L Ring Efect 2 Strokes

8/14/2019 L Ring Efect 2 Strokes

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L-Ring Effect on Air-CooledTwo-Stroke Gasoline Engines

Shoichi Furuhama and Hiroshi lchikawaDept. of Mechan ical Engineering, M usashi Inst i tute of Technology, Tokyo

A PISTON RING which has L-shape cross section is called anL-r ing. Rece ntly, i t has been used for some air -cooled two-stro ke gasoline engines with a good engine perform ance o b-tained . The reason for this L-ring effect has no t been ma declear up to da te .

High-power two-s trok e gasoline engines have been used forsmall cars , motorcycles , outbo ard motors , snowmobiles , and soon. These vehicles require their engines to endure higherthermal loads for a long t ime. Therefore, the maximum powerof the engine is l imited practically by i ts endurance against thethermal load. The piston and cylinder temperatures becom ethe most important factors to the engine performance.

In this paper , a solution of th e L-r ing effects is exa mined bypiston temperature measurement.INFLUENCE O F PISTON AND CYLINDERTEMPERATURE ON THE ENGINE ENDURANCE LIMIT

Fig. 1 is an example of the tem perature dis tr ibution of thepiston a nd cylinder fo r a small size air-cooled two-stro ke en -gine. I t shows tha t the par ts of pis ton and cylinder at tain sohigh a tempe rature th at the running endangers i tself when inhigh power and low velocity of the vehicle. From m anyexper iences, i t has been determined tha t ab out 3 50 C for pis-ton and 2 50 C for cylinder are the cr i tical temperatures forthe lubr icat ing surfaces.

An e xper im ent on p iston seizure was carr ied out using theengine mentioned above with the sam e pistons and dif ferent

bore cylinders . Then the pis tons were overheated owing tothe lower velocity of cooling air . Fig. 2 shows the effe ct ofpiston clearance upon resistance against seizure. When loadand speed are the same, the larger the pis ton clearance and thehigher the tem pera ture . Tha t is, a large clearance piston hasan infer ior cooling effect because the heat t ransfer f ro m th episton to the cylinder is low, and a large am oun t of gas f lowsthrough th e clearance. In the case of this exper iment, thepistons were seized by the cylinder regardless of the clearancewhen the cylinder temperature at point A reached ab ou t2 6 0 C .Anoth er exam ple of seizure is shown in Fig. 3. These pistons

3were used in a 440 cm (D X S = 6 6 X 44 m m) eng ine; a two-cylinder air -cooled two-stroke engine, made infer ior in th e gastightness by enlarging th e gap clearance of piston ring.

Fr om this e xper im ent, i t is also cer tain that with the largerclearance, the pis tons suffer more severe seizure than the pis-ton s with smaller clearance. The cause of the seizu re, there-fore, is not the therm al expansion of pis ton, but i t deter iorate5the rubbing surfaces and lubr icat ing oil at such a high tem pera-l u r e .SE A L IN G E F FE C T O F L - R I N G

DYKES' THE ORY ON L-RING - The L-ring was researchedby Dykes ( I ) * in former t im es. In his research of L-r ing,

*Numbers in parentheses deisgnate References at end o fpaper .

ABSTRACTAn L-ring (a pi ston ring with an L-shaped cross sectio n) has

been used on some air-cooled two-stroke gasoline engines. is l imited by i ts thermal load endurance. So piston and cylin-Goo d performance has been obtained; the reason is unkn own . der becom e the most im portant factors to the engine's perfor-The maximum power of these small engines (used mainly for manc e. L-r ing effects are examined in the l ight of these tem-small cars, motorcycles , outboa rd motors , snown ~obile s , tc.) perature measurements .


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\CYLINDER H E A D

Upper value : minimumEXHAUSTPORT 1 :maximumfl1 - T e m p e r a t u r e d i s tr i b ut i on o n e x h a u s t p o r t s id e o f 5 0 c m 3

l e ; ai r -cooled two-s t roke , under fu l l load a t 600 0 rpm andk m / h c o ol in g a ir

4 Engine stop b y seizureC Mi nlmum p i s ton c le a rq p ce i n dia.

5 10t ime min

N Normal rings and normal clearance cylinder( a ) Large gap rings and normal clearance cylinder( b ) Large gap rings and 0.05mm over size cylinder( c ) Large gap rings and 0.lOmm over size cylinder

D x S = 66x 6 4 mmFul l thrott le I

3Fig . 3 - Seized pistons of 44 0 cm snowm obile engine an d engineper formance . A - Seized pistons; B - M a x i m u m o u t p u t w i t h s e iz e dpiston

- Effec t o f piston clearance upon seizure under full load and 2 0/h cool ing a ir


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, p22000rpmp,5OOO rpm

+- T - -4b: r ubb i n g pressure( b )

Fig. 4 - Pressure dis tr ibut ion aroun d to p r ing. A - Pressures upper and lower the t op r ing; B - Lower surface contact ; C - Upper surfacecon tac t ; D - L-ring

Dykes em phasized on sealing effect of L-ring as follows:when a r ing makes contact with th e lower surface of th egroove, the radial pressure distribu tion is explain ed as shownin Fig. 4B (2), where th e force acting to th e cylinder surface is

So the r ing would go away from the cylinder surface , andblowb y would increase excessively. I t is understo od f romFig. 4 D tha t th e L-r ing seems to be an effective countermea -sure for avoiding this danger .

In general , however, this phenom enon never occurs. Thef i r sb easo n is tha t the to p r ing does no t l i f t up a t the wideopen thr ott l e running, even a t very high speed. When a fric-t ion an d conglutination force are neglected, the l if t up of thepiston r ing must occur under the following condit io n:where:

pe = elastic pressure of the ring.I t must be balanced to the hydrody namic lubr icating loadcapacity, that is

where :So the ring never goes away from the cylinder surface.I f the r ing l ifted up and m ade contact with the upper sur-

face of the groove by an inertial and frictional force, in spiteof the large pressure difference ( pl - p2), th e pressure distri-

y = density of ring materialcu = acceleration of the ring

bution would change as shown in Fig. 4C. In this case , thedirection of radia l force would turn inward and i ts force wouldbe

Fig. 5 show s a comparison of each value of the lef t and rightside of Eq . 4 (calcula ted f ro m Fig. 4A). I t is understo od th atthe t op r ing never lif ts up. For the second reason, even if ar ing l if ted up, i t does no t go inward f rom t he cylinder wall sofar as elastic pressure pe is larger than the (pl - p2) /2 ; tha t i s


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1. Pis ton bod y2 . Separate piece of top land3 . Separate piece of second land4. Top r ing5 . Second ring6 . Oil ring7 . Elec t rode for capac i tance8. p7 gas passage-9 . Elast ic p la te for p measurement2

10 . Bakelite piece11. Coil1 2 . Lead wiresFig. 6 -Test piston consisted of three pieces

5 0 0 0 rpm,

c rank angle5 -Comparison of axial forces of pressure and inert ia to r ing

E q . 3 .ssible for a ring to lift up and also to go inw ard only

en he condiiion fulf i lls Eqs. 4 and 5 at the same time.i s:

In orde r that the r ing detaches itself f ro m the cylinder wall , peByshould be smaller than - a ..!2

For example , B = 0 . 2 c m , 7 = 0 . 0073 kg /c m 3 , a nd a = 1 0 0 0) 2g, t he n 1 . 46 pe kg/cm . After all, in the case of usua l rec-tangular t op r ing, i t never lif ts up an d never goes away; there-

fore. excessive blow by never occurs. O n this point, the L-ringeffect is out of discussion.

LOWER S UR F AC E C ONTAC T O F L- R I NG TO TH EGR OOVE - On the o ther han d, as the L- r ing , to make m at te r sworse, has a weakpo int (which will be described below), i tmust be used carefully.

Axial movements o f some piston r ings have been measu redby a special device [Fig. 6 ( 3 ) ] in a water-cooled four-strokeautom obile gasoline engine. Fig. 7 shows a typical record ofaxial mov ement s of two r ings and changes of pressure p l andp2. %

Fig. 8 shows a record of the rectangular rings of pe = 1 .7kg/cm 2, in which it is c lar ified that the to p r ing does no t l if tup until high speed. Fig. 9 shows a case of L-ring as the to pring with large elastic pressure pe( = 2.4 kg/cm2) . The upper -most l ine of Fig. 10 is a typical mov ement of L-r ing. O nly atposition c in Fig. 10 , in which the pressure p l is hg h , does thelower surface of the L-r ing make cont act completely w ith th e


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Flg. 8 -Ef fect of engine speed under full loadrmg in case of rectangular .iouo I ptn

Fig. 9 -Mov emen t of strong L-ring (as a top ring) under full load . :!ooo w n r 3600 rw

r lng c on tac t t o upper surface o f g r o o v e! / lower su r f ace o f a r o o v e

Fig. 7 - Typical record with rectangular rings

groove surface. At posit ion b in Fig. 10, i t does not m ake con-tact because the L-r ing deforms in arch-shape in the cylinder(Fig. 11) by the elastic force. So that , at posi t ion b in Fig.10 , the blowby through the L-r ing may increase.

2Using a weak L-ring (pe = 0 .38 kg /cm ), however , as thedeformation is small, the contact of the lower surface of L-ring is improv ed (Fig. 12) .

Lastly, the amo unt of blowby is measured in the same en-gine as above, with pistons having only one com pression ring.As a result , the deformation effect of L-ring on the b lowby isproved again (Fig. 13 ). In this figure, "Lap" means tha t thering is finished with la pping its lower surface after insertin gth e ring in to a lapping device whose bo re is coincident withtha t of the test engine cylinder . Tha t is , the L-ring is no t moreeffective in gas tightness tha n the usual rectangular ring: andth e weaker in elastic pressure the L-ring is, the mo re it a p-proach es the rectangular ring in gas tightness.L-RING EFFECT ON OUTPUT PERFORMANCE

TEST ENGINE - For th e purpose o f th i s exper iment , twotypes of two-stroke gasoline engines were used.

3T y p e A - Two cylinders (D X S = 6 1 .5 X 6 0 r n m ), 360 cm ,air-cooled light car engine.

Fig. 10 - Typical movement of L-ring

l o w e r s u r f a c e', of groove

Fig. 11 - L-ring deformation in archshapeType B (p roduced by Tohatsu Co .) - Tw o cylinders (D X S =

66 X 64 m m ) , 440 cm3, air-cooled snowmobile engine.Piston s and rings for the expe rimen t we;e prod uce d in spe-

cial form an d size to serve each purpo se. These engines ran atthe co ndit ions of minim um spark advance and leanest air - fuelrat io for best to rque ; each lubr icant-fuel rat io was abo ut 1 :30.

I N FL U E N C E O F R I N G SH APE A N D G R O O V EPOSITION -

Engine A - The test engine piston had three compressionrings. Th e test was carried out using the three arran geme ntsof the piston ring as shown in Fig. 14. The engine perfor-mance o f Fig. 15 was obtained. I t was found that each ar-rangement does not have the same maximum power . but the


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2000 rp m 7CIUO r pm 4000 r p nFig. 12 - Movement of a weak L-ring (as a top r ing) under ful l load

30

25

5 20I-150"j

0 10

5

0laM MOO 3000 4000 3

14

12

10

CE 8.?4a

2

01OOO MOO 3000 4000 MOO( b) rpm

Fig . 1 3 Am oun t o f b lowby in 1 300 cm3 au tomobi le eng ine wi th one compress ion- ring p i s ton . A - Ful l load ; B - Half load

ei

w i t h ou t r l ng

cL - to p r in g R e c - t o p r lng ~ e c - s e c o n d n d

t h i r d r i ngI d )

. 14 -Te st pis tons and r ings for engine A. A - Rectangular top r ing, lower posi t ion; B - Rectangular top r ing, upper posi t ion; C - L top r ing ;- Ring cross sect ion


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Fig. 16 - Test pistons and rings for engine B. A - Rect-angular -7 m m; B - Rectangular-2.5 mm; D - L-2.5 mm;E - L-ring; F - Ring cross sections

L- to p r lng Rec- top rl ng Rec- second r l n g( f )

2 3 4 5 6 73x 10 r p m

Fi g . 15 - L-ring effect on maximum power in engine Arpm

Fig. 17 -Rin g e f fec t on m aximum power in engine B


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c o n d u i t pipe_j:

0 - r i n g*Fig. 18 - Combust ion chamber across and c ircular band method used inth is expe r im en t

ing is super ior to the rectangular ring. Anothe r imp orta ntr is tha t the engine with the upper posit ion of t he r ing

lower posit ion. There-usefulness o f th e L-ring is caused by either i ts L-

at the L-r ing can be posit ioned a t thef p i s ton shou lder .

Engine B - The piston of this engine had two compressions. The r ing arrangemm ts of the test pis tons are shown in16 ; (A) is the lower position of t he rectang ular rings, (B)

In (C) and (D), the L- top r ing is in th e sames (A) and (B); (E ) is in the usual Lr in g

As a result , a performance as shown in Fig. 17 was ob ta ined ,1 . The higher the r ing posit ion, the more power is obtained2 . When th e position is 7 mm lower than the upper edge ,

Fig. 1 9 -T w o se ts of p i ston t empera tu re measu remen tdevice; A - Engine A ; B - Engine B

the engm e cannot run for a long t ime at a speed higher thanab o u t 5000 rpm because of potential seizure.3. L-r ing out put is a l i t t le greater than with the rectangular

r ing at the same posit ion.L - R I N G E FFE C T O N T H E P I ST O N T E M PE R A T U R E

T E M PE R A T U R E M E A SU R E M E NT O F T H E P I ST O N S -Tem perature measureme nt of the high-revolution two-strok eengine was difficult because the connection of lead wires be-tween th e pis ton and the s tat ional place was not easy.

In this exper im ent "Combustion Cham ber Across a nd Circu-lar Band Method" (4 , 5) was used . The t i~ermo coupiewires ofi ron and cons tan tan were 0 .1 5 mm in d iameter , enamelcoatedand glasswool was wound o n them . A spher ical hot junctionof 1 m m in d iameter was made b y silver soldering. Each hotjunction was plugged ont o the pis ton surface. Therm ocoup le


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No. 2 cy l i n de r

I b )Full throttleNo.) cylinder

Fig . 20 -Comp ar i son o f each p is ton andcy l inde r t empe ra tu re in fu l l th ro t t l e

Fig. 2 1 - L-ring effect on pis ton temperature . ARec tangu la r - lower ; B - L-ring; C - Rec tangu la r -upper

wires were cemented with thermostable b ond in the condu it found: f i r s t, tha t each tempera ture of t wo p is tons i s no t thepipe which was f ixed t o the piston he ad, so the pipe recipro- same , and th a t the maximu m di ffe rence a t ta ins about 30 C;cated across the com bustio n chamber . The wires were stuck second , a t max imum power , a par t o f the p is ton a t ta ins theon a c ircular s tee l ban d from the to p of the pipe to the sta- cr i tica l temp erature for se izure .tiona l place (Fig. 18). The weakes t endurance po in t o f th is Fig. 21 shows the cooling effect of L-r ing on th e piston. Cer-appara tus was to overheat a par t of the pipe just above the ta inly, the piston w ith the L-ring has lower te mpe ratures , andpiston head of Fig. 18. the piston with rectangular r ings a t the upp er posit ion a lso has

Fig. 19 shows an exte r ior veiw o f this apparatus insta l led o n lower tempera tures than a t the lower posi t ion . Compar ing thee n a n e A an d B , each of which used two sets to measure the tempera tures of a p iston unde r the same power , the tempera -temperatures of t wo p is tons . ture dif ference becomes much larger (Fig. 22).Engine A - One example of the measur ing temp erature is In order to understand the heat f low in the shoulder pa r t ofshown in Fig. 20 f rom which two impor tan t ma t te r s a re the p is ton , an i so the rma l cha r t was ob ta ined by ha rdness


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LOO

La,'C

35 0i?U

uaJL3df 300aEaJ

250

20C

Fig. 2 3 - Isothermal chart o n rectangular-lower piston I-

10 15 20o u t p u t PSFig. 2 2 -P is ton tempera ture aga inst power ou tp ~i t

method. Fig. 23 is the result in the case of the piston withrectangular ring in the lower position. It is made clear fro mthis that the heat flows into the piston not only from thecrown surface, bu t also from the top land. Each piston withrectangular-lower, rectangular-upper, and L-ring has an area2of the top land peripheral surface of 13.5 cm2, 5.8 cm , an d

22.0 cm , espectively. On the other han d, tile area of crown2surface is 29.7 cm . The further u p the piston ring, the m ore

effective the cooling of the piston. The first reason for this isthe flow path of heat fro m the crown surface to the pistonring is short . The second reason is the am ount of heat inflowfrom the to p land to the piston is reduced. There fore, it iscertified that the cooling effect of the L-ring is caused by thesituation of the ring, but is not caused by the sectional shapeof L-ring.Engine B - Using the pistons with lower positioned rings, asit was in danger of seizure during the high speed and longperiod running, the temperature measurement experiment wasl imited to the eng ne speed at which the maximum tempera-ture reached about 37 0 C. The piston with 7 mm d epth ringwas l imited to the 4500 rpm maximum speed. From these "experimental results, temperature distributions are compa redwith those of each ring position and each ring shape in Fig. 24.I t is clear that the lower the position of the rings, the higherthe piston temper ature becomes. The tempera ture on thecro wn , especially, has a large differen ce. Then t he 7 m mdepth ring position could not be used practically in this engine.When the ring positions of the L-ring and the rectangular ringare the same, the piston temperature of L-ring is almost thesame or a little higher.


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Fig. 24 - Influence of piston ring shape and posit ion on piston tern.pera ture when fu l l open thro t t le in h igh tem pera ture cy l inder ofengine B. A - Rectangular-7 mm; - L-7mm; Rectangular-2.5mm;D L -2 . 5 m r n ; E - L - r i n g

Fu l l l o a d


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. During the operation of a recent air-cooled two-strokeoline engine near maxim um powe r, the piston tem perature

the critical tempera ture-350- 370 C at the crown cen-In the critical circum stance, the rubbing surfaces of thelubricating oil are deterio-

There fore, the more the piston is cooled, the more. The L-ring has more of a cooling effect than the usual. The cooling effect of the L-ring is caused by its upper-

ulder, but it is no t caused by its. When the ring is in the upper p osition, the piston crown

rature becomes lower not only because of the shor t pathflow from the piston he ad to the ring. but also thee in heat inflow area from th e to p land.

. The large tension L-ring is inferior in sealing effect be-e of its arch-shape deform ation. So the tension of the L-

as weak as possible.perature of L-ring was a little higher. Neverthe-

the o utp ut of L -ring was slightly greater. It seems tha t theer o utp ut of L-ring was obtained by reason of its small

research of the L-ring effects on the performance ofh-output air-cooled two-stroke gasoline engine, the

on the sealing and cooling effect of the L-ring

were carried out comparing it with usual rectang ular ring. Thefollowing results were obtained:

1. The p iston reaches so high a temperature that the rubbingsurfaces of the piston and the lubricating oil are deterior ated.The n the frictional resistance increases and , the piston some-times falls into the seizure.2 . The L-ring has more cooling effec t, so it can increase th eengine power safely.3. The L-ring effect does not depen d on its cross-sectional

shape, but upon its position in the piston because it can bepositioned at upper edge of the piston shoulde r.

4. Cooling effect of the piston with uppe r positioned ringsis caused by not only shortening the path of the heat flowfrom the head to the ring, but also decreasing the heating areafrom the top land.REFERENCES

1. P. De K. Dykes, "Piston k n g Movement during Blow-byin High-spee d Petrol Engines." Trans. Inst. Mech. Engrs.. Vol.2 (1947-1948), NO. 71.

2 . S. Furuhama a nd M. Tsuruta, "A Dynamic Theor y ofPiston-Ring Lubrication (4th Repo rt, Load)." Transactionsof the JSM E, Vol. 27 , No. 178 (1962), pp. 919-926.

3 . S. Furuh ama a nd M. Hirum a, "Axial Movement of PistonRings in the Groove." Presented at the 27 th ASLE AnnualMeeting, Houston, May 1-4 , 197 2.

4 . S. Furuh ama, "The Temperature of a Crankpin Bearingof an Automobile Engine." ASLE Transactions 10 (1967),pp. 203-213.

5 . S. Furuhama, T . Tada , and T. Nakumura, "Some Mea-sureme nts of the Piston Tempera tures in a Small Type Gaso-line Engine." Bulletin of JSME, Vol. 7 , No. 26 (1964) , pp .4 2 2 4 2 9 .

his paper i s subject to rev~s ion . S ta tements and opinions been edi ted by SAE for uni form s tyl ing and form at . Discussion will be pr intedadvanced in papers or discussion are the author's and are with the paper if it is published in SAE Transac t ions . For permission t o p u b l nhhis responsibdity, not the Society's, however, the paper has this paper in full or in part , co ntact the SAE Publications Divislon and the-... L .-.

ety of Automot ive Engineers, Inc.O P t N N S I L V I N I A P L A Z A N E W " 0 . K N Y l O O D l

i lULI IU I>.

16 page booklet. Pun ted in U.S.A.

L Ring Efect 2 Strokes

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