Extra Shit Flashcards
What is TDC and BDC
Piston at max distance from crank shaft.
Piston at minimum distance from crankshaft
What is clearance volume and swept volume
Clearance - the volume remains above the piston of an engine when it reaches top dead centre
Swept - the volume through which a piston moves as it makes a stroke.
What is compression ratio?
Swept volume + clearance volume
What is firing interval?
How often you can have a power stroke.
The number of degrees per cycle/number of cylinders.
What is valve lead and lag
Lead - early opening of exhaust valve on power stroke to assist in scavenging burnt gases.
Lag - late closing of inlet so allows more charge to get in meaning increased pressure.
What is valve overlap and its advantage
Both valves being open at same time.
Increase amount of charged induced into cylinder, helps with scavenging and cooling.
What is spark advance?
Supply of the ignition spark on the compression stroke earlier than TDC. Done so highest pressure is developed before con rod and crankshaft are at 90 degrees.
What is crankthrow
Radius of camshaft
Where is brake power measured
Propellor hub
What is engine torque
Turning force
T=fd
What is brake horsepower
Actual power output at crankshaft
What is indicated power
Total power developed within the cylinders by the combustion process. (What the engine manufacturer says engine has)
What is friction power
Power lost due to friction and other things.
Brake power formula
BHP = IP - FP
What is rated power?
The brake power that can be continuously maintained by an engine at a stated rpm (and manifold pressure if with a CSU)
E.g 112hp at 2600rpm
What is rated/critical altitude
The altitude at which engine will develop its rated power.
As altitude increases, density decreases so engine develops less power. So for non supercharged engines it’ll be close to sea level.
What is full throttle height?
The altitude at which a given manifold air pressure set can be maintained at a given RPM.
Lower the map selected, the greater the altitude to which it can be maintained.
What is brake thermal efficiency.
The overall efficiency of the engine. Losses are due to cooling, exhaust gases and friction.
Can also be expressed as how much fuel is being used at any one point in time (brake specific fuel consumption)
What is mechanical efficiency.
Part of the overall thermal efficiency of the engine. It’s the ratio between indicated power and brake power.
Most efficient rpm it is 90%
What is volumetric efficiency
How efficient the engine is at breathing or taking in the induction of the fuel air mixture.
100% efficiency, volume drawn into the cylinder must be equal to volume displaced by piston.
Factors reducing it is drag from walls of pipes/manifold, inertia of the charge and rate of inflow.
How are the efficiency equations remembered.
Thermal efficiency = fuel flow/brake power (To Fly Bravely)
Mechanical = brake power/ indicated power (Means Being Into)
Volumetric = volume of charge/piston displacement (Vicious Vibrating Planes)
What are the ideal conditions for an engine?
Low temp, high pressure, low humidity
Throttle butterfly valve wide open
Low rpm
Cool induction manifold temperature.
What is manifold pressure?
The measure of the pressure in the intake manifold which is made up of the fuel air mixture and ambient air temperate
What is the relationship with manifold pressure and ambient pressure?
Ambient air pressure decreases with altitude so manifold air pressure must also decrease. So efficient also decreases and power output.
