broken turbo

[Greg Hermann]

>Greg,
low and correct at will if you feel like it.
>
>Does bsfc  = basic fuel consumption?

Breake Specific Fuel Consumption (units= pounds of fuel/ brake horsepower-hour)>

>>Just thinking,
>>
>>Maybe I am confused about the definition of duty cycle (%)

I believe that you are.
>>
>>My duty cycle meter is a simple multimeter jobby that I think
>relates
>>on time to off time as a %.
>>
>>I thought that duty cycle is the % of time the injector is open
>>compare to the time is can be open until it has to open again.
>
>It is.

OK, you mis-spoke here, and I missed it before. Duty cycle is the % of time
that an injector is open as a percent of the total TIME IN A CYCLE AT AN
GIVEN ENGINE SPEED--in other words, the total % of the total time that the
injector is open.
>>
>>So as rpm increases the available open time decreases.
>
>It does.
>>
>>Therefore at 6000 rpm,
>>
>>Assuming the injectors fire once every cycle (these actually fire
>>twice on this motor) that gives 3000 pulses every minute.
>>
>>Which equals 50 pulses per second
>>Which gives a maximum open time of 20 msec
>>Therefore 80% = 16 msec
>
>Correct.
>>
>>Now at 1000 rpm - 8.33 pulses per second
>>Which gives a maximum open time of 120 msec
>>Therefore 2% = 2.4 msec
>
>Correct.
>>
>>So from this I get 15% total power which equates to 30 hp (different
>>from my other figure)
>
>I don't see how you got to this.
>
>For simplicity with the numbers, assume that bsfc at idle is same as
>at
>WOT, 6000 rpm, as it is at idle. I know--not true, but really only 10%
>or
>so different, so no biggy in terms of order of magnitude calcs.
>
>OK--with the 80% duty cycle @ WOT 6000 rpm, the injectors are open 80%
>of
>the time (16 ms/20ms) and are therefore flowing 80% of their rated
>flow to
>make 200 HP. With the 2% duty cycle @ idle, the injectors are open 2%
>of
>the time (2.4 ms./120ms.) and are therefore flowing 2% of their rated
>flow,
>(Please bare with me)
>This is where I think there could be a problem - 2% duty cycle doesn't
>mean 2% of rated flow I don't think,

It does..

as we both agree that duty cycle
>is relative to available open time which varies with rpm. (20 ms vs. 120 ms)

>I think that pulse width is what determines flow.

It does, in the sense of fuel flow PER CYCLE, but duty cycle determines
fuel flow PER UNIT TIME. The second is what relates pretty directly to HP
output.

>2% at 1000 rpm is a lot greater width than 2% at 6000 rpm (when I say
>greater width I of course mean time length)

Also,  you are forgetting how tremendously much longer 98% off time is at
idle (117.6 ms.) vs. 20% off time (4 ms.) at WOT 6000 rpm is. This is where
the great disparity in fuel flow per unit time comes from.
>

>
>So 1.8 ms is 11.25 percent of 16ms  which equals 22.5 hp - still a
>lot

But it is only happening 1/6 as often, which would reduce the fuel flow
rate per unit time from 11.25% down to 1.875%, or 3.75 HP.
>

>Regards, Greg