Chapter 4, April 08
A lot of time taken up trying to get the hang of the ultra-high pressure injection control. Plodding on.
Meanwhile, here's some updating of the cylinder head. A diagram of the layout looks simple, and it is. I believe that's the beauty of it.
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It's an oversimplified drawing. But remember
in a two-stroke both inlet & exhaust overlap hugely. So clean air tends to go up the exhaust spout (note Z). Here, by creating a barrier to airflow towards the exhaust, spent gas is pushed out first. (Don't mention exhaust tuning - impractical in an aeroplane).
But (I hear you say) there's a barrier to a
portion of the air trying to get in. True, there has to be (note Z), and does air flow
mainly to the side opposite the exhaust, but
also out at the side of the valves - and
also, not shown - there's a clam shaped bleed (expanding air slightly) on the central side of the inlet valve, letting air go straight down.
So plenty air gets in but shouldn't mix with the exhaust. It should force the spent gas out.
To test this, I made a scale model in wood. It isn't as crude as it looks - the plasticine seals blunt the image. The flow is shown by sparks (which aren't quite like air, but make a good foto). Sparks bounce around. When I sift flour in, the flow is seen beautifully but it doesn't foto well.
You'll notice there's a stagnant zone under the inlet valve head. With modification with plasticine, I could show that seeds, stuck on pins with butter, were whisked off. So there
is airflow under the inlet valve also. Other Modifications didn't help much.
Keep it simple.
In the picture, the shovel pushing sparks rightwards is the inlet valve and the tract on the left is the exhaust. The horizontal "barrier" is the ex valve head. All shapes were profiled, tho' the picture doesn't show this. The bottom is the piston top, and a small ramp on this was helpful.
As I get the hang of adding fotos, I'll give some pictures of the head being machined in stages.
Malc
