Hello TR.
Thank you for clarifying what you meant by OBC, as On Borad Computer.
Now going back to your posting of 1 week 3 days ago.
TheTravellingRooster said:
...
It is a known fact that OBC's offer wildly and widely optimistic figures because of the laboratory conditions that they are conceived in. They are not nor have they ever been collected in real world situations.....
Your statement is too strong. It is not a 'known fact'. Some examples may read optimistically some of the time. But equally I have witnessed some OBC giving both optimistic and pessimistic results and there could be good reasons for it.
I am certain that none of the car manufacturers will be claiming 100% weights and measures accuracy for their OBC readings, they are just guidelines, but equally I am certain none of them will be deliberately making their products read optimistically.
OBC results are gained from a rolling average over several readings. It will depend on the specification of each car, but of one particular car I owned the manufacture explained the averaged MPG was derived from the last 800 miles of motoring.
The disadvantage of this is the results are always lagging the instantaneous results you might get from a brim to brim check.
So if you have been running your car solo and in light traffic for 800 miles the averaged mpg will have improved. If you the do a tank full of towing, the brim to brim value will be lower than the cars cars 800 mile average so you will see an optimistic discrepancy.
The converse is also true, and I have seen pessimistic results from the OBC
Rather than just comparing one brim to brim result, if you were to check it over several brim to brim fillings you are more likely to see your results converge with the cars read out.
Its unlikely you will see exactly the same readings, because the only way the car can record the fuel used is to add up each of the small amounts of fuel it injects into each cylinder. The margin of error proportionally increases as measurement values become smaller, so the sum of the injected fuel has a higher probability of being slightly different to total fuel measured in one go.
In reality the difference could go either way.
The summation of the injected fuel is as much real world as the brim to brim method, its just a question of what is reasonable accuracy for the method employed.
For example if I were to ask you to add 200 5ml teaspoons of water to a bottle, Ill bet it wont contain exactly 1000mL of water, because of the inaccuracy of the teaspoon and the way you fill it.
Consider a car that does say 10Km/Litre when travelling at 60km/h (1kM per minute) using a 4 stroke 4 cylinder engine running at 2000rpm. will give 4000 power strokes per minute (psm).
That equates to 100mL of fuel per minute so that means 100mL/4000psm = 0.025ml per power stroke. Measuring that small amount accurately so frequently is bound to introduce errors which will be multiplied up by the number of samples used.
Its horses for courses, and the OBC output should be considered a guide rather than an absolute measure.
Facebook
Twitter