Re: Open Loop v/s Closed Loop. Difference? Actually, the ratio may be different, but no matter petrol or diesel, you will have to take feedback.
What is a closed loop system? Its simply saying what I do next is dependent on what happened before.
both diesel and petrol engines have oxygen sensors.
So if oxygen sensor says -> Rich. ECU will decrease fuel
If oxygen sensor says -> lean, ECU will increase fuel in the ratio
Open loop is I do not care what came before me. So the fuel/air ratio will not depend upon oxygen sensor.
When your engine starts, O2 sensor is cold, so ECU uses something called a Fuel map.
another condition when ECU goes to fuel map is when you floor the pedal. you need fuel then. If you were closed loop, ECU will keep trying to fight the accelerator output, and you won't get quick acceleration. So beyond a certain threshold, ECU goes into open loop.
Diesels work a little differently using Lambda sensor. i think its because AFR is load/rpm dependent in diesels. you do not have a set AFR. Since diesel is "lean burn" you need a wideband sensor, as opposed to simply oxygen sensor.
I am a bit rusty on how this all works, but base principle is same for petrol or diesel. In diesel it just becomes more complicated... Engine techs here could elaborate more
Last edited by tsk1979 : 3rd January 2014 at 16:32.
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