Principles Of Piston Engine Flashcards
What Is The Otto Cycle
4 Stroke Constant Volume Engine Cycle
4 Stages in Otto Cycle
Induction,Compression,Power,Exhaust
8 Throws
Crank Throw is the distance between crankshaft and crank pin
Firing order of 4 cylinder engine
1,3,4,2
Reduces stress on crankshaft
Advantage of a smaller stroke
Saves weight as less mass
How many degree does the crankshaft turn for the cycle
720 degrees
One Stroke TDC to BDC
180 degrees
Crankshaft
Converts piston linear motion to rotary motion
Camshaft
Rotates half the speed of crankshaft
Operates valves via push rods
Crankcase
Main structural element of engine
Light/strong alloy magnesium
Mounting points
Crank Assembly
Compromises crankshaft, piston, connecting rods
Induction 1st stage
Inlet Valve Opens TDC
Volume increase/pressure/temp reduce
BDC valve closes
180 degree rotation from TDC to BDC
Compression 2nd stage
Inlet Valve/Exhaust valve closed
BDC to TDC
180 degrees
Pressure/temp increases
Volume decreases
Power 3rd stage
TDC to BDC
Volume increases/pressure and temp reduce
180 degree rotation
Exhaust
Exhaust valve inlet opens (smaller)
Pressure/temp increase as piston returns to TDC
Inlet Valve Lead/Lag
Inlet valve opened on return to TDC after exhaust stroke
Inlet valve remains open beyond BDC after induction/prior to combustion
Exhaust Valve Lead/Lag
Exhaust opened at end of power stroke
Remains open after TDC
Overlap
Period when inlet/exhaust open at the end of exhaust phase
“Scavenging” help draw mixture
Ignition Timing
Time before TDC on compression
+ increases peak pressure/power
-Retarded on low rpm to prevent damage/ineffectiveness
Piston engine compression ratio
The cylinder volume with the piston at bottom dead centre to the cylinder volume at top dead centre
Compression Ratio
Largest volume to smallest volumes
Total volume to clearance volume
Volume at BDC to volume at TDC
Clearance volume
Volume in cylinder at TDC
Total Volume
Volume in cylinder at BDC
Mechanical efficiency of a piston engine
Around 80%
Ratio of actual power produced at propeller shaft to theoretical power
Piston engine thermal efficiency
33%
Ratio of work done by engine to the mechanical equivalent of heat energy released
Detonation during flight corrective actions
Reduce manifold pressure (bring throttle back)
Fully enrich the mixture
Purpose of camshaft
Opens the valves at half crankshaft speed
What do valve springs do
Closes the valves
The Bore
Area of piston and rings
Stroke
From TDC to BDC
Compression ratio
Is the ratio of the largest volume (total volume) to the smallest volume (clearance volume)
Thermal Efficiency of a piston engine
30%
Mechanical efficiency of a piston engine
95%
