If German have access to high ocatane fuel, how does that impact the performance of their fighters?

mig-31bm said:

I watched a video on youtube, the author explained that, even though BF-109 is lighter and has bigger engine than P-51, the P-51 ended up being much faster because USA has fuel with much better octane rating of upto 150 while German fuel octance rating is around 80-100.
So my question is, what would happen if we give FW-190, Ta-152 150 octane fuel ? Would they get a huge boost in performance? Or their engine can't handle it?

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From an engineering point of view an interesting core aspect of octane and knock is combustion chamber design. Which engines / variants had the best engineered chambers? For example, if you did test cell work and monitored oxygen content to compare at identical mix ratios, then adjusted boost to match combustion chamber pressure prior ignition and mapped up to detonation, what would the data say? An idea chamber avoids pressure reflections causing detonation after ignition, and avoids sharp corners that heat up causing hot surface pre ignition. But here is a not widely known German attribute; surface gap igniters. Spark plugs with protruding electrodes risk the electrode edge reaching ignition temperature. Some German engineers realized they could design spark plugs with semi conducting flat insulators that avoided this issue. These spark plugs permitted sparking at much higher pressures than air gap and also permitted lower voltages out of magneto thus increasing reliability of cables and distribution at altitude. The patents were dissolved and taken up by various USA manufacturers and the concept proved critical to success of gas turbine engines.

Surface discharge sparkplugs for piston engine or automotive use are a niche product. Generally, piston engine combustion benefits much more from moderate amounts of spark plug electrode projection into the combustion chamber. Modern high performance spark plugs are made to survive in very harsh conditions and are mechanically strong. The electrodes are made to not cause pre-ignition or unwanted detonation. They also last very well, 40,000 miles is a common service interval for modern high spec spark plugs. Also, the fine quality and small size of Iridium type electrodes give maximum exposure to the flame kernal, while offering minimum resistance to gas flow.

Eng

Engineman said:

Surface discharge sparkplugs for piston engine or automotive use are a niche product. Generally, piston engine combustion benefits much more from moderate amounts of spark plug electrode projection into the combustion chamber. Modern high performance spark plugs are made to survive in very harsh conditions and are mechanically strong. The electrodes are made to not cause pre-ignition or unwanted detonation. They also last very well, 40,000 miles is a common service interval for modern high spec spark plugs. Also, the fine quality and small size of Iridium type electrodes give maximum exposure to the flame kernal, while offering minimum resistance to gas flow.

Eng

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But, on the WW2 German engines where used, the attribute of interest was the reduced tendency to become a hot surface ignition source. Plume shape can be controlled and plume size increased with spark energy. Electrode wear wasn't a concern when engine TBO was 100 hours. Automotive spark energy is tiny, maybe 20 mJ. From memory, the big Seimens mags on WW2 German engines were at least several times that. It would be interesting to compare spark energy from say DB605 to Merlin. The other constraint is quench at high combustion pressures. Very good boost was available at max operating altitude so combustion chamber pressure at spark event was very high, but outdoor ambient pressure very low. These 1940 engines were flat rated due supercharge out to ~25,000 feet altitude. With air gap igniters say on Merlin, the gap had to be reduced so it would avoid quench at the peak open circuit firing voltage available. With 1940 materials, it was impossible to run extreme voltages without flashover at mag or cable. So the gap selected was not the gap ideal for ignition but rather the biggest gap they could set for the limited reliable peak open circuit voltage. Meanwhile the surface gap would fire at much lower voltages. I think someone told me of aero engines where mag 1 ran different gaps than mag 2, the intent to get optimal ignition at majority operating condition and avoid miss at max boost. I remain in awe of WW2 technology.