idea..

[Brad Sheridan]

>This mechanical engineer had an idea related to this thread and I
>haven't a clue a clue how to implement it.  Would it be easy to use one
>or more of the standard IC's to make a visual instantaneous fuel usage
>meter?  If the fuel pressure to the injectors is constant, then the
>variable of fuel delivery is injector pulse.  If you knew what the
>longest potential injector pulse length is, then could you make a
>display of ten LED's and have the LED's light up as the pulse length
>goes up?  I realize the pulse length is rather small in relation to the
>respomse of the LED's and your eyeball, but it seems like a resonable
>project.  I'm more interested in if it could be done easily rather than
>begging someone to do it.

  You would need to know more than just the pulse length, as a 1ms pulse at
1000 rpm and a 1ms pulse at 20000rpm are quite different in terms of fuel
consumption. Forgetting about injector opening/close times, 1ms at 1000 rpm
is keeping the injector closed most of the time, opening once every 60 or
more ms. This means its delivering fuel at less than 2% of its max. flow
rate. At 20000 rpm, the injector is opened for 1ms every 3ms, delivering
fuel at 33% of its max flow rate. Measuring duty cycle would be the way to
get instantaneous fuel usage, this can be calculated from pulse width and
frequency. And yes, I'm sure it can be done quite easily, although I've
never done it. I'm sure there's plenty of averaging circuits or duty cycle
circuits already designed that could be used.

Brad