How to calculate fuel consumption from RPM tachometer readings of car engines. Is there any formulae and also all the possible parameters that are needed to do the calculations and any basic assumptions if they exist?
I do not think there is a relation between fuel consumption and tachometer reading. As a matter of fact engines consume more fuels when running at low speeds and very high speeds. In between there is a speed where fuel consumption is minimum and that speed is called the economical speed of the engine and it differs from engine to engine.
Dear Muhammed
No, the tachometer can not be related to fuel efficiency as the tachometer is measuring the amount of rotations per minute (RPMs) of the engine.
In the same gear and at the same speed your tachometer will always be at the same RPMs.
However, you can be at 2000 RPMs and be barely touching the gas pedal (or completely off of it) because you are coasting down a hill or you can be at 2000 RPMs towing a trailer up a hill with the pedal to the floor.
The only things you really can try to infer from your tachometer would be the higher your RPMs, the more likely it is that you are burning more fuel assuming all other factors are the same. If you change your cruising speed to keep the tach at 2000 RPMs instead of 2500 RPMs, then yes, you will probably save fuel.
But you can use read data from car fuel consuming property that depended on the Tank fuel reading with driven distance to give KM per Litter.
RPMs and fuel consumption have only a very slight correlation. (As higher RPMs correlate with an increase in friction losses.)
The image would change if you were able to measure the torque as well: rpms multiplied by the torque delivered is the current power delivered - a reasonable basis to estimate fuel consumption.
The tachometer only reads engine speed, it is in no way linked to the fuel delivery system, it takes its reading electronically or mechanically from the engine and not through fuel flows. It would be possible to calculate fuel consumption from RPM readings with a static engine, with a given and constant load and an accurate flowmeter, but this would have no relevance to real-world consumption figures.
Actual fuel consumption will vary according to differing road, load and speed conditions, the position of the throttle will have to be adjusted and gears changed to maintain either the same road-speed or RPM reading, with more fuel being delivered the higher any of the above are added to the equation.
You therefore need to measure fuel flow to calculate fuel consumption, which will be affected by a combination of engine load and RPM.
you really can try to change your cruising speed to keep the tach at 2000 RPMs instead of 2500 RPMs, then yes, you will probably save fuel.
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