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There are so many more ways to improve recip efficiency and fuel economy, it is just not attainable for jets or turbines. And why all the gear box talk about the props I showed? I was not suggesting to hook them to a turbine that turns in the 10,000 plus rpm range.
Overhaul? Some industrial diesel type engines are in the 16000 to 20000 hour range, so again with proper engineering desired effects can be obtained.
A thermal efficiency of 98% would require a compression ratio of 50 to 1, and a peak temperature of about 15000 K. And that's for an idealized Carnot cycle, which is unattainable. An efficiency of 60% is remarkably high for heat engine. 98 % is bollocks.Its about 98% or so with diesels on some cruise ships.
No need for a gear box for reduction when they have propellers that turn at crazy high rpms. I think the one was around the 10K area. Need to watch a few of those NASA videos on the props. In the old model T and A days they would never have dreamed of the 700 plus hp production car engines we have today. It is all about the out of the box thinking and good design and engineering. And wow with the high pressure ratios mentioned I can imagine all the NOx that they produce, but then of course jets are exempt from that sort of stuff. 60% efficiency? Its about 98% or so with diesels on some cruise ships.
And again with propellers did anyone watch the videos?
So along with all the turbine loving going on here, please give me some fuel burn figures for some of the aircraft that are flying nowadays.
So along with all the turbine loving going on here, please give me some fuel burn figures for some of the aircraft that are flying nowadays.
Yeah thats old school stuff, did you watch the video? I'm not sure if rpm is mentioned there but they are way breaking sound barriers with newer props. Even with high speed turbine compressor and fans. As always it seems just because we are talking old aircraft and old piston engines, it doesn't mean there are not new and better developments that have improved on the old school ways. We are in the 2018's not the early to mid 1900's.Low speed diesels -- which are the most efficient simple-cycle engines -- are a bit over 50%.
As for propellers turning at "crazy high rpms," that may depend on one's definition of "crazy high," but propfans aren't designed for particularly high rpm -- or, importantly, tip speeds, but to deal with mildly supersonic Mach numbers near the blade tips at aircraft speeds of M=0.8 or slightly better.
Tip speeds of 500 m/s are considered high for ducted turbomachinery; that would be about 4800 rpm for a prop with a diameter of about 78 inches; for 10,000 rpm, that would be about 1050 m/s tip speed on the same diameter, or about 3 times the speed of sound.
This is a better and longer video link. At 4:44 he mentions 12,000 rpm for the propeller system.
View: https://www.youtube.com/watch?v=51BEbZlps80
It was that little? I figured it was more like 0.80.for example when P & W stuck a two stage fan on the JT3C engine to create the JT3D not only did take-off thrust go from 12,000lbs to 18,000lbs the specific fuel consumption at max continuous dropped from 0.76lbs fuel per pound of thrust per hour to 0.53 LB/LBT/hr.
How does real world compare?This may be test stand data and not real world.
Turbos add weight, they add complexity.
Yeah pretty funny stuff telling me what I know or don't know, thanks a bunch. So lets see turbines spin at what over 12k rpms, average recip 3k max.If the tips are inside a shroud or engine cover then the noise outside is reduced.
your last sentence shows you are having a little trouble understanding what is going on.
"Nothing says a recip needs to spin up like a turbine does and also cuts down on the air requirements"
Basically the amount of power you get is directly related to the amount of fuel you burn per unit of time (second or minute or hour) for the complete engine.
And the amount of fuel you can burn depends on the pounds (or KG) of air you can put through the engine in that amount of time.
Granted diesels don't use the same fuel/air ratio as gasoline engines but they close and not as different as some other fuels (like alcohol).
Basically the only way you can cut down on the air requirements is to cut down the power.
A WW II Allison that was running 10,000lb of air through the engine was making a theoretical 1672hp in the cylinders. After you take out for internal friction and the power needed to drive the supercharger you got 1285hp to the prop of an engine using the 9.60 gears. Using lower supercharger gears, if they still supplied 10,000lbs per hour, got you higher power to the propshaft from the same fuel/air burn.
Lower the RPM and lower the boost and less air goes through the engine and it makes less power.
The turbine T-56-A-15 engine of 4910ehp moved 32.4lbs of air per second or 116,640 lbs per hour.
A P & W PT-6A-65 of 1376shp moves 9.5lb a second or 34,200lb of air an hour. It has a max cruise rating 956shp and a fuel burn at the take-off rating of 0.506lb per hp hour. The PT-6A-65 weighs 463lbs dry and that is a big reason the reciprocating engine is not coming back in commercial aviation (or military). The Allison went about 1350lbs dry. Granted it is WW II technology but the chances of making a 1300hp for take-0ff reciprocating engine that weighs less than 500lbs and will last for thousands of hours is about zero.
See: Orenda OE600 - Wikipedia
for long tortured tale of trying to bring an aviation version of the old 1970s Can-AM race car engine to aviation use. It weighed 740lb dry for about 600hp take-off in one version (at 4400rpm).
Please note that the PT-6 target engine was not standing still.
from wiki" From 1963 to 2016 power-to-weight ratio was improved by 50%, brake specific fuel consumption by 20% and overall pressure ratio reached 14:1"
Impart due to competition from newer engines.
Turbos add weight, they add complexity.
Many turbines are simply flat rated. The fuel management system is set up to provide less than full power under standard temperature and altitude conditions so the official rating (and actual power of the engine) doesn't change under hot and high conditions, at leas up until a certain point.
you can't make a reciprocating engine big enough to replace even medium turbine engines without getting into monstrosities of well over 24 cylinders.
as far as fuel additives go, I have a bottle of specially tablets, just put one in your gas tank and add 10 gallons of water and you can drive your car 200 miles,only 200 bucks per bottle of tablets.
Yeah pretty funny stuff telling me what I know or don't know, thanks a bunch. So lets see turbines spin at what over 12k rpms, average recip 3k max.
The power is related to the type of fuel used and how well that fuel is used and not always how much is used to fuel a given device, meaning adding more of said fuel could blow the thing apart, I'll hear some crap over that one I'm sure. When it comes to alot of inventions and ideas there is a huge lack of thinking out of the box and why when the new invention comes along everyone says I wish I would have thought about that. Its funny how some like to battle an idea rather than think of how can it be done.