Fuel flow through injectors? 1

[HunterA]

I am trying to find a way to calculate HP and BSFC by using the data from the injector fuel flow, EGT, and a good WBo2 sensor. Along with other data from the engine itself; Displacement, RPM, Valve timing etc.

Is it possible to accurately determine the actual injector fuel flow by fuel pressure, pulse width etc.?

Therefore, with a known amount of fuel entering, and a known A/FR (WBo2)(reasonable accuracy) =Volume of air. Add RPM = VE

Obviously the date could be input to a good engine sim program, with decent results. However, it would be nice to know some efficiency numbers when tuning EFI and Carbs.

Any input would be helpfull...
Thanks.

 

[dgallup]

If you have a conventional constant delta P system (not a returnless system) and you know the injector static flow rate and offset you can calculate the flow quantity from the pulsewidth. The ECU works the equation the other way around, it calculates how much fuel is needed and then calculates the pulsewidth that will deliver that fuel quantity. It is a simple linear relation.

Q = ( Pulse Width - Offset ) * Static Flow rate

You will need an injector flow bench or access to someone elses data to get the static flow rate and offset.

 

[NickE]

Is there a tool like:

http://www.ecutek.com.au/delta-dash.htm

Available for your vehicle?

I have DeltaDash for my car and it outputs duty cycle in %, wouldnt that be able to be figured with flow rate of the injectors to provide exact volume of each injector opening event? DD also priveds various information on the intake air charge. (IE: temp, pressure, mass in grams) so you should be able to calc out your required results. (Of course the error in your calculations could be huge if the data isnt good. And I dont know how accurate the measured values are.


Nick
I love materials science!

 

[dgallup]

DeltaDash website says it outputs injector pulse width.

 

[drwebb]

How sensitive is the flow rate to temperature? I assumed the ECU used the O2 sensor to adjust the fuel delivery via pulsewidth, but I don't know much about EFI control systems.

 

[dgallup]

The mass flow rate varies with the square root of fluid density (Bernoulli equation) so mass flow rate goes down as the fuel heats up. The injector offset increases with temperature because the injector coil resistance increases. The magnitude of this effect depends on the type of electrical drive and injector coil material (copper or brass wire). The ECU uses a simple lookup table for temperature compensation along with voltage compensation then uses short & long term corrections from the O2 sensor feedback to come up with the pulsewidth. There are a lot of additional factors used for transient conditions to account for fuel going into and out of storage on the port walls, etc.