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I know this question might not be new, but I am still asking this question as I haven't yet got any satisfactory answer to this. I have done quite a research on this topic and will sum up it here:

  • To calculate the fuel consumption we need to know different parameters like below:
    • Engine capacity
    • Load on engine
    • Atmospheric conditions
    • How much fuel is injected by injectors
    • Vehicle's drag co-efficient
    • Vehicle's rolling resistance coefficient
    • And the list is longer...

I have checked a few articles/answers that state that the OBD2 port can provide information about the fuel injectors. I have also seen a few answers that state that we need some sort of custom-built device which can monitor the fuel injectors. But I am not sure about those claims and how to do that.

I have referred few articles that state formulas to calculate fuel consumption, but I am not sure if they are correct or not, so I want to validate them as well. Here is one of them - https://x-engineer.org/real-world-fuel-consumption/

In short, what I am trying to achieve is, that I want the data regarding the amount of fuel consumed by the engine at any moment of time, for each 1 minute or lesser duration. How can I get that data, either using hardware+software or just using software using the mobile device's accelerometer, map (location), and vehicle's configurations? I am NOT trying to get the fuel economy or how much my vehicle will travel in what amount of fuel. I want the data regarding fuel usage/consumption in real-time as I mentioned.

Thank you.

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    Surely you need to know the volume of fuel passing through the injectors ONLY. Why is anything else relevant?
    – Chenmunka
    Commented Jul 10, 2022 at 21:40
  • There's an iOS app that can do this & much more. Free download but pay for full version (can't remember how much but not expensive) Follow their recommendations for which ODB hardware to use. UK App Store link. apps.apple.com/gb/app/car-scanner-elm-obd2/id1259933623
    – Tetsujin
    Commented Jul 11, 2022 at 10:22
  • You want to measure or you want to estimate? A good long-term measure is the gas station pump counter. Flow meters for fuel lines also do exist. On the other hand, if you want to estimate the fuel consumption given the driving conditions... well, an university degree in a related field is a good start.
    – fraxinus
    Commented Aug 10, 2022 at 14:58

2 Answers 2

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It’s possible to get fairly close just by monitoring the open time of a single injector. Some time ago I built a trip computer that did so by connecting to the controlled side of one injector, in that case a 2000 era Honda Odyssey. With some calibration I recall it being less than a gallon error per 20 gal tank.

I’m not super familiar with newer stuff, but one key element to tracking it this way is going to be consistent rail pressure.

The two key points to calibrate something of this nature are:
#1 flow rate
#2 time from 0 to 100% flow.

Obviously the newer ecu’s have an edge on calculating something of this nature, so if the manufacture exposes it via obd2, it’s going to be more accurate.

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  • You are missing one element, that being a fuel injector will flow differing amounts of fuel at different pressures. IOW, if the fuel system pressure is 58 psi, it will flow more fuel through a given injector in the same amount of time as if the system fuel pressure is 43.5 psi. This is very linear, so easily compensated for in any calculations. Changing the fuel pressure is one way to help fueling without changing injectors. Commented Jul 11, 2022 at 11:37
  • So basically, it is not possible to find the amount of fuel consumed by the engine without any sort of hardware attached to it? I mean through any mathematical calculations and inputs received from different mobile sensors and vehicle configurations? Commented Jul 11, 2022 at 17:07
  • what is "vehicle configurations" ? Commented Jul 11, 2022 at 18:52
  • I meant vehicle specs like curb weight, cross sectional area, drag co-efficient, engine size, fuel type, etc. Commented Jul 12, 2022 at 1:58
  • How are you going to factor in the 20mph headwind some days? Commented Jul 12, 2022 at 10:48
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I think the best variable to measure is air flow. Any engine needs to measure air flow anyway and to do calculations for how much fuel to inject.

A given amount of air requires a given amount of fuel to burn.

In theory, there might be variations in fuel composition (how much oxygenates?) so there could be very minor variations in the amount of air a liter of fuel needs to burn. But any other approach suffers from inaccuracies too: for example by measuring injector open time, you need to know the fuel pressure, if the injectors are partially clogged it could give false data, and also fuel viscosity changes how easily it flows through the injector.

About the only problem you might have with this approach is if the airflow meter is defective but you have a working lambda sensor. Then it's possible the airflow reading doesn't match true fuel consumption.

Also this doesn't work for lean burn engines, and immediately after a cold start.

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