One would think that given the huge push for ever more performance and reliability on piston engines during the heat of WWII would push the designs to their absolute limits, however, most American engines seem to be comfortable with the old carburetor technology which is prone to icing, hiccups and perform poorly under high Gs. Reading the literature of how Pratt & Whitney optimized the Double Wasp to an extreme (to the extent that the crankshaft is taking so much force that it needs a pair of torsional dampers even after forging) is quite jarring when one comes to realize it still uses the good old carbs to suck in fuel, when at the other side fuel injection was adopted eagerly.
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asked Jan 24, 2019 at 15:58
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2$\begingroup$ Could reliable fuel injection systems have been mass-produced with the technology of the era? It wasn't until half a century later that they became common in automobile engines. $\endgroup$– jamesqfJan 24, 2019 at 18:26
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1 Answer
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Those engines didn't use carburetors as in gravity operated float carburetors. They used "pressure carburetors". Pressure carbs are mechanical fuel injection systems that inject the fuel from a single point at the start of the manifold instead of injecting fuel at the intake port via a distribution system. Not quite as theoretically efficient as point fuel injection, but it has all the other advantages including automatic mixture control and no G sensitivity, as well as being less sensitive to damage by not having small high pressure fuel lines running to each cylinder.
On cars in recent years you had a similar system called "throttle body fuel injection", more or less an electronically controlled pressure carb.
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1$\begingroup$ so the so-called pressure carb is essentially before-supercharger single port injection? that makes sense $\endgroup$ Jan 24, 2019 at 16:48
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1$\begingroup$ @meatball I think fuel is injected after any air compressor, not before. $\endgroup$– EugeneJan 24, 2019 at 21:31
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$\begingroup$ @John K thanks for another fine answer. This one ties with the question about carburetors, fuel richness, and altitude currently active on this site. Injecting into the intake manifold makes a lot of sense in that it will beneficially cool the compressed air from the turbocharger and feed pre-mixed charge right into the cylinders. Turbos also work wonders for power output, as well as eliminate the possibility of carb icing. $\endgroup$ Jan 25, 2019 at 1:24