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What occurs in each combustion chamber during operation of a 4-stroke-cycle Otto engine.?
- Away-ward motion of piston draws Fuel-Air mixture into chamber via Intake Valve (Exhaust Valve closed).
- Intake Valve closes as piston begins toward-ward motion (Exhaust Valve still closed).
- Fuel-Air Mixture compresses as piston continues motion to maximum-squeeze extent of motion towards combustion chamber.
- Just before maximum compression of Fuel-Air Mixture (also called BTDC), Spark Plug "fires" to produce spark across its cathode-anode gap and ignites Fuel-Air mixture causing rapid burning and (now) gas expansion.
- Piston is forced away from Combustion Chamber with explosive force.
- Usable force of burning, expanding gas has been expended as piston reaches maximum distance from Combustion Chamber.
- Inertia and impulse from other cylinders causes piston to reach limit of travel away from Chamber and, then, to begin travelling back towards Chamber (and towards TDC) during which Exhaust Valve begins to open (Intake Valve closed).
- Reducing cylinder volume as piston continues toward TDC causes burned combustion products and unburned fuel product from previous plug firing out of the Chamber via the now-fully-opened Exhaust Valve.
- Piston reaches TDC, at which point Exhaust Valve closes, then reverses direction and begins travelling away from chamber again under its momentum as well as impulse from any other cylinders via the crankshaft to which pistons are connected in the crankcase.
- As Piston travels away from Chamber, Intake Valve opens, drawing in fresh fuel mixture and beginning a new cycle (starting again at 1. above).
So what you have then is a description of Combustion Chamber status during each "stroke" portion of the 4-stroke-cycle (Otto) internal combustion engine:
- Intake (10. and 1. & 2. above) of fuel mix into Chamber
- Compression (2. & 3.) of fuel mix in Chamber
- Expansion (4. - 7.) of exploding fuel mix in Chamber
- Exhaust (7. - 9.) of fuel mixture from Chamber
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