement
(3) The way they are cooled,
(4) The way they are supplied with air and fuel.
(5) Number of piston strokes per cycle,
(6) Cylinder arrangement
Parts of a petrol engine
Following are some of the important parts of petrol engine:
1) Cylinders
2) Cylinder block
3) Piston and Connecting rods
4) Cylinder head Crankcase
5) Valves
6) Crank shaft Flywheel
7) Exhaust system
8) Camshaft Fuel system
9) Lubrication system
10) Ignition system
Working of a petrol engine
Generally the vehicles using petrol/gasoline engine have four strokes as they are more efficient than two stroke engine and give complete combustion of fuel to optimum use.
The four-stroke cycle engine has four strokes namely intake, compression, power, and exhaust strokes.
a) Suction or intake stroke:
Initially when engine is started piston moves downwards towards bottom of the cylinder which creates low pressure at top. Due to this intake valve opens and the fuel mixture containing petrol vapors and air are sucked in by the cylinder. Carburetor now decides in what ratio gasoline/petrol and air should be mixed.
b) The compression stroke:
After this the inlet valve gets closed. The piston now moves towards the top of cylinder and compresses the fuel mixture to one tenth of its initial volume. The temperature and pressure inside the cylinder increases due to compression caused.
c) The power stroke:
During this stroke the inlet and exhaust valve remains closed. As the piston reaches near top position spark plug produces an electric spark. Combustion is started by an ignition system that fires a high voltage spark through a field replaceable air gap called a sparkplug. The spark produced causes explosion of fuel. The hot gases expand and force the piston to move downwards. The piston is linked to the piston rod and the piston rod to the crank shaft. They all move each other due to the link between them. The crank shaft is connected to the wheels of a car. As the crank shaft movess, the wheels rotate and move the car.
d) The exhaust stroke:
In this stroke the exhaust valve remains open at the start. The piston is forced to move upwards because of the momentum gained. This forces gases to move through the exhaust valve into the atmosphere. Now the exhaust valve closes and the intake valve opens. After this the four strokes of the engine are repeated again and again
Carburetor
It is the heart of gasoline engine. They meter the fuel and mix it with the air in precise proportions. Old carburetors do spark advance by measuring the difference in pressure between the outside and inside of the carburetor. The amount of throttle advance is also measured. The engine's remains which may be carbon monoxide or unburned hydrocarbons shows how well the carburetor is working.
Applications:
These engines are widely used in vehicles, portable power plants to supply the power to run pumps and other machinery on farms. Many small boats, aero planes, trucks and buses also use it.
Future Scope:
Continuous research is being carried to increase the fuel efficiency, reduce the pollutants and make it more light and compact. Recently engineers at the University of Birmingham have made the smallest petrol engine that can replace conventional batteries. The engine is so tiny that it can be handled on a fingertip.
This project is done by
Anju.V.S, Adthya.P.R IX.N &
Anagha V. Sankar IX.P
Govt G H SS Cotton Hill,Tvpm.