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Hydrogen as an additive to diesel fuel?

  1. Feb 5, 2008 #1
    Let me start off by saying that I understand conservation of energy and the laws of thermodynamics. I know you can't use water for fuel, and you can't power a vehicle soley on hydrogen produced by an onboard electrolyzer.

    But... I have read quite a few claims that using an onboard electrolyzer, and pumping that hydrogen into the air intake will increase the fuel mileage. The claim is that, because hydrogen "burns" very hot and very fast, it will cause the diesel fuel to burn more completely. A more complete burn would mean that less fuel would be required to perform the same amount of work.

    Thoughts?
     
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  3. Feb 6, 2008 #2

    mgb_phys

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    Injecting hydrogen will certainly give you power from burning the hydrogen.
    I woul dhave thought it would DECREASE the efficency of the diesel since any significant amount of hydrogen will consume some of the oxygen that the diesel could have burnt. Diesels run at pretty much their optimum temperature naturally becuse of the way the ignition operates.
     
  4. Feb 6, 2008 #3
    Getting a fuel to burn completely in general does not depend on temperature but more on mixing and adequate time in the combustion chamber. Just because there are claims doesn't make them true.
     
  5. Feb 6, 2008 #4

    brewnog

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    You can definitely mix a combustible gas with the intake air for a Diesel engine and have it operate with lower running costs; this is the idea behind dual fuel engines. However, the benefit generally comes from gas (not gasoline) being cheaper per kWb output than Diesel as a fuel.

    I don't believe the notion that hydrogen gives a hotter, faster burn causing the Diesel to burn more completely. Diesel has no problem burning completely. Hydrogen on its own is a horrible fuel in an IC engine.
     
  6. Feb 7, 2008 #5
    > Hydrogen on its own is a horrible fuel in an IC engine.

    Could you explain how you came to this? Cause I would have thought that mixing hydrogen with the intake air can potentially make the carburator obsolete, as we have an ignitible mixture in the inlet already. Only timing of valves and ignition might need to change a little.

    In fact I have a very old car that should soon be withdrawn, and thinking of trying to mix some hydrogen at the air inlet and see what happens. It would be cool if the engine still runs after the gasoline has run out. Even cooler if the car explodes. :)
     
  7. Feb 7, 2008 #6
    I am aware the carburator is obsolete already btw, replaced with injection. So injection can potentially become obsolete if we find a way to produce and store hydrogen, instead of gasoline.
     
    Last edited: Feb 7, 2008
  8. Feb 7, 2008 #7

    mgb_phys

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    It has a tendancy to pre-ignite when it gets near anything hot - like a piston engine.
    It has lower energy/mole than something like LPG simple because there is more hydrogen in the hydrocarbon - so you have difficulty pushing enough gas into the cylinder.
    The main reason though is that if you have gone to all the trouble of distributing and storing H2 it is much more efficent to use it in a fuel cell + electric motor.
    Using it in an IC engine is like burning batteries on a fire and using the heat to run a steam turbine.
     
  9. Feb 7, 2008 #8
    > if you have gone to all the trouble of distributing and storing H2 it is much more efficent to use it in a fuel cell + electric motor.

    Do you have any data to support this statement, any efficiency calculations?

    Because I thought electrolysis too is inefficient, fuel-cell inverse electrolysis might be about as bad. And what is the efficiency of an IC engine, after 100 years of development?
     
  10. Feb 7, 2008 #9

    Mech_Engineer

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    mgb is correct in that an IC engine isn't a very efficient way to extract energy from gaseous hydrogen. IC engines are inefficient, and hydrogen has a relatively small amout of energy/volume when compared to petroleum based fuels (or even alcohols).

    Modern internal combustion engines are still only about 15-20% efficient at extracting power from gasoline or diesel. Some compresion ignition engines (diesels) that have turbochargers or other beneficial aids may have peak efficiencies as high as 40%, but average still works out to about 22%. Gas engines' efficiencies are slightly lower.

    New fuel cells have efficiencies approaching and surpassing 60%, while the electrical systems paired to them (motor, batteries, current and throttle control, etc.) bring the total system efficiency to around 40%. In european driving tests, fuel cell cars have exhibited tank-to-wheels efficiencies of around 35%.

    Power-plant-to-wheels efficiencies for fuel cell cars have been rated as low at 15%, but the problem is this number cannot be compared to petroleum-based powerplants because their 'energy' already exists and is being mined while any energy put into an electrolysis plant to manufacture hydrogen must first be taken from somewhere else (my vote: nuclear).
     
    Last edited: Feb 7, 2008
  11. Feb 7, 2008 #10

    brewnog

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    Yes, hydrogen is very susceptible to knock.

    I don't know how you arrived at the idea that carburettion/fuel injection could be eliminated.

    How would you meter the fuel? How would you mix it with the air? How would you control the engine speed/load and air/fuel ratio? Would you still use gasoline? How would you meter and mix that?
     
  12. Feb 7, 2008 #11
    > Yes, hydrogen is very susceptible to knock.

    What is knock caused by with gasoline? I thought it's just a matter of valve timing, and if you adjust them right for the fuel, there's no knock. Is it not so?

    > How would you meter the fuel? How would you mix it with the air? How would you control the engine speed/load and air/fuel ratio?

    I was thinking that we'd just connect the pedal to the tap of the hydrogen bottle, and that's all. Injection is defined as spraying fuel directly into the combustion chamber, right?
     
  13. Feb 7, 2008 #12

    Mech_Engineer

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    Last edited: Feb 7, 2008
  14. Feb 7, 2008 #13
    Found a hybrid gasoline/hydrogen one too. The BMW 745h makes 184hp out of a 4.4-liter V8:

    http://www.hydrogencarsnow.com/hydrogencars2001.htm

    Can someone please tell me, can I work out the energy efficiency of a car just by looking at the consumption and the speed and the power curve and the rpm?

    I tried it and got over 100% efficiency so I have made a mistake. Can anyone help me do it right?
     
  15. Feb 7, 2008 #14
    What about this:

    efficiency = power at engine output / energy of fuel burned per s

    Power I look it up on the power curve, given the rpm reading of the dial.

    Fuel burn rate in l/h = fuel consumption in l/100km (from the dial) * speed in km/h from the dial * 100

    Is this right?
     
  16. Feb 7, 2008 #15

    Mech_Engineer

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    Yes, the general method for calculating the engine's efficiency would be to divide the power you're getting out divided by the total possible power you're putting in. So, in the case of a car engine, if you knew how much power it's putting out at a specific rpm, and you also knew how much fuel it's using in time (gal/min, whatever), you could get a gross efficiency by dividing the two numbers.
     
  17. Feb 7, 2008 #16

    mgb_phys

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    Knock is preignition of the fuel. With a gasoline or dielsel engine it is due to injecting the fuel with the cylinder at the wrong pressure due to bad timing.
    Hydrogen will ignite from the temperature inside the cylinder - especially the hot exhast valve. Hydrogen might work better in a rotary/Wankel engine.
     
    Last edited: Feb 7, 2008
  18. Feb 7, 2008 #17
    I would think that all three of those factors would have an influence. Problem is adjusting those factors. Increasing the amount of time in the chamber means you advance the timing. Thats not a good idea in and of itself, but they (the people trying to sell these electrolyzers) actually suggest you retard the timing because of the more rapid combustion. The rapid, hot burn of the hydrogen is supposed to boost the rate of the diesel burn, thus burning it more completely before the end of the power stroke.
    I beg to differ... Isn't all that black smoke spewing out the tailpipe unburned fuel?
    Unless this source http://www.engineeringtoolbox.com/fuels-ignition-temperatures-d_171.html is wrong, Hydrogen has a rather high auto-ignition temperature of 932 oF, almost double that of diesel fuel. Is the air (and surface) temperature inside the chamber higher than this before injection?



    BTW, I'm just as skeptical as the rest of you, otherwise I'd be building one right now. I'm just trying to keep an open mind and so far I haven't heard any concrete evidence why it wouldn't work. For me, it's just a gut feeling that it won't, but I need more than that to completely dismiss it.


    P.S.
    AMEN!
     
  19. Feb 9, 2008 #18

    brewnog

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    Yes. However, it's not difficult to get this not to happen. (Black smoke is generally a sign of overfuelling for one reason or another).

    It's not just high temperatures which cause fuel to ignite in an engine, it's the high pressures. This is how an IC engine works; the key is compression of the charge before ignition.

    As we've seen, it does work. Just not very well, for the reasons that have been stated.
     
  20. Feb 9, 2008 #19

    Ivan Seeking

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    About 1/3.

    According the the Sci Am article "Questions about a Hydrogen Economy"from May 2004, for a grid electric hydrogen fuel cell powered auto, the fuel chain efficiency is about 22%; the vehicle is about 38% efficient, and the total efficiency is about 8%.

    The most efficient option of all is steam reforming - hydrogen from methane using steam -and a H2 fuel cell powered auto. This has a "well to wheels" total efficiency of about 22%.

    I believe the fuel chain efficiency for petroleum is est to be about 80%.
     
  21. Feb 9, 2008 #20

    Ivan Seeking

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    Something else to be considered is the cradle to grave efficiency of the hardware: What is the energy cost of production? What is the life expectancy? What are the recycling energy costs? What is the recycling recovery efficiency? What is the total impact on the environment [mining, smelting, transportation, chemical effluents, all of the workers who commute each day to produce a product, etc]? Also, we have to factor in where the production occurs. For example, would it be produced in China where we have an environmental free-for-all and coal power?

    There is often [usually?] a direct relationship between cost and the energy required to produce a technology, but environmental impact may have no serious consequences for cost and can be a hidden variable.
     
    Last edited: Feb 9, 2008
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