Chinese Engine Development

S

Scratch

Captain
I've stated this in the past and will repeat here that I believe to have observed that "western" engines, which mostly tent to have yellow-ish afterburners, have smaller by-pass ratios of 0.2 - 0.4. Soviet / russian origin engines with the more blue-ish ABs have generally BPRs of greater than 0.5 The idea would be that for a higher BPR engine, there's more unused oxygen to burn the additional fuel in the afterburner. While in the low BPR eniges less oxygen leads to less complete burning of the fuel leads to a more yelow-ish tone.

The B-1Bs GE engines have a somewhat higher BPR and also produce a blue AB flame. The Tu-22's NK-23 engines have a pretty high BPR and burn solid blue.
 
shen

shen

Senior Member
Scratch said:
I've stated this in the past and will repeat here that I believe to have observed that "western" engines, which mostly tent to have yellow-ish afterburners, have smaller by-pass ratios of 0.2 - 0.4. Soviet / russian origin engines with the more blue-ish ABs have generally BPRs of greater than 0.5 The idea would be that for a higher BPR engine, there's more unused oxygen to burn the additional fuel in the afterburner. While in the low BPR eniges less oxygen leads to less complete burning of the fuel leads to a more yelow-ish tone.

The B-1Bs GE engines have a somewhat higher BPR and also produce a blue AB flame. The Tu-22's NK-23 engines have a pretty high BPR and burn solid blue.
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Would that also explain why in the original WS-10 testing photo which sparked this discussion, the edge of the flame (where the bypass air is concentrated) is more blue than the center?
 
S

Scratch

Captain
shen said:
Would that also explain why in the original WS-10 testing photo which sparked this discussion, the edge of the flame (where the bypass air is concentrated) is more blue than the center?
Click to expand...

In my mind, at first glance it does. Though I'm not really familiar with the dynamics inside the engiene. Bypass and core air probably aren't completey mixed as this would create some unwanted turbulances in the AB section, and I also think that this colder bypas air is used as some kind of a boundary layer to shield the material from the hot core air. At least during times when AB is not used.
 
D

delft

Brigadier
Scratch said:
I've stated this in the past and will repeat here that I believe to have observed that "western" engines, which mostly tent to have yellow-ish afterburners, have smaller by-pass ratios of 0.2 - 0.4. Soviet / russian origin engines with the more blue-ish ABs have generally BPRs of greater than 0.5 The idea would be that for a higher BPR engine, there's more unused oxygen to burn the additional fuel in the afterburner. While in the low BPR eniges less oxygen leads to less complete burning of the fuel leads to a more yelow-ish tone.

The B-1Bs GE engines have a somewhat higher BPR and also produce a blue AB flame. The Tu-22's NK-23 engines have a pretty high BPR and burn solid blue.
Click to expand...
I have never looked at closely at engine comparisons, and many numbers are of course secret, but if you are right it looks as if the Russians sacrifice engine time between overhaul and life as well as engine weight to a better fuel consumption. That would explain the amazing range the Flankers already achieved in the '80's.
The explanation might be that the Russians are rarely at war and the US nearly always while the quality of the turbine materials are about the same. That suggests different compromises.
 
S

Scratch

Captain
Though I thought that in the past at least russian built engines weren't on par, in practice, with their "western" counterparts as regards built quality of the turbines. And that this was a reason for the much lower MTBF. Though this may also have made them cheaper and more rugged?
I'm also trying to wrap my head around how this may affect specific thrust and fuel consumption. The russian engines, with a higher BPR (although the diameter seems to be about equal), should have lower specific thrust and therefore be more economical, geared towards cruise conditions.
With a resulting cooler exhaust, there's more room for the afterburner until reaching maximum EGT. And I feel like russian engines gain a rather large amount of extra thrust through their AB.
Which comes at a price in SFC during AB operation?
Yet thrust levels are apparently enough to push those jets well beyond Mach 2.
 
thunderchief

thunderchief

Senior Member
Keep in mind that hot gasses in afterburner are in fact waste of energy . And hotter (and bluer :D ) they are, more energy is wasted . Bomber engines like Kuznetsov NK-25 have relatively high BPR (1.45 I believe) , similar to older passenger aircraft . That is good for cruising, but not good enough for supersonic dashes . In order to propel aircraft to supersonic speed you need to heat up large volume of exhaust gas very fast . And to do that you need large temperature of burning fuel - i.e. blue flame . Down side is large wastage of fuel in process .
 
D

delft

Brigadier
thunderchief said:
Keep in mind that hot gasses in afterburner are in fact waste of energy . And hotter (and bluer :D ) they are, more energy is wasted . Bomber engines like Kuznetsov NK-25 have relatively high BPR (1.45 I believe) , similar to older passenger aircraft . That is good for cruising, but not good enough for supersonic dashes . In order to propel aircraft to supersonic speed you need to heat up large volume of exhaust gas very fast . And to do that you need large temperature of burning fuel - i.e. blue flame . Down side is large wastage of fuel in process .
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Indeed using an afterburner is a waste of fuel that is only acceptable if it is only used for short times. But also a yellow flame shows the presence of unburned carbon, a waste of fuel even in the afterburning process.
There is also the matter of using it at high speed. In the case of the Blackbird family of aircraft the J-58 engines at above Mach 3 got their intake air at the compressor face at a pretty high temperature so little fuel can be burned to prevent the turbines being burned so little energy is available to compress the air further after it was compressed in the engine intake. Much more fuel can be burned in the afterburner so this is really at that speed a ram jet with an energy wasting turbojet in the way of the flow. :)
 
S

Scratch

Captain
thunderchief said:
Keep in mind that hot gasses in afterburner are in fact waste of energy . And hotter (and bluer :D ) they are, more energy is wasted . Bomber engines like Kuznetsov NK-25 have relatively high BPR (1.45 I believe) , similar to older passenger aircraft . That is good for cruising, but not good enough for supersonic dashes . In order to propel aircraft to supersonic speed you need to heat up large volume of exhaust gas very fast . And to do that you need large temperature of burning fuel - i.e. blue flame . Down side is large wastage of fuel in process .
Click to expand...

Althogh I do not see how hot exhaust gases are per se a waste of energy here. After all, the idea of a jet engine is to heat up air as much as possbile to make it expand, wich eventually produces thrust. So the hotter the better.
Higher BPR engines, all other factors being equal, should produce somewhat cooler exhaust gases, since a larger amount/portion of air is routed around the core, not compressed and heated. That means there's more "room" for the AB to heat up the gas flow to maximum EGT, allowing more extra thrust to be produced.
With higher drag and lower specific thrust, higher BPR engines probably provide a little less peak speed in non-AB operation. Therefore maybe more AB power is needed to achieve those peak conditions. However, since something usefull is done with it (extra thurst produced) I do not see this as a waste of energy. AB is always very fuel intensive, but not generally wastefull.
 
L

latenlazy

Brigadier
Scratch said:
Althogh I do not see how hot exhaust gases are per se a waste of energy here. After all, the idea of a jet engine is to heat up air as much as possbile to make it expand, wich eventually produces thrust. So the hotter the better.
Higher BPR engines, all other factors being equal, should produce somewhat cooler exhaust gases, since a larger amount/portion of air is routed around the core, not compressed and heated. That means there's more "room" for the AB to heat up the gas flow to maximum EGT, allowing more extra thrust to be produced.
With higher drag and lower specific thrust, higher BPR engines probably provide a little less peak speed in non-AB operation. Therefore maybe more AB power is needed to achieve those peak conditions. However, since something usefull is done with it (extra thurst produced) I do not see this as a waste of energy. AB is always very fuel intensive, but not generally wastefull.
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Energy being used to produce heat and light is energy not being used to produce thrust. Of course the only way to get perfect conversion into mechanical energy is a mythical one.
 
SamuraiBlue

SamuraiBlue

Captain
latenlazy said:
Energy being used to produce heat and light is energy not being used to produce thrust. Of course the only way to get perfect conversion into mechanical energy is a mythical one.
Click to expand...
In the case of jet fan engine the energy producing heat and energy producing thrust is the same since thrust of a jet fan engine is created through thermal expansion of air. It's the same as an explosion, the power of explosion is due to the rapid chemical reaction resulting to heat that expands the air around it. Without heat there is no thermal expansion thus no thrust.
 
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