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
-
- 1 / 270
-
Lernkarten
4 Stroke piston engine => teh theoretical valve and ignition settings are readjusted in order to increase the:
overall efficiency
Piston Engine vergleich mit gas turbine: Volumen und Vorgang
Piston engines: Constant Volume and the processes are intermittent (sequential)
Gas Turbine: Constant Pressure und in gas turbine engine is continuous
Oil: functions?
1. Schmierung 2. Cooling 3. Protection 4. Cleaning 5. Dämpfer => Kurbelwelle 6. Sealing => oilfilm an Zylinderwand 7. Hydraulic
Oil: 15/50 W ?
15 => wenn dünnflüssig (Sommer) 15 sek. um durchzufliessen 50 => wenn dickflüssig 50 sek um durchzufliessen => Winter
Oil: wenn man 2 verschiedene Oils hat, auf was muss man achten?
synthetisches Oil und Mineral Oil nie mieseren => Mineral Oil braucht man bei einer Überholung
Oil: Flash point
Oil wird erhitzt und bei dieser Temperatur gibt es eine Stickflamme ohne dass das Oil beginnt zu brennen
Oil: Flame point
Temp. bei dem das Oil beginnt zu brennen bzw. wenn man die Feuerquelle entfernt, brennt es weiter!
Unterschied Dry sump and Wet Sump?
Dry Sump: Oil nicht mehr im Motor => Externer Oiltank => Bei Gasturbinen oder Kunstfliger => Return by a Returnpump
Wet Sump: Oil bleibt im Motor => Return by Gravity
Oil System => Wo fliest das Oil überall durch ?
1. Oiltank (Storage) ==> Indicator (Sensoren)
2. Inlet to the pressure pump 2.1 Pressure pump ==> Pressure ==> Pressuresensoren (Pressure low, temp. high!)
3. Filter
4. Heat exchanger ==> Dif. Druck Sensoren + Bypass
5. Scavenage/Return Pump to Oiltank 5.1 Entlüftung von den Gasen (Breather/Vent)
Pressure Pump oder Scavenge/Return pump mehr leisten?
Die scavenge/Return pump muss mehr leisten, denn das Oil muss zurück fliessen, sonst gibt es Defekt
Wo wird der Oildruck gemessen?
Oil wird dort gemessen, wo keine Druckverluste mehr zu erwarten sind => Nach dem Filter ==> Möglichst nahe am Motor
Poweroutput setzt sich zusammen?
Torque x RPM
MAP = Manifold pressure hat es nur bei?
Only by Kolbenmotoren und nicht bei Pistons => Dort Torque nehmen
Was ist der MAP
Manifold pressure ist der Druck, welcher auf die Valves drückt
Wie misst man den Schub bei Turbinen? Denn bei kolben nimmt man den MAP, welcher ja bei den Pistons nicht vorhanden ist.
Nimmt N1 => Kurbelwellen im Fan => Hat vor und hinter dem Treiber an Staticrohr, welcher den statischen Druck misst bzw. den Druckunterschied ==> Wenn abgestellt hinten und vorne 1 ==> 1:1 (Windstill)
Welche ARt von Schmierung ist das?
Nasssumpf => Wenn es im Return flow keine Pumpe hat, wo das Oil zurück in den EXTERNEN Tank bringt, ist es eine Nasssumpfschmierung
3 Tank Arten
1. Bladder tank: WIng or fuselage => synthetic rubber and nylon tissue
2. Drum tank: older aircraft => aluminium container in the wing tips
3. Intergral tanks: larger aeroplanes
Für was ist das Vent System im Fuel Tank da?
a) suction inside teh tank in case of decreasing ambient temperature and fuel usage
b) excessive (übermässig) pressure inside the tank in case of increasing ambient temerature or during fuel refill
Wie kannst du die Fuel quantity im Tank feststellen? Was ist das Problem?
Mit einem float type sensor => Problem: wenn der Schwimmer nicht dicht Ist und sich füllt --> wird zu viel Fuel reingelassen und falsches Gemisch --> Motor stellt ab weil der Verfasser überläuft
For what you have auxiliary pumps or booster pumps in a fuel system?
a) may deliver fuel when the engine-driven pum is not operating ==> Before engine Start
b) during EDP failure
c) they can also be used for vapour suppression within the fuel system by increasing fuel pressure
For what are primer pumps used?
deliver additional fuel from the tank to the cold engine to assure a proper engine start. => in injection type engines auxiliary pumps are used
4 types of fuel pumps?
1. Gear type pump: fluid is picked up by the teeth amd transported around the casing to the outlet
2. centrifugal type pump: In the tank of large transport aeroplanes
3. vane type pump: fluid is transported by the vanes along the eccentrically casing
4. pistom type hand pump
WHat is a pressure relief valve ?
wenn der Druck zu klein wird, schliesst dieses Valve
petrol engines: combustion process is started by?
disel engines: combustion process is started by?
petrol engines: combustion process is started by the spark plugs
disel engines: combustion process is started by teh high compression heat
EGT ?
Exhaust gas temperature
1:25 is which mixing ratio?
Fuel (1)- Air (25) Mixture
CCM
chemically correct mixture or stoichiometric mixture => EGT am höchsten => highest combustion temperature is reached with a fuel.air mixture of 1:15 => Fuel and air are used up completely for combustion
BPP ?
Best power point => 1:12.5 => The power curve, like the flame front velocity, is at its optimum when the fuel-air mixture is 1:12,5
Fuel-Air mixture: temperature can be lowered by?
a) the mixture to teh richer (of fuel) side resulting in cooling fuel surplus
b) leaner (Mager) side resulting in cooling air surplus
Fuel-Air mixture: the advantage of rich mixture is? the disadvantage?
Advantage: cooling effect of the fuel surplus; avoidance of self-ignition
Disadvantage: high fuel consumption; exhaust gas smoke; spark plug fouling (Schmutzig)
Fuel-Air mixture: The advantage and Disadvantage of a lean (weak) muxture is:
Advantage: low fuel consumption
Disadvantage: high temperature at about 1:15; lower power output when leaner than 1:12,5
Fuel-Air mixture: Engine start?
the engine is cold ==> Fuel condenses is high and fuel doesn't vaporize ==> non ignitable => a mixture of 1:10, but too much priming can cause a flooded engine
Fuel-Air mixture: T/O power ?
the engine is extremely heat stressed => a mixture of 1:10 = The surplus fuel provides the necessary internal cooling during T/O => 1:12,5 cannot be used, Sonst engine tooooooo hot
Fuel-Air mixture: Climb Power?
the engine needs internal cooling during climb ==> high mixture of 1:10
Fuel-Air mixture: Cruise power ?
cooling is provided and you need high power ==> BPP of 1:12.5 may be used
Fuel-Air mixture: Lower air density leads to....?
Lower air density leads to air mass flow reduction, the fuel flow (FF) has to be reduced to get the same mixture ratio as at low altitudes
Carburettor: Working principle of a float type carburettor
the intake stroke the air passes through a venturi or throat inside the carburetor => creates a lower static pressure => The pressure differential forces fuel from the discharge nozzle into the intake air stream
What is the => static pressure after throttle by the carburettor?
Manifold Air Pressure MAP
Carburettor: => Idle?
idle the throttle nearly closed =S sufficient suction is now created by the high velocity airflow at edge of the nearly closed throttle, where the fuel is discharged from the id passage => the fuel flows through the slow running duct or idling system
Was machst du mit dem Mixerhebel?
Mixerhebel: wie viel Treibstoff zufliesst und es wird nicht das Gemisch beeinflusst --> Treibstoff beeinflusst dann das Gemisch
