Piston Engines
Piston Engines
Piston Engines
Using the altimeter in the cockpit how can we measure "pressure altitude"?
A rich mixture in terms of piston engine fuel system supply to the induction manifold is a mixture of air to fuel.
For maximum endurance the mixture control should be set to:
What is the best method for limiting the effects of vapour locking?
The purpose of the accelerator pump is?
In an aircraft equipped with a float type carburettor and a constant speed propeller, carburettor icing would probably first be detected by
How is a stable idle achieved in the carburettor?
The octane rating of a fuel characterises the :
For piston engines, mixture ratio is the ratio between the :
Which power settings are most likely to promote detonation in petrol engines?
Which statement is correct regarding fuel energy density?
What effect does the mixture fuel-air have on the flame front velocity
On a climb the decrease in pressure causes ....
When the carburettor air intake is in "Hot Air" the power output of the engine is reduced because:
What is the normal indication that a petrol engine is suffering from "Detonation"?
When would a pilot most likely expect carburettor icing?
Tetra ethyl lead is added to some aviation gasoline fuels to:
The colour of Aviation gasoline 100 LL is:
What is the purpose of the priming pump?
What is the purpose of power enrichment in a carburettor?
2 Groups of engines
1. Piston engines 2. gas turbine engines systems
Piston engines 2 arten
a) Unboosted/ Normal aspirated engine b)boosted
Unboosted/ Normal aspirated piston engine
the ambient air is drawn into the cylinder by the piston
boosted piston engines
a charger delivers compressed ambient air (more air mass) into the cylinder
Turboprop
gas turbine driving a propeller to create the thrust force
Turbofan
gas turbine driving a fan that creates thrust force as the reaction force to the acceleration of the air in the nozzle
Grundprinzip Piston engine
The high pressure inside the cylinder during combustion creates a force on typ of the piston, which is transmitted to the crankshaft, creating torque.
Was kann bei inverted cylinders passierenN z.B. beim Sternenmotor
Es entsteht ein Hydraulicing (oil flood) => Oil flows down into the cylinder head and blocks the movement of the piston. This oil must be drained (Säubern) from the cylinder by removing the spark plug before engine start
Welche Piston engines kommen am häufigsten in Airplanes vor?
Horizontal opposed air-colled engines ==> Boxer => 4-6 cylinder
Sternenmotor
Kurbelwellen in der Mitte => Ungerade Anzahl Zylinder ( bei 2-Reihiger Motor = gerade Zylinderanzahl) => Daraus ergibt sich die Zündreihenfolge
Verschiedene Arten Otto-Motoren
a) Reihenmotor b) V-Motor (Nockenwelle entscheidet, ob schneller oder langsamer Motor) c) Boxermotor (jeder Zylinder hat 2 Kerzen
vgl Bild
1) Zylinder 2) Kurbelwelle (Crankshaft) 3. Kurbelgehäuse (Crankcase) 4. Heat exchange
vgl. Bild
1. Vc (Clearance Volume) 2. TDC Top dead centre 3. bottom dead centre 23. Distance: length of stroke 4. Piston 5. Connecting Rod 6. connecting rod force 7. Crankshaft
Torque
F Rod * Arm F Rod= Connecting rod force
V Total im Zylinder
Vc + Vs = Vt Vc = Clearance Volume = Between TDC and the top of cylinder Vs = displacement between TOD and BDC
Compression ratio
\(Compression ratio = {Vs + Vc \over Vc}\)
Stroke
Distanve between TDC and BDC
Long Stroke engine where teh sroke is greater than the piston Bore (Zylinderbohrung) führt zu ?
Kraft mal Arm ist hier grösser => Grösser Tork
Short Stroke Engine where the stroke is less than the piston bore ist der Fall, wo?
Bei Rennmaschinen
3 factor for the power output of a single cylinder engine
1. Weight of air mixture taken in (Wie viel Gemisch) 2. Amount of compression 3. Number of working/power strokes per Minute = Drehzah
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Lernkarten
2 Groups of engines
1. Piston engines 2. gas turbine engines systems
Piston engines 2 arten
a) Unboosted/ Normal aspirated engine b)boosted
Unboosted/ Normal aspirated piston engine
the ambient air is drawn into the cylinder by the piston
boosted piston engines
a charger delivers compressed ambient air (more air mass) into the cylinder
Turboprop
gas turbine driving a propeller to create the thrust force
Turbofan
gas turbine driving a fan that creates thrust force as the reaction force to the acceleration of the air in the nozzle
Grundprinzip Piston engine
The high pressure inside the cylinder during combustion creates a force on typ of the piston, which is transmitted to the crankshaft, creating torque.
Was kann bei inverted cylinders passierenN z.B. beim Sternenmotor
Es entsteht ein Hydraulicing (oil flood) => Oil flows down into the cylinder head and blocks the movement of the piston. This oil must be drained (Säubern) from the cylinder by removing the spark plug before engine start
Welche Piston engines kommen am häufigsten in Airplanes vor?
Horizontal opposed air-colled engines ==> Boxer => 4-6 cylinder
Sternenmotor
Kurbelwellen in der Mitte => Ungerade Anzahl Zylinder ( bei 2-Reihiger Motor = gerade Zylinderanzahl) => Daraus ergibt sich die Zündreihenfolge
Verschiedene Arten Otto-Motoren
a) Reihenmotor b) V-Motor (Nockenwelle entscheidet, ob schneller oder langsamer Motor) c) Boxermotor (jeder Zylinder hat 2 Kerzen
vgl Bild
1) Zylinder 2) Kurbelwelle (Crankshaft) 3. Kurbelgehäuse (Crankcase) 4. Heat exchange
vgl. Bild
1. Vc (Clearance Volume) 2. TDC Top dead centre 3. bottom dead centre 23. Distance: length of stroke 4. Piston 5. Connecting Rod 6. connecting rod force 7. Crankshaft
Torque
F Rod * Arm F Rod= Connecting rod force
V Total im Zylinder
Vc + Vs = Vt Vc = Clearance Volume = Between TDC and the top of cylinder Vs = displacement between TOD and BDC
Compression ratio
\(Compression ratio = {Vs + Vc \over Vc}\)
Stroke
Distanve between TDC and BDC
Long Stroke engine where teh sroke is greater than the piston Bore (Zylinderbohrung) führt zu ?
Kraft mal Arm ist hier grösser => Grösser Tork
Short Stroke Engine where the stroke is less than the piston bore ist der Fall, wo?
Bei Rennmaschinen
3 factor for the power output of a single cylinder engine
1. Weight of air mixture taken in (Wie viel Gemisch) 2. Amount of compression 3. Number of working/power strokes per Minute = Drehzah
Ablauf 4 Takte
1. Intake stroke 0 - 180 Grad Isochoric: piston from TDC to BDC and sucks in a mixture of fuel and ambient air through the open untake valve of the cylinder
2. Compression stroke 180 - 360 Grad Adiabatic: piston BDC to TDC, the mixture inside the cylinder is compressed due to the closed valves. The ignition and the isochorix combustion of teh mixture finish teh compression stroke
3. Power stroke 360 - 540 Grad Adiabatic: the pressure has increased due to compression and combustion and now pushes the piston toward BDC
4. Exhaust stroke: 540 - 720 Grad Isochoric; Piston trafels from BDG to TDC and pushes teh burned gas through teh opened exhaust valve
The ignition
Die Zündung
Isochoric
Isochor ist ein Begriff der Thermodynamik. Er beschreibt eine Zustandsänderung eines Gases, bei der das Volumen im System konstant bleibt.
spark plugs
Zündkerze
Adiabatic
Eine adiabatische Zustandsänderung (gr. α a „nicht“ und διαβαίνειν diabaínein „hindurchgehen“) ist ein thermodynamischer Vorgang, bei dem ein System von einem Zustand in einen anderen überführt wird, ohne Wärme mit seiner Umgebung auszutauschen.
the real timing of ignition
Because of the relatively low flame front velocity the ignition of the few-air mixture has to occur at approximately a 20 Grad crank before TDC !
The real timing of the valves => the maximum fuel-air mixture charge (closing)
closing the intake valve past BDC (after finishing the intake stroke)
The real timing of the valves => the maximum fuel-air mixture charge (opening)
opening the exhaust valve before BDV towards the end of the power stroke
The real timing of the valves => the maximum fuel-air mixture charge =>= Overlap at TDC
exhaust valve is still open when the intake valve opens before the end of the exhaust stroke and closes only when the intake stroke starts => Some cooling for the exhaust valve
Disel has no spark plugs => Wie zündet er?
durch geh high compression heat => Zum unterschied zum gaseoline stroke is the pressure continuous at constant pressure for a certain time
Which engine (gasonlien or disel engine) has a higher compression ratio?
Diesel
How is the ignition inititated in a gasoline engine ?
By a spark plugs
Wann entsteht der höchster Druck
nachdem man die 0 Grad Grenze überschritten hat => Sonst ganzer Druck nur auf die Kolben => Jetzt ca bei 6 Grad den dem OT den grössten Druck => Bewegt sich schon in die richtige Richtung!
Thrust equation
T = mAir (VOut - VIn) VIn = TAS mAir = the air mass flow rate
Power
Power is needed to turn the propeller
P = Torque * RPM * c ==> Force * distance * RPM * c c= Konstant factor
BHP
Brake Horse Power ==> BHP = SHP ( Shaft horse power) => This is the HP actually available at the propeller shaft and always less than indicated HP due to friction => Um zu messen muss man den Motor belasten => a pony brake or dynamometer
BHP setzt sich zusammen aus
BHP = IHP (Indicated horse power) - Friction Horsepower
Friction Horsepower
Alle Verluste die ich rechnen kann O> Power loss due to friction and power abosorbed by the engine => Pumps; M^magnetos, Alternator
Indicated Horsepower
Nur theoretisch gerechnet => without reference to friction losses within the engine
Thermal Efficiency
5% Wiederstande
20% Cooling Wenn das Gemisch veringert wird, wird der cooling prozess kleiner bis wir so ein grosses Luftgemisch haben, dass es kühlt Best Gemisch: 15 kg Kuft zu 1 Liter Treibstoff verbrennen
45 % Wärme NUR 30 %!!!!!! für useful work
