Posted by Janicholson on February 14, 2012 at 20:58:04 from (96.24.99.126):
In Reply to: fire crater or step head posted by Roger Tomfohrde on February 14, 2012 at 16:27:33:
Fuel use improves with efficiency of pumping and thermodynamics of the combustion chamber. Higher compression improves the expansion ratio. Thus the burning fuel has a greater percentage of volume to expand into from a smaller chamber. The surface to volume ratio of the chamber amounts to the relationship between the TDC volume compared to the surface area exposed to that volume, ie, if the chamber were perfectly cpherical, it would have least surface/volume, if thin areas and convoluted surfaces are present it has more surface to volume. Minimal surface area allows less quenching of the flame and more complete combustion. Strange shapes can produce higher unburned HC and lower net output. BUT-- squish areas and shapes do (or can) contribute to turbulance in the chamber and somewhat better combustion than open chambers. The reality today in newest technology engines provide direct injection. This allows a correct easily ignited mix at the plug with fuel free air near the surfaces reducing unburned HC, and making a gas engine nearer diesel in efficiency and far better in HC emissions and far fewer soot particulate issues. I wpould go with the piston that has the least surface area, but highest compression. Jim
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Today's Featured Article - Timing Your Magneto Ignition Tractor - by Chris Pratt. If you have done major engine work or restored your tractor, chances are you removed the magneto and spark plug wires and eventually reached the point where you had to put it all back together and make it run. On our first cosmetic restoration, not having a manual, we carefully marked the wires, taped the magneto in the position it came off, and were careful not to turn the engine over while we had these components off. We thought we could get by with this since the engine ran perfectly and would not need any internal work. After the cleanup and painting was done, we began reassembly and finally came to t
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