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THE WHITE-WALL ENGINE.

26th April 1921, Page 25
26th April 1921
Page 25
Page 26
Page 25, 26th April 1921 — THE WHITE-WALL ENGINE.
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A Surprising New Development whereby the Shortcomings of the Two-stroke Moi Have Been Overcome and Equal Power Obtained as with a Four-stroke. By Henry Sturmey.

1p011, commercial work the points of

highest desirability in an engine are simplicity -of construction, fewness of parts and fuel efficiency, and, but for the fact that in this last respect the system has hitherto been wanting, there is no doubt but that the two-stroke engine principle would have long since asserted itself. Poor fuel efficiency, however, with petrol at the price it is to-day, cannot be tolerated when low cost per ton-mile is of so much importance,but an engine has just been produced which hide fair to alter all this, as with it the shortcomings of the twostroke engine in this: respect have been overcome, and results comparable with these of a four-stroke obtained, 'Hence, practically the same power can be . developed from two cylinders of any given size as with four on the present universal four-stroke system, whilst, with the exception of the piston and connecting rod, all reciprocating parts are abolished.

This invention is the White-Wall engine with which has just been concluded a series of tests during development) made over a period of 15 months, by Ps-of. Morgan, of the Bristol University. It is the invention of Mr. A. W. Wall, of Birmingham, who has been associated in his work with Mr. John White, Junr., of Handsworth. The engine has been subjected to every variety of test, and has undergone a continuous non-stop run under load of eight hours, as well as much longer tests wifliont attesstion, and speeds up to 3,500 revs, per minute have been attained, which means, not half that number of firings as with a fourstroke motor, but 5.500 completions of Its cycle. The experimental engine of 214 in. bore by n in. stroke shows 6.6 h.p. under a. brake test at 2,700 revs., which is, I believe, rather more thandouble the showing made by the hest two-stroke motor of that size hitherto.

The engine is of the three-port type, using the crank chamber as .the primary fuel compressor, only, instead of having single small restricted ports through which the gases have hard work to struggle during the short time available for doing so, each class of port is multiple, and all are arranged to open simultaneously, so that during inlet, transfer, and exhaust a very large aggre

gate port arca is provided. This is ticularly the case with the exhaust pi which is formed of no fewer than vertical slots, equidistant from e: other around the cylinder, giving a lective area when open equal to 75 z cent. of the piston area.

In this lies the crux of Mr: Wall's vention, for he formulates and adopts 1 principle that time of opening, or ratl of remaining open, is immaterial so k as sufficient arca is provided, holdi that the speed with which gases tile and gas pressures equalize is so infinih beyond any mechanical speed which c be obtained that, if only sufficient pi area can be given., for however short period, the expansion forces in the bus gases themselves will effect the desix scavenge. He argues that if, by. way illustration, the top of the cylinder cos be instantly removed, for however br a period, the whole of the contained ga: would escape at once, and in providir therefore, a port opening equal to per cent, of full opening he has g within measurable distance of this, a: he tells me that inpractice he fin the rush of the imprisoned gases escape is actually so rapid that it earn all particles of carbon, or other ii purities, out of the engine, and that t gases actually so fully escape as to lea a partial vacuum behind them.

In order to obtain this effect, the i venter employs a rotating sleeve vat% encircling the cylinder and perforat, with ports correspondingwith those c in the cylinder for inlet and exhaust, am this sleeve valve, being situated at t: lower part of the cylinder and only contact with it in one part; is not-au jected to the heat stresses which wou be the, case with any valve working or around the cylinder head. All stress being symmetrical and the parts :su jected only to residual and not to e. plosion heat and stresses, there is / chance of warping or distortion, and ti flow of the gases is even in all direction

This valve is operated by a wor

el and worm gear, the former .nted on the sleeve itself and the al on the spindle of a spur wheel ratedlike the half-time Shaft of a .-stroke engine from a:gearwheel on crankshaft. 'Iterate of revolution is one-sixth engine speed, i.e., it.makes ,revolution to every six made by the ikshaft;so that speed of rotation is v and presents no difficulties in lubriOn, as well as absorbing but little ier to drive it. As it rotates it opens i-closes the respective series of ports the openings approach,' coincide, and ede; and the full opening and closing the exhaust ports is obtained whilst piston is .moving through in. space y,,towards the-bottnin of the stroke, creating,a lag in .the worm of actual led of opening of the ports is double at it would be, but for this, with the se piston movement.

t will be seen, therefore, that, as the as are not permanently open, as is case with the ordinary two-stroke gine, there is no loss of force 'as the escapes ,through the gradually open: port, but the piston receives its full ving force almost to the end of its oke, -when all this wide port areais ?own open and the gases escape and ports are closed. Then, during the nod of crank ,movement across the Wan dead point and the further small oft-be piston, the transfer ports are ened by the movement of the piston, d the new charge, already compressed about 3 lb. per sq. in. in the crank amber, rushes in to fill thepartial cuum in' an already closed chamber, so at there can be no escape across the 5ton.and.in the rear of the spent gases d no a,dinixturelwith them, as is the se with the conventional two-stroke

stem. As soon as the transfer ports re closed, the inlet ports, which admit ew mixture to the crankcase, open and smain open Jantil the 'piston gets to the ip of its stroke once more and the cycle I operations is complete. As the transfer and, exhaust ports are ot open at the same time, as with the rdinary two-atrolce,there is no need for baffle plate on the top of the piston, ?hick is just like the pistons used in the

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four-stroke system, whilst, as the cold mixture is drawn in from all sides over the top of the piston, the latter is coolea conveniently.

The engine which Professor Morgan has been testing at Bristol is watercooled, and When I say that he has obtained diagrams showing a mean effective pressure of 74 lb. to the sq. in. at 2,700 revs., the real advance which has been made with this new engine will be appreciated, and it will be seen that the possibility of obtaining engines of only half the weight and with hut a quarter of the working parts and very little reciprocated weight, for a given power,

is within sight as a practical proposition. Mr. Wail is now carrying his experiments further, and has been exploring the possibilities of the application of air cooling to this engineq, a problem which in itself is not easy, owing to the fart that twice the heat is developed in a given time than with engines of the fourstroke type,, and virtually the same applies in comparison with other twostrokes. Mr. Wall has, in this, so far

succeeded as to be within measurable distance of complete success, and I saw an air-cooled engine running at Birmingham quite steadily and at speeds up to 2,700-per minute working against an air brake, and examination showed no signs of overheating, nor did the running of the engine present any such indications, and in carrying this portion of his invention into effect an equally original system has been adopted.

In the ordinary air-cooled design radiating fins are cast upon the -cylinder and combustion chamber, and the air met in the passage of the machine through it strikes the front of the engine, or else a fan creates a current, which it also throws against one side of the engine, and in the Franklin, which is probably the most successful large-sized aircooled engine, the air is fan-forced through a tunnel in which the several cylinder heads are placed. In the WhiteWall design, however, a different system is adopted. The fan blades are arranged round the periphery of the flywheel, which is encircled with a tubular cover after,the manner of a blower, and this projects a continuous blast of air through a tube, which is carried-to the top of the engine. The cylinder and head are furnished with longitudinal cooling ,fins running the whole length of the cylinder casing, and covering also therteasing which encloses the rotating valve, and these fins ire, in their turn, enclosed in a tuliular casing, and the fan-produced blast of air blows straight down the whole length of this cooling system, striking the spark plug and top of the combustion chamber first, and then passing on right down to the crankcase. This results in perfectly even and symmetrical cooling of the whole engine, as the air blast strikes all sides of the engine equally, and strikes the hottest part firstaand by varying the area of the fan blades any desired amount of cooling can he obtained.

Although it has been applied in the first instance to an engine of the crankcase compressor type, the White-Wall system is, of course, equally adaptable to any two-stroke system. It, can also be applied eqnally well to two-stroke Diesel and semi-Diesel stationary and marine engines, and to aero and other engines with separate charge compressors.

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Organisations: Bristol University
Locations: Birmingham

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