Aviation Fuel

[VicParticipant @vic]

I found this interesting.

https://www.quora.com/Did-the-B-36-use-the-same-kind-of-fuel-for-both-its-piston-engines-and-its-jet-engines/answer/Rebecca-Williams-1128?ch=17&oid=1477743796709635&share=856b7f44&srid=o2Ve8&target_type=answer

Edit: There was a film called Strategic Air Command that had lots of good footage of this aircraft and its successor in it.

[JAParticipant @ja]

Interesting – before my time in the aeroengine industry.

Just to explain conventional jet engine fuel (given I retired 15 years ago)-

1. AVTUR (JP1, JP8, Jet-A) – the common fuel. It is paraffin (kerosene) but somewhat dirtier than domestic paraffin.

2. AVTAG (JP4, wide-cut) – A fuel intoduced by the Americans in the late 1940s as a reserve for JP1. It is very similar to petrol (gasolene) and was widely used up until 1980/90s when it fell out of favour because of its volatility (fire risk). However it is still used in cold climates since it gives easy starting in the cold. This would not have contained lead.

3. AVCAT (JP5) – A less volatile fuel used on aircraft carriers.

4. The standard Russian fuel is between AVTUR and AVTAG.

A number of additives are used such as anti-static and biocides.

Other fuels have been used such as Boron based fuels (poisonous and never introduced) and high density fuels.

JA

[SillyOldDufferModerator @sillyoldduffer]

Not sure being able to run piston and jet engines on the same fuel was a good idea or not!    The combination gave the aircraft long-range, but also made it vulnerable to the much faster jet interceptors that were appearing at the same time.  Obsolete before it flew!

The B36 has a fascinating history, and was highly controversial at the time.

Many, many problems, such as ‘Normal maintenance consisted of tedious measures, such as changing the 56 spark plugs on each of the six engines which were often fouled by the lead in the 145 octane antiknock fuel required. Thus, each service required changing 336 spark plugs.’   The plugs were difficult to access, and because the B36 was too big to fit into a hanger, maintenance work had to be done outdoors, no joke during an Alaskan winter!

Dave

[Robert Atkinson 2Participant @robertatkinson2]

Gas turbines “jet engines” can be made to run on just about anything that will burn. That inludes gases and powders. The normal fuel these days is kerosine (paraffin) based. This is called Jet A (-40 degree freeze point  or JetA-1 with additives to give -45 deg) in civil use. In the 60’s and 70’s Jet B was common. Jet B is a wide cut fuel with components coving low grade petrol to light kerosine. The advantage of this was cost and lower freeze point but it is more volatile and more of a fire hazard if there is a leak or accident. Funnily enough it is less likely to cause a in-tank explosion like TWA Flight 800 because the mixture is too rich.*
Jet B is now only used in very cold climates.
Naval aircraft in the UK use a light diesel type fuel called AVCAT. This is safer and is a common fuel for other diesel powered equipment like tugs and generators.
Most gas turbines will run on petrol or diesel without adjustment. One issue is lubrication of high pressure parts. Some engines specify the addition of small quantities of oil if using petrol.
I run my small engines on Jet A1 when I can get it. Unfortunatly because it is unmarked, low tax fuel most sellers will only deliver it directly to an aircraft or ground support equipment. In theory they can charge you the tax but it’s not worth the trouble to them for a few gallons. When Jet A1 is not available a mix of 95% diesel, 4% unleaded and 1% turbine oil works well.
I’ve seen small engines converted to run on sawdust and powdered coal.

Robert.
* aircraft fuel tank ignition prevention is part of my day job.

 

 

[JAParticipant @ja]

Running ground based and locomotive gas turbines on coal dust was the “holy grail” in the 1940s. All attempts failed due to traces of Vanadium in coals that alloyed, distructively, with turbine blade materials. The history of Parson’s attempts was reported recently by the Newcomen Society.

Another absolute nasty in gas turbine fuel is Sulphur. This burns to produce SO2 & SO3. The ratios depend of the pressure but, I believe, SO3 can be the dominant oxide.

One comment, in the UK, and probably through out the world, aviation fuel is not taxed! This led to some interesting difficulties at work with blended fuels (don’t call the fuel diesel).

JA

[Robert Atkinson 2Participant @robertatkinson2]

Aviation fuel is now taxed depending on usage. This is particuarly tricky for jet fuel. Normally it is fully rebated but if used for private pleasure flying duty is payable. So if somone uses a turbine engine aircraft for business no tax. If they then take a private flight they are supposed to pay tax on the fuel used for that flight… AVGAS i taxed at about 38p per litre.

Robert.

[Nigel Graham 2Participant @nigelgraham2]

Interesting thread!

The six engines in the B36: with 56 plugs per engine how many cylinders? 14 with 4 plugs each?

I would have thought coal dust would be more damaging by releasing tiny particles of grit, to erode the turbine blades. Presumably the nozzles and associated pipework would have to made to cope with coal-powder, but this was established at larger sizes in power-station boilers using pulverised-coal burners.

In these enormous water-tube boilers, according to my text-book, the flame temperatures are up around 300ºF (about 1650ºC); but that might not apply in a pulverised-coal turbine.

Aren’t the sulphur oxides are more problematical outside the engine, producing sulphur -ous or -ic acid when dissolved in water?

[Nigel Graham 2]

On Nigel Graham 2 Said:

Interesting thread!

The six engines in the B36: with 56 plugs per engine how many cylinders? 14 with 4 plugs each?

 

No, 28 cylinders with the traditional 2 plug arrangement. It’s a radial with four rows of 9 cylinders.

[duncan webster 1Participant @duncanwebster1]

Engines had 28 cylinders each, twin row 14 per row. It’s no wonder jets replaced them, 168 cylinders on each aircraft. They were also set behind the wing in pusher configuration, and tended to catch fire, which must have been disconcerting to say the least

[simondavies3Participant @simondavies3]

I seem to remember that the reasons for the combined engine types were:

• reaction times – winding a first generation jet from tick-over to full chat was less than instantaneous and not without risk, whereas a piston engine had a much reduced reaction time – and hence could cope with e.g. aborted landings requiring ‘instant’ power
  • fuel consumption – the 1st generation jet engines were thirsty beasts, so the logic was to use the piston engines to do the heavy work and switch to the jets for the high altitude cruising where they were more efficient and didn’t suffer from air starvation that the piston engines had to cope with.
    Once better consumption came along, there was no logic in dragging a load of part-used piston engines adding weight and drag (if there was in the 1st place!)

I’m sure others on here are better able to confirm/deny these assertions and add colour…

Simon

[duncan webster 1Participant @duncanwebster1]

According to Wikipedia, the jets were only used for short bursts to increase speed over the target, the early versions didn’t have jets at all. The jets were fitted with shutters to reduce drag when not in use.

[Andy StopfordParticipant @andystopford50521]

Here’s a look around and inside a B-36:

The piston engines were P&W R-4360s, 4 rows of 7 cylinders, and probably represented the limits of what you could do with pistons:

https://en.wikipedia.org/wiki/Pratt_%26_Whitney_R-4360_Wasp_Major

[duncan webster 1]

On duncan webster 1 Said:

According to Wikipedia, the jets were only used for short bursts to increase speed over the target, the early versions didn’t have jets at all. The jets were fitted with shutters to reduce drag when not in use.

I suspect that the jet engines were used to run away after dropping its bomb or bombs. The penulimate batch of aircraft included one modified to carry a nuclear reactor (these were the days that nuclear powered jet engines made sense).

As for Sulphur we talking about chemistry at high temperatures where the oxides attack the turbine NGVs and blades. Water is present as a product of combustion. Certain environmental elements such as Sodium (from sea water) increase the rate of attack.

JA

[Andy Stopford]

On Andy Stopford Said:

Here’s a look around and inside a B-36:

The piston engines were P&W R-4360s, 4 rows of 7 cylinders, and probably represented the limits of what you could do with pistons:

https://en.wikipedia.org/wiki/Pratt_%26_Whitney_R-4360_Wasp_Major

That makes more sense, I thought 14 in one row was a lot

[Robert Atkinson 2Participant @robertatkinson2]

Always an odd number of cylinders per row in a radial engine with master rod design.

A British aircraft with mixed engine technology was the Shackelton Mk3. This had a pair of Viper turbojets on the wingtips to improve the take-off perfomance. The Viper was designed as a expendable engine for drones and in this apllication had a 5 minute limitation at full power. There was at least one case of a Shacklton returning from patrol using the Vipers following multiple failures of the main Griffon piston engines. When the alternative is ditching you don’t worry about things like engine life.
You get some odd satistics with the Mk3 6 engines and 8 propellers for a start….

Then there were nuclear jet engines. The combustion chambers on an existing design of gas turbine aircraft engine were replaced with heat exchangers. Molten Sodium from a Sodium cooled reactor was circulated through the heax exchangers. That all worked but the weight of the reactor shielding was a problem even when limited to putting the crew in the “shadow” of the shield.

Robert.

[Nick WheelerParticipant @nickwheeler]

It makes more sense than my claim for them having 9 in each row too. I should have known better than to post numbers after returning from a practice where I struggled to count to six and back….

[JAParticipant @ja]

Nuclear jet engines never flew. Like nuclear rocket engines they were run on desert test sites.

I cannot accept that the P&W R-4360 represented the pinnicle of aero piston engine developent. By 1940 there was a whole new generation of piston engines being designed and developed, even more complex than previous. These included the RR Crecy (V12 sleeve valve two stroke) and the RR Eagle (H24 sleeve valve) which went into small scale production. There was also the Napier Nomad (combined piston and gas turbine engine), the Mk2 version was planned to be fitted to the Shackleton.

The GE J47 turbojet used on the B36 was the most successful jet engine ever made as far as numbers made (excluding Russian and Chinese engines). It, along with its predecessor the J35, was the first jet, as opposed to ground running gas turbines, to use a successful axial compressor.

JA

 

 

 

 

 

[Robert Atkinson 2]

On Robert Atkinson 2 Said:

Always an odd number of cylinders per

On Robert Atkinson 2 Said:

Always an odd number of cylinders per row in a radial engine with master rod design.

 

Bristol hydra? https://www.google.com/search?q=Bristol+hydra&oq=Bristol+hydra&gs_lcrp=EgZjaHJvbWUyBwgAEAAYgAQyBggBEEUYOTIHCAIQABiABDIMCAMQABgUGIcCGIAEMg0IBBAuGK8BGMcBGIAEMgcIBRAAGIAEMg0IBhAuGK8BGMcBGIAEMggIBxAAGBYYHjIICAgQABgWGB4yCAgJEAAYFhgeMggIChAAGBYYHjIICAsQABgWGB4yCAgMEAAYFhgeMggIDRAAGBYYHjIICA4QABgWGB7SAQg3MTI5ajBqOagCDrACAQ&client=ms-android-huawei-rev1&sourceid=chrome-mobile&ie=UTF-8

[JAParticipant @ja]

 

I think the Bristol Hydra flew once!

Brian Perkins, a noted model engineer, made a model of one using information from Rolls-Royce Heritage Trust. He could not get it to run successful and consulted RRHT only to be told neither could Bristol.

As far as Bristol engines went, it was just an aberation.

JA

 

[JA]

On JA Said:

Nuclear jet engines never flew. Like nuclear rocket engines they were run on desert test sites.

I cannot accept that the P&W R-4360 represented the pinnicle of aero piston engine developent. By 1940 there was a whole new generation of piston engines being designed and developed, even more complex than previous. These included the RR Crecy (V12 sleeve valve two stroke) and the RR Eagle (H24 sleeve valve) which went into small scale production. There was also the Napier Nomad (combined piston and gas turbine engine), the Mk2 version was planned to be fitted to the Shackleton.

The GE J47 turbojet used on the B36 was the most successful jet engine ever made as far as numbers made (excluding Russian and Chinese engines). It, along with its predecessor the J35, was the first jet, as opposed to ground running gas turbines, to use a successful axial compressor.

JA

I certainly wouldn’t claim that the R-4360 was the pinnacle of piston engine development – to gain that crown I think you’ve got to look at practicality – and size, complication, and dubious reliability tell against it there. The Wright R-3350, although an older design, seems more worthy, in that it was commercially successful and widely used, and technically interesting in Turbo-compound form.

The Nomad definitely wins on wackiness, especially in the Mk1 version. Napier’s liked wackiness, but the Crecy and H-24 Eagle seem decidedly un-Rolls Royce-ish.

The Soviet Union came out with some large and complex piston engines as well, though I can’t remember any names or details.

[duncan webster 1]

On duncan webster 1 Said:

On Robert Atkinson 2 Said:

Always an odd number of cylinders per

On Robert Atkinson 2 Said:

Always an odd number of cylinders per row in a radial engine with master rod design.

 

Bristol hydra? https://www.google.com/search?q=Bristol+hydra&oq=Bristol+hydra&gs_lcrp=EgZjaHJvbWUyBwgAEAAYgAQyBggBEEUYOTIHCAIQABiABDIMCAMQABgUGIcCGIAEMg0IBBAuGK8BGMcBGIAEMgcIBRAAGIAEMg0IBhAuGK8BGMcBGIAEMggIBxAAGBYYHjIICAgQABgWGB4yCAgJEAAYFhgeMggIChAAGBYYHjIICAsQABgWGB4yCAgMEAAYFhgeMggIDRAAGBYYHjIICA4QABgWGB7SAQg3MTI5ajBqOagCDrACAQ&client=ms-android-huawei-rev1&sourceid=chrome-mobile&ie=UTF-8

There is always one….
The Hydra just proved than an even number doesn’t work well.

No aircraft engine was / is the pinacle of piston engine design. Not the fastest, highest power to weight, most powerful (big marine diesels take that prize) or most fuel efficent.

Yes, they lead the technology in the thirties through the fifties but development basically stopped when gas turbines became practical. The majority of piston engines in aircraft today are either based on >60 year old designs or were intended for snowmobiles.

Robert.

[Howard LewisParticipant @howardlewis46836]

Gas turbine fuel in I C Es can cause problems.

Normally it is difficult to feed through a carburettor, without a lot of heat input to vaporise it.

As used in Petrol / TVO tractors. Start on Petrol, to use the exhaust heat to warm the vaporiser, before changing over toTVO. The charge heating reduces power.

Fed thriugh a fuel injection system into a compression ignition engine, the lack of lubricity compared to gas oil, causes wear of pumping plungers and injector needles.

Airport Gensets do run on Avtur, but not without causing problems for the engine and FIE makers, in terms of wear and power output

USA did try using coal slurry as a fuel(Since they have surplus stocks of coal after steam locomotives went out of service) but it was too abrasive.

At one time, Air Blast injection of coal dust was tried as a fuel for large marine engines; but again, the problem was abrasion of the fuel supply components, and of cylinder components.

One use for kerosene type fuels, in the marine sector, was as a boiler fuel, so that the steam generated could be used in turbines to power a generator, so that the propellor was actually rotated by an electric motor. ESSO had at least one tanker operating in this way. A friend was the Chief Engineer on it.

The UK had some Navy vessels that were gas turbine powered. A good application, since rapid changes in turbine operating speed were unlikely.

Howard

[Robert Atkinson 2Participant @robertatkinson2]

Pedant alert

Howard said “Gas turbine fuel in I C Es can cause problems.”
Gas tubines are ICEs so no problem there. Most* diesel engines run fine on Jet A(1) it’s not uncommon to use it for tugs etc on the apron. A bit dearer than red diesel but less logistics.

I assume you mean spark ignition piston engines (petrol engines). Yes they don’t like running on Jet A.

* The US military have a “single fuel” policy for the battlefield. Basically this means diesel engines that will run on JP8 (military fuel basically the same as Jet A1). They had problems with some HUMVEEs running on this. There were two issues both of which varied with pump manufacturer and even batch to batch. One was an o-ring compatability issue. The other was pump seizure due to low lubricity of the fuel. This varied depending on the exact grade of steel used for pump parts and posibly surface finish.
A similar issue arose yeras ago in the Antipodies when they reduced the Sulphur in all fuels. There is no minium Sulphur requirement in the JET A specification. Some engines, specificaly Walter turboprops suffered from fuel pump seizures. The Sulphur provided lubrication.

Robert.

[David AmbroseParticipant @davidambrose86182]

Howard,

Most RN ships have a combination of Diesels and gas turbines, and both the Type 45s and the carriers have electric propulsion.  There have been many steam turbine ships with electric propulsion, such as the SS Normandie, and I believe that French nuclear subs still do.  It has the advantage of quietness, as there is no gearbox, and full power is available for astern propulsion.

David

[SillyOldDufferModerator @sillyoldduffer]

Most of the early IC piston engine designers wasted years trying to get their engines to run on coal dust.   Pioneers like Rudolf Diesel was working long before oil became common, at time when the obvious choice was coal or town-gas.

The problem with coal is that even the cleanest varieties are stuffed with impurities, most of them injurious to the innards of an engine.  The heat value of coal is highly variable too, making the engine awkward to feed.  Somehow, the poor thing has to deal with a hot spray of acidic grit, mixed with tar, heavy and light hydrocarbons, phosphorous, and other nasties.   So far, though many have tried, no-one has made a commercially successful coal-dust burning ICE : the problem isn’t getting coal-dust engines to run, the killer is the cost of keeping them going.  High maintenance costs exceed the benefit of burning cheap dust.    Cheaper to refine coal and oil so the ICE burns a clean consistent fuel, allowing it to perform well without needing endless repairs!

After the early builders had given up on coal-dust, gas engines burning coal-gas became very popular, though their power output was limited by the fuel.   Later, similar engines ran more powerfully on vaporised paraffin.  Then more-power petrol for aero and motor-car engines.    Turbines are good for applications that run consistently at near full throttle : generating electricity, aircraft, warships, fast point-to-point maritime services.   Turbines are hopeless for stop/start, reversing, or anything where the throttle has to be moved a lot!

Diesel proved a hard nut to crack, with many makers struggling to deliver both reliability and economy.  Took 80 years to get to where we are today with diesels doing almost all the heavy lifting; ships, rail, road, and agriculture.

Dave

 

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