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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Cartes-fiches
mechanical efficiency
\(x = {BHP \over IHP} * 100%\)
Piston engine efficiency Volumetric
Ability of an engine to fill its cylinder with air. Normal Conditions 100% => Jedoch einige EInflüsse dass es nicht 100 % sind: 1. HIGH RPM = Frictional losses in th einduction system => Less time to feed 2. internal surface roughness 3. trotlle and venturi restrictions
==> Je weiter du steigst, desto kleiner wird der Druck auf den Auspuff => Zylinder entleeren sich einfacher => mehr neues Gemisch hat platz => Leistung nimmt trotzdem abm weil wir verlieren auf der Einflassseite degen dem Dichteunterschied =====> Je höher desto kleinere Leistung
Piston engine effienncies specific fuel consumption
amount of burnt per hour per unit of power ==> Wenn ich kein Schub gebe = Keine HP =>im Verhältnis immenser Treibstoffverbrauch =>
compression Ratio
The more air/Fuel Mixture is compressed before ignition, the higher the pressure and temp after ignition ==> Compression ratio for piston engines is normally between 8:1 and 10:1
\(Compression Ratio= {Total Volumen \over Clearance Volumen }\)
Compression ratio for piston engines is normally
Compression ratio for piston engines is normally between 8:1 and 10:1
Total efficiency
NTotal = Ni (intern efficiency) * nprop (propulsive efficiency coefficient)
BSFC
Break Specific Consumption => Amount of fuel necessary to produce one horse power per hour ==> FF /BHP = BSFC => The lower the BSFC value, the higher the efficiency of engine
MCP
Maximum Continuous power: output of an engine over an unlimited time period
Take off power
Take off power is the maximum power of an engine => only for a limited time e.g. 5 minutes
vgl. Bild
1. valves 2. crankcase 3. crankshaft 4. connecting rod 5. cylinder 6. piston
Crankshaft, ist aus was produziert?
Kurbel => crankshaft is made of forged steel !!! The crank pins carry the connecting roads
Crankcase
Gehäuse => consists of two halves of aluminum alloy ==> Connecting the engine to the airframe
the crankcase supports and drive most of the accessories by engine power. The accessories are:
fuel pump, oil pump, starter motor hydraulic pump
The Cylinder of an air cooled engine consist of
a steel cylinder v^barrel and an aluminium alloy cylinder head
the crank assembly converts the linear piston movement into the
rotary motion of the Crankshaft
The connecting Road: AUfgabe udn aus was gefärtigt?
transfers the piston fore to the crankshaft and is made of forged steel
Piston is made of and Aufgabe
The aluminium alloy piston is equipment withe steel or cast iron piston rings => transfer heat to the cylinder and control the lubrication Schmieren of piston and cylinder
lubrication
Schmieren
the springs
federn
Wie öffnen sich die Valves
Durch Camshaft => Hydraulic Valve Lifter => Push Road => Rocker Arm
Wie schliessen sich die Valves
Valves springs close the inlet and outlet valves
Wie schliessen sich die Valves
Valves springs close the inlet and outlet valves
What makes the hydraluic valve lifter?
the hydraluic valve lifter keeps the valve clearance at zero
Einlassventil ist grösser als das Auslassvetil wieso?
Das mehr Treibstoff hereinkommt => 1. Auslassventil würde sonst mehr wäre speichern 2. Auslassventil öffnet 10 Grad vor => möglichst klein/ Strömt so oder so raus 3. öffnen sonst gegen einen Gasdruck (Grosser Aufwand zum Ventilöffnern)
Valve Temperatur Delta
80 - 120 Grad
Piston hat einen agefressten Deckel Why? Und für was sind die Piston rings?
dass er die Ventile nicht berührt : Rings sind für das Öl
wie werden die Pistons geölt?
1. Nasssumpf = Oel is unterhalb vom Zylinder = Kurbelwelle schleudert Oel in den Zylinder 2. Trockensumpf= externer Öltank
Ventile haben keine Schmiermöglichkeit, denn es darf kein Oel in die Brennkammer kommen. wie schmieren wir diese?
Durch Blei im Treibstoff!!
Blaucher Rauch? schwarzer Rauch?
Blau: zu viel Öl Schwarz: falsches Gemisch
Was passiert wenn das Ventilspiel zu gross ist? zu klein ist?
zu gross: können Zylinder nicht ganz füllen = Leistungsverlust zu klein: schließt nicht mehr ganz => Ventilsitz geht kaput
Wieso leitet das Auslassventil die Wàrme?
zu 40% mit Natrium gefüllt, leitet die Temperatur => bei 97 Grad flüssig = durch schütteln wird das Natrium flüssig==> Zylinder wird zu 80 - 120 Grad weniger heiss
Was sind bearings?
Bei der Connecting Road => Umschliessen Kurbel => die Kurbelwelle das Gehäuse nicht streifen, deshalb hat es öl dort = Kühlende, schonende Funktion => Bearings sind dazu da, wenn es kein öl mehr hat, dass ie Welle trotzdem nicht an der Conecting Road sch
Wieso hat es Blei im Bearing?
Blei im Bearing ist dazu da, dass wenn es kein Öl mehr hat, dass der Motor trotzdem weiterdreht und nicht blockiert ==> Low öl pressure = stellt der Motor ab
SFC
Specific Fuel Consumption : ratio of mass of fuel required to produce a unit of power per unit of time
The power output of a disel engine without a turbo charger is regulated by:
Fuel flow only
Th ecrank assembly of a piston engine comprises the:
Crankshaft, pistons and connecting road
teh crankcase is the component which:
provides a mounting point for most of the engine components ans in which are the main rotating assemblies located
The Crankshaft of a piston engine rotates at:
Twice the speed of the camshaft => each valve must open and close within two revolutions and to achieve this the camshaft is driven at half engine speed
the combustion
die Verbrennung
Assuming the same swept volume and no turbo charger, diesel engines compared to petrol engines:
produce less max. power output
