FLY2HMO From , joined Dec 1969, posts, RR: Reply 1, posted (3 years 5 months 2 weeks 2 days 15 hours ago) and read 5394 times:
Quoting A342 (Thread starter): What are typical pressures for jet fuel injected into the combustion chamber of jet or turoprop engines?
According to my Rolls Royce book, the typical pressure inside a combustion chamber is around 100 to 200 psi. So theoretically you only need to overcome that pressure to be able to inject the fuel.
BUT the book also mentions that, specially in older types of injectors, pressures of up to 6000psi would be required for proper atomization of the fuel.
Tdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80 Reply 2, posted (3 years 5 months 2 weeks 2 days 9 hours ago) and read 5347 times:
Quoting A342 (Thread starter): What are typical pressures for jet fuel injected into the combustion chamber of jet or turoprop engines?
1000-1500 psi is in my head as the typical output from the high-pressure fuel pump, but I don't have any documentation handy to back that up. As FLY2HMO noted, it's got to be meaningfully higher than the combustor pressure.
Quoting A342 (Thread starter): I'm asking because I'd like to know how the injection pressure compares to that of modern diesel engines, which is up to 2000bar / 29,000psi.
I don't think there's any reason to run that high on a jet engine...they don't have nearly the same atomization issues that a Diesel does.
JetMech From Australia, joined Mar 2006, 2587 posts, RR: 53 Reply 3, posted (3 years 5 months 2 weeks 2 days 9 hours ago) and read 5337 times:
Quoting Tdscanuck (Reply 2): I don't think there's any reason to run that high on a jet engine...they don't have nearly the same atomization issues that a Diesel does.
I suppose another reason diesel engine have such a high injection pressure is due to the finite amount of time available in which to inject the fuel. Obviously, such a requirement does not occur with a jet engine.
Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair.
A342 From Germany, joined Jul 2005, 4655 posts, RR: 4 Reply 5, posted (3 years 5 months 2 weeks 1 day 23 hours ago) and read 5249 times:
Thanks for your feedback!
Quoting Tdscanuck (Reply 2): I don't think there's any reason to run that high on a jet engine...they don't have nearly the same atomization issues that a Diesel does.
Well, diesels also started out at much lower pressures, the figures I mentioned are for engines less than ~10 years old.
What really helped diesels in terms of fuel consumption was direct injection, not so much extremely high pressures. But the main advantage is emissions. High pressures DRASTICALLY reduced the amount of PM emissions, and they also enabled CO emissions to drop a bit.
So gas turbine engines have a lot to gain in terms of emissions, especially since catalytic converters and PM filters are obviously not an option in airborne applications.
Quoting JetMech (Reply 3): I suppose another reason diesel engine have such a high injection pressure is due to the finite amount of time available in which to inject the fuel. Obviously, such a requirement does not occur with a jet engine.
True, there is no such strict requirement. However, having the fuel ignite more quickly can't hurt, since it allows you to better control the place where the fuel is burned (in a gas turbine, the hot air flow carries the fuel molecules towards the exhaust during combustion). I admit I have no clue as to how important the added precision would be in terms of combustor design, but I don't think it is insignificant either.
I might add that I do indeed realize how difficult it would be to design, certify, produce and operate a 29,000psi injection pump that delivers the necessary fuel quantities for a large turbofan.
DBCC From Switzerland, joined Nov 2007, 65 posts, RR: 0 Reply 6, posted (3 years 5 months 2 weeks 1 day 22 hours ago) and read 5227 times:
Quoting A342 (Thread starter): I'm asking because I'd like to know how the injection pressure compares to that of modern diesel engines, which is up to 2000bar / 29,000psi.
Sorry, 2'000 bar or 29'000 psi is not used in fuel injection.
Most high pressure hydraulic equipment has a limit of 640 bar (64'000 kpa / 9'282 psi). 6mm x 2 mm wall seamless hydraulic line tubing is rated at 640 bar working pressure with a factor of safety of 2.0.
For fuel injectors, comprise of single-seam welded tubing, mostly with a maximum working pressure of 100 bar.
Have a good search on the net, and you will find most fuel injection systems run at 25-40 PSI (1.7 to 2.7 bar)
At 600 bar, the stream coming out the end of a pipe can cut 50mm (2") solid steel with no problem. Imagine what 2'000 bar could do, if anyone could make equipment that could run at that pressure.
Speedracer1407 From United States of America, joined Dec 2004, 333 posts, RR: 0 Reply 7, posted (3 years 5 months 2 weeks 1 day 21 hours ago) and read 5218 times:
Quoting DBCC (Reply 6): Sorry, 2'000 bar or 29'000 psi is not used in fuel injection.
Most high pressure hydraulic equipment has a limit of 640 bar (64'000 kpa / 9'282 psi). 6mm x 2 mm wall seamless hydraulic line tubing is rated at 640 bar working pressure with a factor of safety of 2.0.
For fuel injectors, comprise of single-seam welded tubing, mostly with a maximum working pressure of 100 bar.
Have a good search on the net, and you will find most fuel injection systems run at 25-40 PSI (1.7 to 2.7 bar)
At 600 bar, the stream coming out the end of a pipe can cut 50mm (2") solid steel with no problem. Imagine what 2'000 bar could do, if anyone could make equipment that could run at that pressure.
I think that if you "have a good search on the net," you'll find that common rail fuel injection systems used in modern turbodiesel engines (as A342 states) do in fact operate in excess of 1500 bar, up to 2000, and have for years.
VW group diesels are in the 1600-1800 bar range. A very simple searched pulled up this Wikipedia list of VW engines. Yeah, it's Wiki, but it may give you an idea.
Bri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4 Reply 8, posted (3 years 5 months 2 weeks 1 day 20 hours ago) and read 5207 times:
These systems use a much lower pressure fuel delivery system to each injector, and typically use a camshaft-driven plunger to pressurize a tiny amount of fuel to the atomization pressure (2,000bar or thereabouts). This is vastly different from the huge flow rates required in a hydraulic system, or those used in a turbofan engine for that matter.
A342 From Germany, joined Jul 2005, 4655 posts, RR: 4 Reply 9, posted (3 years 5 months 2 weeks 1 day 19 hours ago) and read 5202 times:
Quoting Bri2k1 (Reply 8): These systems use a much lower pressure fuel delivery system to each injector, and typically use a camshaft-driven plunger to pressurize a tiny amount of fuel to the atomization pressure
In the case of a unit injector, that's right. However, common rail systems do indeed use one central pump to deliver highly pressurized fuel to the injector.
Still, as you mention, flow rates are very low in comparison to the fuel requirements of large turbofans.
JetMech From Australia, joined Mar 2006, 2587 posts, RR: 53 Reply 10, posted (3 years 5 months 2 weeks 1 day 14 hours ago) and read 5147 times:
Quoting FLY2HMO (Reply 4): Not to mention Diesels produce much much more compression
I wonder what the ratio would be? Reciprocating engines base their compression process on a mechanically dependant compression ratio, whereas gas turbines base their compression process on a pressure ratio. I would be curious to see what the resulting pressure ratio was at the end of the compression stroke of a diesel engine .
GE claims on overall pressure ratio of 42:1 for the GE90-115B at max power. According to Wikipedia, this is "equivalent" to a compression ratio of just over 15:1, which is apparently a typical compression ratio for a direct injection diesel.
Quoting A342 (Reply 5): However, having the fuel ignite more quickly can't hurt,
With a diesel, you want the fuel to ignite as soon as possible to reduce the severity of diesel knock. However, I think this is also dependent on the temperature at the end of the compression stroke as well as the fuel injection pressure.
Quoting DBCC (Reply 6): At 600 bar, the stream coming out the end of a pipe can cut 50mm (2") solid steel with no problem. Imagine what 2'000 bar could do, if anyone could make equipment that could run at that pressure.
No doubt. With diesel injectors however, I suspect that one wants to quickly "spread" the fuel out to promote atomisation, as opposed to maintaining a focussed stream.
Regards, JetMech
[Edited 2009-12-08 18:01:13]
JetMech split the back of his pants. He can feel the wind in his hair.
Njxc500 From United States of America, joined Dec 2007, 218 posts, RR: 0 Reply 11, posted (3 years 5 months 2 weeks 1 day 12 hours ago) and read 5123 times:
Here's a MFR link that states 29,000 psi
Quoting DBCC (Reply 6): Sorry, 2'000 bar or 29'000 psi is not used in fuel injection.
Tdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80 Reply 12, posted (3 years 5 months 2 weeks 1 day 10 hours ago) and read 5101 times:
Quoting A342 (Reply 5): High pressures DRASTICALLY reduced the amount of PM emissions, and they also enabled CO emissions to drop a bit.
So gas turbine engines have a lot to gain in terms of emissions, especially since catalytic converters and PM filters are obviously not an option in airborne applications.
High pressure drops particulates and CO in Diesel's because it atomizes the fuel more, ensuring faster and more complete combustion before the mixture gets frozen by the temperature drop during the expansion stroke. Gas turbines don't have that problem...they hold full pressure all the way through the combustor.
Quoting A342 (Reply 5): I might add that I do indeed realize how difficult it would be to design, certify, produce and operate a 29,000psi injection pump that delivers the necessary fuel quantities for a large turbofan.
It wouldn't be easy, but it's not impossible either. The pump from a big water-jet cutter could probably do the job. In my former profession, we had pumps capable of 22,000 psi at several *barrels* per minute (equivalent to well over 1 million pounds per hour, more than any jet engine ever conceived). These things are, obviously, really big and heavy but it's old technology.
Quoting JetMech (Reply 10): I would be curious to see what the resulting pressure ratio was at the end of the compression stroke of a diesel engine
If you approximate it as adiabatic compression with an ideal gas, the pressure ratio is about the compression ratio to the power of 1.4.
LTC8K6 From United States of America, joined Jun 2009, 415 posts, RR: 0 Reply 13, posted (3 years 5 months 2 weeks 1 day 10 hours ago) and read 5101 times:
Modern Gasoline Direct Injection engines such as Ford's EcoBoost run over 2,000psi fuel pressures.
JarheadK5 From United States of America, joined Nov 2005, 216 posts, RR: 1 Reply 14, posted (3 years 5 months 2 weeks 1 day 9 hours ago) and read 5090 times:
Quoting A342 (Thread starter): What are typical pressures for jet fuel injected into the combustion chamber of jet or turoprop engines?
The GE T64 turboshaft on the H-53 helicopter runs fuel pressures in excess of 400psi.
JetMech From Australia, joined Mar 2006, 2587 posts, RR: 53 Reply 15, posted (3 years 5 months 2 weeks 13 hours ago) and read 5010 times:
Quoting Tdscanuck (Reply 12): If you approximate it as adiabatic compression with an ideal gas, the pressure ratio is about the compression ratio to the power of 1.4.
That's right on the money! 15^1.4 = 44. If we take away a small percentage to account for losses we get 42 .
Regards, JetMech
[Edited 2009-12-09 18:02:05]
JetMech split the back of his pants. He can feel the wind in his hair.
A342 From Germany, joined Jul 2005, 4655 posts, RR: 4 Reply 17, posted (3 years 5 months 1 week 6 days 18 hours ago) and read 4934 times:
Quoting FLY2HMO (Reply 1): BUT the book also mentions that, specially in older types of injectors, pressures of up to 6000psi would be required for proper atomization of the fuel.
Quoting Tdscanuck (Reply 2): 1000-1500 psi is in my head as the typical output from the high-pressure fuel pump
Quoting JarheadK5 (Reply 14): The GE T64 turboshaft on the H-53 helicopter runs fuel pressures in excess of 400psi.
Quoting MarkC (Reply 16): It is about 600 psi. PW modern engines.
Interesting, it seems the numbers vary widely.
Quoting Tdscanuck (Reply 12): High pressure drops particulates and CO in Diesel's because it atomizes the fuel more, ensuring faster and more complete combustion before the mixture gets frozen by the temperature drop during the expansion stroke. Gas turbines don't have that problem...they hold full pressure all the way through the combustor.
Then the obvious question is: What enabled the reduction of PM and CO emissions in modern jet engines? You rarely see much visible smoke coming out of modern engines, like it was common with turbojets and early turbofans.
Quoting Tdscanuck (Reply 12): These things are, obviously, really big and heavy
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