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Too hard criticism of S-S-V eng in article by R J Raymond?

 
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jaymerich



Joined: 11 Dec 2009
Posts: 20
Location: E28033; Madrid,Spain

PostPosted: Sat Jul 26, 2014 13:31    Post subject: Too hard criticism of S-S-V eng in article by R J Raymond? Reply with quote

Hi!: some of the statements may be in contradiction with other works: both H Ricardo an M Hewland found that the mechanical losses of a SSV engine are reduced respect a Poppet-Valve engine.

Regarding the heat transfer from Piston through Sleeve to Cylinder, H Ricardo, in: 'The high speed internal combustion engine', 1954 reprint, stated that: 'If the working clearance of between the Sleeve and Cylinder was reduced to the bare minimum which would allow of free movement when cold, the clearance at a coolant temperature of 100 C was still satisfactory...for liquid-cooled cylinders of, say, 5 in. diameter or less, and provided that the clearance was controlled within close limits, the combination of an ordinary aluminium alloy and a cast Iron or Carbon-Steel Sleeve was just permisible' [p 347-348].

'Air-Cooled Sleeve-Valve Engines':'...it was decided,...as a temporary expedient, to employ a cast austenitic-iron sleeve...when full load was applied, the Sleeve split from end to end, fortunately, without doing any serious damage. A thicker Sleeve was then fitted, and though too heavy for aircraft use, it otherwise proved very satisfactory'.

About the heat transferred to the cooling water from the head and from the cylinder barrel, experiments indicated:
1) Heat flow to cylinder head was relatively small as compared with a poppet-valve engine.
2) That a moving Sleeve, provided that only a thin oil film was maintained, appeared almost transparent to heat.
3) Because both the apparent thermal transparency of the Sleeve and of its capacity for translating heat geographically up and down the cylinder, it was found that a large part, if not the bulk, of the heat could be transferred from the cylinder head, via the Sleeve, to the upper part of the cylinder barrel well above the combustion chamber. By liquid cooling, separately, the cylinder head and the portion of the cylinder barrel imediately surrounding it, i.e. above the port belt, and by varying the rate of coolant flow between these two circuits, it was possbible to evaluate, at least approximately, the transfer of heat from one to the other via the sleeve.
4) The total flow of heat to the coolant was appreciably less in a Sleeve- than in a Poppet-Valve engine, due to the very much shorter and straighter exhaust passages. All these considerations were encouraging from the point of view of the Air-Cooled cylinder...the centrifugally cast nitrogen hardened austenitic-steel sleeve proved the best solution, and became, and still remains, standard for all air cooled sleeve-valve engines, the one remaining objection being the very poor thermal conductivity of austenitic steels. With this material and a careful control over manufacturing limits, it proved unnecessary to use a silicon-aluminium alloy for the cylinder.

In so far as the cooling of the cylinder head was concerned, the Bristol Aeroplane Co developed a system of ribbing and air ducting which proved adequate for power outputs up to about 60 HP per litre of cylinder capacity, but for the higher outputs they have developed a composite Copper cooled head, which has proved very satisfactory.

In the section: 'Two-Stroke Sleeve-Valve Engines', pag 361, Ricardo tolds about several approaches were tested, including a thinner Sleeve in its upper part, that gave the problem of possible damages when assembling the Sleeve and cylinder: once dented or distorted it would fail to seal and would burn away,...eventually it was found, that not only was there no need to thin the Sleeve at all, but even quite a wide range of tolerances in the Sleeve to cylinder fit had no ill effect except upon starting up from cold, and even this presented no insuperable difficulty if, before starting, a little thick lubricating oil was injected into the annular space immediately above the Sleeve....
Further experiments revealed that the working clearance could be increased to as much as 0.008 in. to 0.010 in. in diameter before the Sleeve failed to seal; under such extreme conditions, however, cold starting on a C.I. engine became impossible.....It appeared that the top end of the Sleeve expanded out to a trumpet shape, until all clerance was taken up, when heat transfer to cylinder walls then stabilized the temperature conditions; since the heat capacity of the Sleeve was extremely small and the intensity of heat flow, more specially while leakage was taking place, very great, stabilized conditions were reached after only a few cycles. It was both surprising and encouraging to find that the permissible range of clearance was well within the usual limits of manufacturing tolerance and of reasonable wear. The author has dealt at some lenght with this question of the evolution of the open-ended Sleeve, because it is an example of a very dubious expedient, tried only in desperation and as last resort, which turned out to be a success, though not quite in the manner that has first been anticipated.

In addition to eliminating the head rings and therefore the main source of the trouble, the open-ended Sleeve conferred the futher advantages:
1) It allowed for a considerable reduction in the overall height of the cylinder and head and therefore the frontal area of an aero-engine.
2) It allowed of the whole in the circumference of the Sleeve being available for exhaust-port area instead of 80% which was found to be the maximum permissible when a ported Sleeve was employed.
3) Since the Sleeve-Valve was operating very nearly in phase with the piston, and since its open end was subject to the full gas pressure in the cylinder, it formed, in effect, an annular piston which contributed slightly to the power output. In practice the area of this annulus was about 10% of that of the Piston, and since its stroke was 30% it therefore contributed about 3% to the indicated power of the engine which was transmitted via the eccentric to the crankshaft -a small but useful contribution.

According to the research by Mike Hewland and John Logan, engineer in charge of the Sleeve-Valve work, as published in Car&Driver, July 1974, the hottest point in the piston was in the center of combustion chamber, at 260-270 C, falling off to about 240 at the edges...and this is in a very high performance engine (70 HP from 500 cc, .45 pounds of fuel per HP per hr, racing version, .39 lb/hp/hr, economy version, they raced it up to 10'000 rpm). The Sleeve which forms the outside of the chamber, we don't think it excedes 140 C, and the cylinder head itself, from all appearances and measurements we've taken, doesn't seem to exceed 150 C.
The engines built by Mike Hewland had no higher oil use, he stated that its oil use was lower than half of the the contemporary poppet valve engines, and also having run their engine on fuel two grades below the standards used with a CR of 10:1

A Petter Brotherhood big size Single Sleeve-Valve engine can be watched functioning in YouTube, as part of the 'Anson Engine Museum'

I still wonder why so little new research seems to exist in this concept of Single Sleeve-Valve distribution, Burt-McCollum type, either for general aviation, or for automotive use.
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