#9 Diesel Engine Flashcards
Structual Parts: Cylinder & Piston
Cylinder: close fitting piston slides in and out (reciprocation)
Piston: connected to crank mechanism which controls its sliding
Structual Parts: Crankshaft
consists of a shaft supported on bearings
crank: turns in a circle while the shaft revolves
connecting rod connects crank to piston
crank mechanisim converts the reciprocating motion of piston into rotary motion of crankshaft
power produced by engine taken off crankshaft by transmission
Mountings
Scavenge valves/ports: let air in the cylinder
Exhaust valve: let out burnt or spent gas after they done their work
Fuel injector: needed to deliver fuel oil for buring as a finely divided spray
2 Stroke Engine
Compression Stroke
Power Stroke
Blowdown
Scavenge
2 Stroke Engine: Compression Stroke
Piston moves up
scavenge & exhaust ports covered by piston, fuel valve shut
Air in cylinder compressed to 90 bars and 550 degree celcius at end of compression
Pison reach Top Dead Centre (TDC)
2 Stroke Engine: Power Stroke
Fuel injected in fine spray when piston reach TDC
fuel mixes with hot air and burns rapidly
gas pressure in cylinder increases rapidly, pushing the piston down
gas pressure falls
2 Stroke Engine: Blowdown
Piston moves down
exhaust valve opens before piston reaches bottom dead centre (BDC)
exhause gas rush out of cylinder
cylinder pressure falls to atmospheric pressure
2 Stroke Engine: Scavenge
Piston moves further down
uncovers scavenge ports (openings cut at lower liner)
scavenge air (1.5 bar) higher pressure than atmospheric pressure, sweeps into cylinder
scavenge ports cut through tangential to cylinder, give air swirling motion
cylinder scavenged by incoming air, expel burned gases out through exhaust valve
when crank passes BDC, piston moves up and covers scavenge ports
exhaust valve closes, air in cylinder compressed to start new cycle
