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CHARACTERISTICS OF AERONAUTIC

RECIPROCATING ICE ENGINES Subject: Propulsion

02/04/2014

·Authors:

Igual Campos, Javier (832) Oliver del Pozo, Antonio (832) Olmos Milotich, Sergio (832)

Palomar Toledano, Marta (832) Vidal Navarro, Daniel (831)

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INDEX 1.- Historical approach………………………………………..……………2

2.- Evolution of ICE engines in aviation………………………………3

3.- ICE nowadays: geometrical and effective parameters……..4

4.- Comparison with no-aeronautical ICE……………………………6

5.- Bibliography……………………………………………………………….8

6.- Annex………………………………………………………………………..9

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1. – Historical Approach Reciprocating ice engines have more than a century of history, and they

have experienced an evolution since then. The first reciprocating ice engine can be

dated back to the 18th century with the steam engine. However, the first ever

considered reciprocating ice engine was built up in 1876 thanks to Nicolaus Otto,

who also established the strategy for the development of future ice engines.

The main characteristic we can consider from any reciprocating ice engine is

that they are volumetric machines where the fluid is inside the chamber limited by

moving walls. When these walls move, the fluid modifies its volume. This is a

characteristic they all share with the steam engine.

They had always been considered as complex but functional machines that

were able to produce mechanic energy. Throughout the years, these engines were

better understood, and it was after the commercial production of petrol by the

middle of the 19th century when the improvements and innovations became

important. Then, by the end of this century, there were many different engines

used in several different applications.

In this 19th century we can remark some important scientists who

contributed to the improvement of reciprocating ice engines: Samuel Morey, who

developed the first engine with gasoline or steam without compression (1826);

William Barnet, who invented the first engine that worked with compression

(1838); Sadi Carnot, who released the thermodynamic theory of the thermal

engines (1824); Nikolaus Otto, who patented the first gas engine with 4S cycle and

compression, and he also was the first manufacturer and seller of a gas engine

(1863-1864); Karl Benz, who patented a 2S engine based on the technology of the

4S engine of Bean de Rochas (1879) and he also created his own 4S engine which

he implemented in his cars: first ever cars (1885); Herbert Akroyd Stuart, who

invented the semi-diesel engines that used a system of fuel ignition by pressure

(1891) and Nils Gustav Dalén, who proposed the first gas turbine (1897).

But it was in the 20th century when the use and improvements of the

reciprocating ice engines took place in the field of aviation. The WWI and WWII

meant a huge improvement for the reciprocating ice engines in aviation: it was

then when Robert Goddard launched the first rocket (1926), Frank White patented

the first reaction engine (1930) and Rolls-Royce patented the first aviation engine

with centrifugal compressor and two stages with intercooler and aftercooler (1942).

Figure: 4S

internal

combustion

engine.

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2. - The evolution of ICE

engines in Aviation The evolution of ICE in aviation followed during a large period of time of

their development the needs of the military aviation of the time.

The use of ICE engines in aviation starts with the first engine powered flight

in 1903 by the Wright Brothers. They used a simple 4-stroke 4 cylinder inline

engine that was used in cars with a displacement of 1655 cc.

On the early days of aviation the type of engines that provided the greatest

amount of power were radial engines in comparison to inline, V, or other type of

engines which were not as developed. For example the Rolls-Royce Eagle V12

engine introduced in 1915 with a displacement of 20 300 cc could only provide 360

hp in its latest version of 1922 whilst at that time a 9 cylinder radial engine such as

the Pratt&Whitney R-1340 Wasp with a very similar displacement (20 000 cc) could

provide up to 600 hp.

So during WWI and before WWII radial engines were more used in aviation

as they were much more developed technologically so they could provide much

more power. Their main problem was the large frontal area they have and as a

consequence the great amount of drag they produced. The objective of engineers at

this time was to improve technologically inline engines as they were much better

aerodynamically. By 1936 we can see a great improvement with the Junkers Jumo

211 35 litre V12 capable of providing 1011 hp. However, radial engines were still

more powerful. For example the 1933 Wright R-1820 9 cylinder radial engine with a

smaller displacement of 30 litres could provide 1000 hp. We can see from the table

in our annex that from 1930 till the end of WWII there was an important tendency

to have supercharged engines capable of providing more power, something

essential for combat aircraft.

By 1938 with the development of the Rolls Royce Merlin engine equipped in

the Supermarine Spitfire we can see that in line engines (V-12 in this case) were

now at their best capable of providing up to 3000 hp with a displacement of 27

litres. Rolls Royce V-12 Merlin engines were one of the most powerful and

sophisticated V-12 engines used in fighter airplanes. The P-51 Mustang, another

mythical airplane also equipped it.

Another type of engine which was very good aerodynamically due to its

short length and capable of providing a great amount of power due to the large

number of cylinders it could have in a reduced space was the H-engine. One of the

first H-engines to be equipped in an aircraft was the one equipped in the Hawker

Typhoon a more sophisticated evolution of the Supermarine Spitfire. It equipped a

24 Cylinder Napier Sabre VA H-engine with a displacement of 36 litres, capable of

providing 3040 hp. This engine became one of the most powerful inline piston

engines in the world. Their development was put aside with the introduction of jet

engines which made the focus of military engine development change direction

from piston engines to jet engines.

Since the end of WWII until today, the evolution of piston engines followed a

different direction as, as it has been previously mentioned, military development

started to focus on jet engines. It can be seen on the table in the annex that the

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tendency of ICE engines in aircraft since WWII has been that of making smaller and

smaller engines as great amounts of power are not required from them any longer.

This type of engines are now only used in small passenger/leisure airplanes such as

the Cessna 172 which equips a 6-cylinder horizontally opposed piston Continental

O-300, with a displacement of 5 litres and a power output of 145 hp. As it can be

seen in the table the power range for this engines since the end of WWII is from

around 100hp till 400hp, much different from the power outputs we obtained from

the massive V-12 engines used in the war.

If we look at the tendency in the cooling system of the engines we can

observe that at first there was a mixed tendency to use liquid and air cooling. It can

be seen that the big engines capable of providing up to 3000 hp all had liquid

cooling as air refrigeration was not sufficient to dissipate the large amounts of heat

this engines generated. Finally engines nowadays in aviation, due to their small size

and improved technology are most air cooled. In addition we can see that most of

them are natural aspiration engines instead of supercharged engines.

Diesel engines weren’t too successful in aviation. The Packard DR-980 was

the first diesel compression ignition engine to be used in aviation in 1928. It was a

9-cylinder radial engine with a displacement of 16000 cc capable of providing

240hp, significantly less than the petrol engines of similar characteristics of the

time. Nowadays due to their better efficiency and advanced development thanks to

the automotive industry general aviation aircraft are starting to use more this kind

of engines.

3. - ICE nowadays: geometrical

and effective parameters We are not going to distinguish between the cooling system, as nowadays

liquid refrigeration is not used except for some particular applications, being the air

flow cooling the most common.

Regarding the classification between the intake pressures, we can observe

that in aviation, naturally aspired engines suffer a decrease in power as flight level

increases. This is due to the fact that the air density becomes lower with height and

therefore the cylinder air-filling coefficient will decrease as well. To solve this

drawback, supercharged engines make a previous compression of the air,

smoothing the effect of density decrease over the power.

As for the cylinder configuration, the most common one nowadays is the

horizontally-opposed, as it has proved to have better power-to-weight ratios than

the in-line one. The higher power-to-weight ratio is, however, obtained with the

radial configuration, but the frontal area of the engine is higher and makes it

unsuitable for aviation purposes.

Figure: 2S internal combustion engine

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If we take some examples of actual engines, which are detailed in the

annex, and we stablish relations between geometrical and operational parameters,

we get to the following graphs:

This first one is relating the power per unit cylinder volume (or specific

power) to the total displacement volume. We can observe that the tendency of the

specific power is to decrease when increasing Vt. This means that bigger engines

will show lower specific power, and the way to improve it would be to use

supercharching or change to a 2T. In the graph we can observe a peak of 70 kW/L

which in fact corresponds to the only one diesel engine that has been taken, so it is

accomplished that CI engines have higher specific power than SI. As well, 2T

engines have higher specific power than 4T.

Model Configuration Power-to-Weight

Havilland Gipsy Major In-line 0,78 kW/kg

P&W R-2800 Radial 1,46 kW/kg

Lycoming O-540 Horizontally opposed 1,12 kW/kg

Jabiru 2200 Horizontally opposed 1,07 kW/kg

0 2 4 6 8 10 12 14

0,000

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

Power/Vt vs Vt

Total Displacement Volume (L)

Po

we

r/V

t (k

W/L

)

50 60 70 80 90 100 110 120 130 140

0

1000

2000

3000

4000

5000

6000

7000

8000

Rotational Engine Speed - Bore

Bore (mm)

Ro

tatio

na

l E

ng

ine

Sp

ee

d (

rpm

)

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Now we have compared the rotational engine speed to the bore dymension,

obtaining that the first one decreases when increasing the second. This means that

engines become slower as their geometrical dymension increases.

In this graph we can see how the efficiency of the aeronautical engines has

been changing along the years. It is increasingly distributed with some picks

belonging to the WWII and its previous years. This was calculated by using the

power per unit of displacement*velocity (rpm).

4. - Comparison with

no-aeronautical ICE ICE engines are not used only in the aeronautical industry, but they are very

important in other sectors where that kind of engine is the only one which is used,

such as the automotive industry.

In general, cars’ ICE have more power and can reach higher rotation speeds

than for aircrafts, although the torque is lower. The reason is that the compression

ratio is higher for the automotive’s ICE than for aeronauticals. Another difference is

that cars’ engines can work at higher temperatures due to their bigger cylinder

heads, while aircrafts cool the engine using the air flow generated by the propeller

which also has the function of engine’s refrigeration.

The ranges of some important functional parameters for SI and CI engines

and for different application fields are shown below:

0

2

4

6

8

10

12

14

16

18

20

1900 1950 2000 2050

BM

EP

Year

BMEP - Year

BMEP

Potencial (BMEP)

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Ranges of imep:

SI cars → imep(max.) = [8, 14] bar

SI sport cars → imep(max.) = [8.5, 25] bar

SI automotive → imep(max.) = [6, 16] bar

CI 4T industrials → imep(max.) = [5.5, 23] bar

CI 2T low velocities → imep(max.) = [10, 15] bar

Ranges of ηe:

SI → ηe = [0.25, 0.3]

SI industrials → ηe = [0.35, 0.45]

CI → ηe = [0.3, 0.5]

Ranges of Sp at Pmax:

SI cars → Sp = [8, 16] m/s

SI sport cars → Sp = [15, 23] m/s

CI automotive → Sp = [9, 13] m/s

CI 4T industrials → Sp = [6, 11] m/s

CI 2T low velocities → Sp = [6, 7] m/s

Usual ranges of relative fuel/air ratio:

CI → φ = [0.04, 0.7]

SI automotive → φ = [0.9, 1.3]

SI industrial → φ = [0.6, 0.8]

The three first engines of the table are aircraft’s ICE that we have compared

with other internal combustion engines. As we can observe, the geometric

parameter represented by L/B is very similar except in the case of the CI engine of

a ship which is twice higher than for the others. The effective power over the total

volume is a bit lower than the one for the automotive industry but very higher than

the tractor’s or ship’s, just because in the last ones the volume they fill is not so

important. The highest effective power over the piston area is the one for aircrafts.

Finally, as we have said, the rotation speeds of the aircrafts’ ICE are lower than for

the automotive industry but they are higher than the ones for ships and industrial

CI:

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L/B

imep (bar)

Pef/Vt (kW/l)

Pef/Ap (kW/cm²)

rpm (min¯¹)

Continental IO-240

A 0,9 10 24 0,93 2800

Lycoming R 680

E3A 1,0 12 24 2,29 2300

Pratt&Whitney R 2800 54

1,0 15 34 9,35 2700

SI automotive 4T (1000cc, 4 cyl.)

0,9 10 45 0,25 5800

SI automotive 4T

(2000cc) 0,9 10 50 0,30 5500

SI competition

(400 kW) 0,6 13 140 0,60 12000

CI automotive 4T Indirect injec.

1,1 11 30 0,22 4500

CI automotive 4T

Direct inject. (100 kW)

1,0 13 50 0,30 4500

CI automotive 4T (300 kW)

supercharged

1,1 17 25 0,35 2000

CI tractor 4T (75 kW)

1,2 7 14 0,15 2400

CI industrial 4T (10000 kW) supercharged

1,2 20 8 0,42 520

CI ship 2T (35000 kW) supercharged

2,2 13 2 0,42 70-200

5.- BIBLIOGRAPHY www.wikipedia.org

“Motores de combustión interna alternativos de uso aeronáutico” –

Belinda Joana Villanueva Comunidad – Unidad “Ticomán”

www5.uva.es/guía_docente/uploads/2012/389/51445/1/Documento.

pdf

http://www.repositoriodigital.ipn.mx/bitstream/handle/123456789/8

003/TESINA-TERM-001.pdf?sequence=1

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6.- ANNEX Next annex contains data of 76 different engines used in aeronautics.

Since the grid is too big, it is distributed in groups two groups of 25

engines and one las group of 26; each group on each sheet of paper.

The data we have collected from each engine is (in order):

Name of the engine

Year when started operations

Manufacturer

Example of an airplane that is equipped with this engine

The type of ignition process and kind of fuel

The cylinder arrangement and the working cycle

Type of Cooling system

Type of Intake pressure

Value of the stroke

Value of the bore

Power (hp or kW)

Compression ratio

Displacement

Bibliography

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