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Tuesday, March 2, 2010


Calculate injector pulsewidth from airflow

First the CPU determines the air mass flow rate from the sensors - Massair / Minute. (The various methods to determine airflow are beyond the scope of this topic. See MAF sensor, or MAP sensor.)
\frac{Mass_{air}}{Minute} \times \frac{Minutes}{Revolution} \times \frac{Revolutions}{Stroke} =\frac{Mass_{air}}{Stroke}
Minutes / Revolution is the reciprocal of engine speed (RPM).
The term Revolutions / Stroke = 1 / 2, whether it's a four stroke or a two-stroke engine.
\frac{Mass_{air}}{Stroke_{intake}} \times \frac{Mass_{Fuel}}{Mass_{Air}}=\frac{Mass_{Fuel}}{Stroke_{intake}}
MassFuel / MassAir is the desired mixture ratio, usually stoichiometric, but often different depending on operating conditions.
\frac{Mass_{Fuel}}{Stroke_{intake}} \times \frac{1}{Mass_{Fuel}/Minute} =\frac{Minutes}{Stroke_{intake}}=Pulsewidth
1 / (MassFuel / Minute) is the flow capacity of the injector, or its size.
Combining the above three terms . . .
\frac{Mass_{air}}{Minute} \times \frac{Minutes}{Revolution} \times \frac{Revolutions}{Stroke} \times \frac{Mass_{Fuel}}{Mass_{Air}} \times \frac{1}{Mass_{Fuel}/Minute} = Pulsewidth
Substituting real variables for the 5.0 L engine at idle.
* 0.55 \frac{lb}{min} \times \frac{1 min}{700 rev} \times \frac{1 revolution}{2 strokes} \times \frac{1}{14.64} \times 2.5\frac{min}{lb} = 6.7 \times 10^{-5} min = 4ms
Substituting real variables for the 5.0 L engine at maximum power.
* 28 \frac{lb}{min} \times \frac{1 min}{5500 rev} \times \frac{1 revolution}{2 strokes} \times \frac{1}{11.00} \times 2.5\frac{min}{lb} = 57.9 \times 10^{-5} min = 35ms
Injector pulsewidth typically ranges from 4 ms/engine-cycle at idle, to 35 ms per engine-cycle at wide-open throttle. The pulsewidth accuracy is approximately 0.01 ms.
* RUMUS ENGINE FUEL INJECTION(EFI) kalah subjek math+science tech...huh~~    p/s : mereng seketika..huhuhuuu~~


  1. reza bkn da mmg mereng ke?

  2. mal : diam2 sudah lah...uhuuu~~

    nazrin : bkn macam dah..dh mmg fizik automotif..
    huh~~ naik glerw blajar bnde nie..huhuu~~


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