The Strokes
This is the 3rd stroke of a four stroke engine.
What is the Power Stroke?
This part moves up and down inside the cylinder.
What is the piston?
This is the job of the intake stroke: get this into the cylinder so it can eventually be burned.
What is the air/fuel mixture?
If the intake valve never opened, the cylinder would have trouble getting this into the engine.
What is the air/fuel mixture?
Before an engine can burn the air/fuel mixture, which happens first: air/fuel enters the cylinder or the spark plug ignites it?
Air/fuel enters the cylinder.
During this stroke, the piston moves upward to compress the air/fuel mixture.
What is Compression?
This part connects the piston to the crankshaft.
What is the connecting rod?
This is the main purpose of the compression stroke: make the air/fuel mixture more concentrated and ready for this.
What is combustion?
Why must the valves be closed during the compression stroke?
So the mixture can be compressed instead of escaping.
During the intake stroke, what happens first: the piston moves down or the intake valve opens?
The intake valve opens as the piston moves downward.
During this stroke, the piston moves downward as air is let into the cylinder.
What is the Intake Stroke?
This rotating part converts the piston's up-and-down movement into rotary motion.
What is the crankshaft?
This is what the power stroke ultimately does: transfer the force of combustion into movement of the piston.
What is mechanical work?
If the spark plug fires during the exhaust stroke, will it create a useful power stroke?
No. The piston is expelling exhaust instead of compressing a fresh mixture.
Put these events in the correct order: spark occurs, mixture is compressed, piston moves down from combustion.
Mixture is compressed → spark occurs → piston moves down.
During this stroke, the exhaust valve opens and burned gases leave the cylinder.
What is the Exhaust Stroke?
This part controls when the intake and exhaust valves open and close.
What is the camshaft?
This is why the exhaust stroke is necessary: remove these from the cylinder so the engine can begin another cycle.
What are burned exhaust gases?
If the exhaust valve stayed closed after the power stroke, what would happen to the burned gases?
They would remain trapped in the cylinder.
Put these events in order: exhaust gases leave, air/fuel enters, mixture is compressed, combustion produces power.
Air/fuel enters → mixture is compressed → combustion produces power → exhaust gases leave.
List the four strokes in order.
What is Intake → Compression → Power → Exhaust?
This component uses an electrical spark to ignite the compressed air/fuel mixture.
What is the spark plug?
A 4-stroke engine needs these three things to happen at the correct time: the movement of the piston, the opening and closing of the valves, and the ignition of the mixture. What is the general concept that coordinates all three?
What is engine timing?
An engine has fuel and spark, but the intake valve never opens. Which part of the 4-stroke cycle is immediately affected, and why?
The intake stroke, because the engine can't properly bring the air/fuel mixture into the cylinder.
Starting with the intake stroke, describe what happens to the piston and valves during all four strokes.
Intake: piston down/intake open → Compression: piston up/both closed → Power: piston down/both closed initially → Exhaust: piston up/exhaust open.