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Low weight diesel pistons

  1. Apr 5, 2013 #1
    I'm looking to design a range of diesel engines for use in road cars (for when i win the euro millions ;) , consisting of a flat 4, straight 6 and v8. all with a cylinder capacity of 666cc (per cylinder).

    As we know the biggest downfall of diesel engines is the weight, especially that of the crank and pistons. The crank and rods can be replaced with titanium versions and the block can be replaced with aluminum.

    What can be done to lighten the weight of the pistons? Bear in mind I am intending these engines to be direct injection so they will need enough height for a combustion chamber. I've heard that beryllium is used in f1 engines, would that stand up to the pressures in a diesel engine?
     
  2. jcsd
  3. Apr 6, 2013 #2
    Before we start an inane discussion on the history and development of diesel engines. You should consider some things.

    First why a flat 4 a straight 6 and a V8? Why the capacity you mention?
    What segment of road car would it be used in?
    Why do you think that the parts are so heavy in the first place?

    Also as an asside the use of beryllium in f1 was banned for two reasons. The first is that its toxic and hard to work with, the second was that it was abusively expensive even by f1 standards.
     
  4. Apr 7, 2013 #3

    SteamKing

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    Sounds like you can call them the Devil's Diesels (666 cc / cylinder).
     
  5. Apr 7, 2013 #4
    devils diesel lol, well it is the fuel of satan

    xxxchrisxxx

    three different engine for the three different cars i would build
    666 well why not
    obviously great care must be taken making beryllium components, but as i said this is a total pipe dream so cost would not be an issue, i just want to know if its possible

    the engines are intended to be as light as possible and very strong, running well within its capability so as to last as long as possible

    I hope this clears the aim for anyone who reads this, and im very grateful for any replies
     
  6. Apr 9, 2013 #5
    Piston's don't weigh jack as compared to the block and, to a lesser extent, the crank.

    Once you lighten up the block, what normally results is a very noisy engine that requires special mountings beyond the typical mounts and suffers from the vibration that isn't being dampened by the heavier block.

    Witness the oldsmobile and early VW diesels for this.

    Even with a iron block, my nissan LD28 is still too loud for my taste.
     
  7. Apr 15, 2013 #6

    etudiant

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    If the focus is to achieve light weight diesels, you might research the diesel aero engines built by Junkers in the 1930s. These were novel designs, with opposing cylinders, that set new standards for diesel power to weight.
    My guess is that if they could be revived and set up with modern high pressure fuel injection, they would blow away any current diesel design.
     
  8. May 27, 2013 #7

    462chevelle

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    I think he is more concerned with the weight of the rotating weight than the entire weight of the engine. if he could get the rotating weight down then he would be able to rev it higher if he wanted to.
     
  9. May 28, 2013 #8
    Seeing as diesels are typically limited by burn duration having light pistons isn't a priority.

    This why the thread makes no sense. The op has arbitrarily picked a design feature to change for no apparent logical reason, with no consideration as to why it's like that in the first place.

    Justifying any change with 'because I want to' is fine, but it's not engineering.
     
  10. May 28, 2013 #9

    462chevelle

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    so youre saying from an engineering standpoint raising the rpms isn't going to help a diesel make more power.
     
  11. May 28, 2013 #10

    SteamKing

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    One can't arbitrarily increase the RPM of an existing engine without consequence. A diesel engine which is designed to run at 1800 RPM will see reduced life and increased possibility of damage if operated at 2400 RPM. Sure, it may make more power for a while, but if it breaks, you're done.
     
  12. May 28, 2013 #11

    462chevelle

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    ..... the reason to use lightweight pistons is to be able to spin it higher and it live longer. and I have seen the new 6.7 ford 4500-5000 rpms and the design of their pistons compared to a cummins is totally different. im not suer if this is where he is at but. if he could lighten the rotating assembly why not design a diesel with a 2000-5500 powerband. not talking about putting lightweight pistons in a cummins and trying to rev it. talking about lightening it up so it can rev without the reduced life.
     
    Last edited: May 28, 2013
  13. May 28, 2013 #12
    Why are you assuming that the heavy pistons are the reason it doesn't rev as high?

    You are making a fundamental mistake in that what works for petrol engines must work for diesels too. The reason diesels don't rev highly is a combination of a slow burning fuel and a limited fuel injection window. As such diesel engines suffer extreme diminishing returns at high rpm far in excess of petrol engines. As they simply can't combust the fuel fast enough.
     
  14. May 28, 2013 #13

    462chevelle

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    I never said that is the reason they don't rev so high. but with a heavy rotating assembly no engine can rev high regardless of the fuel, and im curious. diesel dragsters. how high do they rev? im sure its more than 4000 rpms.
     
  15. May 28, 2013 #14

    462chevelle

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    lets just say for example you have an engine with a rotating assembly that weighs 2000 grams completely. and then you built an engine with a 1500 gram rotating assembly. it would be easier on parts with the lighter weight rotating assembly assuming the strength of the parts equal....
     
  16. May 29, 2013 #15

    SteamKing

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    No one is denying that a lighter rotating assembly isn't desirable. What I am saying is that this is not the only consideration which must be taken into account.

    Like xxChrisxx posted, diesels and gas engines are different, and their design reflects this accordingly. While it is relatively simple to modify a gas engine to make it run at higher RPM, it may not be quite as easy, nor as desirable, to do so with a diesel.

    One thing to remember with drag or race engines: these are heavily prepped by the builders, even if they are supposedly based on production engines. The cost of a single race engine may be several tens of thousands of dollars. Due to the high stresses put on drag engines, an engine might be used for only a handful of quarter mile runs before it is torn down and rebuilt, or scrapped altogether.
     
  17. May 29, 2013 #16
    Precisely.

    You can flow a set quantity of fuel though a diesel injector, based on hole geometry and injection rail pressure. There is also a relatively fixed delay to ignite the fuel.

    The faster you spin the engine the smaller this window gets as you are mixing in cylinder, so the less fuel you can physically get into the engine and burn. The torque drops off faster than rpm rises so power also drops off.

    Its exactly the same problem as a petrol engine with too small an injector. The difference is its easy to make a bigger injector at 4bar for a port injection petrol, its not so easy at 2000bar common rail diesel.
     
  18. May 29, 2013 #17

    462chevelle

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    with that in mind. I wonder if helping the engine rev in its 1500-4000 power range even faster than normal would help a diesel given it had the gearing, fuel system, and turbo technology to keep up. im just rambling though since the op hasn't got back to this. he hasn't really explained a lot about what he is planning
     
  19. Jul 29, 2014 #18
    Could high rpm torque loss be solved by advancing injection timing with rpm like spark advance on a gas engine?
     
  20. Jul 30, 2014 #19

    462chevelle

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    You could only go so far though because the fuel has to be sprayed into the cylinder under pressure so the fuel doesnt un-vaporize (whatever the term for that is). If you sprayed it in to early it would most likely not even start or smoke like crazy.
     
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