mechky
Branch Unspecified
18 Feb 2012

# replacing carburetter with injector system

I am working on replacing a carburetter from a bike engine with an electronic petrol injector (similar to that used in car engines nowadays).

I have planned the whole system to be like this-

Although the system used in cars is more complex & uses more sensors, mainly to outperform carburetter, but my purpose here is just to make the engine run the way as it was with the carburetter.

The mass air flow sensor senses the amount of air flowing through the manifold during the intake stroke and sends this information to the ECU in the form of a 0-5V or PWM signal. The ECU then turns the injector on, and injector injects fuel in the intake manifold which mixes with the incoming air and goes to the engine cylinder through the intake port. The amount of fuel injected corresponds to the amount of air in the manifold to maintain the correct A/F ratio at a particular load.
One thing that I am finding difficult is that how would I know that what A/F mixture is required at a particular load for the engine on which I am working.

ShrinkDWorld

Branch Unspecified
7 years ago
If you can get the information of gear & speed in the form of signal then you can decide the required quality of a/f mixture. By sensing this information you can prepare small program for required strength of mixture.

mechky

Branch Unspecified
7 years ago
ShrinkDWorld
If you can get the information of gear & speed in the form of signal then you can decide the required quality of a/f mixture. By sensing this information you can prepare small program for required strength of mixture.
How will I decide this required quality of A/F mixture. Whatever knowledge of A/F mixture known to me is-
Idling : 12.5 (0-20% of rated power)
Normal Power : 16.5 (20-75% of rated power)
Maximum Power : 13 (75-100 % of rated power)

But this is generalized data as given in books, and I think the values must be varying from engine to engine. How will I get to know what A/F mixture is being used by the engine which I am going to modify?

Taking above values as an example, in the normal power range i.e 20-75% of rated power, the A/F ratio won't be a constant value of 16.5 & its value will be unique corresponding to each load in that range. Correct me if I am wrong.

ShrinkDWorld

Branch Unspecified
7 years ago
I am not a master in IC engine. but i can suggest you that keep these theoretical values in mind & try to run the engine at various loads. Note down the each trial. After this you can get rough but close idea of requirement of a/f ratio of your engine.
And while designing your fuel injector, please find the relation for required power & required acceleration for particular change of speed. Here you have to search/ read lots of reference books of IC engine. have maximum focus on various graphs they are easier to understand how engine work at variable loading conditions.
Keep in touch!😀