Diesel Engine Working Principle

Discussion in 'Automotive Electronics' started by RdAdr, Feb 20, 2016.

  1. RdAdr

    Thread Starter Member

    May 19, 2013
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    The four steps are like this:

    1) The piston starts at the top, the intake valve opens, and the piston moves down to let the engine take in a cylinder-full of air and gasoline. This is the intake stroke. Only the tiniest drop of gasoline needs to be mixed into the air for this to work. (Part 1 of the figure)

    2) Then the piston moves back up to compress this fuel/air mixture. Compression makes the explosion more powerful. (Part 2 of the figure)

    3) When the piston reaches the top of its stroke, the spark plug emits a spark to ignite the gasoline. The gasoline charge in the cylinder explodes, driving the piston down. (Part 3 of the figure)

    4) Once the piston hits the bottom of its stroke, the exhaust valve opens and the exhaust leaves the cylinder to go out the tailpipe. (Part 4 of the figure)

    My questions:
    1) What opens the intake valve? What moves the piston down?
    2) What moves the piston back up?
    3) Now I see that the piston moves down because of the explosion.
    4) What moves the piston back up? And what opens the out valve?
     
  2. bertus

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  3. joeyd999

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    This is not a description of a diesel engine!
     
  4. ISB123

    Well-Known Member

    May 21, 2014
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    1.Starter motor starts the engine by cranking the crankshaft which results in mixture getting sucked in the cylinder and being ignited by compression.Camshaft controls the valves.
    2.Inertia and firing sequence of pistons.
    3.
    4. Firing sequence of pistons. E.g. 4 cyl. engine firing cycle 1-3-4-2.
    Diesels don't use spark plugs since they depend on heat generated by compression to ignite the mixture.

    [​IMG]
     
  5. crutschow

    Expert

    Mar 14, 2008
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    The valves are controlled by the camshaft which is driven by the crankshaft.
     
  6. joeyd999

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    And they don't suck in a mixture either. They compress air, then inject fuel. Combustion is spontaneous due to heat of compressed air.
     
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  7. ian field

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    Oct 27, 2012
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    Apparently some manufacturers are developing solenoid operated valves - but I doubt any are in production yet.

    It may have been Honda that released a bulletin about an engine that can switch off some of the cylinders for economy mode.

    AFAIK: they plan to leave the valves closed on the resting cylinders - Some of the energy gets returned on the downstroke if you compress the gas in the cylinder, the inertia/resistance of shifting cylinder gas through open valves would consume significant energy.
     
  8. Alec_t

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    Sep 17, 2013
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    I don't think I'd buy one. I'd expect increased vibration hence increased engine wear and shorter engine life. Good for car company profits maybe, but hardly economy for the motorist.
     
  9. RdAdr

    Thread Starter Member

    May 19, 2013
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    Thanks for answers. I also found this video:


    So the starter motor provides the initial momentum and then the pistons move by themselves due to inertia and air-fuel explosions.

    I need to read more on this. I have very basic knowledge in engines.
     
    Last edited: Feb 20, 2016
  10. #12

    Expert

    Nov 30, 2010
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    I think you're about a century behind in your understanding of technology. Design them right and you find the observed fact of diesel engines out-lasting gasoline engines by a factor of 2 to 3.
     
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  11. jpanhalt

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    Jan 18, 2008
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    In reference to Ian Field's comment about switching off cylinders:

    Actually, they are becoming quite common. Ford has some models, and the new $100,000 Corvette switches off 4 of 8 cylinders at any one time, unless you stomp on it. Then it really goes.

    John
     
  12. joeyd999

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    This is true. The 'Eco' mode in my Odyssey seamlessly knocks out 3 of 6 cylinders when power is not required, and seamlessly reengages them when it is. All I see is the indicator light going on and off...I've never felt a thing.
     
  13. ian field

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    I think cylinder bank isolation was already around, that simply removed a whole crankshaft serving one bank of cylinders from the drive train.

    Disabling the valves on some cylinders is a newer idea and I don't know how far its developed so far.
     
  14. jpanhalt

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    Jay Leno's review of the Z06 Corvette, as I recall, has electronic controlled valves.



    John
     
  15. crutschow

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    Mar 14, 2008
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    Why would you expect more vibration?
    Most engine vibration is cause by the imbalance of the rate the pistons are accelerated up and down (especially in four cylinder in-line engines), not by whether they are firing or not.
     
  16. ian field

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    It certainly has an effect - as I discovered on a 4-cyl motorcycle with one fouled plug.

    It probably has more to do with power delivery than the reciprocating mass of pistons etc, but it doesn't do the engine any good.

    Presumably the manufacturer would take these things into account and design carefully.
     
  17. Alec_t

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    Oh, at least a century :).
    Because I've experienced increased vibration on a 4-cylinder in-line petrol engine with a blocked injector. Perhaps if two injectors had been blocked I wouldn't have noticed ;). I can see that 3 out of 6, or 4 out of 8 cylinders non-firing would have a better chance of balanced running.
     
  18. joeyd999

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    Variable Cylinder Management
     
  19. crutschow

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    Note that a cylinder with a fouled plug is different than deliberately turning off a cylinder.
    In the latter case they keep the valves closed so that you aren't pumping air through the cylinder.
    Not sure if that would make a difference in the vibration though.
    It's likely that turning off more than 1 cylinder at a time is what minimizes any added vibration, as Alec noted.
     
  20. WBahn

    Moderator

    Mar 31, 2012
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    The idea of effectively removing cylinders from the engine is decades old. I remember see car commercials from the 70's or 80's where they touted how the car would reduce the number of cylinders from 8 to 6 to 4 to achieve really high fuel economy. Since it seemed to be a passing fad, I concluded that the increases in economy, if any, were marginal and the increase in maintenance or initial investment outweighed any savings.
     
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