Motor Vehicle Maintenance & Repair Stack Exchange is a question and answer site for mechanics and DIY enthusiast owners of cars, trucks, and motorcycles. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

If we have the cc of the engine, and its running speed, how can we calculate the mass of gasoline in milligrams sucked in each intake stroke and the mass of gas consumed in a given distance, based on its mass and volume?

share|improve this question
2  
You can't, fuel consumption is based on engine load, not just on revs. – HandyHowie 6 mins ago – HandyHowie Nov 26 '15 at 18:20
    
Yah, ask @HandyHowie how we know that is true ;-) – Pᴀᴜʟsᴛᴇʀ2 Nov 26 '15 at 18:40
    
You'd have to know a lot more information, such as the intake manifold vacuum. The mass calculation is pretty simply, if you can calculate (or measure) the air mass -- it's takes about 14.7 times more air-mass than gasoline-mass for proper combustion. But knowing the air-mass requires knowing what the actual airflow is, which can be measured with a mass airflow sensor (duh) or by computing the airflow curves for steady-state manifold vacuum readings. Or do what one of the answers says and measure actually consumption between fillups. – Julie in Austin Nov 27 '15 at 0:47
1  
@JulieinAustin the trouble with the 14.7:1 assumption is that it won't always be true. – Zaid Nov 27 '15 at 3:08
1  
@IhavenoideawhatI'mdoing ... No, they use a MAF, MAP, and/or O2's as well to calculate, using the amount of air going into the engine. Remember the long discussion on air intake based on load we all had? – Pᴀᴜʟsᴛᴇʀ2 Nov 27 '15 at 11:37

Just a thought of a way to determine what you are looking for...

Your injectors are rated for a certain flow at a certain PSI. Most cars have a Fuel Pressure Regulator to keep this pressure constant relative to the pressure in the manifold. You should be able to find this flow rating for your vehicle's injectors.

Find a way to 'watch' how long the injector is open. This is going to happen is the millisecond range, I'm thinking an arduino using the injector power wire as an input, constantly polling and recording/outputting changes. Not sure if the arduino would be fast/accurate enough. The car is 12v and the arduino needs 5v, so you would need to drop the voltage somehow and use a diode so your reading doesn't effect injector performance.

Once you have a flow rate and how long it is open, you can calculate how much fuel is injected.

share|improve this answer
    
"You should be able to find this flow rating for your vehicle's injectors" - easier said than done! :) Nothing wrong with the approach though, +1 – Zaid Dec 19 '15 at 18:23

How about filling the tank, driving it however far and re-filling the tank. The greater the distance travelled, the more accurate the amount of consumption per unit of distance.

share|improve this answer
    
The question is really asking for a mathematical formula for extracting the data based on two factors. As it stands, the question is unanswerable. – Pᴀᴜʟsᴛᴇʀ2 Nov 27 '15 at 11:33
    
@Paulster2 - Yeah I know. – Rotten Ronnie Nov 27 '15 at 14:10

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.