Petrol Engine, Kartarpur

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.

Types of petrol engines

Working of four stock engine 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

shows a cut-away diagrams of a Two-Stroke Petrol engine. This engine design is the simpler mechanically of two and four stroke as it minimises the number of moving parts which must be kept in sync. The description "two stroke" comes from the fact that the engine fires (burns fuel) on every upward stroke (travel of the piston from bottom of the cylinder to the top), thus there are two strokes for every ignition of fuel, and upward and a downward stroke.

The first stroke moves from bottom to top, where compressed air and fuel ignite and begin the second stroke where the piston is forced back downwards by the

STROKE 1A: PISTON AT BDC In the diagram the piston is at BDC (Bottom Dead Centre meaning it is at the lowest point of travel within the cylinder). The air, petrol and oil mixture within the crankcase is forced into the cylinder and exhaust gases are driven out.

STROKE 1B: THE INSTROKE The piston moves upwards and covers the air intake and exhaust ports closing them. The charge of fresh air is compressed to about 5:1 (20%) of its original volume. The act of compressing the air heats it tremendously. This happens on every upward stroke of the piston.

STROKE 2A: PISTON AT TDC Just as the piston reaches the uppermost portion of it's travel at Top Dead Centre (TDC) the spark plug is fired causing combustion of the compressed mixture within the cylinder. At the same time petrol and oil vapour is being drawn into the crankcase in preparation for the next stroke.

STROKE 2B: PISTON NEARING BDC During the downward stroke the exhaust port opens, and the cylinder is swept clean of burnt fuel by fresh air from the inlet port. The petrol, oil and air charge within the crankcase is compressed during this stroke in preparation for the next stroke.This entire cycle is repeated for every revolution of the crank shaft.Thanks to Dr Gary Zimmer who pointed out the compression ratio was way out for the engines described here. I appreciate it when people who discover errors on the pages point them out so they can be corrected!

Shows how a four stroke petrol engine works. Stroke 1. The downward moving piston sucks a mixture of air and petrol vapour into the cylinder through the inlet valve. Stroke 2. The piston then moves upwards, compressing the gas mixture.

Stroke 3. Just before the piston reaches the top of the cylinder a spark from the spark plug explodes the gas mixture. The pressure from the rapidly expanding gas pushes the piston down and causes a flywheel that it is connected to by the crankshaft to rotate. It is this rotation that is used to drive the wheels of the car.

Stroke 4. The piston moves upwards in the cylinder again to push out the gases through the exhaust valve into the exhaust system of the vehicle. As the piston moves down, it pulls more fuel/air mixture in to begin the cycle again.

SUBMITED BY:1.Ravi Paul 2.Sonu 3.Bikramjeet ClASS : 10th

SOURCES OF INFORMATION

ENCARTA ENCYCLOPEDIA INTER NET TH BOOK OF CLASS 10 (P.S.E.B.)