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Old 09-24-2008, 09:17 AM   #1 (permalink)
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Sensing Injection with Flexiforce Sensor?

Hi All,
I have a mechanically injected diesel engine. I have been assessing options to get fuel usage information for the MPGuino.

I'm wondering if there is any definite reason why a Flexiforce sensor wrapped around one of the injector lines would not work for sensing injector firing and duration. The details of the sensor can be found here: SparkFun Electronics - Flexiforce Pressure Sensor - 25lbs.. I'm not sure whether the 1, 25 or 100lb sensor would be best.

If there is a chance this sensor might work I'm happy to give it a try as it is significantly cheaper then going the dual flow transducer route.

Cheers,
David

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Old 09-24-2008, 09:42 AM   #2 (permalink)
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DieselJohn had mentioned piezos on injectors before also, kind of an electronic mechanics stethoscope. I don't know enough about mechanical pumps to know for sure. The duration if the injection is only half the equation, the flow rate is the other half.

So what effect does the throttle have on the pump? How about RPM? Does throttle affect the duration and rpm affects the flow rate? You could conceivably compute both with a piezo on an injector if so. I don't know about wrapped around the fuel line.
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Old 09-24-2008, 09:56 AM   #3 (permalink)
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Is this the sort of thing we are talking about here?
Robert Bosch type VE Diesel injection pump

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Old 09-24-2008, 11:50 PM   #4 (permalink)
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Quote:
Originally Posted by dcb View Post
Is this the sort of thing we are talking about here?
Robert Bosch type VE Diesel injection pump

I believe it has a rotary (VE) Zexel fuel pump which is made under license from Bosch so it should operate as described. There was not too much said about fuel pressure in that article other than in the timing section. I wonder whether the fuel pressure on the output side is kept relatively constant?
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Old 09-25-2008, 12:25 AM   #5 (permalink)
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i have used timing lights that use the signal from a little split collar that bolts around the injection line. it has a piezo crystal in inside which senses the expansion of the steel line as pressure builds inside before/as the injector needle pops off. looking at the signal on a scope, it does a fair amount of ringing after pop off and during injection. separating the strain from all the acceleration in the area, would be part of the signal processing fun. the timing light only needed the highest peak in the time domain. but the line is definitely expanded while fuel is being delivered. i have used a knock sensor as an accelerometer, but they have their own resonance right the middle of the frequency spectrum to confuse the issue. gas grill igniter...
I need to measure the return fuel to see if it is inversely proportional to the fuel used, one of these days..

Last edited by diesel_john; 09-25-2008 at 12:43 AM..
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Old 09-27-2008, 03:07 AM   #6 (permalink)
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Would it be possible to read the output from one of these using a sound-card without too much trouble?

I guess I'd like to rule out this option completely before I fork over the cash for a couple flow meters.

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