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Starlionblue wrote:Some areas of possible improvement:
- Temperature tolerance of the turbine components. The higher the better. The hottest turbine bits are actively cooled by circulating cool air through them. Even so the temperatures are immense and producing blades that can take a higher temperature would have an impact on efficiency. BTW "cool air" is a relative term. The air in question is over 1000C, but that's still ways cooler than the blades get.
- Improved aero modeling of the various components, most particularly the fans and compressors. I don't think we've reached "peak fan" yet.
- Variable pitch blades. This is already happening, and I bet there's more to come.
- Lighter/stronger fan blade materials.
stinson108 wrote:Just wondering if anyone would know how much more efficient can a jet engine get compared to the cutting edge jet engines out there now on commercial airliners
Does anyone know what the fuel energy ratio
Efficiency is on the jet engine with the best fuel economy is ?
Does anyone know what the next leap in propulsion systems could possibly be?
Hope the questions make sense to the technos
Out there
Thanks
Does anyone know what the fuel energy ratio
Efficiency is on the jet engine with the best fuel economy is ?
mxaxai wrote:Starlionblue wrote:Some areas of possible improvement:
- Temperature tolerance of the turbine components. The higher the better. The hottest turbine bits are actively cooled by circulating cool air through them. Even so the temperatures are immense and producing blades that can take a higher temperature would have an impact on efficiency. BTW "cool air" is a relative term. The air in question is over 1000C, but that's still ways cooler than the blades get.
- Improved aero modeling of the various components, most particularly the fans and compressors. I don't think we've reached "peak fan" yet.
- Variable pitch blades. This is already happening, and I bet there's more to come.
- Lighter/stronger fan blade materials.
From what I've heard, compressors are almost perfect nowadays. You could become an expert and work on it for a lifetime only to achieve ~0.5 - 1 % efficiency gain. I'm sure there are some weight savings possible, though.
Some other areas with room to improve:
- Nozzle & nacelle design
- Manufacturing & maintenance
There is this study: https://docplayer.org/12283395-Fkz-um-0 ... erlin.html that tries to estimate how much more efficient engines can become. It was done for the German ministry of the environment etc. in 2008, but is still pretty up-to-date. Sadly, it's in german.
But there is an image on page 48 with various efficiencies and the conclusion that there is about 27% difference between the GEnX and an ideal (Joule) cycle (using a realistic propulsive efficiency of 75%).
lightsaber wrote:I disagree on compressors being perfect. There is several percent to gain. In particular optimizing the output of the low compressor into the high compressor.
lightsaber wrote:We will see far higher Mach number compressors that are several percent more efficient, but better bearings are required.
lightsaber wrote:Same with both turbines. The gearbox will improve.
JayinKitsap wrote:The investment to gain a % efficiency improvement keeps rising, it gets harder as it closes into the theoretical limit. Initial cost, engine weight, and maintenance cost all rise in the attempt to perfection.
I would love to see the gearbox arrive into the larger jets, but it will be for some new clean sheet design a decade or more out.
ElroyJetson wrote:All engines do work based on the temperature difference between the engine core and outer chamber. Thus, the hotter the core the better. There will need to be material breakthroughs to greatly increase efficiency. Cremarics are one idea being explored. A problem with cremarics is that while they tolerate high temperatures well, they are brittle and difficult to machine.
But to be clear, the greater the temperature variance between the inner and outer chambers the greater the efficiency.
mxaxai wrote:ElroyJetson wrote:All engines do work based on the temperature difference between the engine core and outer chamber. Thus, the hotter the core the better. There will need to be material breakthroughs to greatly increase efficiency. Cremarics are one idea being explored. A problem with cremarics is that while they tolerate high temperatures well, they are brittle and difficult to machine.
But to be clear, the greater the temperature variance between the inner and outer chambers the greater the efficiency.
The core thermodynamic efficiency ("GT") increases but the overall efficiency ("ges") does not neccessarily:
Your propulsive efficiency ("vor") drops because the exhaust velocity increases. So you have to extract that extra power in your low pressure turbine and transfer it to your (larger) fan. It is thus neccessary to increase your BPR simultaneously:
BPR solid lines, massflow specific thrust dotted lines, overall efficiency on the y-axis, turbine entry temperature on the x-axis.
WIederling wrote:JayinKitsap wrote:The investment to gain a % efficiency improvement keeps rising, it gets harder as it closes into the theoretical limit. Initial cost, engine weight, and maintenance cost all rise in the attempt to perfection.
I would love to see the gearbox arrive into the larger jets, but it will be for some new clean sheet design a decade or more out.
Effort per relative improvement tends to be constant ( beyond inflation effects ).
That leads to exponential cost increases for absolute improvements when going near the theoretical limits.
Going from there it is always a good idea to improve on the things that are furthest away from
theoretical optimum. Best overall gain.
stinson108 wrote:Nice graph CowAnon
Thanks
Does anyone know what the next leap in propulsion systems could possibly be?
CowAnon wrote:Does anyone know what the fuel energy ratio
Efficiency is on the jet engine with the best fuel economy is ?
Looks like about 71-72 percent propulsive efficiency, 39-40 percent overall efficiency for the Airbus 350 and Boeing 787.
There are also some interesting graphs here:
MIT: Unified Propulsion: Efficiencies of A/C Engines
kitplane01 wrote:CowAnon wrote:Does anyone know what the fuel energy ratio
Efficiency is on the jet engine with the best fuel economy is ?
Looks like about 71-72 percent propulsive efficiency, 39-40 percent overall efficiency for the Airbus 350 and Boeing 787.
There are also some interesting graphs here:
MIT: Unified Propulsion: Efficiencies of A/C Engines
Interesting graph (I think).
If I read the accompanying link correctly
thermal_efficiency = rate_of_production_of_kinetic_energy / energy_in_the_fuel
propulsive_efficiency = propulsive_power / rate_of_production_of_kinetic_energy
What we really want is the product of these two numbers. That's why the chart is showing the best airplanes at 40% efficient. We have a long way to go. And we can improve things even more by carrying less structural weight, having better aerodynamics, etc.
I find this really hopeful. I had wondered if we had max'ed out on progress, and had only incremental improvements left. But it seems huge gains are possible.