Why no Fuel Cells on Combat Vehicles

[jh316]

Plastics do not necessarily require a petroleum industry. There are alternatives to fossil fuels. But it definitely does require a higher tech base than ICE, which is indicated by Fuel Cell engines having a tech rating of D (the same as fusion), while ICE has one of C.

[Sabelkatten]

I'll have to double check, but I don't think you actually need either polymer membranes or platinum - the first is for the proton exchange interface and can be done with (treated) paper, the second is a catalyst to make it (more) efficient.

But a FCE built without either is going to be like a running a laptop on citrus fruits with electrodes stuck into them... ;)

[evilauthor]

Plastics do not necessarily require a petroleum industry. There are alternatives to fossil fuels. But it definitely does require a higher tech base than ICE, which is indicated by Fuel Cell engines having a tech rating of D (the same as fusion), while ICE has one of C.

Well luckily, the BT universe has been retconned so that the majority of the Inner Sphere has always had this high tech level even in the depths of the Succession Wars. This is especially true if most civilian vehicles have always had FCE in them!

[Redman]

No, ICE's can take advantage of modern electronics, but they do not need them.  You can make ICE's out of exotic materials, but steel and cast iron work fine.  They have to be machined closely, but it does not take a seven axis milling machine to shape them.  You show up at the 1890's locomotive works with fully detailed and dimensioned drawings of what you want produced and pick up your parts a week to ten days later (or whatever their workload allows, custom castings may take longer).   Its an internal combustion engine designed around principles hashed out by Sadi Carnot by 1830.  The amazing thing about Carnot's work is that his formulation of thermodynamics came before the Law of conservation of energy.  Carnot's work combined with some calculus allows you to predict performance based on running speed, displacement, and compression ratios.  Experimentation will need to be done to determine which of the ignored factors is actually important, but the experience with steam engines and getting steam into and out of the cylinders, and friction, will allow quick progress.
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Sure you can build an ICE with the 19th century technology. But it won't be anywhere near modern day performance standards much less the standards of an era a thousand years in the future. Fact is if i gave the construction data for a modern day car engine to an engineer in the late 19th century he would probably be able to understand its basic principle but he still wouldn't be capable of build it on his own. And that's even if we forget about the engine's electronics for a moment.

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The Boeing 787, on the other hand, uses materials that the Wrights could not get in any quantity, like carbon fiber.  It also uses technologies that nobody at the time has heard of, particularly servomechanisms.  The glass cockpit is right out.  The engines require superalloys.  There are lots of reasons that prevent the Wright brothers from making a Boeing 787 that do not apply to Rudolph Diesel building a very efficient ICE in 1893. 

Diesel can understand what the parts do, he can get them made from materials he and his tradesmen are experienced with, and if he doesn't like your design compromises, he has the mathematical and scientific tools to design one more to his liking.  There are mechanical systems to allow for variable valve timing and variable valve lift.  If you told Rudolph about supercharging and powering a supercharger with a heat recover turbine, he could call upon compressor design and consult with Charles Parsons, who invented the steam turbine in 1884.  The analog mechanical engine management unit will be a significant weight penalty at the lower power ratings, but it is just as accurate and easy to adjust (only you use a set of screwdrivers, not a laptop).  Modern pollution controls may be hard to implement.
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You do realize that the jet engines of the 787 are by definition internal combustion engines themselves? No one ever said that the ICE in BT have to be diesel engines. What if they are gas turbines? Even if they were diesel engines who says that the motor blocks of the 31st century are not necessarily made of super-alloys or even completely other materials (like ceramics) to achieve their performance parameters? In Battletech engines are build to specific standards especially in repect to power-to-weight ratios. The question is not whether you can build an ICE but whether you can build an ICE to that standards. There may be a lot of rather primitive ICEs in use in the BTU but they are definitely not used for combat vehicle propulsion.

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If the fuel cells use polymer membranes, they require a plastics industry, which requires a petroleum industry to provide input materials.  If they do not use some kind of plastic, they use an extremely rare material, like platinum.  There may be places where the platinum is easier to recover, but due to the physics of stellar nuclear synthesis, there is nowhere where it is plentiful.
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The first fuel cell was invented in 1838. Its operating principle is also quite simple since it is simply the reverse of electrolysis and would be perfectly understandable for a mid to late 19th century scientist. Indeed fuel cells where for some time thought as the future technology for power generation until power generators driven by steam engines or ICEs proved to be a much more convenient source of electrical power.

So if you insist that in the BTU ICEs can be build and maintained with 19th century technology while FCEs cannot this seems like a double standard to me. Why can ICEs be as primitive as they get whereas FCEs have to be build at least to modern day standards?

[glitterboy2098]

it is possible that the lack of FCE's, in universe, was not due to technological or performance issues, but instead due to politics.
that when the Procurement contracts for various vehicle development projects were done, the great houses tended to either specify ICE powerplants for the non-fusion vehicles, or the selection process group chose the ICE powerplant models over any FCE competing designs. such preferences could be due to perceptions of ICE vs. FCE's, influence by political elements, even preferential contracts being offered by the various companies in order to curry favor.

[rlbell]

You do realize that the jet engines of the 787 are by definition internal combustion engines themselves? No one ever said that the ICE in BT have to be diesel engines. What if they are gas turbines? Even if they were diesel engines who says that the motor blocks of the 31st century are not necessarily made of super-alloys or even completely other materials (like ceramics) to achieve their performance parameters? In Battletech engines are build to specific standards especially in repect to power-to-weight ratios. The question is not whether you can build an ICE but whether you can build an ICE to that standards. There may be a lot of rather primitive ICEs in use in the BTU but they are definitely not used for combat vehicle propulsion.

The masses of BTU ICE's are too large to be gas turbines.  If you leave off the the air filter and exhaust stack, a 300 MW gas turbine (a third more power than needed to propel a Nimitz class CVN to more than 54 km/h) fits on a single railcar and masses less than 100 tons,  possibly as few as 50 tons, and this is for an industrial gas turbine (Westinghouse 501) that makes no effort to reduce weight.  Twenty-five tons gets you a 50MW gas turbine with generator that fits on a semi-trailer..  Aeroderivative gas tubines are much lighter, with 50MW ratings under ten tons (excluding the generator).

Combat vehicles are places where 'primitive' ICE's show significant advantages over gas turbines, despite being heavier.  Outside of vehicles where weight is paramount and fuel consumption is not a consideration, the part load efficiency of a gas turbine is damning, often consuming as much fuel just idling as 40% of the consumption at full rated power.  Achieving 40% thermal efficiency in a gas turbine, without a combined cycle, is very difficult.  Achieving 45% thermal efficiency in a diesel was done in 1949 (the turbo-compounded Napier Nomad).  Small diesels have trouble hitting 50%, but large marine diesels do it merely by being huge--  short burn times and slow piston speed allow a better approximation of the Carnot cycle.

Gas turbines do simplify the transmission by not having the problem of zero torque at zero rpm of the output shaft (no need to slip a clutch or mount a torque convertor).  In fact, a GT with separate compressor and power shafts has maximum torque at zero, but that is not enough to displace the diesel from combat vehicles, and they are adding APU's to the M1 to deal with the abysmal fuel consumption while parked and powering the non-motive systems.

[Redman]

The masses of BTU ICE's are too large to be gas turbines. 
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Since when does BT use anything like realistic masses for equipment?  Last time i checked a RL machine gun didn't weigh about half a ton and multi-ton targeting computers also seem a little off. On the other side in the BTU armour that weighs just a few hundred tons can provide ample protection for warships around a kilometer long and with  masses of about a 1 million tons.  ::)

A lot of the Battletech rules do not make any sense on a closer inspection and engine masses are an excellent example of this. The construction rules were created with a lot of things in mind but realism wasn't one of  them and i refuse to pretend otherwise. My argument is that since battletech is about armoured combat in a far away future it is simply inappropriate that ICEs should not be build according to the technological capabilities of that time. Battletech is not steampunk (or maybe oilpunk, can i get a trademark on that?).

[Nebfer]

Well B-tech engines seem to be more than just engines, B-tech engines seem have have little to no problems going from worlds where the gravity is half that of earths, to roughly twice earths and worlds running from Hoth to Arrakis and everything in between, also worlds with thinner atmospheres to ones with thicker and or with different oxygen ratios...

From a book called the Technology of Tanks (Richard M Ogorkiewicz -1991) It brakes a tank down into various percentages a bit generically perhaps but a interesting approximation.

Armor: per the book it mentions tanks seem to spend 35 to 57% of it's mass on armor (current MBTs seem to be around 45 to 51%).
Tracks: around 8 to 10% (though from what I have seen it seems to very a bit more than that)
Suspension: 11 to 13%
Engine, Transmission and final drive: ~12% (from what I have seen engines and transmissions are in this range, though I can find little on Final Drives, though Turbines are notably lighter than other engine types.)
Weapons and their mountings: 3 to 10%, lighter tanks typically having higher numbers
Items not listed take up the remaining tonnage, though fuel seems to be around .7 to 1.5 tons and ammo around a ton.


What I'm getting at is that in b-tech it seems the armor mass has drooped and the weapons & ammo mass has increased (well we kinda know it did...), the engine ranges from drooped to increased... However the "engine" it seems has to account for the Engine, Fuel tank, Transmission, Final Drives, Tracks and Suspension, the "Internal Structure" might hold some of these but it can not account for them all. 
From the above historically tanks supposedly had ~30 to 35% of it's mass taken up by it's motive systems, if we included much of the IS with the mass of the engine many a B-tech tank spends around historical levels in this area, though their are a number that go as high as 50%, though that's assuming we include the IS as part of the automotive...

So it seems B-tech engines are not as heavy as they seem to be, at lest from a certain view point.


With the Ranges from Tech manual 600km for ICE and 450km for Fuel cell, how do they work with the ranges given in Strat ops, which IIRC indicates a 2,500 km range for active combat units (or oddly 500km for units "idling")?

[evilauthor]

As for engine composition, the refueling rules say that ICE and Fuel Cell engines need to spend 10% of their tonnage to double their range and a further 10% per incremental increase by their base range. This suggests that ICEs and Fuel Cell Engine already spend 10% of their base tonnage on fuel. Admittedly, this rule is only explicit for Industrialmechs (TechManual pg 68), but I don't see why combat vehicles would be any different.