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Old 26th April 2013, 12:32   #46
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Default Re: Open loop or Closed loop - CNG / LPG

What type of CNG kit should I install in my Spark ?
Any Spark owners converted their car to CNG? Do share your inputs.
Any problems faced?
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Old 3rd January 2014, 16:09   #47
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Post Open Loop v/s Closed Loop. Difference?

So my fellow bhp-ians, Those who are familiar with ECU(or ECM) operations will know about the 'closed loop' and 'open loop' profiles of an ECU.
I'd really appreciate if someone explained in details what are the difference between the two.

I know that the ECU runs in 'Open loop' mode post-start up till the 02(Lambda) Sensor is warm enough after which the 02 Sensor kicks in and sends the ECU into 'Closed loop' and maintains an AFR of 14.7(Stoichiometric).I also know that the ECU goes into 'Open loop' during WOT and/or when the sensors are outside their normal operating range.
Please Correct me if im wrong.

PS : I'd also like to know how ECUs for Diesel engines operate with respect to 'Closed Loop' & 'Open Loop' modes. As far as my understanding goes, Diesel Engines won't maintain AFR 14.7.
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Old 3rd January 2014, 16:27   #48
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Default 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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Old 11th January 2014, 19:35   #49
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Default Re: Open Loop v/s Closed Loop. Difference?

Quote:
Originally Posted by tsk1979 View Post
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.
Nice way to put the data. Actually, for day to day city driving, Open or Close loop must not make any difference. When I had Closed Loop System in Baleno, it was horrible. Rather a one off case, but great car was absolutely horrible to drive, it would not idle and shut down on move, if low rpm was tolerable, it would not cross 3K rpm if floored ( YES, FLOORED ). If above 3K was tolerable, even idling would be headache.

Changed evaporator and removed complex Lambda. Now, its running very nice. Yet to use it for long, but as far as closed loop is concerned, never did it feel good. As if somebody is holding the throat of engine and inducing supernatural control. My beautiful drive is back and I hope it remains that way. However, the sequential kits, atleast on paper, are the best.

Given our operating conditions, mainly in city, open or close might not matter much IMO. There are very few who can actually tune closed loop system as the stepper motor setting/other setting might need to be reworked/reset at some intervals.
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