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Aicraft Reciprocant Engines Weeks 5 -6
Eng. JAIRO ANDRÉS GUTIÉRREZ S
2
Cylinders
Place were combustion takes place
• Strong to withstand pressure forces
• Lightweight metal construction
• Good heat conduction properties
• Easy – inexpensive to manufacture / inspect / maintain
3
Cylinders
• Cylinder consists of cylinder head and the cylinder barrel
• Cylinder Head constructed from aluminum alloy
• Barrel usualy built from steel
4
Cylinder Head
• Provides a place for the combustion to happen
• Provides heat conductivity for cooling
• Provides a mounting point for valves, spark plugs and their assemblies.
• In air cooled engines, cylinder heads must have cooling fins
5
Cylinder Barrel
• Usually built from a high strenght material
• Steel alloy forging with inner surface hardening
• Hardening by exposing steel to ammonia / cyanide gas (cianuro / ammoniaco) -> nitriding
• If barrels have got wear they can be overhauled to proper dimensions
Cylinder - Numbering
Source: FAA AMT Powerplant Vol 1
Valves
Source: FAA AMT Powerplant Vol 1
8
Valves
• Intake / Exhaust Valves
• Mushroom and Tulip Types (Hongo / Tulipán)
• Subjected to high temperatures, stresses , etc.
• Intake valves operate at lower temperatures (usually built from nickel chromiun steel)
• Exhaust valves operate at higher temperatures: Cobalt chromiun steel or other temperature resistant alloys
Aviation Reciprocant Engine Valves
Source: FAA AMT Powerplant Vol 1
Mechanical Arrangement
The Exhaust Valve
needs to be open,
to allow the
burnt gases out
The Inlet Valve
needs to be open,
to allow the
fuel/air mixture in
Inlet Valve Exhaust Valve
Valve Operating Mechanism (Opposed Engines)
Source: FAA AMT Powerplant Vol 1
Mecanismo del eje de levas en motores opuestos – sistema hidráulico
Source: FAA AMT Powerplant Vol 1
Valve Operation Push Rod Mechanism
Mechanical Arrangement
Rocker
Rocker Shaft
Return Spring
Valve Seat
Push Rod
Cam Shaft
Valve Lift
Inlet Valve Closed
Valve opening motion:
1) Starts at rotating camshaft
2) Camshaft moves a pushrod and
lift the rocking lever
3) Through a rocker shaft the valve
opens
4) Spring helps the valve returning
to its place
Valve Operation
Mechanical Arrangement
Overhead Cam No Rocker
Overhead Cam and Rocker
Cam Shaft
Return Spring
Valve
Rocker Arm The less parts there are,
the more accurate the work with
opening and closing times,
and the more efficient
the engine.
Some engines feature a
hydraulic system for valve opening
(closing via a return spring),
but driven by a cam.
Some manufacturers now fit
VARIABLE valve timing;
to ensure that the valves
operate at the optimum point
at all rpm values
to gain maximum efficiency
from a piston engine.
Valve Operation The Cam Drive
Mechanical Arrangement
Modern Engines
use a toothed
rubber belt to drive
the cam shafts
Cam Drive Mechanism
Pistons and Crank Shaft
Twin Cam System
Chain Tensioners
Valve Operating Mechanism (Opposed Engines)
Source: FAA AMT Powerplant Vol 1
Mecanismo del eje de levas en motores opuestos
Source: FAA AMT Powerplant Vol 1
Mecanismo del eje de levas en motores opuestos – sistema hidráulico
Source: FAA AMT Powerplant Vol 1
Rodamientos
Source: FAA AMT Powerplant Vol 1
Reduction Gears
Source: FAA AMT Powerplant Vol 1
Source: FAA AMT Powerplant Vol 1
Aircraft Reciprocant Engine Definitions
• DISPLACEMENT (CILINDRAJE) • CYLINDER BORE • PISTON STROKE • TOP DEAD CENTER / BOTTOM DEAD CENTER (TPC Y BDC) - • COMPRESSION RATIO (RELACIÓN DE COMPRESIÓN • VOLUMETRIC EFFICIENCY| • BRAKE HORSEPOWER
DISPLACEMENT
DISPLACEMENENT (CILINDRAJE O DESPLAZAMIENT) REFERS TO THE TOTAL VOLUME DISPLACED BY THE ENGINE IN A THERMODINAMIC CYCLE. IT MAY ALSO REFER TO THE DISPLACEMENT OF A SINGLE CYLINDER DISPLACEMENT= CYLINDER DISPLACEMENT (Cd) * # of Cylinders
ENGINE BORE AND STROKE
REQUIRED TO MEASURE ENGINE SIZE “Engine size is determined by the cylinder diameter (BORE), the amount of piston travel (STROKE) and the number of cylinders”
ENGINE BORE AND STROKE
ENGINE BORE
Diameter of the engine cylinder
Measured across the cylinder, parallel with the top of the block
Cylinder bores vary in size, but typically range from 3–4" (75–100 mm)
PISTON STROKE
Distance the piston moves from top dead center (TDC) to bottom dead center (BDC)
Crankshaft journal offset (throw) controls the piston stroke
MAIN CALCULATIONS
This is the main formula to be used with the given numbers
But also: Crankshaft Offset*2 = stroke
Bore/Stroke Ratio
Bore – to –Stroke Ratio
COMPRESSION RATIO Compares the cylinder volume with the piston at TDC to the cylinder volume with the piston at
BDC
Ratio of swept volume V1 divided by combustion chamber volume V2
Clearance volume = combustion chamber volume
Compression Ratio
Source: FAA AMT Powerplant Vol 1
Compression Ratio
Compression Ratio – Gasoline Engine
Compression Ratio – Diesel Engine
Volumetric Efficiency
• Simply put, it is the ability of the engine to breath in on the Intake Stroke
Formula:
Volumetric Efficiency =
actual volume of air taken into each cylinder
volume of the cylinder
Ratio of air drawn into the cylinder and the maximum amount of air that could enter the cylinder
Volumetric Efficiency
Engines are capable of only 80–90% volumetric efficiency. Restrictions in the ports and around the valves limit airflow. Can you name some of the factors that would impede air flow into and engine?
Brake Horsepower Example
Exercises Examples
If one piston displaces 25 cu. in. and the engine has four cylinders, what is the engine displacement?
25 cu. in. 4 = 100 cu. in.
If one piston displaces 500 cc and the engine has six cylinders, what is the engine displacement?
500 cc 6 = 3000 cc = 3.0 L
Exercises
A continental IO engine has got 6 cylinder, a bore of 5.25in, a stroke 4in. Determine
a) Cylinder Displacement
b) Engine Displacement & Bore – Stroke ratio
c) Compression ratio if volume in combustion chamber(clearance volume) is 11.5in3
Workshop Draw and calculate an engine with the following parameters:
1) Cylinder displacement must be between 50 to 100 in3 per cylinder
2) Compression ratio must be at least 7:1 or more. Maximum compression ratio is 10:1
3) Cylinder number must be 4 or 6
4) Calculate crankshaft distance to crankpin
5) Bore to Stroke ratio from 1:1 to 3:1
Workshop Calculate:
1) Bore size, Stroke Size
2) Crearance volume, connecting rod size, crankpin to crankshaft center distance
3) Draw at scale
4) Find real displacement with a volumetric efficiency of 90%.
5) Find the piston average speed if RPM´s are 2700
6) Use the following website to understand connecting size to stroke (also 2 times crankpin to cranshaft distance) http://www.torqsoft.net/piston-position.html . Compare both your drawing with the website calculations
Assignment 1 – Exposition (35%)
Explain a specific aircraft piston engine system The following options are available: • Aircraft engine Fuel System • Aircraft engine Induction/Exhaust System • Engine Starting, Ignition & Electrical • Aircraft engine Lubrication System • Aircraft engine Cooling System (liquid and air
cooling) • Aircraft engine Propeller System (fixed and
variable pitch)
Assignment 1 – Exposition (35%)
What I want? Groups 3 People – INDIVIDUAL GRADES At least 50 min long presentation • Why is the system important? Main functions • Description and function of system components • A complete exposition of the system (types, parts, system
diagram, work scheme, videos, etc) • Use images from bibliography, AMM, IPC, etc • System Diagrams • Indicating Instruments in Aircraft Cockpit (can use Flight
Simulator) • Maintenance Practices (basic)
Assignment 1 – Exposition (35%)
Nota:
La nota se asignará de acuerdo a:
• Claridad en la exposición.
• Profundidad en la explicación del sistema.
• Ayudas audiovisuales
• Profesionalismo (ejemplos: bajará nota textos largos leidos, letra pequeña, colores que dificulten lectura, etc.)
• Resolución de preguntas
Assignment 1 – Exposition (35%)
REFERENCES: • FAA-H-8083-32-AMT-Powerplant-Vol-1 y Vol-2
(gratis) • FAA Pilot Handbook- Chapter 06 (gratis)
(http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/pilot_handbook/media/PHAK%20-%20Chapter%2006.pdf)
• Antonio Esteban Oñate, Conocimientos del Avión (biblioteca)
• Aircraft powerplants, Michael J. Kroes Thomas W Wild (biblioteca)
• AMM´s, IPC, etc (already given to students)
Assignment 2 (15%)
Search for FAA accident records on Reciprocating engines. Find technical documentation on the type (manuals, views, drawings, TC), and explain to class what happened.
http://www.ntsb.gov/aviationquery/
Assignment 2 (15%)
1) Explain what happened, and the possible causes, type of aircraft, etc. 2) Use technical documentation to detaily explain the parts involved. Give P/N, location, system components
3) If it involves a system, explain how it works
4) Give conclusions and maintenance recommendations so it wont happen again
Piston Engine Types - Layouts
Firing Order: -
1 – 4 – 3 – 2
Horizontally Opposed (Or flat) 4 Vee 8
1 – 8 – 4 – 3 – 6 – 5 – 7 – 2