Vincent

My Feedback: (61)

I would not run diesel in my jets due to my experience in the petroleum service industry (35yrs now). Diesel has a higher viscosity and is no where near as clean as K1. Diesel pumps use special filters for diesel fuel and it has a tendancy to "gel" in colder weather. Kero never has this problem and winter blends of diesel have some kero added to lower the viscosity for winter use. No doubt the motors will run on it for short term but i would really be concerned running it full time. If you do then make sure your filters are serviced on a regular basis and maybe run some kero thru the system to "clean" it on occasion.BTW the diesel smell isnt my fav either...[:@]
Vin...

John Redman

My Feedback: (8)

Hi Gaspar,

I appreciate your input and was not aware of your closed loop operation within your ECU. I have not noticed a post from you towards me regarding this in the past years. I am sorry for that. I do appologize for the misinformation. I do know you are running for a large amount of manufacturers which is great. Because of you the turbine community has grown and advanced. Thank you for that.
As we know the only way to increase thrust is to do one of two things, increase temperature at a given rpm or increase rpm. If the temperatures and rpm's are the same, there cannot be a gain in thrust.

It is good to hear there is a difference in pump operations. My numbers were only off the comparison or numbers from the msds and chemical sheets. Agreed that each pump can deliver different performance. These little items are still one of the more antiquated parts of our systems. Maybe one day a change to brushless motors within our pumps will help this, maybe not.
Thanks for the input Vin.

So Barry, if I call you up does this mean I can get a K-170 for myself? If so I will call after California Jets.

Come to Kentucky Jets Highorse and we will have a few beers. Might be a late night but a hell of a lot of fun!!!!!!

You guys have a good time at California Jets, I have to go to Georgia for SEFF.[:'(]

marquisvns

No, but thank you for your interest!

Cheers,
Barry

marquisvns

Thank you for this important information Vincent, if my research is correct, it seems very safe to operate diesel at 25F or -4C and above.

Barry

marquisvns

Gaspar, John and those who might be interested in the subject of diesel versus kero on pump load,

I have done multiple tests on different days and times of days ranging from 62F to 85F ambient temperatures. The results have been very consistent, with 10 to 12% less pump load (or PW) on burning diesel versus kero during idle and about 5 to 7% less with diesel at full throttle, while EGT being constant (about 1% lower with diesel). Therefore, it is reasonable to assume running diesel is more fuel efficient, at least with KingTech engines, and it is an excellent choice of fuel.

Above results have been consistent to those from the factory. Gaspar, could you tell me your ambient temperature when you were doing the comparison? I wonder if it was substantially lower...? Also wondering why the lack of increased thrust from your testing with diesel, perhaps is the different formulation of diesel fuel between Spain and North America??

Regards,
Barry

Delta Mike

My Feedback: (18)

Barry explain how you can get a increase in Thrust using diesel fuel.. Am I missing something here? Doesn't the RPM of the turbine determine thrust? If your ECU settings stay the same for the MAX RPM, then where does the increase in trust come from when using diesel fuel over JET A?

Dennis

Eddie P

My Feedback: (4)

Maybe I can give a layman's perspective on this. I'm not saying I'm right on the money but this is how I understand it and anyone like Gaspar who might be able to correct me please do so, I'd like to know for sure myself.

Turbine engines have two major operational limitations. RPM and Temperature. One can set thrust pretty closely by RPM, but not exactly. One can even set thrust by temperature, but again not exactly and probably not as closely as using RPM due to variable levels of wear and tear in the temp probes. But you can set thrust using each one of those to variable levels of accuracy and that gives us insight to what's going on inside a turbine.

RPM is a secondary thrust measurement value really - the true measurement of thrust is the pressure ratio between inlet and exhaust pressure, and that brings the chemical reaction of the burned fuel into the equation along side of the basics of the engine RPM. So the specific energy of the fuel comes into play - in addition to spinning the turbine and the compressor wheel it's adding dynamic mass and acceleration (force) to the exhaust. A "good" engine and "good" fuel can make more thrust at the same RPM than an identical model "sick" engine, for example, or one with "mild" fuel contamination.

In many full size jet engines, "EPR" (engine pressure ratio) is used, as a cockpit display (often), but always by the engine control unit directly, to measure and control desired thrust. Some engines (some P&W's for example) use N1 or "main rotor RPM" as a primary thrust setting indicator for operational simplicity. A known down side to this (splitting hairs on a normally decent day) is the fact that a certain N1 or rotor speed is not always giving an exact measured thrust. On a bad day, simply setting an "N1" without good situation awareness can get you nowhere close to the thrust setting thought to be set. But that's beyond the scope here. Where as, a specific "EPR" setting (for the many engines that use EPR as the primary thrust setting indication) is in fact giving true thrust -EPR is EPR, and that means specific thrust.

So, N1's, or rotor speeds, are widely understood to be capable of small variances for a given actual thrust achieved in normal operations.

This is not to confuse the above with the simple case of a difference in density altitude. For example, on a hot day at 150K (let's say that's the Max RPM on the model engine ECU) you may get 25 pounds of thrust. And on a cold day at 150K, you may get 27.5 pounds of thrust. (Assuming you don't reach the EGT limit first in either case). Or on a hot day on an older engine you may reach the EGT limit at only 147K, and have just 24 pounds of thrust. Again, this is a little different than the question of a different fuel chemistry giving more or less thrust to an engine.

So, engine thrust on a specific day, temperature and altitude is not specifically dependent on specific rotor RPM, though it is very closely linked. It is reasonable to expect minor increases (or decreases) in thrust (or EPR) at specific RPM for either environmental reasons or chemical reasons (diesel).

highhorse

My Feedback: (2)

Great Q Dennis, and if the above explanation doesn't do it for you then please let me try, in simpler terms that help me, anyway: For recips it's intake, compression, power, exhaust. Turbines= Suck, squeeze, bang, blow.

The thrust isn't "made", if u will, by the rpm. Rpm does the suck and squeeze part (nit pickers hold ur piece, we are NOT talking about high bypass engines), but the amount of thrust can be enhanced by a "higher calorie" fuel, which gives more bang and blow at the same level of suck and squeeze (RPM). Diesel fuel has more calories than Kero and JetA, and more energy is released when it's burned. That extra energy makes for more bang, which makes more blow(aka Thrust).

Hope that helped?

Don.

Eddie P

My Feedback: (4)

Don, what you laid out there was a thing of beauty. Way better than my try [8D]

highhorse

My Feedback: (2)

LOL, I try to 'splain things at my own level......where if I can get it then ANYONE can

Gaspar

Sorry, no, not true. We are talking of gas turbines that work on the Brayton cycle here, not piston engines.

If the fuel have more specific heath, then at same mass of fuel burned will produce more heath. This heath will increase the temperature of the air on the intake of the turbine wheel, expanding it. This expanded gas will make the turbine wheel to spin faster, and at this point the ecu will "see" that there is more rpm than maximum and will reduce the mass of fuel to restore the correct amount of heat so that the turbine wheel turn at the correct speed.

Anyway, I can think of 2 possibilities of that a different fuel make different thrust, but hardly applicable our engines. One is that the thrust of a engine is the mass flow in the exhaust (grams of air trough the exhaust of engine each second) times the exhaust speed. The massflow at the exhaust is the addition of the weight of the intake air added to the weight of the fuel burned. So using a heavier fuel with less heath capability will increase the thrust at the expense of a higher fuel consumption by weight. But to put thing on perspective, a engine of 90N of thrust use 210gram of air and 4,4g of fuel each second, so doubling the weight of fuel used it would increase only a 2% the thrust. The second possibility is that there is some unburned fuel past of the turbine wheel that burn in the exhaust, making a sort of reheat, out of the control of the ecu, but this would seem to me a remote possibility.

About the pump power between the diesel and kerosene, my particular experience is that the pump worked harder on my test. Diesel, at least here, is thicker than kero, so the pump should work harder to have it trough the engine injectors. Could be that a engine with bigger diameter injectors be less sensitive to thickness of fuel, and this, coupled to the less mililiters (not grams) of fuel needed for same heat, be unnoticeable by reading the pump power.


Gaspar

highhorse

My Feedback: (2)

Gaspar, thanks for bringing the weight of your experience to the discussion. My comparison between reciprocating and turbine engines was an illustrative one and not meant as a literal correlation.

In the simplest terms possible (so that myself and others who are in over our heads might follow along), I'm hoping you can address two things:

1) Why DOES then, as reported by two seperate and presumably credible sources here in independent tests, Diesel produce more thrust than Kero?
2) With regard to exhaust gas expansion -vs- RPM and your statement that one equals the other (please forgive me if that was not your assertion), are you certain that it's a 100% efficient conversion from one to the other at the turbine wheel? In an Open Brayton Cycle (vs closed cycle) engine, must 'X' % more heat heat energy released result in 'X' % more RPM and a corresponding reduction in fuel flow as commanded by the ECU, or might there be some degree of increase in exhaust velocity that "slips by" or "slips through" the exhaust turbine? Is it not true that only 'some' of the energy added by the combustor is then extracted mechanically by the turbine wheel, and that is why the pressure at the exhaust remains higher than the pressure at the inlet (resulting in thrust rather than mechainical energy)?

Thanks again, Don.

highhorse

My Feedback: (2)

Seems to me that as interesting as the theoretical stuff can be in it's own right (at least I think it's fascinating) , what we need is for more folks with reliable measuring equipment to do their own tests and report back here with some answers regarding the following:

1) Does Diesel make more thrust than kero in a given engine during repeated, back to back runs?
2) What were the exact fuel flows, in terms of both weight and volume, at max thrust during those runs?


After all, the only thing we really care about at the end od the day is how much thrust we get and how much weight in fuel we need to carry around to make that thrust, right?

Oli, weigh in any time here my man. You guys at RCJI have always done a bang-up job at this stuff, so how about it? Please?

Eddie P

My Feedback: (4)

I'm interested too, and we haven't really gotten down at all as to the "why or how" of it here yet. Sounds like a project from the ancient past, of my old university "propulsion" classes I've forgotten more than I learned about. But over time we may get more "anecdotal" evidence as to thrust values but it will be just anecdotal until some sort of accurate testing can be done. As with all things, the devil is in the details.

marquisvns

Here's an update on KingTech Diesel Start development,

http://youtu.be/goCMZM6Jv9Q

Had about 10 flights at Van Nuys yesterday with flawless diesel starts by using a 7 cell NiMh pack at 4500mAh,

http://www.hobbypeople.net/index.php...-trx-conn.html
$40 each from us.

Sorry about the blurry ECU, totally over estimated the depth of field

Barry

http://youtu.be/goCMZM6Jv9Q

megafly

Ji, I read the entire pots, I'm new to turbines and I have a Kingtech K80 propane start, I'v only flyed on Jet fuel with turbine oil, but, my father want to see my plane fly, we have a Piper Mirage, and I'm not alowed to transport the fuel for jet in the plane, but in our farm we have a lot of diesel, I don't know if it's a pure diesel like you guys have in the USA (I'm from Brazil). I told him I canot fly the jet there because I have no fuel, but after this, I'm thinking I can.
Can I run my turbine with diesel wellll filtered? Because I really don't know if the diesel is pure like yours, we use for trucks and work in the farm. But I will use for like 10 fights, and them back to jet fuel. can I do that?

That's our runway



Sorry for my bad english, But I'm learning, and I'm posting know after manny years!!!! I'm very happy I can talk to you guys!!!!


Thanks.

jblloyd

My Feedback: (17)

Barry - Are you saying that the "F" versions can nowrun diesel? According to the specs on your web site,only the "E" versioncanbe runondiesel fuel.

mavrick

My Feedback: (1)

HI Mate
Yes you can I have been running diesel in my K80E for 2 years now and in my kero start 140F & 170F I run 50/50 diesel and jetA no prob's at all and with a longer fuel burn.
Regards
Mav

marquisvns

Yes, F series is now Kero/Diesel start and running engines. One thing to note, when using 7s NiMh pack the solenoids get a little hotter at this voltage, make sure you safety wire solenoid connections, don't want the heated barbs to soften tubing too much.

I have been doing torture tests on solenoids (since they were designed around 6 to 8 volt), powering it with 3s LiFe, which is about 1.5v higher than 7s NiMh and have not been able to burn one shut. I had one connected 1 hour straight last night, and tonight 5 hour straight and still works fine. In real life, the fuel solenoid will most likely be on no more than 15 minutes per most flights and with cool fuel running through it during most of the time.

Barry

megafly

Thanks! As for the battery I'm using a LIPO 2S is that OK?

marquisvns

No, please do not use 2s LiPo to Diesel start, it simply doesn't have enough voltage to provide consistent starts. For those who are having difficulty kero starting their KingTech, I would also recommend giving this 7S NiMh a try.

Thank you Megafly, that's a beautiful field you have there.

Barry

jblloyd

My Feedback: (17)

Although a 7S NiMh pack working voltage is 8.4v, a freshly charged pack can deliver as much as 10..5v.  If the ECU and valves can handle this high a voltage, could you not use a 9.9v 3s LiFe?

marquisvns

Very good question John, NiMh will peak at around 10.5v but deplete easily down to 9.9 or 9.8 soon after the charger is unplugged and then some more for the next day's flying. It'll have a good flat overall curve around 9V, which is why I would recommend charging it at Pb (8v lead acid) mode that peaks only at 9.8V. I think 3S LiFe will have an over all slightly higher voltage, I will do some testings on the 3S LiFe as well.

Barry

marquisvns

This is why I choose to use 3s LiFe to torture test the solenoid valves, at a higher voltage.

marquisvns

Here's another option for you to still operate the ECU with 2s LiPo but jump start with a higher voltage pack during the start up. This was the config that I did the flights at van nuys the other day, obviously after some liquid tape to insulate.

Barry