Veloce 600, 6 seat pressurized twin auto-converted engines.

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lelievre12

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  • As fuel evaporates from the surface, the fuel near the surface becomes both cooler and more resistant to evaporation. Yeah, there is some mixing, but it is not high order in most gasoline tanks, and so the fuel remaining becomes more resistant to evaporation, and the fuel at the surface even more so;
  • Evaporation is a powerful cooling effect on mixed liquids - wide ranges of molecular weight - and so will cool fuel quite strongly with even modest evaporation.
Great post. Thanks.

Its important to note that the fuel is actually boiling (not really evaporating) however the effect is the same as you say, ie the fuel cools by giving up its enthalpy of vaporization and stays liquid. And also, yes, the lightest molecular weights (eg isopentane) boil off first. Its important to note the change in Octane of the fuel when the lighter fractions are lost.

As we climb, to altitude the lighter fractions boil/evaporate and the fuel loses its octane the higher you go. The irony, of course, is that engines rely on higher octane to avoid detonation, vapor lock etc. but as we climb, the fuel is losing the very octane needed to fly high. I guess this fact hurt the B29's trying to get to Japan hence all the fuel research at that time. The 'fix' was to fly lower which I always thought was to improve bombing accuracy, but maybe it was the fuel as well.

Its also worth noting how much fuel can be lost through boiling/evaporation. Up to 20% in the charts up to 50,000 examined in the old NACA E5H27 report.

I guess some of this discussion is finding its mark as Veloce 600 Specs now lists 25,000 as the cruise ceiling. A lot less to worry about at 5.45 PSIA.
 
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tspear

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One other point - mention of fuel evap at localized low pressure spots. Yes, it is cavitation. The bubbles tend to exist only a very short time downstream of their generation, usually popping back to liquid very shortly after the bubble leaves the low pressure site of its formation. These discontinuities in flow and thus in pressure are why cavitation makes so much noise in a cavitating spot in a system.

Ain't engineering great?

Billski
I thought the noise was actually shock waves created when the bubbles collapse and the liquid effectively slams into itself.

Tim
 

Vigilant1

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If the liquid is turning to vapor only at the surface, it is evaporation (not boiling). If the phase change from liquid to vapor results in cooling, then it is evaporation (not boiling).
 

rv7charlie

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As we climb, to altitude the lighter fractions boil/evaporate and the fuel loses its octane the higher you go. The irony, of course, is that engines rely on higher octane to avoid detonation, vapor lock etc. but as we climb, the fuel is losing the very octane needed to fly high.
Can you elaborate, in terms a non-chemist can grasp?

My understanding has been that 'octane' (actually, the stuff that enhances octane numbers) actually 'slows the burn' (non-chemist terms) but also reduces the energy content of the fuel. And that at least with avgas, the octane enhancer (TEL) is really difficult to get into the atmosphere (most seems to stay in the spark plugs ;-) ). My understanding has also been that the lighter stuff is what lights off the easiest. This belief has been enhanced by my experience running 'old' mogas in both aircraft and small lawn care equipment, where the engines get very hard to start on old fuel, but once running, seem to run just fine. Also enhanced by the fact that in most areas of the US, vapor pressures of mogas go up in winter, and the reason given is to improve starting in cold weather.
 
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BBerson

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ie the fuel cools by giving up its enthalpy of vaporization and stays liquid.
Enthalpy of vaporization is the same as latent heat of evaporation that I proposed :rolleyes:in post 66 Veloce 600, 6 seat pressurized twin auto-converted engines.
 
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rv6ejguy

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Its important to note the change in Octane of the fuel when the lighter fractions are lost.

As we climb, to altitude the lighter fractions boil/evaporate and the fuel loses its octane the higher you go. The irony, of course, is that engines rely on higher octane to avoid detonation, vapor lock etc. but as we climb, the fuel is losing the very octane needed to fly high. I guess this fact hurt the B29's trying to get to Japan hence all the fuel research at that time. The 'fix' was to fly lower which I always thought was to improve bombing accuracy, but maybe it was the fuel as well.

Its also worth noting how much fuel can be lost through boiling/evaporation. Up to 20% in the charts up to 50,000 examined in the old NACA E5H27 report.

I guess some of this discussion is finding its mark as Veloce 600 Specs now lists 25,000 as the cruise ceiling. A lot less to worry about at 5.45 PSIA.
TEL is primarily responsible for the octane rating in leaded avgas. You're not losing octane rating by climbing and B29s switched to low altitude night bombing to carry higher bomb loads, higher bombing accuracy, reduced time spent at climb power which was wearing out engines quickly and to reduce losses since Japan had very limited night fighter and radar guided flak. Lots of B29s were carrying out missions at or above 30,000 feet in daylight. I've never read any discussion about fuel in this regard.

Now we're talking about 50,000 feet? You started out at 22,000 feet. Nobody is talking about flying piston aircraft at 50,000 feet here except you. Where are you stopping with this? You've presented conjecture and unresearched information which doesn't agree with real world, actual flying aircraft at high altitudes.

The facts are at least 2 aircraft we know of went to over 47,000 feet on avgas and thousands have done long missions at over 30,000 feet in WW2 , Korea and post war.

Mark will have a lot more important challenges to solve than this non- issue.

I suspect any reduction in operational altitudes on this design were driven by the turbocharger pressure ratio requirements as I said initially in this thread, plus the reality of the ATC environment above FL290.
 
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PMD

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I thought the noise was actually shock waves created when the bubbles collapse and the liquid effectively slams into itself.
That is correct. There are two things that happen when liquid flow separates. The pressure drop dramatically leaving a "bubble" of nothing (vacuum) that immediately starts to fill with evaporation or dissolved gasses from the bulk liquid at the surface of the evacuated "bubble". Evaporation/degassing takes a bit of time, but the pressure differential has already started pulling the walls of the bubble inward on itself. There isn't enough vapour in the short time to dampen the collapsing liquid face that then smashes into itself (noise) or smashes up against something such as the propeller of a ship or the wall of the cooling system of a liner or bored cylinder in an engine. That smash is sufficiently violent to be able to blow a piece of cast iron out of the sleeve or prop (even bronze props can pit from cavitation)
 

wsimpso1

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I thought the noise was actually shock waves created when the bubbles collapse and the liquid effectively slams into itself.

Tim
A shock is a discontinuity in behavior. I believe we are talking the same thing.
 

Flyfalcons

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Great post. Thanks.

Its important to note that the fuel is actually boiling (not really evaporating) however the effect is the same as you say, ie the fuel cools by giving up its enthalpy of vaporization and stays liquid. And also, yes, the lightest molecular weights (eg isopentane) boil off first. Its important to note the change in Octane of the fuel when the lighter fractions are lost.

As we climb, to altitude the lighter fractions boil/evaporate and the fuel loses its octane the higher you go. The irony, of course, is that engines rely on higher octane to avoid detonation, vapor lock etc. but as we climb, the fuel is losing the very octane needed to fly high. I guess this fact hurt the B29's trying to get to Japan hence all the fuel research at that time. The 'fix' was to fly lower which I always thought was to improve bombing accuracy, but maybe it was the fuel as well.

Its also worth noting how much fuel can be lost through boiling/evaporation. Up to 20% in the charts up to 50,000 examined in the old NACA E5H27 report.

I guess some of this discussion is finding its mark as Veloce 600 Specs now lists 25,000 as the cruise ceiling. A lot less to worry about at 5.45 PSIA.
Not for the "Pressurized" version.
 

lelievre12

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Mark will have a lot more important challenges to solve than this non- issue.
This is what 'non-issue' fuel pressure variation at 18,000 looks like. My plane looks exactly the same on a hot day and the fix is to switch tanks to colder fuel where the fuel return has not yet heated the header.


I suspect that if this is a 'non issue' in converted auto-efi engines that probably the rail pressure is not being measured? Certainly would be good in any testing to altitude to know for sure. Vapor mixed with fuel makes for a leaner mixture than calibrated with possible detonation and CHT/EGT issues thereafter.

I agree that this debate is becoming a little moot as Veloce have tempered their marketing material to focus on a 25K ceiling where vapor issues are less troublesome. My initial gripe was simply with the 'blue sky' unproven 35K claim.
 
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Voidhawk9

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This is what 'non-issue' fuel pressure variation at 18,000 looks like....
The digital gauge right below it shows no variation. Perhaps a gauge fault? I don't see proof the your repeatedly beaten dead horse has come to life?
 

Dan Thomas

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The digital gauge right below it shows no variation. Perhaps a gauge fault? I don't see proof the your repeatedly beaten dead horse has come to life?
Digital gauges are usually damped to prevent constant flickering of the numbers. Analog gauges will twitch and show those brief variations that the digital won't.

For that reason I find analog multimeters much better at finding spurious changes in voltage or resistance. Makes troubleshooting much easier.

Why would switching tanks to get colder fuel stop the erratic indication if the gauge was at fault?
 

Flyfalcons

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I agree that this debate is becoming a little moot as Veloce have tempered their marketing material to focus on a 25K ceiling where vapor issues are less troublesome. My initial gripe was simply with the 'blue sky' unproven 35K claim.
Scroll down on their website. They are still claiming 35K for the pressurized version.
 

Victor Bravo

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Rich Trickel (mentioned on their website in the "History" section) may or may not be a qualified designer. A guy I knew (Vance Jacqua, RIP) was the highly trained engineer who KISS Aircraft later hired to upgrade or improve the original design.

The website as it appears in the above post does not look completely legitimate to me. The way is is written reeks of an amateur sales guy, or someone who is just learning English, as opposed to an airplane company that has real-world airplane people in it. The writing of course doesn't make the airplane legit or not legit, but it raises valid questions, and the factual answers to those questions do affect the aircraft's legitimacy.
 

Cardmarc

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I absolutely agree with you. I watched the entire ‘sales’ video and was left with many questions. They don’t have a legitimate flying article to prove anything.
 

ScaleBirdsScott

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There's been a thread on this with more discussion.


I don't have much comment on the matter other than that. From the talk, looks like there's some good signs that it could have a future but there's some ways to go yet... And a lot of talk about fuel systems 🤪
 

Cardmarc

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Is the Aeromentum Psru used:
1. Planetary as is used in turboprops and turbine helicopters?
2. Set up for oil controlled CS props?
3. Have a track record over 1000 hours without failure?
 

mcrae0104

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Great post. Thanks.

As we climb, to altitude the lighter fractions boil/evaporate and the fuel loses its octane the higher you go. The irony, of course, is that engines rely on higher octane to avoid detonation, vapor lock etc. but as we climb, the fuel is losing the very octane needed to fly high.

Would you please explain the relationship between octane and vapor lock, and also why fuel loses octane at increased altitude?
 
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