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Pages: (7) 1 [2] 3 4 ... Last » ( Go to first unread post )

 Building an engine tutorial
Vault 10
Posted: Jun 23 2007, 05:45 PM


Unregistered









Hey, it's Sumer's tutorial! I don't want to take the wrong credit. I'm just discussing things.
[ Mine will be about ships and later... ]


So, 2 Sumer: Don't take it as if I'm ignoring advice, but here the conditions are so rough that just plain nothing, which isn't a solid thick metal, can be relied upon. Some things which complicate it:

- Freefall lifeboat will be launched from aboard ships up to 60m freeboard, at list angles up to overkeel, 180 degrees. The worst case is rapidly increasing list, where, say, the portside boat is released at heavy list to starboard, where it has to fly fast enough not to hit the side. It means up to 60m/s, or 110kts, or 200km/h hit. Or, in real worst case, hitting the side, not that fast, but the hull will be damaged. So compartment integrity is not guaranteed. Storm weather will increase damage further.

- The boat might have to be launched after the ship has submerged, or in that overkeel case. The hatch might be not closed properly, so the boat may be totally flooded. Buoyancy blocks will let it surface, but it must still start the engine after that, to operate the pump and heat the boat before people inside freeze. Tolerating total flooding is a standard requirement for lifeboats.

- Naval vessels, which have enemy fire as a frequent case of destruction, with possible arsenal explosions, fragments around, and other issues, might have the boat breached, but sometimes with just small caliber fire or fragments. The engine must have the power to operate the fast pumps and create overpressure, sufficient to keep a non-watertight boat with some air inside, even if flooding is continuous. If it fails and it has too many breaches, then at least warm the water, provide forced ventilation, give light to treat the wounded.

- A tanker, which will at best carry oil, and maybe kerosene, poses fire hazard; the boat must have fireproof version. That means moving, all covered in burning liquid, through a pool burst in flames at 1000C. Even a steel hull and syntactic foam insulation wouldn't save it for long. The engine must work to operate the sprinkler system and escape the fire rapidly. It will have half-burned, hot air taken in, and may not drain the internal air - it's needed to keep the people alive, who can't breathe the hell outside.

- In cold water, human has 5 minutes to survive, some of which might be already used up if he reaches the boat after being outboard. Then the person must be warmed and dried. The engine will have good batteries to help, but must start very fast, to rapidly turn the lifeboat into a dry, warm shelter. Even an initially flooded one.


These are only some of the requirements for the lifeboat engine. I'll use two engines on larger lifeboats for reliability. Still, each must be reliable and tolerant. The engine might not have a large air buffer, just the often splashed snorkel pipe to breathe. If it's not possible to make it "skip cycles" through that, at least let it restart fast.
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Sumer
Posted: Jun 23 2007, 08:49 PM


You have way too much time on your hands ...


Group: Admin
Posts: 6,060
Member No.: 8
Joined: 10-April 07



You can't make a diesel engine run submerged. The best you can do is provide adequate water removal systems and route the intakes and exhaust right so that water does not get in. Beyond that you need bateries. You could do a diesel-electric drive if you want.


--------------------
QUOTE
“I believe that the sound of racking the pump of a shotgun is universally recognized as ‘kiss your ass goodbye’."

Proudly Canadian
user posted image
QUOTE ("L3 Communications")
Well...next to Sumer's juggernaut of death, the MCA-7G.
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Vault 10
Posted: Jun 23 2007, 09:15 PM


Unregistered









I understand it can't run submerged, and I don't want that. It only must continue to run through harsh conditions, like after being submerged, but drained later. It might get partly flooded, and pretty wet.

Or could you clarify what do you mean... Just some situations:

- What will happen if the water gets through the intakes, the final valve stops it, but the running engine receives no air at all for half a second or so?

- What will happen if the final valve fails to act, and a bit of water gets inside the engine?

- Will anything bad happen if the boat is 100% flooded, apart from the intake and exhaust?


"What will happen" means how serious the problem is - is it just choking for a while, or stopping to restart later, or receiving permanent but non-fatal damage, or receiving fatal damage.

The boat won't submerge, it will be on the surface, and have intake/exhaust high enough to receive some air even if flooded inside. That's what the buoyancy modules are for. It's also self-righting. Air will be available, but wet and still not always.
Yes, there will be high-capacity batteries, and they will smooth out lack of power, but they don't have the capacity to run the high-performance pumps for long.
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Sumer
Posted: Jun 23 2007, 09:30 PM


You have way too much time on your hands ...


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Joined: 10-April 07



1: The engine will hickup but if it's diesel it will keep going.
2: depending on the layout of the intake system then a little water won't be an issue, combustion should occur as normal.
3: as long as the engine is water tight, no.

The intake system should be shaped like a T on it's side. Designed to take air in but have a drain area incase water comes in. Exhaust isn't quite as bad, and if designed for the right pressure can be completely submerged as long as the engine is running, a valve in the exhaust can keep water from comming back when not running.

The only way you're going to permenantly harm the engine is if it is completely submerged in salot water, both inside and out, for long enough time to rust enough to cease it. Other then that you could probably leave it completely submerged an hour, drain it, refill the oil and start it up.

The electronics will be a problem. But diesels don't need them that much. Turbochargers will be completely ruined if submerged though.


--------------------
QUOTE
“I believe that the sound of racking the pump of a shotgun is universally recognized as ‘kiss your ass goodbye’."

Proudly Canadian
user posted image
QUOTE ("L3 Communications")
Well...next to Sumer's juggernaut of death, the MCA-7G.
Top
Vault 10
Posted: Jun 23 2007, 09:54 PM


Unregistered









Thanks, that clarified it. So no turbochargers, got it, though their slow startup was a problem anyway. I also don't want to depend much on electronics... They can be made very reliable, and fully waterproofed, but they aren't necessary, after all, so why complicate it.

Now, some more things. In general, what layout and what if any "extras" would you suggest? I guess inline 6 is quite a good idea, but maybe not. The engine would better be flat enough (within 0.5m high) to fit conveniently into the double bottom, to keep weight low.
Power output should be... well, not sure, but maybe around up to 300-500hp. It should either operate efficiently in a wide power range or be compact enough to put two half-power ones. Also, what about the technology in MTU 890 series? Their small size seems attractive, and 2 is better than one, but I'm not sure if anything from there can be applied here.

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Hotdogs2
Posted: Jun 24 2007, 10:26 PM


4% Armaments Designer


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Joined: 10-April 07



Yeah sorry about that, Mac pointed that out to me, i think its because i saw the last poster when i looked at the thread, and failed to note the actual author! Sorry about that one. Edited the post anyway.

A diesel will be easier to run through water because it can be waterproofed easily, mainly because it doesn't use any spark plugs. That said how stuff works(source of so much knowledge biggrin.gif) says you would have to water proof the electrics for the engine for it to continue running underwater, probably important in a boat.
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Vault 10
Posted: Jun 25 2007, 11:13 PM


Unregistered









OK, so, let me make the first try.

To give an impression of what is it for, some craft specs.
ALC MFLB-50
Freefall lifeboat for transport vessels, capacity 24 nominal, 50 maximum
Fully closed, motorized, SOLAS compliant, steel+CFRP construction
Dimensions: L 12.8m, B 3.10m, H 4.25m, Tnom 1.0m, Dnom 28,000kg
Weight: 16,000kg empty, 3,000kg supplies, 7,000kg fuel oil, 2,000kg nominal passenger load
Buoyancy modules: 20,000 liters of low density syntactic foam


So, the engine.

NCR Heavy Industries DE-120
4-stroke diesel engine

Construction

Configuration: Inline 6 [Or take V12? Flat 12?]
Material: Titanium [? I'm not sure, but I need to save weight if possible, and corrosion resistance helps...]
Dimensions: ?
Mass: 500kg [?]
Bore: 120mm
Stroke: 120mm
Displacement: 12L

Operation

Induction: Natural, T-shaped valve
Fuel used: No.1 to No.3 Fuel oil, marine gasoil, marine diesel oil
Compression ratio: ?
Speed: 1600rpm optimum, 3200rpm max
Power output: 200 kW at 3200rpm, outside temperature 300K
Optimum 120kW

Specific fuel oil consumption: 200g/kWh optimal, 220g/kWh average within 20%-100% output
Specific lubricant consumption: 1g/kWh optimal, no more than 1.5g/kWh
Torque: ? [if needed at all]

Is it right? Anything which would better be different? I mostly just put guesses.
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Sumer
Posted: Jun 25 2007, 11:52 PM


You have way too much time on your hands ...


Group: Admin
Posts: 6,060
Member No.: 8
Joined: 10-April 07



You'd be fine with aluminium, but making it out of steel regardless of the weight might not be a bad idea. Makes it more rugged.

You only need an I6, you might even be able to go as low as an I4 8L engine.

I wouldn't worry about compression ratio.

Your torque would be between 10% and 20% more then your power output in horsepower.


--------------------
QUOTE
“I believe that the sound of racking the pump of a shotgun is universally recognized as ‘kiss your ass goodbye’."

Proudly Canadian
user posted image
QUOTE ("L3 Communications")
Well...next to Sumer's juggernaut of death, the MCA-7G.
Top
Vault 10
Posted: Jun 26 2007, 12:05 AM


Unregistered









QUOTE
You only need an I6, you might even be able to go as low as an I4 8L engine.
But I4 is unbalanced, and particularly bad in this aspect.

QUOTE
You'd be fine with aluminium, but making it out of steel regardless of the weight might not be a bad idea. Makes it more rugged.

I don't need long life; would it affect engine survivability? Titanium seems attractive due to no risk of corrosion creating problems for an engine which might be neglected and just stay there for years not even checked. For aluminium, it has some tendency to react with seawater under some circumstances.

What about other specs? I also wonder which speed would serve the purpose best. Another question is how to reach maximum range of efficient operation. More than 200kW could be useful, but if it doesn't hamper slow operation - ~25kW will be needed constantly.
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Sumer
Posted: Jun 26 2007, 12:31 AM


You have way too much time on your hands ...


Group: Admin
Posts: 6,060
Member No.: 8
Joined: 10-April 07



Maximum range will depend more on any number of things I can't answer for you, including your gearing, propeller, hull form, sea state, and other stuff.

The bottem line is, you can't have an engine that will run if left alone for even years at a time and not maintained. It's impossible.

Honda makes engine blocks out of aluminium already, I don't see a problem. Maybe some form of aluminium alloy. But I still believe steel is your best bet. Titanium will flex too much and require extensive reengineering of the block design, which will hamper any number of your needs, especially low maintenence.

Balance is a funny issue with engines. If you have more then one cylinder, it can easily be well balanced. Four, five, six, eight, ten, they're all able to balance great, especially with marine engines. General rule of thumb however is that more cylinders means more balance, at the cost of smaller cylinders. This is great for things like a Ferrari where that gives more speed and power with less strain and minimises vibrations to almost nothing, but on a diesel, especially a marine diesel, it's bad. More smaller cylinders here will reduce your engine's ability to injest seawater and just hickup. the difference between a I4 and a V8 for instance, if they're both 8L displacement, could be as dramatic as 1L of seawater causing complete failure in the V8, but only a minor hickup in the I4. I4 and I6 are the ideals for smaller marine diesels like this, but it doesn't matter as much when you get massive V18 engines in like submarines that have plenty of displacement to spare.


--------------------
QUOTE
“I believe that the sound of racking the pump of a shotgun is universally recognized as ‘kiss your ass goodbye’."

Proudly Canadian
user posted image
QUOTE ("L3 Communications")
Well...next to Sumer's juggernaut of death, the MCA-7G.
Top
Vault 10
Posted: Jun 26 2007, 08:35 AM


Unregistered









QUOTE
Maximum range will depend more on any number of things I can't answer for you, including your gearing, propeller, hull form, sea state, and other stuff.

I mean not the craft's range, but engine's. Retaining, say, 220g/kWh consumption, even if working at 10% output (20kW out of 200).

QUOTE
The bottem line is, you can't have an engine that will run if left alone for even years at a time and not maintained. It's impossible.

Well, but they do, somehow... Lifeboats often get neglected on cargo vessels (like if anything didn't), but still work. And the thousands of tanks from T-34 to T-72 standing in reserve with only checking each 5 years apparently aren't there just to stand.
Of course, what is meant is not just stopping it and leaving for years, but rather preparing for low-maintenance operation.

Or, in general, what specifically is the problem which won't let a diesel left alone for some years to work?


QUOTE
the difference between a I4 and a V8 for instance, if they're both 8L displacement, could be as dramatic as 1L of seawater causing complete failure in the V8, but only a minor hickup in the I4. I4 and I6 are the ideals for smaller marine diesels like this,

Well, then inline 6, I guess, a narrower prolonged engine will be good for the structure. BTW, how will bore/stroke ratio affect this? Will wider bore with shorter stroke be better, or not?
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Sumer
Posted: Jun 26 2007, 12:26 PM


You have way too much time on your hands ...


Group: Admin
Posts: 6,060
Member No.: 8
Joined: 10-April 07



That will be entirely dependant on how often it is maintained, how it is built, and how underpowered it is, in a sense. If it's able to say put out 600 shp, but is rated at 350 shp, maintained regularly, given a steady supply of fuel, and designed for long running condition, then you can easily run it for days, maybe as high as two weeks. That's just a hypothetical set up to let you know, I'm in too much of a rush to convert kW to hp right now so I'm pulling figures out of my ass.

Fluids. Like all piston engines (And this is even worse for a wankel by the way) the fluids break down. To prepare an engine for long term storage it's left in what's called dry storage, meaning it's literally drained of every fluid. Then they can keep it as long as they want, but it will have to be reoiled, refueld, in many cases it will have to be taken apart and given a somewhat extensive overhaul, and then run. Those Russian tanks in storage for instance are overhauled every few years and run a few times, then dried up and packed away. Lifeboats on container ships or other ships that opt for an enclosed lifeboat instead of the more modern life rafts, are maintained in port every time they sit in for supplies and stuff. Sometimes they're even maintained at sea. It only takes a few hours every couple of weeks to do.

Bore stroke won't really mean anything here. All that matters is that it has the individual cylinder displacement to take punishment. You may want to increase stroke over bore to get the desired displacement and save space around the engine though, as a lot of marine diesels of this size tend to do.


--------------------
QUOTE
“I believe that the sound of racking the pump of a shotgun is universally recognized as ‘kiss your ass goodbye’."

Proudly Canadian
user posted image
QUOTE ("L3 Communications")
Well...next to Sumer's juggernaut of death, the MCA-7G.
Top
Vault 10
Posted: Jun 26 2007, 12:50 PM


Unregistered









QUOTE
Fluids. Like all piston engines (And this is even worse for a wankel by the way) the fluids break down. To prepare an engine for long term storage it's left in what's called dry storage, meaning it's literally drained of every fluid. Then they can keep it as long as they want, but it will have to be reoiled, refueld, in many cases it will have to be taken apart and given a somewhat extensive overhaul, and then run.

Of course, refueling and reoiling will be in order. If you mean just that, then OK, I guess it's possible to do while working on batteries.
For overhaul, how can I avoid these cases where it's needed?


QUOTE
Lifeboats on container ships or other ships that opt for an enclosed lifeboat instead of the more modern life rafts, are maintained in port every time they sit in for supplies and stuff.

Actually SOLAS rules require enclosed lifeboats on all large international vessels. Life rafts have been known for very long, but due to poor reliability of this method are only accepted as replacement on small or local lines vessels. Since 2004, for bulk carriers it's even required to have not just enclosed, but even heavier and faster-launching freefall lifeboats.
While relying on maintenance is an option, and it by no means is supposed to be cut, having the engine tolerate neglect is still better than not. Anything that can be done to ensure this? Or maybe just enforce a test run once in a while?

QUOTE
It only takes a few hours every couple of weeks to do.

BTW, what specifically is included? Is it possible to make the engine as low-maintenance as a car one?
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Sumer
Posted: Jun 26 2007, 01:00 PM


You have way too much time on your hands ...


Group: Admin
Posts: 6,060
Member No.: 8
Joined: 10-April 07



Keep it filled with the right fluids treated for long term non-use and run it every week for half an hour or so. You can keep it fueld and ready to go indefinatly that way.
And keep in mind changing the fluids takes time and equipment like pressure systems and air compressors that will mean you won't have much room for people. You'd need to effectivly cram an entire mechanic shop into this thing, plus be sure to always have the mechanic onboard when it deploys.

No need for a test run. Just have the ships engineer walk over to it once a week, start the engine, let it run 15-30 minutes, and then go back to his regular duties. He can do it on a coffee break.

It will be lower maintenence by far. Car engines are run on a regular basis though and so don't need storage care. But all your mechanics need here to maintain this is a basic set of hand tools and a few other things like a timing gun.


--------------------
QUOTE
“I believe that the sound of racking the pump of a shotgun is universally recognized as ‘kiss your ass goodbye’."

Proudly Canadian
user posted image
QUOTE ("L3 Communications")
Well...next to Sumer's juggernaut of death, the MCA-7G.
Top
Vault 10
Posted: Jun 26 2007, 01:14 PM


Unregistered









QUOTE
It will be lower maintenence by far. Car engines are run on a regular basis though and so don't need storage care.

Well, you can leave a car for a year, get back and start it, even though not instantly, but quickly and without any special tools [may depend on car, though].

QUOTE
Keep it filled with the right fluids treated for long term non-use and run it every week for half an hour or so. You can keep it fueld and ready to go indefinatly that way.

What about making it start up regularly automatically, say, biweekly, if not checked manually? Through auxiliary electronics, I mean. No, doesn't mean it won't be maintained, but Murphy's Law says if it can be done wrong or neglected, it will.
I guess some non-vital electronics, which only supplement normal manual control, won't hurt.



By the way, back to the efficiency curve. So how good can it be done? Can engine rated for 200hp optimal (say, 210g/kWh or 155g/hp*h), 300hp maximum, work efficiently at 30hp? How efficiently, and how can it be improved?
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