Petrol Engine(nehru Garden)

Govt. Girls. Sr. Sec. School, Nehru Garden. Jalandhar City.

PETROL ENGINE Petrol engine was introduced by the engineers Gottlieb Daimler and Karl Benz (both from Germany) 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. It is made up of about 150 moving parts. 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 internalcombustion 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.

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 Classification based on number of stokes per cycle: a) Two Stroke b) Four Stroke A)

TWO STROKE PETROL ENGINE From the name itself we get the idea about the functioning of the engine. The engine ignites fuel at every upward stroke, so there are two strokes for every ignition of fuel. They are called upward and downward stroke. As the piston moves in upward direction from bottom to top in the first stroke the air and fuel mixture gets compressed and ignited by spark plug as upward stroke comes to end. This results in an explosion of mixture which forces the piston to move downwards thereby producing power.

Since they have less moving parts they are light in weight .Also the design is simple compared to four stroke engines. Big size bulky two-stroke cycle engines have lubrication systems like that of four-stroke cycle engines.

B)

FOUR STROKE PETROL ENGINE: The four stroke engine is called so because the working of an internal combustion engine is divided into four stages called four strokes of the engine.

PARTS OF A PETROL ENGINE Following are some of the important parts of petrol engine: 1) CYLINDERS - Cylinders are rigid tubes that serve as a bearing for the pistons that move up and down inside them. They have highly polished surfaces. This permits a close fit between piston and cylinder and prevents gases from leaking past the piston. The cylinders in most car engines are part of the block. Some engines have a cylinder sleeve made of specially hardened steel or cast iron pressed into the cylinder block. 2) CYLINDER BLOCK - Cylinder block is a rigid frame that holds the

cylinders in proper alignment. If the engine is liquid cooled, the block is jacketed, so that it can be surrounded by the liquid, or has passages for the liquid around each cylinder. In automotive engines, the cylinder block and crankcase form a single unit. Most cylinder blocks are made of cast iron or aluminium. 3) PISTON AND CONNECTING RODS - There is a piston fitted in the cylinder. This piston is connected to a connecting rod which in turn is connected to the crank shaft. When the fuel-air mixture burns, the expanding gases exert a force on the piston. This force is then transmitted through a connecting rod to the crankshaft. The piston has two to six rings to prevent the gases from escaping and to keep lubricating oil from getting into the combustion chamber. 4) CYLINDER HEAD - Cylinder head is a casting bolted to the top of the cylinder block. The cylinder head, together with the upper end of the cylinder and the top of the piston, form the combustion chamber where the fuel-air mixture burns. A cylinder head and block may be one unit. 5) CRANKCASE - Crankcase is a rigid frame that holds the crankshaft and the crankshaft bearings. In small engines, all or part of the crankcase may be a part of the cylinder block 6) VALVES - In a four-stroke cycle engine, each cylinder has one or two intake valves, to let the air-fuel mixture into the combustion chamber, and one or two exhaust valves, to let the burned gases escape. These are

called poppet valves, because they pop up and down as they open and close. The opening in the cylinder block or head uncovered by the valve is called the port. In many two-stroke cycle engines, the movement of the piston takes the place of separate valves. As the piston moves, it covers and uncovers the ports. 7) CRANK SHAFT - Crankshaft changes the reciprocating motion of the pistons into rotary motion. The crankshaft has a number of cranks, or throws. These cranks are displaced at angles to each other. For example, in a six-cylinder, in-line, four-stroke cycle engine, the cranks are displaced at 120° angles to each other. As a result, the engine delivers three equally spaced power strokes in each revolution of the crankshaft to assure smooth operation. 8) FLYWHEEL - Flywheel stores energy during a piston's power stroke and releases it during other strokes. This helps to keep the crankshaft turning at a constant speed 9) CAMSHAFT - Camshaft opens and closes the valves at the proper point in the engine cycle. It runs the length of the engine and has one cam (lobe) at each intake and exhaust valve. In a four-stroke cycle engine, the camshaft is geared to the crankshaft so that it runs at half the crankshaft's speed. The camshaft may be located in the head of an overhead valve engine, or in the crankcase. 10) FUEL SYSTEM - Fuel system includes : (1) a storage tank for petrol, (2) fuel lines to carry the petrol to the carburettor, (3) a carburettor to mix the petrol with air, and (4) an intake manifold to distribute the fuel-air mixture to the cylinders. The fuel system also includes a filter to clean dirt out of the fuel and an air cleaner to take dirt out of the air that is mixed with the petrol. In addition, the system may include a governor to limit the engine's speed. 11) EXHAUST SYSTEM - Exhaust system consists of one or more parts. It may include (1) an exhaust manifold to collect the burned gases from the cylinders, (2) an exhaust pipe to carry the burned gases, and (3) a silencer to silence the noise of the exhaust gases. 12) IGNITION SYSTEM - Ignition system is the electrical circuit necessary to set fire to, or ignite, the fuel-air mixture in the different cylinders at different times. In a car a storage battery provides electric current, which is increased in voltage by an induction coil. The high-voltage current is carried through a distributor, which delivers the electricity to each cylinder at about the moment the piston reaches the top of the compression stroke. There the electric current jumps a gap between two terminals and sets fire to the petrol-air mixture. The terminals are encased in insulating material and called a spark plug. 13) IGNITION SYSTEM - Ignition system is the electrical circuit necessary to set fire to, or ignite, the fuel-air mixture in the different cylinders at different

times. In a car a storage battery provides electric current, which is increased in voltage by an induction coil. The high-voltage current is carried through a distributor, which delivers the electricity to each cylinder at about the moment the piston reaches the top of the compression stroke. There the electric current jumps a gap between two terminals and sets fire to the petrol-air mixture. The terminals are encased in insulating material and called a spark plug. WORKING OF A PETROL ENGINE The working of an internal combustion engine is divided into four stages called four strokes of the engine and hence the engine is called a four stroke engine. THE INTAKE STROKE : When the engine starts, the piston moves downwards in the cylinder, because of which a region of low pressure is created in the cylinder, above the piston. At this moment, the intake valve opens and the fuel mixture(petrol vapour and air mixture) is sucked into the cylinder from the carburetor.

THE COMPRESSION STROKE : When the sufficient amount of the fuel mixture (petrol vapour and air mixture) has entered the cylinder, the intake valve gets closed. The piston is then forced to move upwards which compresses the fuel-mixture to about one-eighth of its original volume. Higher the compression ratio, more will be the efficiency of the engine.

THE POWER STROKE : Before the piston completes its upward movement, compressing the petrol vapour and air mixture, the spark plug produces a little electric spark inside the cylinder and this spark sets fire to the petrol-air mixture. The petrol vapour burns quickly in a little explosion, producing a large volume of gases and enormous heat. The heat thus produced expands the gases rapidly. The pressure of rapidly expanding hot gases pushes the piston downward with a great force. The piston pushes the piston rod and the piston rod pushes the crank shaft. The crank shaft is joined to the wheels of a car. When the crank shaft turns, the wheels rotate and move the car.

THE EXHAUST STROKE: When the piston has been pushed to the bottom of the cylinder by the hot expanding gases in the power stroke, then the exhaust valve opens. After that, due to the momentum gained by the wheels, the piston is pushed upwards. The upward movement of the piston, expels the spent gases through the exhaust valve into the atmosphere, carrying away the unused heat. The exhaust valve then closes, the intake valve opens up, and the above 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. In new engines, a small computer is used to calculate these parameters and control one or more electric injectors. Most of the new cars use electronic fuel injection as it allows the engine computer to precisely control the fuel air mixture which increases energy efficiency and reduces pollution. 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.