autogyro wrote:I do not believe the interest in sleeve valves was motivated by the problems with poppet valves. Sleeve valves give a far higher potential for better gas flow.
Loop scavenged two strokes are probably unbeatable in this respect.
The interest in sleeve valves was based on Ricardo's finding that sleeve valves ran cooler than poppet valves, this improvement wrt detonation enabled much higher mep (supercharged) with the low compression ratios envisaged with 1920s fuel (a skewed comparison, like so many). That apparent advantage largely disappeared with the sudden improvement in fuel quality that followed.
Once Heron's internally cooled exhaust valves were fully developed (in the USA, handily before WW2), the sleeve valve was redundant. The huge US sleeve valve engine programs were abandoned early in WW2
If RR had known to silver-plate the bigend faces of the Vulture (like Wright etc) the Sabre would not have appeared in numbers. The Sabre was a reserve engine, resulting from a policy of having technical reserves.
C.F.Taylor said that the usual (eg Sabre) type of sleeve valve was lacking in port area. I think this was why Ricardo's interest turned to the 2 stroke open sleeve as realised in the Crecy.
All cylinder ported engines are relatively starved of port area as larger bore:stroke ratios are used (for higher power via higher revs). This is broadly a historical trend, associated with broad historical progress in fuel quality.
Poppet valves are advantageously aligned wrt gas flow and size, and to use overlap. Crucially, poppet valves areas are relatively larger at larger bore:stroke ratios. F1 uses this to great advantage, now that valve action is so improved via pneumatic springs. F1 b:s ratios are now around 2.4:1 (this is startlingly large)
Poppet valves are used in some 2 strokes ?
Would the 2 stroke prevail in current F1 ?
GP motorcycle 2 strokes always had relatively low bore:stroke ratios to allow sufficient port depths (a fraction of stroke). Shortening the stroke for more revs and power wouldn't work because the port areas would not increase. All these engines had b:s ratios close to 1
GP motorcycle noise limits introduced about 35 years ago were very hard on the 4 stroke, the last ever (flat 4, never raced) MV Agusta failed the noise test at full rpm when producing no power (driven electrically) ! The last MVs that actually raced made as much noise as a grid full of 2 strokes. They were competitive, having a stroke short enough to rev about 40% higher than the 2 strokes
Would 2 strokes work in 2014 style F1 ? ...... good question !
The Ford Ka was designed for a 2 stroke (that's why the engine bay could only take the pushrod engines as substitutes).
Don't modern 2 stroke outboards meet exactly the same environmental rules as 4 strokes ? ............
but F1 is pretending to be 'road relevant', and has been forcing the conventional for 30 years.