High-compression engines are investigated with the three main objects being elimination of vibration, increase of maximum efficiency, and conservation of this efficiency at the highest possible speeds

Ziembinski, S

English

NASA Technical Reports Server

J-, ---- -----
-1
. . .
.
.
. . . . . -, .---,. -. - -—. — -.
. .
.
, ‘“+.
.WTIC~WL,.-~pViSO~.,MCC~l.T- FOR AERONAUTICS.
. ,.. -
-. ..
. .
. .
.
. .
POSSIBLE IMPROVWEllTS IN GASOLINE ENGINES.
By S. Zlembinskl, Engineer,
L. Renault Automobtle Company.
From “Premier Congres Intwmat ional de la l?avl~tion Adrienne,”
Paris, November, 1921, Vol. IV.
, L?.ktira:iyyl
.-...!
. .,.! ,,. , -.
.,. -. . . .
- e.. .. . -,s . .
January, 1923.
https://ntrs.nasa.gov/search.jsp?R=19930083396 2020-06-17T19:22:09+00:00Z
~Illllllllmmllllw~
31176014410147 \
—
POSSIBLE I~O$EMEETS IN GASOLIHE EMGIMES.*
By S. Zi~binskS.
,. ,. .. . . .. .~., ,.,,------., .,
MinesJ ZOrhula for determining engine power,
Fisk for automohileq, leads aonstruotors to build
great powet per liter of stroke volume.
. .
emplbyeclby
engines of
Up to the present year, the Renault Company had not follow-
.
ed this method; preferring, first of all, as in steam engines,
to increase the efficiency, I.e. full eoono~’ and.long funo-
ttoning without appreolable wear.
But In the year (1921) we ytelded to the former method
and studied high-mmpressiou engines, Sinoe such studies are
of the greatest Importance for aircraft engines, we csonsider
it of interest to give an aeoount here of the e~eriments tried
with a speoial engine, whl.chhas served for investigating the
different points in the progxam adoptec%
This progrsm had three main objeots:
1. ??Elimination of vibrations; , .-—.
2. Inorease of maximum effiolenoy; ..
‘\
3. Consemratl,onof this efficiency St the highest possible
,
speeds. /
The fIrst ob~eot was aooomplished by reinforcing the crank-
shaft, lengthening the oonneotlng rods and lightening the pis-
tons or masses-in alternating motion.
The seoondobjeot was aooomplisheciby a’reaso&ble In- “
Grease of the compression;by making the ocmpreselon 6Mimbez
* From “Premier (longrbsInternational de la Navigation A6rlenne,”
Paris, November, 1921, Vol. IV, PP. 4~8-4!34.
-—.
\ ‘2-
as oompach as poselble, so as to insure good mtxlng and per-
feot oom~uation of the gasss; andlzy giving ths right shape
-.. .- ... .-..,.=—F. -,, .,.F.-
—,y
to the Intake and eihaust
tion of.the engine.
The third ob~eot was
first, sinae they Improve
pipes, for assurlug a good respira-
aooompllshed by the same means as the
the me@anl=l efflolenq; also by
a suitable shape of the Intake and exhaust pipes”,enabling the
preservation of a high effioien~ in spite of high gas veloci-
ties, exoeeding 100 m/seo (328 ft/seo~. In an automobile engine,
this is neoessary in order to retain the iow (or idling) speed,
The basis of our study was an engine with four oylinders
.
95 x 160 mm (3.74 x 5.3 In.), with the valves on the side,
these oharaoteristiosbeing retained,
Intake.- Several engines were mounted with the carburetor
faolng the valve side of the oyllnders and with dbannels east
in the oylinder blook. We have always found losses of power
resulting from dlffitities of oasting, pipes with elbows, oon-
strlotions, roughness and even ridges Impossible to remove.
Ariengine with the carburetor on the valve side immediately
regained the lost power, beoause it
the preoa~tions for assuring a good
evaporation of the garaollneand its
was possible to take all
flw of the g&es, good
uniform distribution in
the oyllnders,... TMs arrangement, however, only gave good re-
sults when the gases were heated. The first heating was pro-
duoed ina jaoket traversed by the exhaust -es. As soon as
the engine began to give a good total power, It oould not run
.
.
—. .-
-3-
--
-withoutthis ~aoket..Alth~~@ it ~t~ing~ a t~parat~e of about -
100% (~@F), its flanges were not heated, but, at a dlatanoe of
.“. . . .. . ... .~. -
10 mm (~39 in.) fkom the exhaust gases, were oovered with dew on
very sam days~ even in September.
“ The most Important results were obtained with the following
arrangement: The.gases, after leaving the carburetor, aontained
globules of gasoline whioh, at the first bend, are thrown by
their centrifugal foroe against the wall of the pipe. ThiEI
wall was brought
interposition of
conduction. Ali
into oontaot with the e~ust manifold by the
an aluminum blook, foz Insuring rapid h-t
olassic?treatises on engln& had predioted
a diminution of power due to the expansion of the gases admit-
ted into the oylinders, but the engine investigated gained
“greatly in power and eepectally in regularity of functioning.
We found that a knowledge of the flow of gases, based on
study in an aerodynamic laboratory, gave very important re-
sults. Applied alone, however, this knowledge may had to
false oonolueione. It was ~ometimes mscsssazy to depart from
ttA +n accler to regularize the distribution or evaporation
of the globules. Thus (from this departure] me might lose 1$
of the power and yet gain I@ from the improv%i evaporatior~.
A Renault airplane engine only ran well titer a sharp bend was
,,.lntroduoe~.I.nto,the,int-@e plpp. .PTPVIWIY, a pipe with
rounded elbows led many globules into the manifold. These
were almost totally absorbed in the first oylinders, whioh in
thik way reoelved a muoh rioher mixture th.m the following
-1
oylinders.
.-
.-
-4F
The introduction of a sudden bend, at the entranoe to the
manifold, oreatefiat this point a violent eddy, whloh evapo-
..-, .. ..........
rated a large portion of the globules and pxojeated the a-iii-
der of the gasoline farther into the manifold. In this way,
alth~gh the quantity of gases introduced ido the engine =6
slightly diminished, its quality was muoh,improved.
Em gust manifold.- l%w oonstruotors have paid attention
to the faot that, in engines oontainiug more than four ~lin-
ders, the exhaust of each ~llndez overlaps the following.
The first oyl.inderiS near the gti of the exhaust stroke, at
.
low preesure, though there is yet muoh gas to exhaust, when
the following oylinder begins to+efiaust with a muoh greater
pressure. If the latter reaohes the manifold suddenly without
speoial preoautlone, it oreates a baok pressure and naturally
arrests the exhaust of the preceding aylinder, whioh is thus
prevented from mmpletely emptying itself. Our investigations
have led us to the oonetruation of a manifold in which ea~
exhaust, instead of hindering that of the””preoedingoylinder,
serves, on the oontrary, to e~ust It better, by drawing away
the remaining gases.
The engine with our old manifold gave less power than
without any manifold at al’1,but with the new manifold it gave
“more power. In.@ manifold of thislind.,..hlghgae.speeds are
obviously possible. ,
Valve chambers.- In
with the beet intake and
nearly all existing engines, provided
exhaust pipes, there are sudden ohanges
-5-
bf oross-seoticnin the valve ohamber and ridges against wW.C.h
Ven~i tube, thm to allow
BY applying this principle,
power.
e.bruptohanges
we obtained an
in cxose-seation.
appredable gain In
Cornpmss?.on chqmbcr.- Up to the present time, this h!isre-
ceived very little attemttou Only one improvement has been
adopted by the oonstrutioti~and this oonsists in plaolng tke
valvea direotly on the aylinder head, whioh naturalw- makas
the oompresslon ohamber uriichmore oompaot. In an engine with
the valves on the side, ths Elan of the chamber is automatical-
ly determinedly the bore of the cyllnder and the dia&eter of
the valves. The height is riearlyconstant and corresponds to
the desire~ compression. We found that this shape could be
advantageously modified In aoocmiance with the
pr~noipl.es:
L To aompress the gases into as mmpaot
two following
a vol&e as poe-
sible, either above the piston or above the valves, by qedua-
ing to the minimum the height of the upper side.
2. To cause the entering gases to sweep the walls of the
oylinder md the piston head during the intake stroke, in order
to evaporate the adhering globules of gasoline, and to mix the
gaees well d~lng the compression stroke, in order to have a .
perfeot homgenetty at the moment of ignition. Lastly, to
-.— — -..—
-6-
brlrigthe spark as near the c$enterof the mixture as possibls.
power. ...
l
Lemth of”oonnecti~~roas.- It
gave .--a 30jlinorease of
would be foolish to insist
on t~e Importance of gtvlng to the oonneoting-rodsa le~th
always in exoess of &ioe the stroke. All old and new treat-
ises advocate it, but oonet~otors show an increasing tendenoy
to reduoe this length, especially In aixoraft engines. Some
engines have a length of conneothg-rod as lW as 1.6 times
the stroke and In no ease does it exoeed twloe the stroke.
The reasons for this lengthening are well known, so we
need not repeat them. We will simply call the attention of
oonstruotorsto Fig. 1 (curves 1 and 2), whioh speaks for it-
self.
It would likewise appuz trite to say that the pistons
must be as light as possible. However, this truism remains in
the domain of theory, without penetrating sufficiently into
the bureaus of researoh. In Fig. 1, three cilfferentweights
of pistons were employed: ordinary oonneotions made without
regard to lightness; others lightened Z@; and still others
.
with their weight reduoed 47% from the original weight (o=ves
2, 3 and 4). The results are sufflolently eloquent to oen-
.
vinoe any one, They are all the more Impor-tant,beoause they .
correspond to an Intake and exhaust veloutty of over 100 m/&eo
(328 ft/see) and to an average piston speed of 17 m/seo,
(55977 fWseo) ~~lthout~=ring the 00E*~ s~f=es.
1 —.
-7.
Pif;tmna.- It has been possible to effeot this lightening
anly w%mbhahmdmm pistons. !fhsgreat objeotion to employing ‘
ifimnlim Fistons are ool.d, We easily remedied this djffIoulty
>? ohanging the axis of the piston or by giving speolal shapes
,“
“COthe piston, so as to enable its being heated without appre-
otable inorease
Zt is also
Imparted by the
.
in diameter,
neoeseary for the greater
gases to the pititonhead,
.
4
portion of the heat,
to be transmitted tc
the oylinder -11s by the part of the piston oontainlng the
rings, without heating the surfaoe of the piston proper.
Piston rinm.- It is very important that these should not
be too hard. The friction between the piston rings and cYl-
, inder walls considerably diminishes the mechanical effioienoy.
The experiment of r~oving two rings out of three per piston
resulted in an @ gain of power. It is evident that too hard
piston rings wear the oyllnders as likewise too short pistons.
We aooordingly adopted very light piston ring~ and VW!Y ohort
pistons.
The problem of the piston rings is essentially a metallur- “
giual probl~ If the metal is homogeneous, soft ~d elastio,
perfeot tightness oan be obtained, even with very light rings.
Orank shaft.- In the constructionof the cmank shaft, we
endeavored to avoid the vibrations of the engine”due to flex-
ure and torsion of the orank shaft, ~hioh are the principal
.
oauses of vibratlona in polyoylinder engines. It Is a recog-
1 ---
-0-
nized fact that six-oyiinder engines often give more vibratimu
.
than four-oy~inder ones, even with the plstpns, the orank shaft
wM. the-fly=whde~--~lan~d to”the”la&t’’&-am,“whichreduoos to
zero the resultant of the foroes of inertia and of the cen-
trifugal foroes. This is due to the faot that the orank shaft
of a slx-qlindes en@ne IS muohmotie subject to torsional vi-
brations and espe~ally to the fad that its vibration period
.
1s muoh longer. It may therefore become t~oublesome in a six-
oyllnder engine below the maXinUIII speed, while not appearing at
all In a four-oyllnder engine.
We took an engine whioh vibrated strongly at all speeds. 4
We balanced the oonnetiing-rotiand pistons, the orank shaft
and fly-wheel. The engine ceased to vibrate, save at two Far-
tioular speeds in the ratio of one to two, thus demonstrating
that the orank shaft is the ohief cause of engine vtbratimns.
Scientists are now giving speoial attention to torsional
vibrations. It seemed to us there might be other, no less im-
portant, vibration due to the flexure of the orank shaft In the
vertlckl plane passing through its axis, espeolally in fouX-
oylltier engines with three bearings and In six-oylinder engines
with three or four bearings. To test this point, we took the
orank shaft of a four-~linder engine with three bearings,
whioh”vibrated, and relnforoed it simply from the torsional
.. ..-
point of view. We made it more rigid about its longittiina~
axis and lightened as muoh as pos.aiblethe me.asosoutside its
axis of rotation, eepeolally the orank pins. The engine~ how-
I -.
may therefore be stated that orank shsf%s
bearings have two kin& of vibrations,
irgs, i.e. ..Ifi”the~-=~~””-”
third and fourth orank
CisapFeare&
in oonolusion, it
with a small rnmber of
those of torsion and of flexure, mhlle sank shafts with bear-
ings between every oyllnder aml the neti havg pratiioally onlY
tor~ional vibratilono.
Engine vibrations ehould be el~minatcd at any cost, even
aside from the question of the oornfortof the passengers.
First, beoause many breaks are due to the vibrations. The reo~~
ent large German airoraft enginee~ with bores of over 200 mm
(7.87 in.), have ali failed from th8 ruptuxe of parts (Inoludlng
even the orankoase) caused by the vzbratlons. In the seoond
plaoe, vibrations absorb power and Ioss=n t.hg~’-~ioal effi-
oienoy of the engines.
A third ~lsadvantage of vibratioma (wlxichhas as yet re-
oeived but little attention) is the more rapid wsar of the con-
taot surfaces. We have observed t-hatthe w~ar of the orank Fins
and the ovalizat”~onof the cylinders were appreciably more rapid
in strongly vibrating engines than in non-.vlbratlagengines.
After taking all the above-mentioned prooautlons, i.e.
after we had reinforced the orank shaft, lightened the pistons
the most possible and eliminated the vibrations, we mere able
—.
-1o-
io keep the dimensions of the waiet pine the same as before.
‘&e engine nevolved twioe as fast and developed twioe as much
power. T.hswrist pine presentid perfect oontad; surfaoes -i%h-
out the least play.
In passing from a SDELIl, engine to a lar~g= oze, the bear-
ings wear out more rapidly, even If they are ma~e aooordlng
to the same coefficient of wear, i.e, a quantity whioh ie the
pkoduot of the rapidity of fritiion timeEItke unit pressure
and whioh consequently represents the work of friotlon.
This results, in our opinion, from the fsmt that the oo-
effiolent of friction ia considered constant and Independent
of both speed and pressure. This is far from the truth, sinoe
the ooeffiolentof friotion varies greatly with these two con-
ditions. The last German edition of E&tts, not yet translated
into Frenoh, ooatains a very oomplete surmary cf tests by dif-
ferent e~erlmenters on the friction of lubricate surfaces.
Fig. 2 shows the variations of this coefficient.
In seeking to egress the variations analytically, we
found that p correspondedvery awurately to the formula
U= k($)*, k being a constant, Independent of v and p.
Under these conditions, the ~ork of friotlon is not pro-
portional to v and p, but to v*p~ and, in computing the
bearings of a drank sh&ftj acoount at be taken of a ooeffl-
oiqnt of’friotlon K correspondingto the expression K = V: p~.
At the present date, our investigations are not yet fin-
.. .. . . . . . . .
iahed, but we have already
previOuo].yhad only 43 HP,
., .,. ... . .
.Z1*
given 105 HP to an engine
applicable to air~’aft ongine~ and muld inoreaee their effZ’-
cieucy =d longevity. .
We insist principally on the need of raduoing, to the
uttoxmo~t, the weight of the
connecrting-rods;and al~o on
orank shafts and lengthening
pietonm and Of llght~ the
the need of stmn@henlng the .
the bcerin~s. i~ lengthening
the bearings, the engine will be lengthened several oentimet-
eps and its weight inoreased sevexal kilograms, but it will
become much more reliable and will be able to revolve muoh
fastez, so
It IS
to that of
that Its total power will be inoreased.
no longer necessary to liait the speed of the engine
the propeller. Redu&?.ou gear~ are keing demand-
ed more and more. The adoption of a reduotion gear allowa
the engine speed to be inoreased up ta lunits zequlred by other
considerations. We thirk 2500 R.P.M. can be profitably a~e%?ed
from now oz
We aooordingly predict a
very .llghtpistons and longar
rapidly revolving
oonnedwlng-rods,
engine, with
It will easily
develop 25 HP per liter of stroke-volume and will funotion
satisfatiorlly for the needs of oommexcial aviation.
Translated by the”Natlonal Advisory Oommittee for Aeronautlos.
.-
——-..
1
6
10
8
5
6
3P
4
2
R,p.?~.
Fig. 1.
1
2
3
4
5
6
Old engine.
It 7 connecting rods lengthened.1! !1 11 II II light pistons.11 II II II II extra light pistons.
t? II II fl II light pistons;
[~ewcompression chamber and manifolds;
valve lift increased.
New engine;connecting rods lengthened;
extra iig’htpistons,
v w
v
Fig, 2. Variation of coefficient of friction &
with velocity and pressure (V and p).
..
.. .. ... . . .
.I
I
ullllllllllllBmMfllllllllllllllll
31176014410147
!
,“
. .
.
,. .
-4 ,
. .
.,.
. .
.,
.
.,
,,
. . ..
.
. .
-.
. .
.,, . . ,.
:-.
.,
.,
.,
. . . . .


Possible improvements in gasoline engines

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server