Dafydd made discovery about hot spots pn undetside of cylinders. Limbach mahe shells but need to extend thru furthet. Removing hotspots increase engine life, reduces oil consumption & gives more power an the end of engines TBO. Limbach do a version of shells but think it is time for sn improved vetdion.
Read on if interested ian m ---------- Forwarded message ---------- From: "Dafydd Llewellyn" <[email protected]> Date: 30/10/2014 10:06 PM Subject: Re: Been thinking To: "Ian Mc Phee" <[email protected]> Cc: > Ian, I am of the view that forcing the cooling air to pass as far as possible around the entire circumference of the cylinder, is most definitely the way to go. See attached. The ideal is to get uniform heat transfer to the air so the cylinder stays at a uniform temperature around its full circumference. The principle is that the rate of heat transfer is controlled by two things - firstly, the difference in temperature between the metal and the air; and secondly, the air velocity - because the higher the velocity, the thinner the boundary layer and thus the better the heat transfer. > > In the "open" part where the air is coming in, the air is at its coldest, so one can reduce the liklihood of local over-cooling by keeping the passage wide, and thus the velocity low. As the air starts to pick up heat its temperature naturally rises, so to maintain the rate of heat transfer, the baffles force the air to pass through a much smaller passage, thus increasing its velocity. Ideally, one would arrange the baffling so the velocity continued to increase all the way to the outlet - and in fact it does, because as it heats up, it expands. So baffling of the form illustrated is a pretty good practical approach to achieving reasonably uniform temperature around the circumference. > > The expanding outlet passage is there to recover some of the pressure loss involved in accelerating the flow around the barrel; it would allow the cooling to be achieved with a smaller overall pressure difference between the cowl inlet and the cowl outlet - which also reduces the cooling drag. However, there is seldom space under the engine to do this; about the only engine I've seen baffled this way was the Bristol Centaurus - and it could be done that way because it had no pushrod tubes, being a aleeve-valve engine. So mostly people do without that added feature. > > Cheers, > > Dafydd
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