[BITList] Scott Still engine

[HUGH]

Thursday,

Mike,

Further to my earlier on the Scott Still engine.

As I said, Johnston F Robb was director with Scotts Engineering Co (formed when British Shipbuilders split Scotts into ship and engine), and when he retired he did a PhD at Glasgow on the Scott family and firm, 1820-1920.  His thesis is in the Watt Library, Greenock, and I betook myself down to Union Street this afternoon for a look.  The thesis, as far as I was able to see (there is no index to the relevant volume), omits the Scott Still engine, but all was not lost, it is covered elsewhere.  A history of Scotts to 1920 was published in Engineering : Two Centuries of Shipbuilding, by the Scotts at Greenock.  This was reprinted (partially, it says) in a hefty volume in 1920, and the Watt has a number of copies. Here is a very condensed and edited version.

Iin 1916, Scotts entered negotiations with the  Engine Development Company, by 1920 called the Still Engine Company Ltd, who held the patent rights for the Still engine. The main source of power for this engine was the downstroke, 2 cycle diesel - steam on the upstroke gave "supplementary power".  WW1 held up development - in 1919 work began on an experimental engine of 350 bhp - this, evidently single cylinder, was running in June, 1920.  I've two not very good photocopies of this engine from the book - I could take better with the camera and probably will.  It was 22" bore x 36" stroke, and they envisaged this configuration being a standard for each cylinder, up to six, in line, single or twin screw, up to 4,200 bhp. Greater horsepowers (so much for the standard) would be met by bigger bore cylinders.  They say the idea of the Still engine was to reduce heat losses to a practical minimum, and that "the engine is practically free from the array of rods, valves and cams associated with oil engines".  This, as with other features quoted, simply reflects the early stage of diesel development, 2-cycle v 4-cycle, simple v complex.  They say manoeuvring is greatly facilitated by the existence of the steam side, but give no details of how.

I've a copy of a machinery arrangement, twin screw 6 cyl, 4,200 bhp, showing two vertical oil-fired boilers to supply steam for engine starting. Once the engine is started, the boiler oil burners are shut down and the boilers become steam and water reservoirs.  These are in circuit with the engine cylinder jackets and exhaust pipe jackets. The cooling water leaves the cylinder jackets at a constant temperature, regulated by the pressure of the steam  (I don't understand that either).  During compression, owing to the cylinder walls being at steam temperature, the entering charge (combustion air) picks up heat instead of losing it during the greater part of the stroke.  During combustion and expansion, heat is taken up by the water circulating in the cylinder jacket, all of which goes to form steam.  Steam is also produced from regenerators via heat recovered from exhuat gases (these will be the exhaust pipe jackets mentioned above).  Steam generated is for use on the undersides of the pistons and for auxiliary purposes.  They claim the Still engine delivers more power for less weight than conventional diesels.

The story stops before any ships were fitted with the engine.

I sent this also to Bill Power who had asked the original question elsewhere.

Hugh.
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