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Direct Injection or Fuel Injection?

Discussion in 'Gen 4 Prius Technical Discussion' started by Elt31987, Sep 13, 2016.

  1. MikeDee

    MikeDee Senior Member

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    I just bought a new Tacoma. It uses both FI and DI. The V6 engine is both Atkinson and Otto cycle. Gas mileage still sucks though. Power isn't all that great either.
     
  2. Samprocat

    Samprocat Active Member

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    It's a work truck...not a saver....


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  3. Mendel Leisk

    Mendel Leisk Senior Member

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    There used to be cars with a single injector at the throttle, as opposed to one-per-cylinder. Is this still in use, any pros/cons?
     
  4. jdenenberg

    jdenenberg EE Professor

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    From Wikipedia:

    "Modern gasoline engines also utilize direct injection, which is referred to as gasoline direct injection. This is the next step in evolution from multi-point fuel injection, and offers another magnitude of emission control by eliminating the "wet" portion of the induction system along the inlet tract.

    By virtue of better dispersion and homogeneity of the directly injected fuel, the cylinder and piston are cooled, thereby permitting higher compression ratios and earlier ignition timing, with resultant enhanced power output. More precise management of the fuel injection event also enables better control of emissions. Finally, the homogeneity of the fuel mixture allows for leaner air–fuel ratios, which together with more precise ignition timing can improve fuel efficiency. Along with this, the engine can operate with stratified (lean-burn) mixtures, and hence avoid throttling losses at low and part engine load. Some direct-injection systems incorporate piezoelectronic fuel injectors. With their extremely fast response time, multiple injection events can occur during each cycle of each cylinder of the engine."

    JeffD
     
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  5. bhtooefr

    bhtooefr Senior Member

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    That doesn't answer Mendel Leisk's question - they were asking about port injection vs. throttle body injection, not direct injection vs. throttle body injection, presumably.

    The actual answer is that throttle body injection, to the best of my knowledge, only exists nowadays in kits designed to retrofit fuel injection to carbureted engines. TBI has better air/fuel mixture than a carburetor, due to the fuel being sprayed into the intake manifold under pressure through a nozzle, rather than a venturi sucking fuel into the manifold. (In World War II-era aviation, it was known as a "pressurized carburetor" (used because it wasn't sensitive to gravity, and therefore worked while flying inverted), although in a more primitive form than 1980s-1990s TBI.) It's also easier to control it with a computer as a result. However, because it's being centrally injected, air/fuel mixture varies depending on how far a cylinder is from the center - on a TBI 4-cylinder, cylinders #2 and #3 get more fuel, and #1 and #4 get less fuel. Also, the further cylinders can have fuel condense on the manifold, worsening air/fuel mixture.

    Modern port fuel injection delivers fuel only when a cylinder's intake valve is open, and right at the valve. This gives less time to condense, better throttle response, and more even mixture control between cylinders.
     
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  6. Mendel Leisk

    Mendel Leisk Senior Member

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    We had a Honda Civic loaner car one time with throttle body fuel injection, maybe early 2000's. Just while getting some body work done on our car. IIRC it had an odd lag in the throttle response, you had to press further, further, then it would kick in with a surge. That got old real fast, even in the few days we had it. I'm not sure if it was the fuel delivery system, or the throttle cable, or a combination of the two.
     
  7. bhtooefr

    bhtooefr Senior Member

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    That might've been simply how it was tuned (or not tuned as the case may be), especially if it was an automatic, especially considering how Honda went for high-revving small displacement, and then it may well have been reluctant to downshift for economy reasons.

    TBI won't usually feel that bad, AFAIK, if it's working properly. Just a slight delay between a change in throttle application, and the corresponding change in engine power.
     
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  8. Trollbait

    Trollbait It's a D&D thing

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    What year was that Civic? Sounds like that might be their variable valve system going from economy to power.
     
  9. Mendel Leisk

    Mendel Leisk Senior Member

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    No, I don't think so. Our 06 Civic Hybrid had the dual-height cams, I'm familiar with how that feels. It was quite smooth. Satisfying too: there's one overpass in our neighbourhood with moderately steep rise, and I guess because you encounter it while accelerating, the car would always shift over to the higher lift cams for that rise. Very seamless.
     
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  10. Trollbait

    Trollbait It's a D&D thing

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    But if your loaner was of the same era, then it was very unlikely it had throttle body injection. Wikipedia has it being phased out after 1995 for American cars.
    Fuel injection - Wikipedia
     
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  11. Mendel Leisk

    Mendel Leisk Senior Member

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    Yeah I'm likely muddled about the year. Maybe was early 90's.
     
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  12. bhtooefr

    bhtooefr Senior Member

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    And it looks like 1991 was the last year for a Civic to have Honda's DPFI, which was really a dual-injector throttle body injection setup.
     
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  13. alanclarkeau

    alanclarkeau Senior Member

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    It could well just need cleaning - my 940 VOLVO which I think had throttle body injection was running rough, my mechanic cleaned Throttle Body and a couple of other parts, didn't take long or cost much but made a huge difference.