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Diesel efficiency and Aircraft Engines in WWII
Ok, this has been playing out a long time, interesting discussion. More fuel for thought.
I think efficiency come from the effective use of the power generated by the expanding gas. A diesel engine has been more efficient due to the fact that the long stroke capable with a diesel engine allows the gas to be harness longer, ie think of the muzzel velocity of a revolver and a rifle. The other factor is the higher temperatures reached and the more complete combustion of the material at the higher temperatures. The down side of this is the NOX produced.
Efficiency in a gas engine is dependent on the surface area of the piston as the expansion is less. A few years ago the Ausies developed a new engine called the split cycle. It is a revolutionary design that used large piston that moved only a few mm. It had efficiencies un attainable with current gas technology. The design would work with diesel or gas.
As an aside the diesel engine cycle can use any fuel of choice including finely powdered coal and gasoline.
During WW II, I think, the gas areo engines were super charged not turbo charged. At least I have not seen any. I don't recall whether the diesel areo engines were turbo, super or not.
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Diesel efficiency and Aircraft Engines in WWII
The 3 banked P&W wasp I think had only one supercharger (AKA F4U engine). It has been nearly 20 years since I looked at one.
I don't know of an WWII engine with 2 stage. I thought maybe the Napier Sabre, but the 2 stage was never implemented despite 4000 hp out of 2238 cu in. The Sabre is a sight if you have never seen one. It is hard to believe they could develop such an engine in war. It certainly had some teething.
I guess the later Griffons had 2 stage.
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Diesel efficiency and Aircraft Engines in WWII
Super chargers require energy a turbo is running on waste energy. I don't believe there was the turbo technology during WWII. The ability to keep a fan running in hot exhaust gasses took a while even for the auto. A seized turbo when flying would be.........!!!!!! Maybe the Germans Diesel had it?
The Rolls Royce Merlin engine used water and 30% glycol mixture at greater than 18 PSI. Yes engine temperatures would dictate that the fluid would be in liquid form at sea level pressure or even more likely at 30,000 ft, but not at that pressure.
The same engine, the Merlin was manufatured by Packard during the war although the parts were not fully interchangable. Something to do with the difference in standard inch.
The Merlin was on the Spitfires, Hurricanes, P-51, Mosquito, Lancaster, Halifax, etc.
The Griffon was larger displacement but was never developed as much as the Merlin so never produced as much HP.
Diesel engine manufactures have gone to short strokes and a precombustion chamber (so have some gas engines). Volume in the smaller combustion area is less than the full surface of the piston therefore allowing similar compression rates with out the longer stroke. This allows the higher RPM engine and greater power to weight. The chamber can be designed to give better mixing and ignition of the fuel, therefore cleaner burn.
Limitation in materials is something that has plagued the internal combustion engine. Better burn could be achieved if hotter temperatures could be reached in the combustion chamber. Much of the energy of the combustion is lost in waste heat. Ceramic materials have shown promise but cost and manufacturing consistancy have kept them from use.
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Diesel efficiency and Aircraft Engines in WWII
Tom;
Both a supercharged engine and a turbo engine will produce more HP per lb. The difference is that the turbo uses less energy than the supercharger and at some combinations or RPM and pressure it is essentually free.
Turbos are used on aircraft engines today, but the piston powered aircraft does not normally fly at the high altitudes and the boost is sufficient from the turbo.
Mark
The F4U had a 3 banked of 6 I believe. The only time I have encountered this engine was on the Martin Mars. I worked mostly with the smaller singles on the Beavers and Otters.
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