Fuel consumption display

[sirvo]

Hi Sirvio,
The short answer is, likely not. The OEM computer in your car keeps adjusting injector on time based upon sensor input from the oxegen sensor in the exhaust, the throttle position sensor, the mass airflow sensor, if equipped, a MAP sensor, if no MAF sensor, temp sensors in the air and water, a BARO sensor, a data lookup table, Knock sensor, and probably the engineer's astrologer too. So there is no design requirement for the injectors output to be linear, in fact most computers have what they refer to as BLOCK LEARN, which is most likely flash or eeprom memory to keep track of fuel curves so as to alter the computer's calibration around your driving habits. I notice my old exCHP car sure runs better after the wife drives it for a while.

Hi Joe.. thanks for answering..
I agree with you but, let me ask you in another point of view. Lets think that the pressure on the gas line is constant (~3bar). The same way, lets think that if you let 1 injector 1s on, it will output 15ml, it means, the injector outputs 15ml/s. If I can measure the injector on time, It does not matter the fuel curves and engine maps, only the on time. Isn't that write? In other words, the sensors, maps, curves, engineer's astrologer (heheh) and so... only change the on time, but not the 15ml/s. Could you get it?

I did not mean to be rude or anything. Don't get me wrong please! I'm not english neither north american so sometimes my english does not help me to be clear.

Thanks a lot..!

Regards..

[Acetronics2]

Hi, Servo

You're right, fuel pressure keeps steady ... so, just measure how long your injectors are open, make a "real life" calibration ( how much fuel vs total injectors "bleeding" time ) and that's it ...

It's very simple ... just look at fluid mechanics laws for quasi-ideal liquids, and you'll see volume is a function of time and pressure @ 99.99% !!!

so, you just have to measure the pulses driving your injectors ... just 5 wires to wire !!!

Alain

[calzaman]

I am trying to calculate fuel consumption as a function of RPM. So for a given rpm and an engine size I can fetch the approximate fuel consumtion (liters per minute). Does any one know of an equation that can achieve that.

Also your equation which you have used (Fuel consumption (liters/100km) = (RPM * injector open time * injector flow) / speed * 100000) is quite good and it is working for me. However, do you have a reference for where you got the equation for. Also is the 8 ms a standard for flow open time for all engines.

Thank you kindly for your help

[Tobias]

You will be closer at guessing the next lottery numbers than using just RPM to measure fuel consumption. You need to know BSFC and AF ratio as a starting point.

[rshaver]

Just a thought but if you can get 2 fuel flow sensors you can get a pretty accurate reading. You have to get the flow in and out of the system and then just do a little subtraction. Can't remember where I saw it. But someone did this and it worked over all driving conditions. If you have a flow of 5 gallons per hour(GPH) in and 3GPH out then you are using 2GPH. Or what ever measure you use. You get the in and out because the injection system has a return line to the tank for the fuel not used. Only problem with this is trying to find the flow sensor. I have been trying to find just one for my old truck and they seem to be non-existent now. They used to be every where.

[Tobias]

The flow sensors we use in drag racing are about $2000!!! They are deadly accurate but very pricey.

[ardhuru]

Guys, I'm no authority on this, but if that data is available on the OBD2 connector in your vehicle, how about just getting a bluetooth OBD2 adapter, and couple it with a tablet/phone running Android (App: Torque)? Would be an inexpensive, and easy solution.