Engine Flashcards
What are the 4 strokes in a 4 stroke cycle?
1) Induction/intake: piston moves down
2) Compression: piston moves up
3) Power/combustion: piston is forced down from combustion
4) exhaust: piston goes back up
Describe what happens in each stroke
1) intake: piston moves down from top dead center to bottom dead center. Intake valve opens
2) Compression: intake and exhaust valves are closed while piston moves up. Air and fuel becomes compressed which allows cleaner combustion of fuel
3) Power/combustion: combustion happens
4) exhaust
What is scavenging?
When the remaining exhaust gas leaves the exhaust port. Helps cool combustion chamber and fresh air comes in
How does the fuel air mixture get inducted?
Atmospheric pressure forces the fuel/air mix into crankcase (under the piston)
What produces torque at the crankshaft?
The force of the expanding gas pushing down piston. Force is produced via the connecting rod
What is the transfer port?
Port in the engine used to transfer charge from crankcase to cylinder head. The fuel/air mixture is transferred through transfer port to top of cylinder (top of piston) where it’s then combusted and exhausted
How do you increase efficiency of scavenging process?
The port exposure timing and the gas dynamics
How do you prevent losing fresh charge down the exhaust?
The piston crown has a deflector
How are 2 stroke engines well lubricated?
The oil from the in the crankcase. It provides oil mixed in with fuel air mixture. Oil is burnt in with the combustion process and produces hydrocarbon emissions
What are the pros and cons of 2 stroke engines?
Pros: more power due to extra power stroke
Cons: expansion stroke is short and gas efficiency is poor. Emissions are higher too
How does a diesel engine create combustion?
The air is sucked into the chamber, gets compressed to raise temp above self ignition point of fuel
In a 2 stroke engine, how are exhaust gases exited?
The incoming charge forces the exhaust gases out of the engine via the valves
