289 Sleeve-Valve Engines. 19
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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 Ex 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. Downloaded from pau.sagepub.com at WEST VIRGINA UNIV on June 4, 2016 SLEEVE-VALVE ENGINES. 29 1 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 tempera- tures 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 re- membered 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) Downloaded from pau.sagepub.com at WEST VIRGINA UNIV on June 4, 2016 292 THE INSTITUTIOK OF AUTOMOBILE ENGINEERS. 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. Downloaded from pau.sagepub.com at WEST VIRGINA UNIV on June 4, 2016 294 THE INSTITUTION OF AUTOMOBILE ENGINEERS. 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.