cobra said:rv6ejguy,
Sodium filled valves tend to be bulky and very expensive- seen occasionally, but "commonly found" might be a bit optimistic outside of racing circles. Are they even available for Lycs, Subaru's, etc., we are discussing here?
From your F/A notes targeting 13:1 ratios in boosted operations, I'm curious if you run only 100LL in your turbocharged engine? The turbo guys I know prefer a little wider margin-of-safety running turbos on mogas, particularly given subtile differences in pump gas quality. 100 octane would provide an excellent safety buffer.
Regarding turbocompounding, the process was hard on exhaust valves in the reciprocating engine trials (source of parts bin comments?) - My understanding is that the achievements reported were based on downgraded (limited) output levels and not optimised. Removing exhaust valves from the equsion eliminates a major limiting obstacle.
The 35% efficiency estimate I referenced came from Paul Lemar who has recently completed a prototype system for his rotary engine and has posted data on his website at http://www.rotaryeng.net/turbo.html ; the next step involves obtaining dyno data to provide credible comparions.
Sodium filled valves are common in aircraft engines and in the STI Subaru but relatively uncommon in other auto engines. They don't seem to be required even in racing applications. I've used stock type valves in all my turbocharged racing engines and never had a burnt valve. Most auto valves use a two different alloys for the head and stem.
For road racing and aircraft, we tune AFRs for 13-13.2 in most cases for max power. Richer costs power. We never run close to detonation margins in these applications are you are just asking to blow something up. Fix is proper timing, proper octane and proper CR to go with the manifold pressure and hp targets.
The turbo compounded R3350s were the highest output ones available if memory serves me correctly. 3750-3800 hp in one version with water methanol injection. You are right, these were not the most reliable engines in the world in this form. My father flew maritime patrol in Argus' and Neptunes fitted with these engines. The Neptune had 2 jets also so if the Wright packed up on one side over the ocean, it was not so scary. The standard quip was- "two turnin' and two burnin'"
PL is a great theorist but many times has been proven wrong by people actually doing it and he still isn't flying a Wankel after all these years. He has often insisted he is still correct after several people have proven him wrong through empirical testing. With no more than 40% of the total fuel energy contained in the exhaust in the Wankel, it would take an extremely efficient turbine and coupling system to recover 35% back to the eccentric shaft. We are talking 85-100%. Consulting one of my old texts says this is highly improbable especially considering that small turbines rarely exhibit efficiencies of much over 80% alone. Allison experimented with turbocomponding on their V-1750 (E-27) near the end of the war (it is a huge device). BSFC was improved from .47 to .392 which is pretty impressive but nowhere near 35%. I think Wright found similar gains. I await the dyno results to confirm PL's theory.
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