Presentation on theme: "Four Stroke Gas Engines The four strokes of a internal combustion engine are: Intake Compression Power Exhaust Each cycle requires two revolutions of the."— Presentation transcript:
Four Stroke Gas Engines The four strokes of a internal combustion engine are: Intake Compression Power Exhaust Each cycle requires two revolutions of the crankshaft (720˚ rotation), and one revolution of the camshaft to complete (360˚ rotation). Each stroke = 180˚ of crankshaft revolution.
Intake Stroke First Stroke The piston moves down the cylinder from TDC (Top Dead Center) to BDC (Bottom Dead Center). This movement of piston causes low air pressure in the cylinder (vacuum) Mixture of Air and Fuel in the ratio of 14.7 : 1 (air : fuel) is drawn into the cylinder. Intake valve stays open and the Exhaust valve stays closed during this stroke.
Compression stroke Second stroke The piston moves from BDC to TDC Intake and exhaust valves stay closed Air and fuel mixture is compressed 8:1 to 12:1 The pressure in the cylinder is raised
Power stroke Third stroke At the end of compression stroke the sparkplug fires, igniting the air/fuel mixture. Both the valves stay closed in this stroke. The expanding gases from the combustion in the cylinder (with no escape) push the piston down. The piston travels from TDC to BDC.
Exhaust stroke Fourth and last stroke The momentum created by the Counter-weights on the crankshaft, move the piston from BDC to TDC. The exhaust valve opens and the burned gases escape into the exhaust system. Intake valve remains closed.
Four strokes All four strokes
Four Cylinder Engine
Valve Timing The ratio of cam to crank sprocket is 2:1 For every two revolutions of Crankshaft, the Camshaft turns once. Belt driven Chain driven Gear driven
Carburetor The job of the carburetor is to accurately meter extremely tiny quantities of fuel and mix it with the air entering the engine, so that the engine runs properly. It works on the principle of High and low pressure High and low pressure is created with the help of Venture
Ignition system Provides high voltage surges – as high as 47,000 volts to the spark plug Parts permanent magnet. armature assembly. breaker points. condenser. spark plug.
Lubrication In the engine, dippers on the connecting-rod bearing caps enter the oil pan with each crankshaft revolution to produce the oil splash. A passage is drilled in each connecting rod from the dipper to the bearing to ensure lubrication.(used only on 4-stroke small engines)
Cooling Air cooled Fins are used to dissipate heat Liquid cooled Coolant is used to dissipate heat.