289 Sleeve-Valve Engines. 19

SLEEVE-VALVE RNGIXES. 289

SLEEVE-VALVE ENGINES.

BY E. B. WOOD [MEMBEROF COUNCIL). --_

TIIN author desims in this paper to bring to notice some of the intaresting features of this type of engine, since he feels that it ha not rewived the attention it deserves. This may be due, partly, to the intensive oonoentration on the poppet-valve type during the war and partly, perhaps, to the restriidive effeot of a mon o po 1:-

Sleeve Poppet FIG. 1.

The paper is entitled “ Sleeve-Valve Engines” as this is the popular &mi, but it is really intended to draw atstention to some advantages of the “straight-through” type of valve a5 against the poppet-valve, which mi’ght be called the “ round-the-oorner ” t.ype, Fig. 1. The authdr here wishes to make it clear that, in the hope of raising an interesting discussion, he will endeavour to stat0 the case for the sleeve-valve engine-and, therefore, should not be blamed if he may owasionally appear unfair to the poppet-valve engine, which will have many able dvoaates. Piston Val-, rotary valveas and two-cycle engines would in certain fornis be included in the above definition, but it is not proposed to deal WOOD. 19

Downloaded from pau.sagepub.com at WEST VIRGINA UNIV on June 4, 2016 2,90 THE INSTITUTION OF AUTOMOBILE EKGINEEHS. specifically wit.11 these, though iiiany of thc general coucludoiis would apply. 11,is intended to deal oiily x:itli:--- (1 j The double-sleeve type as eseiuplilied by the Iiiiight engine used by Daiinler, Mioerva, etc. (3j The single-sleeve type as eseuiplified by the Burt- MaColluni Patents used 011 Barr mid Ytroud iiiot.or cyclels, Argyll and Pic-Pic cars, the Caledoii lorry aid the Wallace tractor. (3) The Howard cuff-ralve, or split-&eve type. l’hi,~latter is not strictly a sleeve valve if a sleeve mlve be

Push rod to spi

Push rod to cam \~is~onrin 9 FIG.2 .--Ihvard C II If-valve. defined i~b‘‘ a tubular valve-menlber working betweell the piatoil and cylinder .” ,4. both the Knight and Rurt-M~d2olluinengine. lia~e beeii frequently illustrated and described in the technical l)re,as, it is unnecessary t,o describe their mechanical details. One form of the Howard cue-valve was ,exhibited iii the 30 11 p. Vulcan Sports Model in 1921, and a diagraniinatio sketch i.; given in Fig. 2 of the earlier form of this valve, which sinipl! comi5ts of a single wide expanding ring operated in one direction by a and returned by springs or moved both up aid down by cams. ,4 feature of both types of this valve is that it is -tationary at the period of high gai pressures.

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It is proposed to discuss the ,adValitages ,of the sleeve valve in aonndoiii with the following two axioms on obtaining maximum power It is elssentia1:- (I) To get the greatest possible weight of combustible mixture into the engine per minute, i.e.,high volumetric efficiency. (2) To ignite this mixture at the right time and under the best conditions, i e , using the highest oonipression-ratio compatible with absence of pre-ignition and “ pinking.” Starting with axiom (I), the author oonsideis that the high volumetric. efficiency of the sleeve valve is due to:- Cs) The “ stsaight-through ” nature of the vahe paysage to the cylinder In this oonnectioii the Clarke-Tomson Research” gives the efficicnoy of a poppet valve, with a lift equal to 0 25 of its diameter, a5 only 67 per cent of that of its port It may bc urigied with somc truth, that tho= were oontinuous-flo~~~speriiiients and not stricltlg- ;Lpplicable to the intciuiittent flow and islying valve lift of praotice (b) Tho absenoe of a highly heated hsifle-plate. i c) . tho valve- head at right angles to the flow of the iiicom;ng charge Aitchi- sonf- gives the teinperatum of thc inlet ,valve5 of aero engiiies as reaachinlg 600°C in spite of petrol oooling, and that of exhaust valves a< high as 860°C. The author lilts been unable to find any otliei definite figures regarding the temperature of automobile enginu inlet valvea. Several investigations have been made, however, with gas engines on the temperature of inlet valves and of the charge at the beginning of oonipression. Prof Dalhp$ iised a thermometer valve to proteot the very fine platinuiii wire during the explosion period Fig. 3 shows the variation of tmipeiature obtained during the suction stroke. L4s the theriiionieter valve was airailged to open at the lmginning of the suction stroke, it is probable that the maxiniuiii temperatures of the ciwvc’s would be tho-e of thc inlet valve The maximum temperature shown is 860” C. Fig. 8 also shows two curves from Coker and Sooble’s investigation of the cyclical variation of temperature in a gas engine, obtained by a different method In the disoussion these suction temperatures were attributed to excessive exhaust baclk-pressure It should be noticed that the temperatures increase with the speed and mixture strength. Coker and Scobles qive 311°C. as the temperature attained by the inlet valve of a 7 in. by 15 in gas cngine It miirt be remembered that the B.Th.Us liberated per $q in of coiiihnution- chamber surface a1.e only about 10 ,a- ao.aiust 67 to SO for Ricardo’s

* See “ Air Flow through Poppet Valves.” 4th Annual Report. Report No. 24, p. 27. American National Advisory Committee for Aeronaiitics. t See Proc. 1.A.E , Vol XIV., p. 32. i See Callender and Dalby. Gaseous Explosions Committee. British A.souiation, 1914. 6 See Proc. Inst C.E., 1913-14, Part II., pp. 19 arid 41. 19 (2)

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engine a1 1,500 revs. per minute. It is therefore probable that the automobile engine valve attains a higher temperature. It will now be interesting to aonsider the cooling effect of (1) tho liquid fuel, and (2) the valve seating. Burstall* shows that thc valves (which in his engine were water cooled) absorbed about, 3 per mnt of the total hieat liberated. An automobile inlet valvc will oocupy a rather larger proportion of the combustion- chamber surfaae, but will be at a higher temperature, so it will not be unfair to assume that it receives about 1.5 per cent of khe heat liberated. If we msume a valve of a size capable of giving 8 b.h.p atr the point where the mean effective pressure begins to drop, and a petrol amsumption of 0.6 lb. per brake horse-power per hour, the

Crank degrees FIG.3.--Variation in temperature during suction stroke.

valve will receive about (13,000 x 0.6 x 1.5 x 8.0)/(60 x 100)=224 R.Th.Us. per minute. The latent heat of the petrol (135 B.Th.Us per pound) amounts for (135 x 0.6 x 8.0)/60 = 10.8 B.Th.Us. per minute. (2) Remingtan's experiments: indicate that, wl1en his heated valve mas placed on the water cooled seat, the cooling was at the rate of about 340" C. per minute at 450" C If a probable figure is msumed for the weight of the valve-head the heat-flow is about 5.1 B.Th.Us. per minute or 12.8 B.Th.Us. per sq. in. of smting This leavas nearly 7 B.Th.Ue. which go to the heating of the charge. If, however. the valve is hotter there will be a greater

* See Proc. I. Mech.E., 1908. p. 30. t See Proc. I.A.E.. Pol. XIV., p. 104.

Downloaded from pau.sagepub.com at WEST VIRGINA UNIV on June 4, 2016 SLEEVE-VALVE ENGINES. 293 flow to the seating. The author considers that these figures are only approximate but has included them to indiaate the proba- bilities. Remington's tests may give too low a figure for the flow of heat. to the valve heating, p.s from the nature of his experiment more soale would be formed on the valve than would be present in the ease of an inlet valve under working oonditions,. In this oonneotion it must be remembered that besideis causing loss OS volunietrio effioiancy by heating and expanding the charge, there is a powibility of slow burning being started in the mixture

Conventional gas velocity ft.per sec

FIG.4.-Conventional gas velocity per R. W.E. P. The author has shown elsewhere" that CO? is formed when a nlix- ture of petrol and air is passed through a tube heated to only 370" C. In Fig. 4 some figures of brake mean effective pressure given in 'Fable I have been plotted against convpntivnal gas ve1oait)- t

SeeProc. I.A.E.,Val. VI., p. 383. t Conventional velocity = nD?XSXN 1440 A where D = cyl. dia. in in. S = stroke in in. N = revs. per minute. A maximum value area in hq. in.

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16 nil1 be noticed that the mean effective pressures of the poppet- ialrn engines all begin to drop at a velocity of about 140 ft per seoond, while that of the Knight engine only begins to drop on approaching 200 ft per seoond. The Howard engine curve indicates much the same effect, but, ws it had no flywheel, it wai not possible to test this engine over a wide range of speed The single-sleeve-valve engine curve begins to fall at about 170 ft. per seoond, but this may be attributed to it. having a

Engine. Data from

sq. om. )er litre Ricardo (2 valves) . . 2,080 14.9 Variable 41 Engineering. Ayimed Ricardo (1 valve) , .. , 2,080 7'46 1 41

MercCdSs (Aero) . . . , 3,620 9.7 4.9 49 Zneruy Aircraft Znginea. Vaiixhall (R) . ,. . .. . , 780 12.0 4.8 44 (1.4 sq. in. valve area) Proc. I.A.E., Vauxhall (A)...... 762 11.8 4.8 47 VOl. XIII. (1.4 sq.in. valve area) i Vauxhall (A)...... 762 5.9 4.8 47 (O.? sq. in. valve area) Knight-Daimler . . . 936 9.9 4.5 40 Author. Howard ...... 1,300 10.5 5.7-5.2 40 Author. (experimental) Burt-McCallum . . . 654 9.3 4.8 15 Makers. (dow-speed setting) Bstr and Stroud . . . 349 18.0 4.0 35 Makers. (air cooled)

don-speed setting, i e., inlet closing 15 degrees late, whereas the inlet.. of all the other engines close ,about 40 to 45 degree8 late. Tho Mer&dhs is an aero engine* with a cylinder capacity of 3 62 litres, while the Ricardo; inight be dewribed a5 the last word in liigh-5peed experimental engines. In the latter caie, the ourve is an estimated one for a oompreesion-ratio of 4.5 : 1, and tlw abqolute values of the brake inean teflective pressure iiiay not be

* See Enemy Aircraft Engines, pp. 14-25. t See Engineering, Sept. 31-4 1920, pp. 328-3::O.

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cluite accurate, but the point at mliicli the inem effective preslsure begin. to fall will be substantially correct. These examples have been in~ertdto show that this point of droop is approximately the came for poppet-valve engines varying coixsiderably in cy liridei capacity Tliesc graphs are in agreement with the COntinUOU~-flQ~experi- tneut- in the Clarke-Toins~onResearch referred to above in that thc iatio 0.7 of tlie conventional velocities at which the mean effectiie pressures begin to drop is nearly the same as the ratio betweel, the air flow through a poppet valve having 0.25 dia. lift and the flow through tlie port with the valve stem only projecting. Thc author thinks it best to oompare the Knight-Daimler engine with the Vauxhall engines A and B* ,as the first two were hi18 a5 touring-ear engines and are of approximately the same cylinder capacitj and specific valve area (Knight 940 C.C. and 9.9 5q em. per litre and Vauxhall 760 C.C. and 11.8 sq. em. per litre) For the Vauxhall engine the ratio of maximum brake horse- power to the brake horse-power at which the brake inearl effeotive prewuw begins to drop is about 1.4. Applying this figure to the Knight engine, the maximum brake horse-power per fiq. cni of inlet-valve area is Knight 1.83, Vauxhall A. 09.5, Vauxliall B, 1%. Pomeroyi also give6 0.683 to 0.985 h p. per sq. am. for Vauxhall engines. That is, one unit of inlet-valve area is approsiniatdy twice as effective wit.h a sleeve valve as with a side-by-sih poppet valve, and nearly 50 per cent more effeotive than with overhead poppet valves The comparison is, if any- thing. unf'avourable to the Knight engine, as, to the best of the author'a reoolledion, it was tasted with cold water entering the jacket&. Dr. Watson$ has shown that 60 per cent more friction war observed with water entering at 35" C. than at 65" C. Similar effects have been observed in gas-engine tests. It should be noted that the 1.4 factor must be used with great caution as it is greatlj affeoted by conditions other than valve friction and hae heeu found to vary between 1.1 and 1-5 on published brake horse- power filgurea. Carburettor wire-drawing must be taken into account as, very frequently, that rather than valve area limits the brake horse-power. It is probable, however, that this does not affect the factor, but the incidence of valve bouncing would cause the ratio to be low.

VOLUMETRICEFFICIEKCY There hare been few published relsults of volumetric-efficiency tests of petrol engines under aotual running conditions. The comphonlsive series of tests by Ur Watson on a four-cylinder

* SeeProc. I.A.E., Vol. XIII., p. 163. t See Proc. I.A.N., Vol. VIII . p 408. See Proc. LA E., Vol. VII , p. 48.

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Talbot * engine and on a single-cylinder Knight: euginr wntaiii some volumetric-efficiency figures obtained by the diaphragni method of air measurement. They are, however, so much atfectecl by aarbumttor wire-drawing that the author has show-n in addition in Fig. 5 several points for eaioh engine corrected from light- spring indimtor diagrams of the indudifon-pipe pressurn, but no allowance has beon made for exhaust back-pressure. A dimt oompmhon of the volumetric ,efficiencies, under bench- bast conditions, of a poppet-valve engine ,and B sleeve-valve eagine may be of interest. A four-cylinder ,overhead poppet-valve engine (Engine A) of 1,500 0.0. capacity was available, and Mews Wallam (Glasgow), La., kindly lent a singlie-cylinder Rarr and Stroud 350 0.0. engine--single-sleeve type-(Engine B )

Revolutions per minute FIG.5.

Diaphragm methods of air ineasurenient were not cotidered mffioiently reliable owing to the number ,of corrections necbbary and tb faat that one engine had four cylindelrs while the other had only a single cylinder in which the variation in flow would be limp, and the apparatus shown in Fig. 5 was therefore fitted up. Here a motor-driven high-pressure blower was connected through a shut-off cock to an existing gas-holder of about 40 cu. ft. ppaoity. As it was inoonvenient to disturb the existing %in. ppe oonneetbnng, the air was taken through a %in. to +in. expansion-pipe to an expansion-box and thenae to the engine hy a 4-in. pipe. The float-chamber of the carburettor h,td to Ire

* See Proo. I.A.E., Vol. ITT.. pp. 397 and 400. t See Pror. 1.-4.E.,Vol. VIT., pp. 3.5 and 51.

Downloaded from pau.sagepub.com at WEST VIRGINA UNIV on June 4, 2016 SJ,EEVE-VALVE ENGINES. 297 connected to the air supply by p presure-equalising pipe The pressure in the bell of the gasometer was about 1.5 in. of water and less in the expansion-box when running. Tho temperature of the air was measured at the expansion-box The method of making a test was to keep the gasometer-bell floating at a point above the first gauge-mark. When the engine oonditions were steady the oock on the blower-delivery was closed and the engine began to draw from the gas-holder When the first gauge-mark was reached the observer started his stop-watch, another observer starting his revolution-fiouribr and watch simultaneously; on reaching the rseoond gauge-mark the observer signalled and both counter and watches were stopped The arrangement shown in Fig. 6 is probably better than that having a T-piece near the engine, as the conditions of flow in

FIG.6.--hir measuring arrangement. the pipes from the gas-holder to the engine are unaltered on starting a test. The air measurement was corrected to 760 mm. and 15°C allowances made where necessary for the engine cooling-water outlet temperature which was taken as 90" C. This correckion was about 0.1 per oent per degree C. for Engine A. Frequent tests were made for air leakage in the system and allowance made; an allowance was also made foT fuel vapour. Fig. 7 shows the volumetric efficiencies obtained plotted %gainst conventional gas velocities, and Table 11. gives the maiu par- ticulam of the two engines. It will be seen that under the same conditions (i.e., straight-through oarburettor and no external heat) the sleeve-valve engine has a volumetric efficicncy at least 20 per cent, better than that of the poppet-valve engine, due, a$ will he shown later, to the lower temperatnre of the inlet ehntp

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Khether this low temperature can be utilised efficiently imsanother iiiattei, hut if the charge has to be he&ed, this hewting can be under oont.rol, which is not the mse with the poppet-valve engine. It. is interesting to note that the above i8 in agreement with Fig.. 4 as regards the oonventional velocitieis at which tlie curves begn to droo,p. Kith regard to axiom 1 (b ), " the higlily lieatd baflie-plate," or the heating effect of the valve, tlie author is unaware of aiiy dcfinito figures as to the te'mperature at,tained at the inlet ports of sleeve valves under working ooadition's, but that it oaiinot be high as oompared with that attained in the poppet valve there is a aert.ain amount of indirect evidence in the well known popping in t.he mrburett,or, and lack of power in a sleevle-valve engine, xhei; cold, when t,he throttle is $opened, even if the mixtuw is iiiucli richer than it should be. The poppet valve is much lem trouble8sonie in this respect, as the valve soon heats up and

-5 9

lqoriaes the petrol sprayed on it. A sleeve-ral\e engine will. however, often start easily and run fairly well at nearly dosed throttle, as then the vacuum in the indadion pipe lowers the boiling point of the fuel. In the earlier Howard engine (see Fig 21, the trunnion-pins operating the valve were set-screws, liaring thin flat heads inside the valve rinp These heads never showed a temper-oolour higher than brown (given as 260°C.), even after a six-hours continuous run at 2,000 rev5 per minute ion open throttle. As tliia form of joint is known" to have a aonsiderable resistance from ,I heat-conductivity point of view, it is obvious that the cast-iron ling itself must have been at a lowm temperature than 260" C Coming now to axiom (a), it is desirable for eoonomy to use the highest expansion-ratio possible aonsistent with the engine not being what is aptly described by Dr Ormaiidp as a "Super- Kuiwiiiac '' In this, the normal practioe is nieant in mhich the compression-ratio is approximately the same as the cxpansion- * See Proc. 1.A.E , Vol. XIV., p. 75

Downloaded from pau.sagepub.com at WEST VIRGINA UNIV on June 4, 2016 ratio The practical liiiiit is reached at a coniparatively low figure coinpared with gas-eugine piaotice by the jiicidence of " pinking ' and subsequent pre-ignition. Now the authnr submits that with pnasent knowledge it k pilemature to lay down definite cunipression-ratio limits which apply to olne type of engine only or possibly to one particular engine. Ricardo's toluene values* may be definite plipical pmliasities of the fuels and so bear $he same relation to one another when tested in other types of engine. TABLE11. .~ Engine. A. B. Noteu.

Poppet overhead Jingle - sleeve. Effective compreli- push-rod sion-ratios include operated. allowance for volrime of indicator Bore mm...... 63 i0 conncctiona. Stroke mm...... 120 90.5 Engine A, 4-cgI water cooled. Cylinder capacity C.C. 374 349 Enginc R, nornially Normal compression- 4.70 1.0 air cooled, but for ratio. tcnts, water cooled barrel, air cooled Effective compres- 3.95 3.55 head. sion-ratio. Specific inlet-valve 22 1s area, sq. cm. per litre. Inlet valve closes 52 35 degrees late. Per cent of swept 83 ss volume at whic) inlet - pressure is taken.

Tlie " pinking " phenomenon is at prwent little undcratood, and the author can only make the miien-hat vague statement that it depends on- ( 1) The time element. 121 The oomprei&on-pressure. (3 Some temperature-area function of the surfaces against which the charge is compressed. (4 I The temperature of charge at the beginning of compression (5I The natum of the fuel as regards ignition temperature it; 1 The proportion of reriduals present. * See Engineering, January ith, 1921, p. 28 ; also 1.A E., Data Sheet, No. 72.

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.As regards (1) and (3), Burstall,* working with produaer ga at 170 revs. per minute, state,s that cutting off the supply of oil oooling his sparking-plug, at once caused pre-ignition at the high oompmssion-ratio, although its area wm only 0.3 per cent of the oombusItilon-chambersurface and all other parts' were water ooo,led. C;ibs.on,i howevetr, states that pre-igniti,on is not eqmiencied with air cooled am0 engines until the oylinder head reach= at temperaturn of over 280" C. and the exhaust valve a temperature of 720" c. Some think it is a ariine to allow an automobile engine to exert full torque at speeds under 1,500 revs. per minute, while others consider that a high percentage of maximum torque sho,uld be obtainable at 500 to 600 revs. per minute. In fact a virtue is often made of the neoessity, and we are told that it is ve'ry wrong to let an engine pull at a low speed. The author$ found that a aonipression-ratio of 12.0 : 1 with a corre,spondinig preesure of 350 lb. per sq. in. was mquired t,a ignite Pratt's motolr spirit in a Diesel engine when mld. This figure is fairly in agr,ee,me,ritwith those obtained by Dixon,§ mhu gives minimum oompressio.n-ratios of 11-4 and 7.6 as being required to ignite hexane and air from temperatures of 50" C. and 100" C. respectively. In both the ab,ove easels there was no dilution from residual produots of combuIstion, and the time element would be larlge. Ricardo /I gives 4.85 : 1 as th,e compression-ratio limit €or aroniatio free petrol and 5.05 : 1 as that for hexane at 1,500 revs. per minute (assumed). This suggests a high temperature of the change at the beginning of the stroke or that the hot surfacves (valves, etc. against which the charge is coiiipressed Itatvc a very great effe'ot, hading to actual chemical combination or pre-flame oombustioa already referred to. In a four-valve poppet-valve engine of 5.0 : 1 compression-ratio, the valve's mcupy from 20 t'o 30 per cent of the conibustion-chamb,er surface (piston excluded) and may attain teinperatuiw as high as GOO" and 860°C. for the inlet and exhaust xalve respeckively Under similar conditi,o,ns the area of sleeve exposed in the Knight engine is 33 per oent, no po'int of which is more than 8 mm. from a water ooolebd surface in an engine of 90 niin. bora arid that only insomentarily . 111 discu8minlgthe higher toluene value fu,els, the questhn may be aslcd: With such a large propo,rtio,n of hot surfaoe, is therc 8°F chanae of lubricating oil, generally .of paraffin (low tolueno value) base, acting a pilot ignition for the fuel being twted? * See Proc. I.Mech.E., 1908. pp. 17 and 56. t See Proc. I.A.E., Vol. XIV.. p. 257. 1 SeeProc. Inst. C.E., Vol. CLXXIX., 1909-10, p. 351. 6 See Imperial Motor Transport Conference, Fuels Section, 1920, Table VI., 9. 11 See Engineering, January 7th, 1921, p. 26.

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Experinients at the Xatioiial -Physical Laboratory" have .shown that mineral lubrimting oil will ignite at atmoapheric prelsisure when dropped oln a plate h'iaated only to 330" C. A small preliminary injection of petroEeum oil is often used to obtain satisfactory aombust.ion of tar oils in Diesel ei1gines.t Prof. Hopkinson stated that a drop of oil falling on an exhaust valve at 400" C. would oause pre-ignition in a gas engine. In the Gas Engine Research conduchd by Prof. Burstall,: in spite of e,.ve,rypart being water .or oil cool,ed, at the higher min- pression-ratio8 extreme care had to be $aken with piston lubriw- tion, as an excrelss of oil oaused pre-ignition. The author has no figures as to the compression-ratio limits of sleeve-valvle ea'ginels, neither is it suggested that a rati'o of 7.5 : 1 would be suitable for all purpolses. It is thought, howlever, that the ratio's used on "sports" type poppet-valve engines could easily be used on sl'eeve-valve engines for any purpose. Some advantago might result from increlming the expansion-ratio without inmehsing the oompiwsion-pressures as Ricardo has shown$, that the gain in efficiency of a 6 : 1 ratio over a 4 : 1 ratio is 42 per mn)t for 04 full load as against 31 per mnt for full load. The manufaoturers of these enginmes have concentrated on pro- dulcing an extremely quiet engine giving excellent torqw at low and moderate speleds, and have as a rule restricbd the und'olubtd power oapacity 09 these engines at high speeds. At any rate oriticism of their pollicy is quite out of place in a teclinical paper. The only two occasions on which the author has experienced " pinking " with a sleeve-valve engine were (1 1 mhen, during some experime'ntal road tests, th,e oarburettor jacket relaehed a, temperature of 200" C., and (2) when, omwingto a drain-tap being- left open, all the water was drained off from the cylinder heads. Of oourse, with higher volumetric efficiency and higher oompmssion-ratim, sparking-plugs would probably give trouble, but that difficu1t.y should not be insuperable as plugs are not moving parts.

TEMPERATUREMEASUREMENTS While disoussing the alteration of the apparatus for the measurement of volumetric efficieacy, it was considered that with little further trouble some interesting and fairly reliable figum of temperaturels during the oompre'slsion stroke might be obtained. The first essential, apart from the volumetric efficiency, was t.0 know aaourately the presssure in the cylinder at some definite pinf of the omprmsion stroke, preferably just after the olosing of the inlet valve.

* See Engineering, July 7th. 1922, p. 8. t See Proc. I.A.E., Vol. XIII., p. 480. $ See Proc. I.Mech.E., 1.908, pp. 17 and 66. $ See Engineering, September loth, 1920, p. 361.

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The presswe thus obtained will be called the ” Ijilet L’yessure.” A small hole, drilled t.lirough the cylinder wall, was arrailged SO as to he clotssed by the toy pi,stolii ring a few degrees after the closing of the inlet valv,e, a3 iiidicated in Fig. 8. In :he ease of khe poppet-valve eiigine this hole would also be uiicovere 1 during the exhaust stroke; a rotary valve mas therefore inserted, driven at, half engine spee,d, which interrupted coiriuiriiiication ritrring t,lte exhaust stroke. The rotary valve aoininunim.t,ecl with

FIG.8.-i%rrangernent for obtaining “ inlet pressure.”

:t delic;tt,e lion-leturn valve a.3 described by Morgan,* md tiic pressure mas measured 011 a water colunln. With the sleeve-valve eitginc t,he rotary valve was not ne80es8smy,as the h’oles in sleeve niid cylinder only registered about the end of the suctioii ,drake.

From the L‘ Inlet Preissure ” and volumeltric efficiency were obtniiied the ‘‘ fresh charge ” temperature. (See Note hy Prof. W, Morgan, 1)ap $314.’) ‘I FI-ezh charge ” teiiiperatirre i.; s cviiveiiieiit tlivugli * See Proc. I.A.E.., Val. XVII., Part I., p. 279 (Charging of Two-strokr Engines).

Downloaded from pau.sagepub.com at WEST VIRGINA UNIV on June 4, 2016 SLEEVE-VALVE ENGINES. 303 not quite accurate dspre#ssion,as any exliaust back-pressure ill- measea the apparent fre#shcharge teiiiperature by decreasing the rolumetsic effioiency . The Illlet ?'e~pemtzc/,exv&s then obtained by taking into amount t,lie heating of the residuals in the olearance voliume. Their temperature was assumsed to be that of the exhaust gams measured by a theriiio-c.ouple within 2 in. of the exhaust valve. The error is likely t.0 be negligildc owing to tlic iiiass of the residiials being small compared to that of the fre'sh charge.

co~lr~~I~:ss~oNTEMI'EI<.\TUHKs. A iVat,soii-L)alby iiidicator was available, but it was not considered suffic.ieutly reliable for 0btainin.g the '' Iulet Preasu1.e " owing t.0 (1) the closeness of its soale (1 nini. = 1.67 1L. per sq. in.,), and (2)the difficulty .of phasing. It was therefore used ody a4 a iiiar;iiiiuiii-~ressureindicator, and a'i such was directly cali- brated 011 engine A for spee'ds ranging froni 1,000 to 3,000 revs. per minute. Care was taken to obtain photographic,ally the first winpression diagraiii iinniediately after shorting the sparliing- plug, as subsequent coiiipressions (the cliarge being undiluted with, residuals) showed a pressure of 2 to 3 Ib. pe'r sq. in. Iii'gher. Compression teinperat~ui~swere calculated froni the '' Inlet Pmswre." iiibet t'e'iiiperature and cioiii~~~cssion-],ressure.Fig. 9 also slio~vs (clotted) coui~~ressiOr~-~~~~essure~calculated froni the lurmuln PVl.Y3 = C. iLsing the actual inlet pressure and the effective volume, i.e., the total voluiiie ,of cylinder and clearslice space .at the point at whioh the " Inlet Pressure " is taken. The aom- pi>essioln-ratio thus obt.ained dlbe called the I

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Revs. per mln. FIG.9

Downloaded from pau.sagepub.com at WEST VIRGINA UNIV on June 4, 2016 SLEEVE-VhLVE ENGINES. 305 number of observations gave the corrected voluinetric efficiency as 85 per cent. This effect is also noticeable in the “ Inlet Pres- sure ’ graph, and is attributed to the effect of the pipe joining the carburettor to the expansion-box. This pipe is 4 in. dia. and 6 fs. long. It was hoped that with such a small engine, disturbing effeds would be eliminated by using ,a large diameter pipe. Thi8 wa3 certainly not the case, and it would be interesting to lcmw what error5 would be introduced by using a pipe with a bore 1e5s than that of the cylinder. (b) “ Inlet Pressure.” This has, in pneral, the same Fharacter as the volumetrio efficiencj graph except that it does not show the sharp drop after 2,500 revs. per minute. (c) “Fresh Charge ” Temperature. This graph gives some idea of the heating effect of the valves during the suction stroke. If it is assumed that the whole of the fuel is evaporated, the air should be reduced in temperature about 30 degrees C. Actually, in spite of this effect, at 2,000 revs. per minute the charge is 45 degrees C. hotter than the air. This would be equivalent to a rise of temperature of 75 degrees C. far a charge of dry gas. These figures show why a better volumetrid sfficiency is obtained with fuels such-as alcohol having a latent heat about three times that of ptrol. (d) Inlet Temperature. This graph shows the effed of the addition of the residual exhaust products in the clearance to the fresh chmge. It also shows the rapid rise in temperature after 2,500 revs. per minutel due to the increased proportion of exhaust. It will be seen thao as the greater part of the graph lies above 100” C., there cran be no gain of heat from the Stctual walls, valves and piston exduded. (ej Compression Tempwature. This graph shows how erroneous it is to give one definite compression temperature oorrasponding to a compression-ratio, as the variation here reoorded (86 degrees C. ) over quite a normal range of speed exoeeds that calculated (60 degreas C.) for a range of compression-ratios from 4 : 1 to 8 : 1. The maximum temperature obtained is, however, in agreement with that given for an engine of the same nominal compression-ratio . (f) Compression-Pressures. This graph does not need much comment, as the diagram is a “hand” diagram and not of the aonventional type. The point of maximum pressure wais dearly marked, and as the actual height varied from 40 to 50 mm. there should be no great error in reading. Tho dotted line shows the pressures calculated, using the observed “ Inlet Pressure,” tbe “ Effective Compression-Ratio ” and 1.33, tlm usually accepted value for th0 exponent ‘‘ ?t ” of the expression PV“ = c. (g) The exponent “n.” This graph is of great interest, as it would appear to support WOOD. 20

Downloaded from pau.sagepub.com at WEST VIRGINA UNIV on June 4, 2016 306 THE INSTITUTION OF AUTOMOBILE ENGINEERS. tho author’s oontention that owing to the high temperature of the valves pre-flame combustion is likely to take place. In this connection it is in ting to note that H. Wood,* in describing his work on the indicator designed at the Royal Aircraft Estab- lishment, gives 1.30 as the exponent of an aero engine compression ourve between the limits of 30 degrees and 105 degrees from in-centre. If this is oorreet, what then can be happening during the last portion of the stroke to ,give an exponent of 1.39 over 130 degrees as observed by the author, who believe6 that this R.A.E. indiaator is the only one that has any preten’sions to giving an aacurate average diagram at high speeds? Practically all aocurate indicator work on the value ,of “n” has been done on slow-speed gas engines in which the inlet valve closes sol neaa tho out-centre as to make it justifiable to use the normal compression-ratio . In the weof automobile engines with inlet valves closing 40 to 45 degrees late this is not so, and the author is inclined to think that the value of “ n ” has been adjusted to reconhle the normal compression-ratio with the observed niaximum compression-pressures, which latter are more easily obtained. This has probably prevented these abnormally high values from being noticed before Engine B (single sleeve) is an air cooled motor-cycle engine, but to make the results more comparable with those obtained from Engine A, the cylinder body was water jacketed, though the head had to be oooled by an air blast. Fig. 10 shows the results obtained with this engine. It will be not.iaed that the temperatures recorded are considerably lower and that the volumetric efficiency is very high. The value of “ n,” 1.34, is miom what would be expected from the properties of the hge. Ln order to investigate further this question of pre-flame oom- bwtion, EngineB was fitted with a “hot spot” aa shown in Fig. 11. The portion projeding into the oylinder ww amanged to have an ama approximately the same as that of an exhaust- valve head in Engine A -and fitted with a thermo-oouple by which its tempera* oould be meaured. FUELECONOMY. Much of the inferior road economy often experienced with sleeve-valve engines is probably due to the praatie of fitting oarbudtors dle&gned for ordinary poppet-valve engines, whioh type appears to doal with one only of the functions of oarburation, that is, the ‘‘metering” or supply of a stream of fuel more OT hs proportiond to the amount of air entering the engine. “Vaporisation” from the carburettor point of view is neghted. Any jacket provided is kvariably external ho the induction pipe amrl is of value only in assisting slow-speed running and the * See Proc. I.Mech.E., January lSth, 1923. ‘‘ Indicatore,”

Downloaded from pau.sagepub.com at WEST VIRGINA UNIV on June 4, 2016 SLEEVE-VALVE ENGINES. 307 eva.poration of fuel creeping over the induction pipe surfacm. With the modern high-effiaienuy poppet-valve engine it mms essential, even with th0 low limit !of oompmsion-ratios, to inbo-

SLEEVE-VALVE EXQIS 1,;.

Revs. per rnin. FIG.10. duce tho &ge in the form of air mixed with a spray of liquid fuel, antrusking the vaporisation to the inlet valve. An id4 carburettor giving a perfectly proportioned and vaporised mixture 20 (2)

Downloaded from pau.sagepub.com at WEST VIRGINA UNIV on June 4, 2016 308 THE INSTITUTION OF AUTOMOBILE ENGINEERS. would pTobably give a much harsher-running engine than the ordinary article. The hebrogerwxus nature of the chaxp must adversely affect distribution in the multi-cylinder engine, and would amount for the presence of both oxygen and carbon mum- oxide in the exhaust gases. This, as well as the inmased volumetric eaciency, would explain the general opinion that a rather rich mixture is neoesmry for maximum mean effective pressure, as when the cylinders which are normally starved of fuel get an optimum mixture the others will get too rich a mixture. The “hot-spot ” induction pipe may be advantageous with the

To pyrorneter

FIG.11.--“ Hot-spot ’’ fitted for test purposes. lower gmde fuels now supplied, but hs at present applied appeass ssmewhat unoonhollable and likely to cause pinking in a high- ampmsion engine. In a sleeve-valve engine the water, if a carburettor or induction pipe jaaket is used, can never attain a temperature high enough to deal adequately with present-day fuels, only 25 to 40 per oent of whioh distill at 100” C. The sleeve-valve engine particiularly seems to require thermostatic control of some description if mly from the point of view of reducing the viscosity of the oil mid aomequently sleeve friction.

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For the lower speed range of sleeve-valve engines some form of carburettor might be deairable, such as that described by Keith and Whatniough,* in which the fuel only is first completely vaporised and then mixed with air. It appears ridioulous to suppose that muoh real atoniisation mn take plaoe in the ordinary carburettor with its limit of about 0.5 lb. p0r sq. in. pressure-drop in the induction pipe, when pressures as high as 4,000 to 6,000 lb. per sq. in. are found newssary in solid-injection Diesel engines. The Voisiu ems fitted with Knight engines have put up some very creditable performanoes in economy trials in France, and on tho ben& the sleeve-valve engine gives quite good results aa regards fuel eoonomy. For instanoe, in the 133 hours R.A.C.

0 20 40 80 80 100 120 140 180 180 200 220 Crank degrees

FIG.15.-Inlet valve diagrams. teat of the Knight-Daimler engine, the mean figure of 0.668 lb. per brake horse-power per hour oompmes quite favourably with the 0.7 lb. of the more modern Vauxhall engines given by Pomeroy . The Howard engine referred to (Fig. 2) gave a mean aonsump- tion of 0.486 Ib. per brake horse-power per hour on a number of ktumde during a twelve-hour full-load trial at a speed of nearly 2,000 revs. per minute. The even bettsr result of 042 lb. pw brake horsepower per hour was obtained with a compression-rah of about 5.7 : 1. In both mw the hmse-power was that measured through a 2 : 1 reduction-gear, no allowance having been made for the low in transmission. As the quantity of petrol measured was 1 gallon and the time taken to consume it was about 79 * See Proc, I.A.E., Vol. XVII., Part I., p. 32;. A New System of Carburation.

Downloaded from pau.sagepub.com at WEST VIRGINA UNIV on June 4, 2016 310 THE INSTITUTION OF AUTOMOBILE ENGINEERS. minutes, these were in no seme snap hts, and the author aonsihs them an exoeptionrtlly good perfman-. Tho author suggwts that these results are due to the low temperatms of the cycle in the sleeve-valve engine. It h bean noted generally by many observers that maximum thermal effioiency is obtained in the petrol enigine with mixtures wedtea than the optimum, and Ricardo? has shown that the thermal efficienq on the “air a~ fuel” bmis is highest when the mixture is cooled by ex0895 fuel.

MECHANICALDETAILS. It is not proposed to deal with these at any patlength, though

0 80 90 i0 20 30 40 50 60 70 80 90 Per cent stroke FIG.13.-Knteraction of Knight engine sleeves. the author oowiders that both design and material have been responsible for the fact that the rsleeve-valve engine has not attained the position it deserves. The two real or pretended dis- advantaps most usually brought against the sleeve-valve engine me:- (1) The weight of the sleeves. (2) The interposition of sleevas and oil films between the piston and the aylinder.

t. See Automobile Engineer, October, 1922, p. 305.

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(1) Tho Knight-engine sleeve is admittedly heavy, but the proportion would not be great oompared to the weight of the engine. The point to remember is that it has a motion eimihr

Inlet obout to open n

Inlet fully open -

Inlet closed

Firing point

Exhaust about to open n

Exhoust fully open Relative pospon of engine piston

Cylinder ports Sleeve ports

Path ofports PIG.14.-Port openings in Wallace sleeve-valve. to that of the piston, but that its accelerations are only ah& one-twentieth of those of the piston, so that the final limit of spd as regards the sleeve will not be reached until its 4ght &p- proaches 20 tidehs that of the piston. In the Howaid engine

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referred to previously, the cast-iron cuff or sleeve only weiglied 0.5 lb. on an engine of 4.125 in. bore. (2) Interpwition of sleeves between piston and cylinder-wall. No objection, other than that of cost, seems to have been taken ta the modern praatioe of fitting a steel liner to an aluminium-alloy cylinder-barrel, though this method has not the help of the moving oil film to transfer the heat. It must be remembered also that a oonsiderable portion of the heat from a piston is probably conveyed to the jacket by the oil film.

MATERIAL. Up to the present cast iron has been by far the most generally used material for sleeves, though steel or aluminium-alloy might possibly be more suitable but more expensive. Surely our metallurgists, who have provided a material that will stand IIP to the onerous cronditions under which an exhaust poppet valve has to work, oould provide suitable materials for the far less severe conditions of the sleeve valve.

VALVE DIAGRAMS. The comparative inlet-valve diagrams of the diiTerent types reduced to a common maximum valve opening as shown in Fig. 12 will probably be of interest. It will be noticed that the Knight diagram is approximately triangular. The Howard diagram is not shown. but its opening portion is sinii1a.r to that of the single- sleeve engine, as the valve is then travelling at its maximud velocity at the point of inlet opening, while the closing portion (the valve being cam-operated) is simibar to that of Riaardo’e masked inlet valve. Graphs showing the interaction of the Knight engine sleeves are also given in Fig. 13 and of the 1Vallaae sleeve in Fig. 14.

CONCLUSION. The author cionsiders that little further progress can be expected in the development of the oonstant-volume cycle unless means aro taken to eliminate the large areas of highly-heatetd metal such as the valves, which he considers are now the limiting factor. In spit0 of the fact that the temperature of the piston never iapproached that of the valves (though its area is considerably greater). considerable improvement has been effected by the use of aluminium in lieu of cast iron for the piston. The alternatives appear to be either the development of some form of sleeve valve or the use of the two-stroke engine with some method of fued injedion. Here the author cannot do better than quote from the Report of the Gmeous Explosions Committee of the British Asso-

Downloaded from pau.sagepub.com at WEST VIRGINA UNIV on June 4, 2016 SLEEVE-VALVE ENGIXES. 313 ciation: " Provided that the surfaoes of the combustion chamber could be kept 0001 and clean much higher compression-ratios could be used ." Unfortunately, the latter aondition appears diffioult to attain, as mbonisation takea plaoe at quite low temperatures. It might be pointed out that any improvement effected by " doping " the fuel would be quite as advantageous to the sleevs- V~VQengine as to the poppet-valve engine, even if not more so. The author wish- to acknowledge his indebtedness to Prof. W. Morgan, the Society of Merchant Venturers and the CoLstm Society, Bristol, for assistance and permission to use their Auto#- mobile Engineering Laboratory; to Messrs. Wallaae (Glasgow), Ltd., for the loan of an engine and for information; to Messrs. Minerva Motors, Ltd., the Wessex Engineering Co., Ltd., and Mr. W. E. Castello for engine and test dab; to Mr. Hix fw erecting the apparatus and to various ptudents of Bristol Uni- versity for assistance as observers.

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