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Bomb lab warms up diesel technology

Discussion in 'Technical Discussion' started by Marmot, Jun 19, 2012.

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  1. Marmot

    Marmot Senior Member

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    From the folks who brought us the atomic bomb:

    Materials for High Efficiency Engines

    The recent "discussion" regarding engine temperatures was closed before any real information could be passed along but for those who are interested in such things, there is a lot going on in the world of diesel engine development.

    A diesel gets it high efficiency by taking advantage of the fact that the greatest return on energy input (the fuel) can be obtained by allowing the greatest drop in temperature of the working fluid, air and combustion gases in the case of a diesel.

    The trend in engine design and development over the past few decades has been to increase the amount of heat in the cylinder. The combustion temperature of diesel fuel is around 3000*F (1600*C) and the closer to that temperature designers can keep the combustion zone of an engine, the higher its efficiency will be. The same applies to turbine engines as well and the search for ever higher working temperatures has led to ceramic turbine wheels and coatings for diesel engine pistons and cylinders.

    One bottleneck is the inlet and exhaust valves. While inlet geometry and other tweeks of the air flow within the cylinder contain the high temperature combustion zone to prevent hot gases from melting the piston or cylinder walls, the valves get to experience the fire first hand. This is what is behind the money flowing into research labs today.

    The search for better valves isn't just American effort either:
    http://www.engineaustralia.com.au/downloads/File/pdf/seb/sb020.pdf
  2. captholli

    captholli Senior Member

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    I've recieved enough Exhaust temp / Cylinder temp info in the last week to write a short stoy. Marmont , Thank you for the info as it was spot on. It's obvious that your experitse and knowledge is outstanding on this catagory and you've pretty much put this topic to bed in the last thread that was closed. Or lets just say that you've "exhausted" ;) this topic so lets not keep flogging this poor doggie anymore . I'm thinking up a good gas turbine question for you.Hummm , how about this, Have you ever heard of Ground up media like Walnut shells being used to clean G.T's for impact cavitation purposes?? kinda sound hokey to me but would think that its possible because the would incinerate if online or would be ejected or collected when off line when the waste gate is dumped. whata you think??
  3. Marmot

    Marmot Senior Member

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    Yeah, I think you are probably correct. I just wanted to avoid "blowing smoke" since there was enough from other sources, but if enough people are interested we can continue since the latest trend now is to reduce combustion temperatures to reduce NOx production.

    The efficiency of the large slow-speed two-stroke engines has actually been reduced in order to reduce NOx output. Gas turbines still look to increasing turbine temps to increase fuel efficiency but since NOx is an issue with them, designers are looking at other areas like compressors to gain a few nanopercent of improved efficiency.


    Ground walnut shells were among the first media to be used for compressor cleaning, still is in some applications but detergent liquids are more commonly used now.

    Most marine applications use a water wash system where a cleaning mixture is sprayed into the air inlet while motoring (turning the engine on the starter without ignition) and allowing the liquid to drain through the compressor and burner drains. Solid media like walnut shells is used with the engine running at idle and yes, the media makes its way to the burner cans and burns up. You have to be careful not to let the stuff get into the bleed air system and in some engines into the bearing cooling air which is not valved off.

    Large diesels use a pure water wash into the turbo compressor at high power output and what doesn't evaporate and go into the engine drains out the water separator at the aftercooler. The impact of the water cleans the wheel. The exhaust turbine can be cleaned by water (thermal shock instead of impact) or nut shells (impact) at low power but water is the usual method as it is easier and does a better job.
  4. Yachtjocky

    Yachtjocky Senior Member

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    turbo washing

    I wonder how many young engineers have been told to open the valve on the Turbo charging washing line and then to get the fright of their lives when the 6 foot diameter wheel spinning at close to 10,000 rpms "Surges"

    Walnut shells are being used as a blasting (cleaning) material along with foam balls, sand, grit, volcanic dust depending on the material to be cleaned.

    ...and so you now know that water comes out of the aftercooler ;)
  5. Marmot

    Marmot Senior Member

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    I guess you could say its "bark" is worse than its bite. ;)
  6. Bamboo

    Bamboo Senior Member

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    How many "general yachting" (since that is the category here) vessels have 6 foot turbine wheels turning at 10K?
  7. K1W1

    K1W1 Senior Member

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    Hi,

    The yachts are getting bigger so one never knows what will be next and what will be required to power it and whatever it is will most likely be turbocharged so anything is possible.
  8. Marmot

    Marmot Senior Member

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    That's a fact! Just in the past week I have been on two boats powered with medium speed diesels. I think we will be seeing more and more of them in the future.
  9. Yachtjocky

    Yachtjocky Senior Member

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    Progress

    I think you will find that the equipment, electronics and machinery start life on the ships and then are either adopted or changed slightly to move onto yachts.

    So what we saw 20 years ago on ships you are seeing on yachts nowadays. :)
  10. Grecko

    Grecko New Member

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    Improving exhaust valve life is a good thing, but that's really tough to do with ceramics. Their brittle nature means that some will work fine and others will fracture for no apparent reason. There have been some ceramic success stories in turbines, but they have been few and far between. Been there, done that, got the T shirt.. In small turbines it may actually be easier, since the shock loading isn't there, but trying to get a valve in a high speed engine to work. There's also a bigger % payoff in applying the technology to turbine, which is why the DoE is interested in the application of ceramics to small turbines. My company is under a DoE contract to do a ceramic turbine rotor test this year and even if you design it very carefully, then you have to make the parts (very difficult and expensive) and the cost of ceramic powder prices have lately gone thru the roof.

    The real problem is that high speed diesels are only about 35% efficient (and yes, I know big, huge 2 cycle diesels are more efficient, but a practical size diesel in a boat like we are talking about here is going to be a lot closer to 35% than 45%). What is happening is that about 30% of the energy is going out in cooling of the engine (both oil and water) and the other 35% is going out of the exhaust.

    There isn't much heat that you can recover from the cooling system. The water is only around boiling, and you can't efficiently recover heat that is that cool and do any useful work from it.

    The exhaust is hotter, but by the time it goes through the turbocharger it is less than 1,000 degrees F and even if you could capture it with a 25% efficient waste heat recovery system, you are looking at an 8.75% improvement in fuel consumption. Considering the weight, initial cost and and maintenance of the waste heat recovery system, that's not going to ever pay off the initial investment.

    A gas turbine, otoh, is somewhat less efficient to start with, but since all the waste heat goes out the exhaust, theres almost twice as much energy that can be recovered. Gas turbine waste heat recovery systems are currently being investigated by the Navy for systems as small as 4MW, and the amount of power gained can be about 25% of the base engine power. That would be a system that would supply an additional megawatt of power when put behind a 4MW system. To put it another way, if you can cut your fuel bill by 25% for a destroyer or cruiser, that's a lot of fuel.

    I think you will see more of these combined cycle systems in the near future and they will shrink in sized down to something that will eventually find civil applicaton
  11. Grecko

    Grecko New Member

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    Pratt & Whitney developed "Carboblast", soft walnut shells, for cleaning turbines in the 1950's You can still put that kind of stuff down older turbines, but newer engines have tiny laser drilled holes in the combustor and airfoils that would be clogged in seconds with that much junk going thru an engine. Water washing is mostly used now, even on big commercial engines to clean the junk out of compressors. Plain water can be used at low speeds to clean up the first few stages while the engine is running, but it boils off and in the later stages doesn't do much good. For a complete cleaning they motor the engine on the starter and then inject a mixture of cleaners and then the engine is cleaned that way. Also solid carbon dioxide is another thing that seems to work well, and won't clog small passages.
  12. Marmot

    Marmot Senior Member

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    I have never heard of anyone trying to make valves out of ceramic materials, or even coat them. Liners and piston crowns, yes, but valves, no. If they find commerically viable ways to heat up the liner and crowns then they need valves to handle the high temperature and I think that will come from the exotic metals and turbine blade folks.

    That will open the market for SCR or other aftertreatment NOx reduction techniques but that is another thread altogether I think.

    A few years ago there was a lot of research effort to produce a coolant-free diesel based on ceramic components but that seems to have faded away with the new emphasis on reducing NOx since high temps and low NOx are mutually exclusive.

    It must be a hoot to be involved with small and micro-turbine research.
  13. Grecko

    Grecko New Member

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    All of this stuff goes back to the "adiabatic diesel engine" that was the big talk a while ago... except they forgot that lubricants burn at the temperatures they wanted to run at, and things that would be lubricants at that temperature are solid at room temp.....

    I was just looking at the links in the first post and there were pics of SiN, ceramic valves... SiN is tough stuff, but I'm not so sure I'd like to make valves out of it... It took us a long time to get geometry that we felt would work on a turbine, and we gave up some tip speed to do it, but you don't know until you run it..

    What was the old John Denver song.. "some day's are diamonds, some days are stones" The good day's are when your proposal gets accepted and you win a big program, that says your concept was a good idea and you get to prove it... Or when something works in the test cell, no problem getting pumped up for that. But then, six months later when you're fighting to keep awake at 3:00 in the afternoon if you screwed up and had too big a lunch...
  14. Capt J

    Capt J Senior Member

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    I think on the largest of yachts, we will see more of a trend of Diesel electric with pods, like their larger cousins (the cruise ships) are using and have been using with good results.