the aircraft propulsion the aircraft propulsion - VUT [PDF]

THE AIRCRAFT PROPULSION

Aircraft propulsion Contact: Ing. Miroslav Šplíchal, Ph.D.

[email protected] Office: A1/0427

Aircraft propulsion Organization of the course

Topics of the lectures:

1. History of AE, basic of thermodynamic of heat engines, 2-stroke and 4-stroke cycle 2. Basic parameters of piston engines, types of piston engines 3. Design of piston engines, crank mechanism,

4. Design of piston engines - auxiliary systems of piston engines, 5. Performance characteristics increase performance, propeller.

6. Turbine engines, introduction, input system, centrifugal compressor. 7. Turbine engines - axial compressor, combustion chamber. 8. Turbine engines – turbine, nozzles.

9. Turbine engines - increasing performance, construction of gas turbine engines, 10. Turbine engines - auxiliary systems, fuel-control system. 11. Turboprop engines, gearboxes, performance. 12. Maintenance of turbine engines

13. Ramjet engines and Rocket engines

Aircraft propulsion Organization of the course

Topics of the seminars:

1. Basic parameters of piston engine + presentation (1-7)- 3.10.2017

2. Parameters of centrifugal flow compressor + presentation(8-14) - 17.10.2017 3. Loading of turbine blade + presentation (15-21)- 31.10.2017 4. Jet engine cycle + presentation (22-28) - 14.11.2017 5. Presentation alternative date Seminar work: Aircraft engines presentation

A short PowerPoint presentation, aprox. 10 minutes long. Content of presentation: - a brief history of the engine - the main innovation introduced by engine - engine drawing / cross-section - engine performance - operational use - derivate version - technical attractions

Aircraft propulsion Organization of the course

List of engines: • •

Wright Flyer (4-cyl): First engine to fly Anzani Three-Cylinder Engine

•

Anzani (6-cyl): First two-row radial engine

•

Curtiss OX-5 Engine

• •

Continental A-40 (4-cyl): Ancestor of current opposed engines Jendrassik Cs-1 Engine

• •

Allison V-1710 (12-cyl): Most highly developed U.S. V-12 Daimler-Benz DB 605 Engine

•

Pratt & Whitney R-2800 Double Wasp

• • •

General Electric J35 turbojet: First U.S. production axial-flow jet Klimov VK-1F turbojet: Last large centrifugal-flow engine Rolls-Royce Dart.

• •

Bristol Centaurus (18-cyl): Last large British radial Rolls-Royce Conway

•

Pratt & Whitney J57

• • •

Pratt & Whitney TF30 turbofan: First afterburning turbofan Rolls-Royce/Snecma Olympus 593 Engine CFM56 Engine

•

Rolls-Royce Trent Engine

•

General Electric GEnx Engine

•

SMA SR305-230 Engine

•

Continental O-300 Engine

•

Pratt & Whitney Canada PT6 Engine

•

Garrett-Honeywell TPE331 Engine

•

Franklin Six-Cylinder Engines

•

Williams FJ44 Engine

•

Honeywell TFE731 Engine

•

Pratt & Whitney Canada PW600 Engine

Aircraft propulsion Organization of the course

End of course:

1. Seminars syllabus and presentation complete. 2. Exam

– written form – 15 test question 1 (select a,b,c,d) questions reflect the fundamentals working principles and terminology corresponds to ATPL theoretical question – one simple computational example ( for example computing engine power or thrust from given values) Only from memories no additional materials allowed – 45 minutes Exam terms: – First term: 12.12.2017 – Second term: 19.12.2017

Aircraft propulsion Materials

Course materials: 1.

File name:

Location:

Password:

OLE-A_1, OLE-A_2, OLE-A_3 …etc

http://ulozto.cz LU2017

Aircraft propulsion

Source materials:

WARD, Thomas A. Aerospace propulsion systems. Singapore: John Wiley & Sons, c2010, xxvi, 527 s. ISBN 978-0-470-824979. CUMPSTY, Nicholas. Jet propulsion: A simple guide tio the aerodynamic and thermodynamic design and performance of jet engines. Cambridge: Cambridge University Press, 1997, 276 s. ISBN 0-521-59674-2 Rolls-Royce engineers "The Jet Engine, 5th Edition" Technical Publications Department, Rolls-Royce, Derby, England | 1996 | ISBN: 0902121235 https://er.jsc.nasa.gov/seh/ANASAGUIDETOENGINES[1].pdf

Aircraft propulsion 1.Lecture

History of aircraft propulsion The aircraft engines always want more power, more durability, and more efficiency. They also want it in the smallest, lightest package possible.

And it should be easy to manufacture and not cost too much.

More than 100 years to the engineers trying achieve this.

History of aircraft engines Steam engines – first attempts at powered flight

Boiler

1894: Hiram Maxim – 180hp

weight steam engine+boiler aprox 1000kg

Airplane TOW aprox 3200gr

History of aircraft engines - piston

• Application of Internal combustion engine • Flyer Wright - 1903

The engine was modern designed with valve gear

Power - 18 hp , weight aprox 82 kg

Historie leteckých motorů

History of aircraft engines - piston 1908

Cooling was problem first generation of aero engine

Rotary engine Gnome – 50hp at 1200 rpm Weight aprox. 80kg

Crankshaft with cylinders rotate for good cooling

History of aircraft engines - piston

Antoinette Engine 1909 - 1910 50hp weight. 50kg. Liquid cooled

Engine with very good weight /power ratio, but the reliability was not good.

History of aircraft engines - piston

Liberty (Curtiss J2 „Jenny“)

1917 First engine for serial production

History of aircraft engines - piston

modular design allowed create engines with different outputs power Many manufacturers use the same strategy

Liberty engine 12V – 400Hp 1919

Engine of many WWI airplane. Currtis „Jenny „ is most known. More than 30 000 unit was made

History of aircraft engines - piston Pratt &Whitney - Double Wasp engine – 1943

The end of piston engines era. For large aircraft it has been difficult to design more powerful engines

2250 hp – 2800hp

45883 ccm,18 cylinders

History of aircraft engines - piston

Allison Division engine V-1710 engine :

maximum power 1325 hp at 3000 rpm and 51,0 in Hg

nominal power 1150 hp at 3000 rpm and 42,0 in Hg

28021 ccm, 725 kg

The large piston engines have two major groups - radial air-cooled engines and ordinary liquid cooled engines

first run 1930

History of aircraft engines - piston The Lycoming XR-7755 was the largest piston-driven aircraft engine ever produced, with 36 cylinders totaling about 7,750 in³ (127 L) of displacement and a power output of 5,000 horsepower (3,700 kilowatts).

Low TBO of large engines caused the rapidly transition to turbine engines after technology maturing

History of aircraft engines - turbine

First jet engine Heinkel-Strahltriebwerk 1, engine prototype 1936. First flight at 1939. Fuel was hygrogen based gas.

The principles of jet propulsion had been known, but there was no technology required for the construction of up to thirty-20th century

Improved engine was HS3 – Weight 360kg Thrust 450 kg

History of aircraft engines - turbine

Jet engine Rolls-Royce Nene:

thrust 22600N at 12 400 rpm

weight 726 kg , first run 1944

Successful engine, manufactured under license in many countries

History of aircraft engines - turbine First turboprop engine Jendrassik Cs-1 (1937) First run at 1940 Power: 400hp

Efforts to overcome the weaknesses of powerful piston engines

Development was not completed due to war.

History of aircraft engines - turbine

Turboshaft engine - Garrett TPE331 (1961)

Power: 575hp at 2000 rpm (shaft), gen 41700 rpm Dry weight: 153kg

Turboprop engines are dominated in category of regional aircraft

History of aircraft engines - turbine

Turbofan - first commercial motor low bypass ratio Rolls-Royce RB.80 Conway Trust 50 – 70 kN Bypass ratio 3:1 weight 2000 kg

Build year.1950 B707,DC-8

Turbo fan represents a certain combination of advantages of efficient propeller propulsion with speed of jet propulsion

History of aircraft engines - turbine

General Electric CF6 ( 2000) – High bypass ratio engine Thrust 234 – 274 kN Fan diameter 2,6m

Higher fuel efficiency, low emissions

Bypass ratio 4,4

First high bypass ratio engine was Pratt & Whitney JT9D on Galaxy C-5 prototype build year 1968

History of aircraft engines - turbine

General Electric Genx ( 2000) – High bypass ratio engine Thrust 240 – 330 kN Fan diameter 2,8m

Higher fuel efficiency, low emissions

Bypass ratio 19:2

First high bypass ratio engine was General Electric CF6 on DC 10-10 prototype build year 1971

Airlines JET development SUBSONIC ENGINE SFC TRENDS

(35,000 ft. 0.8 Mach Number, Standard Day [Wisler])

Future …..???

Still looking for the perfect propulsion unit

History of aircraft engines in the Czech rep.

Walter - traditional Czech manufacturer of aircraft engines from 1923

Scolar 1936

Power:

volume:

weight: 155kg

180 hp at

2200 rpm

7800 ccm

History of aircraft engines in the Czech rep. Mikron III – 1938 Power:

Volume:

Weight (dry):

For light aircraft or motorgliders like L- 13SW

65 hp at

2600 rpm

2400 ccm 60kg

History of aircraft engines in the Czech rep. 1951

Minor 4-III

Power: 80hp

volume: 3981 ccm

Light training airplanes - Zlín Z-126

History of aircraft engines in the Czech rep.

Walter M337 – 1959

Power 210 hp at 2700 ot.min-1, stroke volume 5970 ccm

History of aircraft engines in the Czech rep.

Walter M 601 - successful turboprop for L410 airplane family

Types of engines and working principles

Type of power plants for airplane • Piston engines + propeller • Turbine-powered • Ramjet • Pulse jets • Rocket engines

Speed range and applications of different types of engines

Aircraft propulsion - terms • Thrust is the force which moves an aircraft through the air. Thrust is used to overcome the drag of an airplane. • Thrust is generated by the engines of the aircraft through some kind of propulsion system. • Thrust is generated most often through the reaction of accelerating a mass of gas.

Aircraft propulsion - terms

Propulsion

• Propulsion means to drive forward. Therefore a propulsion system is a machine that produces a thrusting force to drive an object forward.

Thrust

• Most aerospace propulsion systems produce Thrust (FN) by applying Newton’s Third Law of action/reaction. •Thrust is produced by accelerating a working gas

Thrust of aircraft engines From Newton’s Second Law: •

The rate of change of momentum of an object is directly proportional to the resultant force applied and is in the direction of the resultant force. The resultant force is equal to the rate of change of momentum.

c2  c1 m F m  m.a  F  c2  c1   m c2  c1  t t

Mass flow

steamline

Thrust:

F  m c2  c1   H 2  H1

m   .S .c Kinetic energy production rate

Thrust of aircraft engines Thrust of propeller propulsion unit: m  S1c1  S 2 c2

R   F  m c2  c1 

Control area 1

Control area 2

Increasing of airstream speed outside engine

Thrust of aircraft engines Thrust of jet engine: m  S1c1  S 2 c2

R   F  m c2  c1 

Increasing of airstream speed inside engine

Thrust of aircraft engines Thrust of rocket engine: H1  m .c1  0

H 2   .S 2 .c2  m .c2 2

H 2  H1  m .c2

R  m .c2

Increasing of propellant speed

Thrust of aircraft engines • In aircraft's propulsion system's, performance is measured by: • Propulsive Force (Thrust)

– The force resulting from the velocity at the nozzle exit

• Propulsive Power

– The equivalent power developed by the thrust of the engine

• Propulsive Efficiency

– Relationship between propulsive power and the rate of kinetic energy production

Thrust of aircraft engines Propulsive Force (Thrust) in (a)

 mV   F   g  c exit

exit (5)

 mV     g  c in

m F  V5  Va  gc

Propulsive Power The power developed from the thrust of the engine

W p  FVaircraft

 m   W p   V5  Va   Va  gc 

In this equation, the velocities are relative to the aircraft (engine). For an aircraft traveling in still air,

Vaircraft  Vin  Va

http://web.mit.edu/16.unified/www/SPRING/propulsion/notes/node81.html

Thrust of aircraft engines

Propulsive Efficiency  propulsive 

Kinetic energy production rate

W p

m air  ke5  kea 

Propulsive power

m air / g c V5  Va Va  

  propulsive 

m air 2 V5  Va2   2 gc

2Va 2  V5  Va V5 / Va  1

2 V5  Va Va  V5  Va V5  Va 

Do 328

Thrust of aircraft engines

Do 328 jet

Do 328

Full thrust cond.

Do 328 jet

Thrust of aircraft engines

Air stream velocity: 30 m/s

2x 1,625 kW ( 26,9) kN Cruise speed: 620 km/h Range: 1,852 km Max payload 3,404 kg Takeoff Field Length– MTOW 1075 m

Air stream mass flux: 120 kg/s

2x 26.9 kN thrust Cruise speed: 750 km/h Range: 1,600 km Max payload 3,266 kg Takeoff Field Length– MTOW 1367m

Thrust of aircraft engines

Propulsion fundamentals

• Thrust depends on both the amount of gas moved and the velocity, we can generate high thrust by accelerating a large mass of gas by a small amount, or by accelerating a small mass of gas by a large amount. • Because of the aerodynamic efficiency of propellers and fans, it is more fuel efficient to accelerate a large mass by a small amount. • That is why we find high-bypass fans and turboprops on cargo planes and airliners.

Engines - Propulsion system change input energy into propulsive power - Engine is a machine designed to convert one form of energy into mechanical energy or some kind of output energy. (a mechanical part of propulsion system)

Characteristic power quantities engines Engine Power definition:

• Pe – Effective power or shafthorsepower(shp) can be measured on shaft, or estimated from the indicated horsepower and a standard figure for the mechanical losses

• Pi – Indicated power

power equivalent to the indicated work per cycle , it is completely frictionless

• PN – Nominal power tj. maximum engine power time unlimited

• PTOF – Takeoff power or peak power. maximum engine power - time limited (aprox 3 min)

Characteristic power quantities engines

Engine Power definition:

• Ps – Specific power (typical for turboprops

engine) is the power generated by the engine divided by the mass flow through engine P / Qm (W / kg.s-1)

• Power-per-liter - typical for piston engine Pe  kW  i.Vz  liter 

The power per liter is one of the fundamental characteristics of the efficiency of engine design. The highest ratings, about 74 kilowatts (kW) per liter (100 hp per liter).

Characteristic weight quantities engines

Weight of aircraft engines :

• mDry – Dry weight (engine without coolers, engine mount, oil, cooling fulid an another equipments • Power-to-weight ratio • Specific power

W   kg    N  kg   

Characteristic engine performance Fuel consumption :

• Qm,p – fuel consumption (fuel flow)

• Cm – specific fuel consumption Cm 

3600.Qm , p F

Ce 

3600.Qm , p Pe

1

for jet engine:

kg   N . hod

• Ce – specific fuel consumption

kg.s   

for a shaft engines

kg   W . hod

 

Characteristic engine performance Operational performance:

• Nominal power – engien provides long-term maximum usable power. Typically for climb

• Takeoff power – time-limited maximum power of the engine . • Cruise power – typically 75 to 90% of rated power time unlimited power

• Economic – the lowest fuel consumption • Idle - motor provides the power necessary to overcome internal

resistance and resistance to prop windmilling. In this mode, the engine operates with minimum speed .

Basic requirements for aircraft engines: • Reliability the ability to maintain the engine within • • • • • •

the permissible limits of its properties within a specified time and a specified operating conditions Low weight and minimum dimensions High efficiency Long service life Simple maintenance Price Other - noise, starting porcedure, aceleration, emision

Piston engines

Piston aircraft engines A reciprocating engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. Engine with the internal combustion

Piston engines can be categorized: •

•

By cycle

By fuel (Or by iniciation of combustion)

2 -stroke

4 - stroke Petrol engine – combustion inciated by ignition

Diesel engine – combustion iniciated by injection of fuel

Piston aircraft engines Piston engine types: • By mechanical arrangement

Rotary piston Reciprocating piston

Thermodynamic minimum for heat engines Basic variable: – cp specific heat capacity at constant pressure [J.kg − 1K − 1] – cv specific heat capacity at constant volume [J.kg − 1K − 1] – q specific heat [J.kg − 1] – m mass flow [kg.s − 1] – r gas constant [J.K − 1mol − 1] – χ adiabatic exponent – h enthalpy

Thermodynamic minimum for heat engines



Heat is the random motion of the particles in the gas, i.e. a “degraded” from of kinetic energy.

Ideal Gas Characteristics of an ideal gas : It remains in the gaseous state at any temperature and pressure. Exactly follow the basic laws of ideal gas. Constant volume and constant pressure heat capacity are constant.

Ideal Gas Ideal Gas:

 An ideal gas is a theoretical gas composed of many randomly moving point particles that do not interact except when they collide elastically. The ideal gas concept is useful because it obeys the ideal gas law, a simplified equation of state.  An ideal gas can be characterized by three state variables: absolute pressure (P), volume (V), and absolute temperature (T). The relationship between them represent the ideal gas law:

Ideal Gas

The Ideal Gas Law:

PV = nRT

P = Pressure (in kPa) V = Volume (in L) T = Temperature (in K) n = moles

R = 8.31 kPa • L K • mol

R is constant. If we are given three of P, V, n, or T, we can solve for the unknown value.

Thermodynamic laws

First Law of Thermodynamics energy can neither be created nor destroyed

One form of work may be converted into another or, work may be converted to heat, or, heat may be converted to work. Every time: final energy = initial energy

Thermodynamic laws The net heat taken in by a system is equal to the sum of the change in internal energy and the work done by the system.

Q = U + W

•Isochoric Process: •Isobaric Process:

V = 0, W = 0 P = 0

•Isothermal Process: T = 0, U = 0 •Adiabatic Process:

Q = 0

final - initial)

Thermodynamic laws

Enthalpy

We can define a new state variable (one where the path to its current state does not affect its value) called enthalpy:

H = Ei + PV

Enthalpy = Internal Energy + PV

dH = dq + VdP

Thermodynamic laws

Second Law of Thermodynamics

naturally occurring processes are directional

• Heat flows from higher to lower temperatures and NOT the other direction. – i.e., heat flows “downhill” just like water – You cannot raise the temperature in this room by adding ice cubes.

• Thus processes that employ heat are inherently irreversible.

Thermodynamic laws

Second Law of Thermodynamics It is impossible to construct an engine that, operating in a cycle, produces no effect other than the extraction of heat from a reservoir and the performance of an equivalent amount of work.

Thermodynamic laws

Efficiency of a Heat Engine

An amount of heat Qh is supplied from the hot reservoir to the engine during each cycle. Of that heat, some appears as work, and the rest, Qc, is given off as waste heat to the cold reservoir. The efficiency is the fraction of the heat supplied to the engine that appears as work.

Thermodynamic laws

The Third Law of Thermodanymics

Absolute zero is a temperature that an object can get arbitrarily close to, but never attain.

Temperatures as low as 2.0 x 10-8 K have been achieved in the laboratory, but absolute zero will remain ever elusive – there is simply nowhere to “put” that last little bit of energy. This is the third law of thermodynamics:

It is impossible to lower the temperature of an object to absolute zero in a finite number of steps. * There is a concept of “negative temperature”, but it is based on a more subtle and general definition of temperature, and not the average kinetic energy of atoms

Work in thermodynamic system Work Done by a Gas   

Work=(Force)x(distance) =Fy Force=(Presssure)x(Area) W=P(Ay) W=PV

Thermodynamic process

The basic reversible processes in a closed system: • Isochoric process– constant volume

• Isobaric process – constant pressure

• Isothermic process – constant temperature • Adiabatic process – without sharing heat • Polytropic process – p . vn = const

Thermodynamic process

Isochoric process at constant volume (v = konst.) p

2

p2

p2 v  rT2

The pressure is directly proportional to absolute temperature.

q 1,2

p1

p2 T2  p1 T1

1

p1v  rT1 v

q1, 2  cv (T2  T1 )

The added heat increases the internal energy of the gas. Volume work is zero!

Thermodynamic process

• Isobaric process– at constant pressure (p = const.) p 1

q 1,2

p1v1  rT1

v2 T2  v1 T1

2

p2 v2  rT2 a 1,2

v1

v2 v

The volume is directly proportional to absolute temperature.

a1, 2  p (v2  v1 ) a1, 2  r

The gas constant is equal to the volume of work done by one kilogram of gas heated by one Kelvin at constant pressure

q1, 2  c p (T2  T1 )  I 2  I1

The supplied heat at constant pressure is consumed to increase the enthalpy

Thermodynamic process

• Isothermic process– at constant temperature (T = const.) p

p 2 v2  1  p.v  konst p1v1

1 p1v1  rT1

Internal energy id. gas does not change. The supplied heat is converted into a volume work

p2 v2  rT2

q 1,2 a 1,2 v1

q1, 2  a1, 2

2

v2

v

p1  p1v1 ln p2

Thermodynamic process

• Adiabatic process– without heat exchange with the environment

p1v1  p2 v2  p.v   konst 

p

1 p1v1  rT1

p1



internal energy id. gas varies at volume work

p2 v2  rT2

p2

a 1,2 v1

2

a1, 2

 1     p2   1   p1v1 1      p1    1  

izotermic

v2

v

Poisson constant



cp cv

Thermodynamic process

• Polytropic process– p . vn = konst p

p2  V1     p1  V2 

1 p1v1  rT1 q 1,2

v1

T2  p2     T1  p1 

p2 v2  rT2 a 1,2

2

v2

1 n  

n 1 n

n

 v1      v2 

Volume work

v

a1, 2

n 1

n 1   n  p2   1   p1v1 1      p1   n 1  

Carnot Equation: Efficiency • Any heat engine, the maximum work that can be produced is governed by:

.

Wmax Tcold  1 Qhot Thot

• This ratio is called the Carnot efficiency, . • Importance Carnot cycle to compare the effectiveness of various cycles of heat engines

The Carnot Principles • The efficiency of an irreversible heat engine is always

less than the efficiency of a reversible one operating between the same two reservoirs. th, irrev < th, rev

• The efficiencies of all reversible heat engines operating between the same two reservoirs are the same. (th, rev)A= (th, rev)B •The Carnot heat engine defines the maximum efficiency any practical heat engine can reach up to.

Working Cycles of piston engines

Cycle of gasoline engines Ideal cycle assumptions: • The working fluid is an ideal gas • Combustion is replaced by a supply of heat from outside • The exhaust is replaced with heat dissipation from the cylinder • Compression and expansion are Isoentropic • Specific heat capacity of the working fluid are temperature independent, • There are no losses • Not considering valve timing

Ideal cycle of gasoline engines 4 - stroke P

TDC

BDC

3

T

q23 2

Wo – cycle work

2 4 1

Vc

Vd

Vcylinder

Heat convert to work

q14

V

q2,3 - q4,1

3

4

1

S

Cycle of gasoline engines Real cycle: • The working fluid is a real gas, • Poisson constant is changing after burning • Including chemical losses, e.g. thermal dissociation at temperatures above 2000 ° C

• considering valve timing losses

Real cycle investigations

4 - stroke engines

Woking cycle of 4 stroke piston engine:

1 – Induction: 2 – Compression

3 – Power / expansion 4 – Exhaust

4 - stroke engines

Working cycle of 4-stroke engine: 1 – Induction

Unsteady flow a real mix accompanied by heat and evaporation of fuel.

Opening the intake valve starts before top dead center in order to reduce suction losses. Closing the intake valve is behind bottom dead center to utilize the kinetic energy stream. This will improve cylinder filling .

2 – Compression (polytropic)

Complex process with variable value of polytropic exponent. In calculating the mean value is considered in interval 1.27 to 1.39. At the end of compression is created a homogeneous mixture to facilitate ignition and rapid combustion of the fuel without detonation

4 - stroke engine

Working cycle of 4-stroke engine: 3 – Expansion

The moment of ignition has great importance. It is necessary to choose the moment of ignition for achieve a maximum of gas pressure in interval 10 to 15 degrees after TDC.

The expansion of gases acting on the piston and changing heat into mechanical energy. Expansion proceeds according polytropy with variable exponent. In calculating the mean value is considered in interval 1.15 to 1.30.

4 – Exhaust

The exhaust valve opens before the bottom dead center. After opening the valve quickly escape 2/3 combustion gases and the pressure drops rapidly. When piston is moving toward the top dead center, piston pushes the residual combustion gases. The exhaust valve closes after top dead center, utilizes the kinetic energy of exhaust gas for better exchange of the cylinder charge. Angle, which exhaust and intake valve are open, is indicates as a valve overlap angle.

4 - stroke engine Indicator diagram 4-stroke petrol engine : Valve overlap

suction

TDC

BDC

exhaust

Engine design parameters Cylinder Terms: The geometry of cylinders is described by specific terms: Stroke (s) – The total length of piston movement from the top dead center (TDC) position to bottom dead center (BDC) position. Bore (b) - Diameter of the piston

Engine design parameters Cylinder Terms:

The geometry of cylinders is described by specific terms: • Clearance distance (sc) - The piston cannot travel the entire length of the cylinder. There has to be room at the top for the compressed mixture. This is called the clearance volume or combustion space. The clearance distance is the length from the top of the cylinder to the piston top dead center (TDC) position.

Engine design parameters • Stroke volume

Vz  • Stroke ratio

 .D 2 4

L

L  D

• Mean piston speed

cs  2.L.n

On aircraft engine usually 8-14 ms-1 and has an impact on engine life

Engine parameters - overview

• Type of engine power:

– Indicated Power (Horsepower) Pi

• The power developed in the combustion chamber without reference to the friction losses within the engine

– Brake Power (Horsepower) (BHP) Pe

• The power delivered from the engine to the propeller for useful work

– Friction Power (Horsepower) Pm

• Indicated horsepower minus brake horsepower

Engine parameters - overview

• Engine working pressure: – Mean Effective Pressure

• Pressure used to create frictionless power

– Indicated Mean Effective Pressure pi

• is a fictitious constant pressure that would produce the same work per cycle if it acted on the piston during the power stroke. IMEP does not depend on engine speed, just like torque.

– Friction Mean Effective Pressure

• The pressure used to overcome internal friction

– Brake Mean Effective Pressure pe • The pressure used to produce useful work

Engine parameters - overview

• Engine efficiencies: – Thermal Efficiency t

• The ratio of useful work done by an engine to the heat energy of the fuel it uses, expressed in work or heat units

– Mechanical Efficiency m

• The ratio that shows how much of the power developed by the expanding gases in the cylinder is actually delivered to the output shaft.

– Volumetric Efficiency v

• A comparison of the volume of fuel/air charge inducted into the cylinders to the total piston displacement of the engine

– Combustion Efficiency ch

• The combustion efficiency is defined as actual heat input divided by theoretical heat input:

Engine cycle parameters • Compression ratio:



Vcylynder

Vcompresion

– The normal value is 7-11 restricted the emergence of detonation combustion

• Theoretical Heat efficiency : t 

q2,3  q4,1 q2 , 3

– Utilized heat is equivalent work of cycle Wo and can be expression:

t  1 



1

 1

for Diatomic gases and air χ = 1,4

Engine cycle parameters Parameters influencing overall efficiency: • Chemical (combustion) efficiency

• The time for combustion in the cylinder is very short so not all the fuel may be consumed or local temperatures may not support combustion • A small fraction of the fuel may not react and exits with the exhaust gas. The combustion efficiency is defined as actual heat input divided by theoretical heat input.

Qrel  ch  Q fuel

The ratio of the heat released by the combustion Qrel of the theoretical heat content of the fuel Qfuel

Engine cycle parameters Parameters influencing overall efficiency: • Thermal efficiency

t = work per cycle / heat input per cycle t = W / Qin = W / (c mf QHV)

Where Qin = heat added by combustion per cycle mf = mass of fuel added to cylinder per cycle QHV = heating value of the fuel (chemical energy per unit mass) • thermal efficiencies are typically 50% to 60% • depend on compression ratio a temperature of combustion

Engine cycle parameters Parameters influencing overall efficiency: • Volumetric Efficiency v

• Due to the short cycle time and flow restrictions less than ideal amount of air enters the cylinder. • The effectiveness of an engine to induct air into the cylinders is measured by the volumetric efficiency which is the ratio of actual air inducted divided by the theoretical air inducted:

v = ma / (a Vd) = nR ma / (a Vd N)

where a is the density of air at atmospheric conditions • Typical values for WOT are in the range 75%-90%, and lower when the throttle is closed

Engine cycle parameters • Fullness ratio of indicator diagram 3

Pmax

2

Qi p  Qt

Represent a specific reference value in internal combustion engines. Is used to describe the effectiveness of the actual working cycle of the engine, to the theoretical model.

Calculated from the ratio of the value of work corresponding to the theoretical circulation in the same conditions and indicated work calculated from the measured-indicated pressure values directly in the combustion chamber of the actual circulation.

Wi

4 vz

1

Engine cycle parameters • Indicated efficiency

Qi i  Q pal

Conversion efficiency of energy released by burning fuel Qfuel to the indicated work which corresponds to heat Qi

i   ch .t . p

Qrel  ch  Q fuel

Qi Qt   t  p Qt Qrel

• Overall efficiency

 e  i . m

Current internal combustion engines achieve effective efficiency in the range of 0.3 to 0.4

Engine cycle parameters

Engine cycle parameters

Indicated Work

Given the cylinder pressure data over the operating cycle of the engine one can calculate the work done by the gas on the piston. The indicated work per cycle is

Wi   pdV

Compression W0

Exhaust W0

Engine cycle parameters • Indicated power (horsepower) •

multiplying indicated work by the number of revolutions per second

1 Pi  Vz . pi .n 2

Only for 4 stroke engine

Power can be increased by increasing: • the engine size, V • compression ratio, rc • engine speed, n

Engine cycle parameters • Effective power

– Output decreased by mechanical losses

Pe  Pi . m

 m - mechanical efficiency

Determination:

-Numerically from the low pressure part of the P-V diagram -Engine brake

-By measuring the time to stop from a certain speed

Engine cycle parameters

Mean indicated power – derivate from indicator diagram

pi

Wi  Vz . pi

Pi  Vz . pi .n

Engine cycle parameters • Effective power

Pe  Pi . m

4 stroke engine

1 Pe  Vz . pi .n. m 2

• Mean effective pressure

The pressure (assuming it is constant) of the piston in the power stroke is called the mean effective pressure

pe  pi . m

Pe  Vz . pe .n

Pe for 4 stroke engine 0,6 - 0,9 MPa For one cylinder

it is a useful figure of merit for comparing the performance of different engines and operating conditions because it normalizes out the effects of engine size, rotational speed, and cycle

Other concept of piston engines in aviation

2 - stroke engine

In two stroke cycle engines, the whole sequence of events i.e., suction, compression, power and exhaust are completed in two strokes of the piston i.e. one revolution of the crankshaft. There is no valve in this type of engine. Gas movement takes place through holes called ports in the cylinder. The crankcase of the engine is air tight in which the crankshaft rotates .

2 - stroke engine Upward stroke Compression)

of

the

piston

(Suction

+

When the piston moves upward it covers two of the ports, the exhaust port and transfer port, which are normally almost opposite to each other. This traps the charge of air- fuel mixture drawn already in to the cylinder. Further upward movement of the piston compresses the charge and also uncovers the suction port. Now fresh mixture is drawn through this port into the crankcase. Just before the end of this stroke, the mixture in the cylinder is ignited by a spark plug (Fig 2 c &d). Thus, during this stroke both suction and compression events are completed.

2 - stroke engine Downward stroke (Power + Exhaust) Burning of the fuel rises the temperature and pressure of the gases which forces the piston to move down the cylinder. When the piston moves down, it closes the suction port, trapping the fresh charge drawn into the crankcase during the previous upward stroke. Further downward movement of the piston uncovers first the exhaust port and then the transfer port. Now fresh charge in the crankcase moves in to the cylinder through the transfer port driving out the burnt gases through the exhaust port. Special shaped piston crown deflect the incoming mixture up around the cylinder so that it can help in driving out the exhaust gases . During the downward stroke of the piston power and exhaust events are completed.

2 - stroke engine

Indicator diagram 2-stroke petrol engine : TDC

exhaust

TDC BDC

suction

2 - stroke engine

Indicator diagram of real 2-stroke petrol engine : TS 510 7500 min-1; full load, 3.8 kW; INDICATOR DIAGRAM; High Pressure Part

3

Pressure [MPa]

2.5 2

1.5 1

0.5 0

0

0.02

0.04 0.06 0.08 Cylinder Volume [dm^3]

0.1

0.12

2 - stroke engine

Scavenging in two-stroke engines is performed mainly by one of three methods:

a) Cross scavening – Simple but not suitable for larger filling pressures b) Loop scavening – the most commonly used

c) Uniflow scavening – complicated, requires camshaft

2 - stroke engine Weaknesses:

Imperfect scavening

Loss of stroke volume, a lower compression ratio Higher thermal load

Irregular running at low revs worse emissions

About 30% more fuel consumption

Benefits:

Simplicity of design Low weight

Easy maintenance Low price

http://1.bp.blogspot.com/-w9TV3EfVfkc/TqLpVfrbCvI/AAAAAAAAAtA/ntwGcZYRos4/s400/yr+tu.jpg

2 - stroke engine

2/4- stroke engine comparation

Rotax 912 80Hp 4T

Rotax 582 65Hp 2T

2 - stroke engine

An example of modern 2- stroke aircraft engines: ROTAX 582 – 45kW, 36 kg

HIRTH F30E - 61kW, 42 kg

Diesel engines Differences : • Ideal cycle diesel engine - the heat is supplied at constant volume and partly at constant pressure. • The compression ratio is approximately 2 times greater than the petrol engine. The diesel engine has a higher thermodynamic efficiency than a gasoline engine. • Combustion of fuel in real cycle is realized by isochoric and isobaric process.

Diesel engines

Indicator diagram 4-stroke diesel engine :

t 

Q2,3  Q3, 4  Q5,1 Q2,3  Q3, 4

fuel injection Real cycle

Diesel engines

Indicator diagram 2-stroke diesel engine : :

Two-stroke diesel engines are used more often in aviation due to better weight to power ratio

Diesel engines

Example of diesel aircraft engine with opposed pistons:

Junkers – Jumo 205

2 stroke diesel engine Power: 647kW

weight: 595 kg suchá bore: 105 mm

stroke: 160 mm Cylinders: 12

Compression ratio: 17:1 First run: 1932

cut of the engine:

Diesel engines

Junkers – Jumo

Diesel engines

cutaway of the engine:

Junkers – Jumo

Diesel engines

Example of modern diesel aircraft engine with opposed pistons: JUMO – redesing www.keros.in Fuel: JET A1

Power: 420hp @2900ot.min Dry Weight: 180kg.

Displacement: 3000 ccm Compression ratio : 20:1

Diesel engines

Example of modern 4 stroke diesel aircraft engine

Centurion aircraft engines

Diesel engines

Example of modern 4 stroke diesel aircraft engine

Centurion 4.0

Power: 257 kW

Weight: 272 kg suchá

consumption 40 – 50 l/hr

Engine was derived from the Mercedes car's engine

Diesel engines

Comparison of diesel and petrol aircraft engine: Diesel engines

Petrol engines

+

higher efficiency = less fuel consumption

-

-

weight to power ratio

+

-

Hardness running due to higher pressures

+

-

Price

+

+

-

lower speed = smaller gearbox

The technological complexity

-

+

Diesel engines

Comparison parameters of diesel and petrol aircraft engine: Centurion 2.0

Lycoming O-320-A

99 kW at 2300 RPM

112 kW at 2700 RPM

83 mm

130 mm

displacement

1991ccm

weight

134 kg

power bore

stroke

consumption

specific consumption

Weight to Power ratio

92 mm

5200 ccm 110,7 kg 98 mm

15 –20 l hrs-1. JET A1

20 – 30 l hrs -1 LB 100

1,35 g / W

1,011 g / W

220 g / kWh

200 g / kWh (Other specific density of fuel.)

Piston engines - Another concepts

The Wankel engine:

Using an eccentric rotary design to convert pressure into rotating motion.

Piston engines - Another concepts

Advantages of the Wankel engine are : • A far higher power to weight ratio than a piston engine • It is approximately one third of the weight of a piston engine of equivalent power output • It is approximately one third of the size of a piston engine of equivalent power output • No reciprocating parts • Able to reach higher revolutions per minute than a piston engine • Operates with almost no vibration • Not prone to engine-knock • Cheaper to mass-produce as the engine contains fewer parts • Superior breathing, filling the combustion charge in 270 degrees of mainshaft rotation rather than 180 degrees in a piston engine Continue

Piston engines - Another concepts

Advantages of the Wankel engine are : • Supplies torques for about two thirds of the combustion cycle rather than one quarter for a piston engine • Wider speed range gives greater adaptability • It can use fuels of wider octane ratings • Does not suffer from "scale effect" to limit its size • On some Wankel engines the sump oil remains uncontaminated by the combustion process requiring no oil changes. The oil in the mainshaft is totally sealed from the combustion process. The oil for Apex seals and crankcase lubrication is separate. In piston engines the crankcase oil is contaminated by combustion blow-by through the piston rings.

Piston engines - Another concepts

Disadvantages:

Many of the disadvantages are in ongoing research with some advances greatly reducing negative aspects of the engine. the current disadvantages of the Wankel engine in production are: • Rotor sealing. This is still a problem as the engine housing has vastly different temperatures in each separate chamber section. • Apex seal lifting. Centrifugal force pushes the apex seal onto the housing surface forming a firm seal. Gaps can develop between the apex seal and troichoid housing in light-load operation when imbalances in centrifugal force and gas pressure occur. • Slow combustion. The combustion is slow as the combustion chamber is long, thin, and moving. • Bad fuel economy. This is due to seals leakages, and the "difficult" shape of the combustion chamber, with poor combustion behavior and mean effective pressure at part load, low rpm. • Poor emissions. As unburnt fuel is in the exhaust stream, emissions requirements are difficult to meet.

Piston engines - Another concepts

Mazda has had substantial success with two-rotor, three-rotor, and four-rotor cars.

Piston engines - Another concepts

• Wankel engine should be ideal for light aircraft, as it is light, compact, almost vibrationless and has a high power-toweight ratio. Further aviation benefits of a Wankel engine include: 1. Rotors cannot seize, since rotor casings expand more than rotors; 2. A Wankel engine is less prone to the serious condition known as "engine-knock", which can destroy the plane's engines in midflight. 3. A Wankel is not susceptible to "shock-cooling" during descent; 4. A Wankel does not require an enriched mixture for cooling at high power; 5. Having no reciprocating parts, there is less vulnerability to damage when the engines revolves higher than the designed maximum running operation. The limit to the revolutions is the strength of the w bearings. main

Piston engines - Another concepts Austro-engines AE5

Power arpox 40Hp

Piston engines - Another concepts

Rotationskolbenmaschine (RKM)) The machine's inventor is Boris I. Schapiro, along with coinventors Lev B. Levitin and Naum Kruk.

Despite their apparent geometrical similarity, the RKM and the Wankel engine are quite different in design The Wankel engine working chamber is mobile while the RKM chamber is stationary. The axis of rotation in the Wankel engine moves in a circle while that of the RKM is fixed (in the single power shaft version, temporarily with two possible positions). In the RKM motor, the ignition takes place in a compact recess, while the Wankel's is in the work chamber itself. The RKM's sealing elements are in surface contact with the work chamber and pistons, as opposed to the Wankel's line contact.

Although developed in the 1960s, today there are no runnable RKM engine demonstrated

Piston engines - Another concepts

A nutating disc engine :

Piston engines - Another concepts

A nutating disc engine :

A nutating disc engine (also sometimes called a disc engine) is an internal combustion engine comprising fundamentally of one moving part and a direct drive onto the crankshaft.

The disc wobbles inside a housing and, in its simplest version, half of the single disc (one lobe) performs the intake/compression function while the other lobe performs the power/exhaust function. The disc lobes can be configured to have equal compression and expansion volumes, or to have the compression volume greater than or less than the expansion volume. This means that the engine can be self supercharged (see supercharger), or operate as a Miller cycle / Atkinson cycle.

Back to basics of piston engines

Combustion process

• – – –

Combustion of the air-fuel mixture occurs in a very short but finite length of time with the piston near TDC (i.e., nearly constant volume combustion).

It starts near the end of the compression stroke slightly before TDC and lasts into the power stroke slightly after TDC.

Combustion changes the composition of the gas mixture to that of exhaust products and increases the temperature in the cylinder to a high value. This in turn increases the pressure in the cylinder to a high value.

Normal combustion is a complex chemical process, it is not explosion

Combustion process • Normal combustion is the burning of a fuel and air mixture charge in the combustion chamber. It should burn in a steady, even fashion across the chamber, originating at the spark plug and progressing across the chamber in a three dimensional fashion. The flame front should progress in an orderly fashion. The burn moves all the way across the chamber and , quenches (cools) against the walls and the piston crown. The burn should be complete with no remaining fuel-air mixture. Note that the mixture does not "explode" but burns in an orderly fashion.

Combustion process

• There is another factor that engineers look for to quantify combustion. It is called "location of peak pressure (LPP)." It is measured by an in-cylinder pressure transducer. Ideally, the LPP should occur at 14 degrees after top dead center. Depending on the chamber design V and the burn rate, if one would initiate the spark at its optimum timing (20 degrees BTDC, for example) the burn would progress through the chamber and reach LPP, or peak pressure at 14 degrees after top dead center.

C

TC

B

L

l

s q

a

B C

Combustion process Petrol

Diesel

Combustion process

Effect of compression ratio on ignition timing 50° 40° 30° 20° 10° 0°

2

4

6

8

Compression ratio

10

12

14

Effect of ignition timing on engine performance

Effective power Pe

optimum

Setting the correct ignition timing is crucial in the performance of an engine. Sparks occurring too soon or too late in the engine cycle are often responsible for excessive vibrations and even engine damage. The ignition timing affects many variables including engine longevity, fuel economy, and engine power.

Modern engines that are controlled in real time by an engine control unit use a computer to control the timing throughout the engine's RPM and load range.

Optimum angle of ignition φ

Fuel mixture and combustion process

Fuel mixture

• Air–fuel ratio (AFR) is the mass ratio of air to fuel present in a combustion process such as in an internal combustion engine or industrial furnace. The AFR is an important measure for anti-pollution and performance-tuning reasons. • If exactly enough air is provided to completely burn all of the fuel, the ratio is known as the stoichiometric mixture, often abbreviated to stoich. • For pure octane the stoichiometric mixture is approximately 14.7:1, or λ = 1.00 exactly. • AFR numbers lower than stoichiometric are considered "rich" λ < 1. Rich mixtures are less efficient, but may produce more power and burn cooler, which is kinder on the engine. AFR numbers higher than stoichiometric are considered "lean " λ > 1 .

Fuel mixture and combustion process

Effect of speed of burning on the coefficient of excess air

lean

Speed of burning

rich

L*  Lt 0,6

0,8

Supplied air quantity Theoretical amount of air

1,0 1,2 Air–fuel ratio λ

A stoichiometric mixture burns very hot and can damage engine components if the engine is placed under high load at this fuel–air mixture. Due to the high temperatures at this mixture, detonation of the fuel–air mix shortly after maximum cylinder pressure is possible under high load (referred to as knocking or pinging). Detonation can cause serious engine damage. As a consequence, stoichiometric mixtures are only used under light load conditions.

For aircraft piston engines it is possible mixture control

Abnormal combustion

Abnormal combustion like Knocking (also knock, detonation, spark knock, pinging or pinking) in sparkignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder does not start off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. External manifestations: • • • •

Engine vibration and knocking Loss of power The temperature rise in the combustion space Black smoke in exhaust

Detonation combustion Causes:

Under certain conditionsa subsonic flame may accelerate to supersonic speed, transitioning from deflagration to detonation. The exact mechanism is not fully understood,¨and while existing theories are able to explain and model both deflagrations and detonations. A deflagration is characterized by a subsonic flame propagation velocity, typically far below 100 m/s, and relatively modest overpressures, say below 0.5 bar.

Detonation combustion Causes:

The main mechanism of combustion propagation is of a flame front that moves forward through the gas mixture - in technical terms the reaction zone (chemical combustion) progresses through the medium by processes of diffusion of heat and mass. In its most benign form, a deflagration may simply be a flash fire. In contrast, a detonation is characterized by supersonic flame propagation velocities, perhaps up to 2000 m/s, and substantial overpressures, up to 20 bars. The main mechanism of combustion propagation is of a powerful pressure wave that compresses the unburnt gas ahead of the wave to a temperature above the autoignition temperature. In technical terms, the reaction zone (chemical combustion) is a self-driven shock wave where the reaction zone and the shock are coincident, and the chemical reaction is initiated by the compressive heating caused by the shock wave.

Detonation combustion Causes: • Excessive heating of the mixture before ignition. • The chemical composition of fuel • Other influencing factors: – imperfect engine cooling , – imperfect fuel mixture (vulnerable is slightly rich λ =0,9 –0,95 mixture), – ignition timing, the shape of the combustion chamber , – higher compression

Detonation combustion Pre-ingnition

pressure

pressure

Detonation combustion – pressure in cylinder

TDC TDC

Volume

BDC

Detonation combustion

Detonation combustion

Detonation combustion Detonation can be prevented by any or all of the following techniques: • the use of a fuel with high octane rating, which increases the combustion temperature of the fuel and reduces the proclivity to detonate. • enriching the air–fuel ratio which alters the chemical reactions during combustion, reduces the combustion temperature and increases the margin above detonation • reducing peak cylinder pressure • decreasing the manifold pressure by reducing the throttle opening or boost pressure • reducing the load on the engine • retarding (reduce) ignition timing

Aviation fuel for piston engine

•

•

Fuel for piston engines

The most frequently used fuels in aviation are liquid hydrocarbonaceous fuels that are obtained by fractional distillation of petroleum. The distillation range separates groups of hydrocarbons into 2 groups of motor fuels: – (35 - 200)C - easily vaporisable (gasoline), faction C4 - C10 – (150-360)C - hard vaporisable (diesel), faction C9 - C22

Desired composition of hydrocarbons in both groups are regulated by other appropriate technologies (cracking, reforning, hydrogenation, etc.). • All fuel must meet the essential requirements, including, in particular :

– high heating value, – the ability to create quality mixture under the conditions in cylinder (combustion chamber) – ability reliable ignition (combustion) of the mixture and an almost complete burnout – high purity as a prerequisite for smooth supply of fuel to the engine – stability properties during storage and transport, still sufficiently for safe handling – minimum sulfur content (free and bound).

Properties of fuels Composed of hydrocarbon fuel

•

Gasoline is composed of a mixture of many hydrocarbon. Figure represents the typical gasoline mixture for SI engines. • The mixture is composed of low and high molecular weight com-pounds. • The low molecular weight compounds aid in the cold starting of the engine while the high molekular weight compounds increase the efficiency by not vaporizing untillate in to the compression stroke. •

The low molecular weight compound is defined as front-end volatility while high-end volatility corresponds to high molecular weight compounds.

Properties of fuels

Octane rating or octane number

• • •

•

It is determined by tests on a special one-cylinder engine with variable compression. Generally Represents the percentage of isooctane in a mixture of isooctane and n-heptane which has the same cardinality of detonations as the tested fuel.

Octane ratings are not indicators of the energy content of fuels. They are only a measure of the fuel's tendency to burn in a controlled manner, rather than exploding in an uncontrolled manner. Where the octane number is raised by blending in ethanol, energy content per volume is reduced.

There are many methods for determining the octane number as Research Octane Number (RON), Motor Octane Number (MON), or Anti-Knock Index (AKI) or (R+M)/2

Properties of fuels

Octane rating or octane number

•

Gasoline used in piston aircraft common in general aviation have slightly different methods of measuring the octane of the fuel. Similar to AKI, it has two different ratings, although it is referred to only by the lower of the two. One is referred to as the "aviation lean" rating and is the same as the MON of the fuel up to 100. The second is the "aviation rich" rating and corresponds to the octane rating of a test engine under forced induction operation common in high-performance and military piston aircraft. • For example, 100/130 AVGAS has an octane rating of 100 at the lean settings usually used for cruising and 130 at the rich settings used for take-off and other full-power conditions.

Properties of fuels

Gasoline additives increase gasoline's octane rating or act as corrosion inhibitors or lubricants, thus allowing the use of higher compression ratios for greater efficiency and power. Types of additives include: – metal deactivators, – corrosion inhibitors, – oxygenates and – antioxidants.

Properties of fuels

Gasoline additives for octane numbers increasing.

Tetraethyllead (commonly styled tetraethyl lead) TEL was mixed with gasoline (petrol) beginning in the 1920s as a patented octane booster that allowed engine compression to be raised substantially. Aviation gasoline with TEL used in WWII reached 150 octane to enable supercharged engines such as the Rolls-Royce Merlin and Griffon to reach high horse power ratings at altitude. In most industrialized countries, a phaseout of TEL from road vehicle fuels was completed by the early 2000s because of concerns over air and soil lead levels and the accumulative neurotoxicity of lead.

Avgas is currently available in several grades with differing maximum lead concentrations. Because TEL is an expensive and polluting ingredient, the minimum amount needed to bring the fuel to the required octane rating is used;

:

Aviation Fuel

AVGAS properties :

Aviation Fuel

Jet fuel properties :

Aviation Fuel

Aviation Fuel

Aviation fuel marking:

Piston engine construction

Design of piston engines

Different ways cylinders arrangement :

The most widely used concept: a) Inline or Straight b) V Engines

upright or inverted

c) Horizontally Opposed d) Radial

Design of piston engines Different ways cylinders arrangement : a) Inline or Straight upright or inverted

Mikron

Design of piston engines

Different ways cylinders arrangement :

b) V Engines with two banks of cylinders with less than 180° between them driving a common crankshaft, typically arranged upright or inverted.

Argus As 10C

Design of piston engines Different ways cylinders arrangement : b) Another .

Argus As 10C

Design of piston engines

Different ways cylinders arrangement : c) Horizontally Opposed (boxer)

Lycoming

Engines with two banks of cylinders arranged at 180° to each other driving a common crankshaft,

Design of piston engines

Different ways cylinders arrangement : d) Radial

Wasp

Design of piston engines

Different ways cylinders arrangement : e)V

Merlin

Design of piston engines

Different ways cylinders arrangement : e)H

Napier Sabre 2000Hp

Design of piston engines

Main parts of piston engines :

Design of piston engines Main parts of piston engines :

Crankcase The crank mechanism Cylinders and cylinder heads Valves and cam shaft Fuel system Ignition system Lubrication system Cooling systems Auxiliary devices (carburetor, starter, generator, etc.)

Design of piston engines

Crankcase :

• Represents a solid foundation for mounting engine components • Transmits thrust from the propeller and other forces from the crank mechanism on the engine mount • The structure is usually divided for easy mounting of the crankshaft and other components . • The main requirements for the crankcase are low weight and high rigidity

Design of piston engines

Crankcase :

Design of piston engines

Crankcase :

Design of piston engines

Crankcase :

Lycoming O-200A

Design of piston engines

The crank mechanism

• Converts the linear motion of the piston into the rotary motion • It is structurally simple but it is not advantageous for the difficulties in balancing the effects of moving masses • The crankshaft is a highly stressed part. A torsional oscillations represent great danger. Crankshafts are manufactured from one piece of material for minimizing the risk of fracture. Steel mostly with the strength of over 1000 MPa (16.440 15.230). Semifinished product is forged, pins shafts are surface-hardened.

Design of piston engines Crank mechanism geometry L=2r l β

s

l.cosβ

r+l

ω v

r

α

r.cosα

Design of piston engines

L=2r

l β

s

v

r

k 

α

r l

Crank ratio (0,25 až 0,35)

r.cosα

l.cosβ

r+l

s  r  l  r. cos   l. cos  

  1  1  s  r 1    cos   cos   k   k 

 1  1 s  1    cos   k  k 

ω

1 s  r 1  cos    k .r. sin 2  2

v  l. sin   r. sin   sin   k . sin  2 2 1  k . sin   2 2  sin   cos   1

1 2 2 1  k . sin 2   1  k . sin 2  2

Editing by binomial series expressing (first 2 members )

Design of piston engines

Crank mechanism dynamic • Piston trajectory

1r 2   s  r 1  cos   sin   2l  

• Piston speed

1r ds dr   sin 2  c .  c  r  sin   2l d dt  

Mean piston speed

• Piston acceleration a

dc ds   dt d

r   a  r  cos   cos 2  l   2

cs  2.L.n

L  2.r

Design of piston engines

Forces in the crank mechanism

• Inertial forces of acceleration moving along a straight line R   F  m p R  cos   cos 2  L   2

• Inertial forces of the rotating masses with crank F   mr R 2

• The forces from the gas pressure on piston F

 .D 2 4

 p  p0 

Forces:

Design of piston engines