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  1. #1
    la vache fantôme phantomcow2's Avatar
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    How fast does an injector inject?

    How fast does an automotive gasoline injector function? Or I guess the appropriate question, what would the maximum speed be in general? Just looking for a ballpark estimate.
    Thanks
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    Señor Member USAZorro's Avatar
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    Faster than you can say "Jack Robinson".

    Engine rpm at redline / 60 / # of strokes = rough ballpark of duration of one injection in seconds.
    The search for inner peace continues...

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    On my TARDIScycle! KingTermite's Avatar
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    Quote Originally Posted by phantomcow2 View Post
    How fast does an injector inject?
    At the injection rate. ya think?
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    - it's pretty well established that Hitler was an *******.

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    Chepooka StupidlyBrave's Avatar
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    don't get started on the woodchucks !

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    Hey guyz? Guyz? Wait up!! Siu Blue Wind's Avatar
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    Really super duper fast.
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    Hey guyz? Guyz? Wait up!! Siu Blue Wind's Avatar
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    Like HELLA fast.
    Quote Originally Posted by Buddha
    We are what we think. All that we are arises with our thoughts. With our thoughts, we make the world.
    Quote Originally Posted by making View Post
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  7. #7
    I'm whats for dinner Versa2nr's Avatar
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    ****Taken from Wikipedia @ http://en.wikipedia.org/wiki/Fuel_injection



    Calculate injector pulsewidth from airflow

    First the CPU determines the air mass flow rate from the sensors - lb-air/min. (The various methods to determine airflow are beyond the scope of this topic. See MAF sensor, or MAP sensor.)
    • (lb-air/min) × (min/rev) × (rev/4-strokes-per-cycle) = (lb-air/intake-stroke) = (air-charge)
    - min/rev is the reciprocal of engine speed (RPM) – minutes cancel. - rev/2-revs-per-cycle for an 8 cylinder 4-stroke-cycle engine.
    • (lb-air/intake-stroke) × (fuel/air) = (lb-fuel/intake-stroke)
    - fuel/air is the desired mixture ratio, usually stoichiometric, but often different depending on operating conditions.
    • (lb-fuel/intake-stroke) × (1/injector-size) = (pulsewidth/intake-stroke)
    - injector-size is the flow capacity of the injector, which in this example is 24-lbs/hour if the fuel pressure across the injector is 40 psi. Combining the above three terms . . .
    • (lbs-air/min) × (min/rev) × (rev/4-strokes) × (fuel/air) × (1/injector-size) = (pulsewidth/intake-stroke)
    Substituting real variables for the 5.0L engine at idle.
    • (0.55 lb-air/min) × (min/700 rev) × (rev/4-strokes-per-cycle) × (1/14.64) × (h/24-lb) × (3,600,000 ms/h) = (4.0 ms/intake-stroke)
    Substituting real variables for the 5.0 L engine at maximum power.
    • (28 lb-air/min) × (min/5500 rev) × (rev/4-strokes-per-cycle) × (1/11.00) × (h/24-lb) × (3,600,000 ms/h) = (34.6 ms/intake-stroke)

    Injector pulsewidth typically ranges from 4 ms/engine-cycle at idle, to 35 ms/engine-cycle at wide-open throttle. The pulsewidth accuracy is approximately 0.01 ms; injectors are very precise devices.
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  8. #8
    Senior Member Michigander's Avatar
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    For an accurate, visual representation, pull an injector from your engine, and have a friend rev it up while you look at it. It will spray gasoline all over and give you a first hand idea.
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    <>< SoonerBent's Avatar
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    Never really tried to time one but if you use a stethoscope on one you can hear the injector opening and closing. You might be able to time it.

  10. #10
    blithering idiot jhota's Avatar
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    do you mean cyclic speed or flow rate?

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    Banned. ModoVincere's Avatar
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    showing my stupidity here, but doesn't the flow rate depend on the pressure with which the fuel is being pushed through the nozzle?

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    Senior Member Michigander's Avatar
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    Quote Originally Posted by ModoVincere View Post
    showing my stupidity here, but doesn't the flow rate depend on the pressure with which the fuel is being pushed through the nozzle?
    Yes, exactly, the wider open the throttle position, the more gasoline will be sprayed into the cylinder.
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  13. #13
    The Site Administrator: Currently at home recovering from a couple of strokes,please contact my assistnt admins for forum issues Tom Stormcrowe's Avatar
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    Wouldn't it also depend on whether it is TBI, Tuned Port, or direct injectors?

    TBI is essentially a continuous flow of fuel into a throttle body in top of the intake manifold and Direct is pulsed directly into the cylinder with a separate air entry system .....
    on light duty due to illness; please contact my assistants for forum issues. They are Siu Blue Wind, or CbadRider or the other 3 star folk. I am currently at home recovering from a couple of strokes. I am making good progress, happily.


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    Senior Member Michigander's Avatar
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    I never did like TBI. I find it difficult to think of a reason for devolving away from carburetors.
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    Master Surfer of Curbs glenng's Avatar
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    How fast does an injector inject?


    Faster than a woodchuck can chuck wood
    Glenn

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    Senior Member Michigander's Avatar
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    Here's a bunch of injectors spraying.

    http://www.youtube.com/watch?v=kHJSRpE5ok4
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    No Rocket Surgeon eubi's Avatar
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    Quote Originally Posted by Michigander View Post
    For an accurate, visual representation, pull an injector from your engine, and have a friend rev it up while you look at it. It will spray gasoline all over and give you a first hand idea.
    Don't forget to hold the spark plug wire in your other hand.

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  18. #18
    Senior Member DannoXYZ's Avatar
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    I've used up to 96-lb/hr (1000cc/min) injectors on my car. Problem with such a high flow-rate is that in order to move the required fuel-volume out of a single hole pintle, it comes out pretty much as liquid stream. Not good for atomization, mixing with incoming-air and power-production. Using 6-hole disc-type nozzles really improved spray-pattern and atomization (less latency too), but it still wasn't good enough.

    So I moved to dual 55-lb/hr injectors (per cylinder) in a staged configuration. The ECU runs one injector up to 80% duty-cycle. Then it holds that one at 80% and brings on the 2nd injector. By the time they're both running 80%, it'll increase flow from both of them to 100%. Using injectors above 80% duty-cycle is not recommend as it gives it too little time to cool off between squirts.

    Quote Originally Posted by ModoVincere View Post
    showing my stupidity here, but doesn't the flow rate depend on the pressure with which the fuel is being pushed through the nozzle?
    Yes, the flow-volume and flow-velocity an injector generates is also dependent upon the pressure-differential between the injector's inlet and outlet (inlet-outlet). The official "size" of an injector assumes a standardized 3-bar of fuel-pressure at the injector's inlet and 100% duty-cycle. However, that 3-bar of pressure is misleading. Even if you feed an injector 3-bar of fixed-pressure, that's not really the pressure-differential between the inlet and outlet. That's because the outlet end of the injector faces intake-manifold pressure, which changes constantly.

    So at idle with 0.3-bar (absolute) in the intake-manifold, the injector is actually seeing 3bar-(-0.7bar vacuum) = 3.7 bar of pressure-differential. And under full-throttle with 0.8-bar in the intake, the actual pressure driving fuel is 3bar-(-0.2 bar vacuum)bar = 3.2 bar. As a result, a 10ms pulse of injector-open time during full-throttle has less pressure pushing fuel than the same 10ms pulse at idle. This makes fuel-volume calculations very difficult if you have to account for manifold-pressure all the time and have to re-adjust pulse-width accordingly.

    Imagine an extreme case of turbocharging at say... 3-bar of boost (43.5psi). The 43.5psi of intake-manifold pressure at the injector outlet perfectly pushes back the 4.35psi of fuel-pressure on the injector inlet and you'd get ZERO fuel-flow at all when the injector opens

    There's a clever way around this. That's to use automatic feedback to adjust fuel-pressure. The intake manifold-pressure is actually fed into the 3bar fuel-pressure regulator to automatically adjust its pressure. The reference-pressure is 0-psi (atmospheric) which causes no adjustments to the FPR's pressure-output. Vacuum in the intake will subtract from the FPR's fuel-pressure while boost above atmospheric will add to the FPR's output.

    So at idle, the higher vacuum will cause fuel-regulator will put out 3bar+(-0.7bar) = 2.3 bar. The injector sees this pressure combined with vacuum in the manifold 2.3bar-(-0.7bar vacuum) = 3.0bar fuel pressure.

    At full-throttle the regulator puts out 3bar+(-0.2bar) = 2.8bar. And the injector gets 2.8bar-(-0.2 bar vacuum) = 3.0bar fuel pressure. The variable-pressure feedback-adjusted fuel-pressure regulator thus automatically cancels out intake-manifold pressure and a 10ms pulse delivers identical fuel-volumes regardless of intake maniold pressure!



    Seems like all this is putting the cart before the mule. What is it that you're trying to do? Define your objectives and desired-results first in concrete terms, and THEN try to figure out a way to implement it.
    Last edited by DannoXYZ; 11-07-07 at 03:19 PM.

  19. #19
    Chepooka StupidlyBrave's Avatar
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    Quote Originally Posted by glenng View Post
    How fast does an injector inject?


    Faster than a woodchuck can chuck wood


    See post #4



  20. #20
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    Quote Originally Posted by ModoVincere View Post
    showing my stupidity here, but doesn't the flow rate depend on the pressure with which the fuel is being pushed through the nozzle?
    No. Most FI systems are constant pressure systems. The pressure in the fuel rail remains constant, the longer the injector stays open, the more fuel it injects and vice versa. In Versa's post above, you can see that the pulse lasts from 4 to 35 ms from idle to FT.
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  21. #21
    Banned. ModoVincere's Avatar
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    Quote Originally Posted by San Rensho View Post
    No. Most FI systems are constant pressure systems. The pressure in the fuel rail remains constant, the longer the injector stays open, the more fuel it injects and vice versa. In Versa's post above, you can see that the pulse lasts from 4 to 35 ms from idle to FT.
    yes, but the flow rate would still be dependent on the pressure, no?

  22. #22
    Master Surfer of Curbs glenng's Avatar
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    Quote Originally Posted by StupidlyBrave View Post


    See post #4


    Glenn

  23. #23
    Senior Member DannoXYZ's Avatar
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    Quote Originally Posted by ModoVincere View Post
    yes, but the flow rate would still be dependent on the pressure, no?
    Yes it does. Flow-rate is dependent to the square-root power of pressure-differential between the inlet vs. outlet ports of the injector. So if you increase pressure by 2x, flow increases by sqrt(2)= 1.4x . There's a misconception about FI systems using constant-pressure, they actually are calibrated for constant pressure-differential between the injector inlet & outlet. This function is served by the variable-pressure FPR and that allows the ECU programming to assume a constant pressure-differential. Thus a 30ms pulse-width can always be assumed to deliver X-volume of fuel regardless of manifold-vacuum/boost. Here's some pictures of FPRs on the market:

    Stock Bosch 3-bar FPR used on a majority of German cars:


    Aftermarket FPRs:



    The fuel-pressure regulator works by being a restriction at the exit end of the fuel-rail. The FPR is bolted to the fuel-rail and the inlet on the side of the FPR is hidden between the two bolt-holes. The large threaded outlet at the end goes to the fuel-line back to the tank. The tiny vacuum nipple is hooked up to the intake-manifold to get the adjustment-pressure based upon manifold-vacuum.

    These aftermarket FPRs also have adjustable initial-pressure with the threaded bolt with locking nut. These set the desired pressure at with 0 vacuum/boost (engine off or vacuum-nipple vented to atmosphere). Then the vacuum-nipple will typically adjust the actual output pressure anywhere from -10psi to +30psi in order to maintain a constant pressure-differential between the injector's inlet & outlet ports.

    It's also easy enough to verify that fuel-pressure in the rail changes with throttle-position and manifold-vacuum. Just hook up one of these gauges at the end of teh rail:



    At idle, manifold-pressure is typically the lowest (most vacuum) and you'll see lowest-pressure on the gauge. Rev it up some and vacuum decrease (more pressure in manifold) and pressure increases. If you've got a turbo car, add boost on the road and you'll see pressure increases even more. All the while, the pressure-differential across the injector remains constant.
    Last edited by DannoXYZ; 11-07-07 at 03:22 PM.

  24. #24
    Pokes On Spokes JPradun's Avatar
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    Slightly OT, but a damn good read for anyone who hasn't seen it before:

    # One Top Fuel dragster's 500-cubic-inch Hemi engine makes more horsepower than the first four rows at the Daytona 500.

    # A stock Dodge Hemi V-8 engine cannot produce enough power to drive the dragster's supercharger.

    # With 3000 CFM of air being rammed in by the supercharger on overdrive, the fuel mixture is compressed into a near-solid form before ig-nition. Cylinders run on the verge of hydraulic lock at full throttle.

    # At the stoichiometric 1.7:1 air-fuel mixture for nitromethane, the flame front temperature measures about 7000 degrees Fahrenheit.

    # Nitromethane burns yellow. The spectacular white flame seen above the stacks at night is raw burning hydrogen, separated from atmospheric water vapor by the searing heat of the exhaust gases.

    # Dual magnetos supply 44 amps to each spark plug. This is the output of an arc welder in each cylinder.

    # Spark plug electrodes can be totally consumed during a single pass. After half-distance, the engine is dieseling from compression plus the glow of exhaust valves at 1400 degrees Fahrenheit. The engine is shut down by cutting the fuel flow.

    # If a spark plug fails early in the run, un-burned nitro can build up in the affected cylinder and explode with sufficient force to blow the cylinder head off in pieces or split the cylinder block in half.

    # In order to exceed 300 mph in 4.5 seconds, dragsters must accelerate at an average of more than 4 g's. In order to reach 200 mph before half-distance, the launch acceleration approaches 8 g's. A Top Fuel dragster reaches more than 300 mph before you have completed reading this sentence.

    # With a redline that can be as high as 9500 rpm, Top Fuel engines turn approximately 540 revolutions from light to light. Including the burnout, the engine needs to survive only 900 revolutions under load.

    # Assuming that all of the equipment is paid off, the crew works gratis, and nothing breaks, each run costs an estimated $1000 per second.

    # The current Top Fuel dragster elapsed time record is 4.441 seconds for the quarter-mile (October 5, 2003, Tony Schumacher). The top-speed record is 333.25 mph as measured over the last 66 feet of the quarter-mile (November 9, 2003, Doug Kalitta).

    # Putting all of this into perspective: You are driving the average $140,000 Lingenfelter twin-turbo Corvette Z06. More than a mile up the road, a Top Fuel dragster is staged and ready to launch down a measured quarter-mile as you pass. You have the advantage of a flying start. You run the Vette up through the gears and blast across the starting line and past the dragster at an honest 200 mph. The "tree" goes green for both of you at that moment. The dragster launches and starts after you. You keep your foot down, but you hear a brutal whine that sears your eardrums, and within three seconds, the dragster catches you and beats you to the finish line, a quarter-mile from where you just passed him. From a standing start, the dragster spotted you 200 mph and not only caught you but nearly blasted you off the road when he passed you within a mere 1320 feet.
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  25. #25
    la vache fantôme phantomcow2's Avatar
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    I would like to know a typical pulse length that an ECU sends to an injector because I am considering building a circuit that can scale this pulse to be longer. This elongated pulse could possibly provide power to a solenoid valve, or even a Ford IAC valve. It'll provide the power to something, I Just need to find out what.
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