Agriculture Engineering-chptr 6
- 1. TWO STROKE ENGINE CYCLE
- 2. Two Stroke Engine • Used to provides power for small machines for farms or in horticultural work • Examples of 2 stroke engine are hand operated hedge trimmers, hand operated chain saws, small rotary cultivators, grass cutters and horticultural sprayers • Valves are not normally fitted in 2 stroke engine, instead opening known as ports are arranged in the walls of the cylinder
- 3. • Inlet port – where the carburetor is attached and fuel/air enters the crankcase • Transfer port – where compressed fuel/air is transferred from crankcase to combustion chamber, ready for compression stroke • Exhaust port – at the end of power stroke the piston uncovers the exhaust port and spend gasses escape
- 5. The Intake Stroke The piston moves down, inlet port closed and induction port opened • This downward movement of the piston creates a partial vacuum and air rushes through the transmission port into the cylinder
- 6. The Compression Stroke • The piston moves up, 2 events is involved; • Induction port and exhaust port closed on compression of a previous charge, a partial vacuum is created in the sealed crankcase • The piston uncovers the inlet port and air rushes through the carburetor taking fuel/air mixture with it into the crankcase
- 7. The Power Stroke When the piston is in Top Dead Centre, the spark plug sets fire to the mixture which burns and expand, and in doing so forces down the piston
- 8. The Exhaust Stroke The piston moves down again, 2 events involved; • The exhaust port open so that the spent gasses escaped • The inlet port closed and induction port opened on compression the fuel/air mixture into the cylinder
- 9. Engine Governor • The governor is a device which automatically controls the speed of the engine under varying load.
- 10. Function 1) Maintain a selected speed 2) Limit the slow and fast speed 3) Shut down the engine when it over speeds
- 11. • Governor on the engine automatically regulates speed at whatever setting you select on the speed control (throttle lever) • If engine machine is operated much faster than the top speed specified, wear increases rapidly • If operated much slower, less power is available and operating costs increases
- 12. Operation of Governor After you set the speed control lever, the job of the governor is to adjust the amount of fuel-air mixture so that the engine speed remains the same even though the load varies The governor must be sensitive to speed changes The governor is mounted on the engine camshaft where it is directly affected by any slight in change in engine speed
- 13. THANK YOU