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Can you calculate fuel use from the injector on time? by Chris Eddy
Started on: 11-14-2017 09:54 AM
Replies: 3 (133 views)
Last post by: kzelisko on 11-15-2017 09:06 PM
Chris Eddy
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Report this Post11-14-2017 09:54 AM Click Here to See the Profile for Chris EddySend a Private Message to Chris EddyEdit/Delete MessageReply w/QuoteDirect Link to This Post
If I were to add up all of the milli-seconds of on time for the fuel injector, would I come close to fuel consumption?
This would probably assume that the fuel pressure is constant..
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cebix
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Report this Post11-14-2017 03:42 PM Click Here to See the Profile for cebixSend a Private Message to cebixEdit/Delete MessageReply w/QuoteDirect Link to This Post
Yes.
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pmbrunelle
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Report this Post11-14-2017 06:29 PM Click Here to See the Profile for pmbrunelleSend a Private Message to pmbrunelleEdit/Delete MessageReply w/QuoteDirect Link to This Post
EFI is based on the premise that the fuel quantity injected is directly proportional to the spray time.

However, the injector takes a finite amount of time to open and close, during which no fuel is injected.

Therefore, the electrical pulse width is equal to the desired spray time + dead time.

Obviously, the injector is inductive. When voltage is applied, it takes some time for the current (and thus magnetic force) to overcome the spring preload, and therefore move the needle away from its seat.

In the ECU, the dead time calculation can be implemented as a 1-D lookup table as a function of battery voltage, or even as a y = ax + b function.

Dead time is on the order of ~1 ms, so at low loads it becomes an important factor.

Fuel pressure across the injector should be constant for most setups, notwithstanding silly GM 3800 fuel systems and the like.

Fuel flow is related to the square root of the pressure difference, so it's not a huge variable anyway.
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kzelisko
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Report this Post11-15-2017 09:06 PM Click Here to See the Profile for kzeliskoSend a Private Message to kzeliskoEdit/Delete MessageReply w/QuoteDirect Link to This Post
Look into mpguino, it does essentially that
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