RD-93 Engine: Strength or Weakness?

[Munir]

Maybe it is not the engine lack behind but the engine that is designed to be a lot simpler... RD93 is extremely simple and rugged engine. RD93 is a lot more tuned with FADEC. You can make it better and better but you need better and better quality control and maintenance... The Russian chose the simplicity and rugged engine. The Americans selected superb thrust.

 

[Sinnerman108]

@niaz,

Could you please be kind enough to explain then why the russian aircraft were smokeless and and the americans smoked during the 60's and 70's----.

Because I am getting a totally different picture from the chemical engineer who analyzed the russian fuel obtained from the defecting libyan aircraft into israel during the 70's---.

The russians already had smokeless engines in the 60's 70's ---- the issue is that what is it now that they are giving out smoke---and the american engines that produced a lots of smoke in the past are smoke less now!

The fuel's grade / quality dictates the length of C-C bonded chains.

The longer the chain, the more difficult to burn; engines are tweaked ; specially the atomizers are tweaked for a very specific range of C-C chained fuel.

This explains what your chemical engineer friend is saying ?

As for why the American engines stopped smoking.... maybe they started using digital air flow sensors around that time ..

 

[niaz]

In order to assess whether the smoke in RD-93 engine is due to the fuel or engine design, we need to look the fuel quality and engine separately.

I am a chemical engineer myself and a Senior Member of American Institute of Chemical Engineers. Having worked in oil refinery, I know a thing or two about manufacture and quality of aircraft as well as automotive fuels. Let us discuss jet fuel first.

Any refinery engineer will know that producing jet fuel is rather straightforward as compared with the catalytic reforming (gasoline production) and fluidized Cat Cracking processes. I have produced Jet fuel in my days as a process engineer way back in the 1970’s.

Per the latest Def Stan specs, Jet A-1 fuel has maximum boiling point of 300 C. Density between 0.775 & 0.840. Flash Point of 38 C Min., Sulphur 0.3% max., total aromatics 26.5 % max. Smoke point 25 mm Min or 19 mm Min with naphthalene 3.0% Max. Freeze point min -47C, Viscosity at -20 C 8cst Max., total particulate matter max 1mg/litre. There are many others specs as well such as JFTOT for thermal stability.

You would notice that Sulphur at 3000 ppm is much higher than the current automotive diesel spec in Europe which is down to 10 ppm for ULSD. During my time as a process engineer, we only treated Kerosene fraction (from 150C to 270 C boiling range) through the Merox unit which converts foul smelling Mercaptans into odourless sulphur compounds without actually removing the Sulphur to produce Jet fuel. This was because minute amounts Sulphur improves lubricity of the fuel and produces less electrostatic when it sucked into the engine at very speed.

Let us be clear that Sulphur does not produce smoke; it produces SO2 which is a colourless gas with a pungent odour.

European Aviation Safety Agency (EASA) ordered a study in 2010. Higher sulphur content certainly produces larger amount of particulate matter in the exhaust. With respect to aircraft engines, it is not clear whether there is a reduction in particulate mass with reduced sulphur content. However, tests made in the automotive industry show that the number of sub-10nm particulates decreases significantly with decreasing fuel sulphur concentration. It is expected that Sulphur limit in Jet A-1 will be reduced significantly by 2025

Paraffin hydrocarbon fractions that constitute Jet A-1 burn much better and produce less smoke. Aromatics & Naphthalenes in the same boiling point range (150 -270C) produce far more smoke. Hence there is a limit on aromatics & naphthelens also a minimum Smoke Point limit.

FYI Smoke Point is the length of the wick in a standardised lamp beyond which kerosene starts emitting lot of smoke.

Now let us come to aircraft engines.

In a pure jet engine (with no by-pass), all the air taken in is passed thru the engine core. Thus pure jet designs require high pressure and temperature because they produce thrust by expanding exhaust gas through a nozzle.

On the other hand in turbo fan engine (RD-93 is a turbofan) part of the air skips the core and is ‘by-passed’. The gas turbine component produces a large net positive power output (power produced minus the power utilised by the compressor). This excess power drives a ducted fan that rearward accelerates air from the front of the engine.

By pass ratio or BPR is the ratio of the cold stream flow (which passes through the by-pass duct), to the hot stream flow (which passes through the engine core). Actually only a small fraction of the hot stream (core flow) is actually used in combustion, but it all passes through the turbines.

Turbofan designs can be high bypass ratio or low by pass ratio.

Turbofan designs pass combustion air through the ducted fan first before passing into the compressor stage. Thus there are two exhaust velocities, one of the air passing through the core and second of the air passing through the ducted fan. Therefore optimizing a gas turbine engine for shaft power output minimizes the exhaust pressure and temperature. As a rough rule high bypass is a turbofan engines are found on modern commercial airliners. It has good fuel consumption and difficult if not impossible to go supersonic.

Low bypass turbojet engines are found in fighters. Poor fuel consumption at low altitudes, better than turbofan at higher flight levels. Good for supersonic flight. Thus all fighter designs are a compromise between high thrust and fuel consumption and power out-put at subsonic, transonic and supersonic speeds. A lot of modern fighters use the bypass air to "augment" the afterburner.

All fuels whether supplied in Ethiopia or at Karachi or New York must conform to the Def Stan specs. It is therefore logical to conclude that given the same fuel input, say in F-16 and in JF-17; it must be the engine design of the Thunder that is the root cause of more visible smoke.

Finally, I admit that I have weaknesses and my judgments are not always 100% correct. I have seen a Rolls Royce Spey Engine opened up in bits and discuss various aspects with the engineers at the overhaul & repair facility in East Kilbride; thus I think I have a good understanding of the working of a jet engine. Nevertheless I ask forgiveness from the hard core aeronautical engineers if my post is not quite up to the mark.

I have little else to say on this subject.

 

[Mughal-Prince]

View attachment 33781

May be by mistake they put diesel in the plane...lol...but older engine had some trail issue...but not that much...

OK Guys I just put up an image but didn't write any thing here ...

These images are not not seems to be Photoshoped cause I am myself a Photoshop expert and a graphic designer for 20 long years and I said that because I have seen these Mig image years back I dont remember. These are the Migs with very basic engines or early age of RD-33 and yes did any one noticed that the image I have posted and another image which is posted by Haider has one thing in common except smoke and that is both are flying low and seems to be in a certain throttle level about which @niaz and some other members has pointed. Now without going in deep analysis which already quiet experienced members has already discussed I would say the newer engines are better and these are less smoky engines.

 

[Irfan Baloch]

Hi,

Thanks for talking about the rd 93----smoke is not a big issue at all---the phantom was a smokers dream---it did no harm to the reputation or the ability of that plane. The plane flew right to the end with smoke coming out through its twin pipes---.

Fighter jet engines are the most difficult engineering ventures that you can ever come across---once the upgraded versions of this engine get close the the thrust of comparable american engine---it will give a big boost to the plane.

Now coming down to the life span---paf has always done a great job at squeazing the most life out of any jet engine in its service---rd 93 will be its biggest challenge in the next 5 years.

I wonder
how easy or difficult it is to commission a US jet engine making company like Boeing, GE or Pratt and whitney to get an existing and suitable engine or request to make one on the rolling basis?
hoping that US administration gives the nod and gives a go ahead to US engine manufacturers

this would just boost its prospects.

 

[VCheng]

I wonder
how easy or difficult it is to commission a US jet engine making company like Boeing, GE or Pratt and whitney to get an existing and suitable engine or request to make one on the rolling basis?
hoping that US administration gives the nod and gives a go ahead to US engine manufacturers

this would just boost its prospects.

That would be a complex undertaking on many levels, and darn near impossible in the present climate.

 

[Irfan Baloch]

That would be a complex undertaking on many levels, and darn near impossible in the present climate.

I agree and will increase the cost too. even when the political climate is friendly

 

[Munir]

These are ex East German Migs that were upgraded to NATO cockpit and then given away to Poland. The engines are the old RD33. So the smokey ones. Seen them dozens time. In action and on the tarmac. Nothing strange. This is the way they burn fuel. No Fadec...

 

[Chak Bamu]

These are ex East German Migs that were upgraded to NATO cockpit and then given away to Poland. The engines are the old RD33. So the smokey ones. Seen them dozens time. In action and on the tarmac. Nothing strange. This is the way they burn fuel. No Fadec...

I thought RD-93 had DEEC. You seem to be saying that RD-93 has FADEC. Is that so? If so, when did that happen?

 

[niaz]

Unlike airline engines where RPM, pressure and temperature limits are not much of a secret, warplane jet engines design limits are well guarded secrets.

Laws of thermo dynamics dictate that getting more power & thrust from an engine without increasing the size would require higher temperature & pressure inside the burning chamber.Unless one use a pure ramjet, maximum pressure generated in the HPT (high pressure turbine) just before the compressed air enters the burning chamber depends upon RPM which in turn depends upon tensile strength of its blades. RPM in excess of 10,000 and temperatures in the 1500 Dec range are not uncommon. Thus excellent thermal stability, good thermal fatigue resistance, good oxidation-resistance & relatively low expansion characteristics and should also be easy to weld with dissimilar alloys are essential requirements for the materials used in a modern aircraft jet engine.

As a very rough guide, about 25% costs of the aircraft is its engine and propulsion system. To the best of my info modern aircraft engine components are made up of Nickel, Cobalt, Chromium & Titanium alloys such as Hastelloy or Nimonic alloys. Understand that 5th generation aircraft engines use a lot of Rhenium (symbol Re). Re melts at 3000 Deg C therefore its alloys can sustain higher temperatures. All of these are very expensive and to be used judiciously.

Aircraft engine manufacture; especially for hypersonic speeds; is highly specialized and sophisticated subject and a good Aeronautical Engineer could write several dissertations on it. For the purpose of this thread, I restate my earlier opinion that an engine design must be a compromise between thrust output, size, weight and cost. RD-93 is a proven reliable engine and unless China can come up with a better alternative, which is also not too expensive; we have to live with it.

 

[IND151]

Although the engine has come under a lot of scrutiny from Pakistani quarters, the main aspect has been over performance issues. The engine is considered to be smoky & under-powered, while reliability has also been expressed as a point of concern. With a presumed low TBO (Time Between Overhauls) the type has been stated as a weak-point.The RD-93 is actually superior to all PAF service engines except the F100 series of the F-16 (however, it does have better response cycle to turbulence & dust), & is more fuel efficient, quieter, & reliable (as well having a longer lifespan) than the Atar 9C (Mirage III/5), WP-7 (F-7P) & WP-13 (F-7PG) in PAF service, all being turbojets & not comparable. The RD-93 itself actually would save the PAF on fuel & logistics, being economical to acquire & operate. It also offers much more thrust & efficiency than even the F100.
Its main weaknesses remain the smoky nature of the engine, & low-lifespan compared to the F100. Other weaknesses can be found in its design. Though not low on thrust (it is actually lighter than the Atar 9C & saved 400kg on South African Mirage F.1s during fits) the type is optimised for the twin-engined MiG-29. One possible solution is to produce the RD-33MK/MR (Naval) standard, with 19,400lb reheat coupled with weight savings on the FC-1.What appears to be unmentioned is that the RD-93 is much more powerful than the European RD199 (Tornado F3) & much more durable than the M53 (Mirage 2000) & is much better performing than both at high altitudes or turbulence. It also beats the F100 in such conditions. It's also designed for rapid repair & field maintenance & contrary to popular belief is not a thirsty engine. Though less durable than the F404 or PW1120 series (its US equivalents) it is actually more responsive to bird-strikes, & FOD.The next phase of RD-93 development would focus on enlarging the blades of the fans (much the same way as the EJ200 or M88 & some re-designs around the engine. This should make it a revolution (as opposed to just an evolution) of the basic design, & may well go beyond 22k at reheat. Coupled with reduced FC-1 weight, this would equalise the F-16C/D with uprated PW F100-229E engines, (note: the F-16C/D is heavier & less agile) & the possibility of super-cruise.My hope is that the Chinese can develop a suitable replacement but in all honesty as this rate they aren't doing too well. The WS-9 (Spey 202 copy) has the power but consumes more fuel & is too big & heavy, where the WP-14 is too under-powered & thirsty (being a turbojet) so improvements to the RD-93 is the only way to go.

First FC-1 is:

14,134 lb (Empty)
20,062 lb (Fueled + Two Wing-tip missiles)
28,000 lb (Max. Take Off Weight)

5,130 lb of fuel



Comparison of engines: (Note: fuel consumption of the Eurocanards haven't been given yet but are lower than both the RD-93 or F404).

RD-93:
- Dry weight: 2,325 lb
- Military Thrust 11,230 lbf
- Reheat Thrust 18,285 lbf

Specific fuel consumption:

0.77 lb/(lbf·h)) military thrust
2.05 lb/(lbf·h)) with reheat


F404:
- Dry weight: 2,282 lb
- Military Thrust 11,000 lbf
- Reheat Thrust 17,700 lbf

Specific fuel consumption:

0.81 lb/(lbf·h) military thrust
1.74 lb/(lbf·h) with reheat


M88:

- Dry weight: 1,978 lb
- Military Thrust 11,250 lbf
- Reheat Thrust 17,000 lbf

Specific fuel consumption:

??? lb/(lbf·h) military thrust
??? lb/(lbf·h) with reheat




EJ200:

- Dry weight: 2,180 lbs
- Military Thrust 13,500 lbf
- Reheat Thrust 20,250 lbf

Specific fuel consumption:

??? lb/(lbf·h) military thrust
??? lb/(lbf·h) with reheat

M53P2:

- Dry weight: 3,340 lbs
- Military Thrust 14,300 lbf
- Reheat Thrust 21,384 lbf

Specific fuel consumption:

0.92 lb/(lbf·h) military thrust
2.15 lb/(lbf·h) with reheat


Perhaps most surprisingly to some, the RD-93 is actually more efficient than the F404 on military thrust but on military thrust despite being thirstier, it's still more efficient from a combustion standpoint. Therefore the RD-93 on merit, but the EJ200 is the best power-plant & the M88 is competitive but just too under-powered.

??????????????

F 100 has thrust of 13,226 kg while RD 93 offers thrust of 8,400 KG.

 

[Asian.Century]

Air Cdre Khalid Mahmood, chief executive of JF-17 sales and marketing. adds that the air force is satisfied with the fighter's Klimov RD-93 engine. The powerplant can currently be operated for up to 800 flight hours MBTO between overhauls, but there is an effort under way to improve this.

AIRSHOW CHINA: Pakistan outlines JF-17 upgrade activity - 11/12/2014 - Flight Global

 

[niaz]

Trouble in Pakistan is that most of us think with our hearts not with our heads. These days Chinese equipment is in vogue. Hence we would like Chinese engine in the JF-17.

China is no doubt fast catching up but in some fields it is still far behind. Aviation engine technology happens to be one such field. Klimov RD-93 is a derivative of the well-established RD-33 engine with proven reliability & useful life of about 4,000 hours. Nevertheless many honourable members would prefer newly developed unproven Wopen engine.

Apart from considerations of performance & cost; an unproven engine poses a serious danger to the pilot as well. PAF are happy with RD-93, must we insist on its replacement with a Chinese built engine

 

[AZADPAKISTAN2009]

Yes need to move with new engine , the engine needs a major update and upgrade

 

[MastanKhan]

S

Yes need to move with new engine , the engine needs a major update and upgrade

Sir,

Engine is fine----F 14 spent all its life on a supposed less potent engine----so did the F 18 for many a years----. The focus should be on production now.