Quick questions about fuel

Good morning!

I'm currently writing my engineering thesis, and for that I need a precise way to measure fuel consumption of my car, 2002 td5 disco 2 manual.
Does any diagnostic interface allows to read the amount of fuel each injector injects to the combustion chamber? I tried TEXA and KTS with no luck.
If it's impossible to measure with a computer, maybe someone has an idea how to measure fuel consumption manually?
Topping the tank, driving and then topping it again would probably work, but it's not precise enough for me, so I will use it only if there is no other way.

Cheers and happy new year!!

Brimming the tank from the same pump each time will be the most accurate way, you'll also need to bear in mind that fuel will have a different volume at different temperatures

Apps like torque will let you extract all sorts of data, if you put the effort in. If your vehicle has a fuel temp sensor you should be able to work things out once exported to excel

As the injectors take their fuel from a common rail, I would doubt if any data would be accurate for individual injectors. Brim to brim is the most accurate way for overall consumption. Bear in mind though, if you know you are measuring fuel consumption you will drive accordingly, whether consciously or unconsciously.

The ECU knows the fuel pressure and knows how long the injector opens for in order to inject a specific amount of fuel. The injectors will have a determined flow rate for this calculation
I agree though, brim to brim from the same pump is the best way

If you do multiple brim to brim measurements any inaccuracies from the temp of fuel, volume etc will cancel out. The more you do the more accurate the calculations.

If you find a way to measure instant consumption through the injectors then a 5% error (for example) will never cancel out no matter how measurements you do. And considering that this number will be through a calculation of a couple of variables (pressure/duration/flow etc) then the error can be quite large.

kermit_rr said:

Apps like torque will let you extract all sorts of data, if you put the effort in. If your vehicle has a fuel temp sensor you should be able to work things out once exported to excel

Click to expand...

That app is for OBD2 compliant vehicles which the Td5 is not...even if it shows some data it will be most probably erratic

kermit_rr said:

The ECU knows the fuel pressure and knows how long the injector opens for in order to inject a specific amount of fuel.

Click to expand...

Unfortunately the Td5 ECU doesnt know the final fuel pressure cos it's delivered directly by the electronic unit/pump injectors... no fuel pressure sensor included like on common rail diesels cos it's a constant 4 bar prssure in the rail managed by the FPR

sierrafery said:

Unfortunately the Td5 ECU doesnt know the final fuel pressure cos it's delivered directly by the electronic unit/pump injectors... no fuel pressure sensor included like on common rail diesels cos it's a constant 4 bar prssure in the rail managed by the FPR

Click to expand...

Does that mean fuel delivery is only approximate based on the fuel map?

kermit_rr said:

Does that mean fuel delivery is only approximate based on the fuel map?

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It's a diesel. So the actual fuel delivery volume (and power) is based on throttle pedal position. If the engine makes more power than the driver needs, then the throttle is reduced.

Maciej said:

Good morning!

I'm currently writing my engineering thesis, and for that I need a precise way to measure fuel consumption of my car, 2002 td5 disco 2 manual.
Does any diagnostic interface allows to read the amount of fuel each injector injects to the combustion chamber? I tried TEXA and KTS with no luck.
If it's impossible to measure with a computer, maybe someone has an idea how to measure fuel consumption manually?
Topping the tank, driving and then topping it again would probably work, but it's not precise enough for me, so I will use it only if there is no other way.

Cheers and happy new year!!

Click to expand...

Measuring fuel at the tank is the best way to measure fuel consumption and the more data sets you collect the more accurate it will become.
This would also give you data over a wide range of driving conditions.
If you want to be more accurate you would have a measured volume feeding the fuel system.
I suppose you could get an in line flow meter to measure flow too.
Measuring how much fuel flows through an injector isn't going to give you any more information, but you will have to add all the injector flows up to get the total.

When we used to do the Shell motor mileage marathon, which was designed to see how far a vehicle would go on a measured amount of fuel, it was exactly that. The would give you a measured litre of fuel and set you off down the track. You circled the track until you ran out, and the distance covered could be very accurately measured.
This is comparable to a brim to brim test, except that the track was flat and there was no traffic.
I usually calculate it on a running basis by filling each time I take fuel on and zeroing the trip meter. The only trouble is that I find it impossible to fill it to the brim each time as a/ the fuel doesn't flow easily into the tank for the last few litres, due to frothing etc in the filler pipe, you, and anyone in the queue behind you, has to be very patient. b/ if you actually do fill it to the brim you tend to inevitably lose some as soon as you take a bend or go up a hill as it overflows, which fecks your reading.
So I go to the same pump every time and fill it till the pump clicks off, then wait a bit and then do the same thing again then once more. This is not to the brim but is to a pretty good approximation of the same point in the tank.
As others have said, different driving styles, starting from cold or hot, weather conditions, traffic, A Road, Mway, etc etc make a huge difference which are only averaged out over a lengthy period of time.
Without knowing exactly what the terms of your thesis subject are, maybe you would be better off choosing a route. Filling to the brim, driving the route, refilling to the brim and doing this over and over again in the same conditions as far as possible. You could fill a jerry can and stop in a layby to top up each time, a measured amount using a measuring jug, to be absolutely sure how much it takes to top up.
Best of luck and I would be interested in your results!!

Thank you all for your responses!!

It's settled then, I will do the brim to brim method, and i'm even lucky enough to have access to a dyno, so all the conditions during testing will be as similar as possible, and the only variable will be the temperature when refuelling. if everything goes as planned, I should start test this week, and after a month or so i will have some results. I'm measuring fuel consumption (among other things) on two different tire sizes, 255/55R18 and 255/70R18, i'm really curious to see the difference in fuel consumpiton, because I honestly have no clue what to expect, on one hand, the bigger tire is more difficult to rotate, but on the other hand, it has to rotate much less than the smaller one (around 4134 times less rotations per 100km if you are wondering)

Cheers and thank you again!!