EFI

[David Doddek]

>1.   How exactly would the controller calculate "load" from "air" and "rpm" 
>and "a constant"? i.e. what would the equation be?  (please treat me as 
>completely ignorant, though I am not quite)
>
I will try to put this in simple terms without using any fancy formula.

The basic theme of the mass air flow system is a device that measures the
volume of air that is entering the engine.  Remember that in a gasoline
engine we want to have a specific ratio of fuel and air mixed together
entering the engine.  Usually for the ideal situation the ratio is 1 part
gas to 14.6 parts of air by mass.  For higher load situations a slightly
richer (more fuel per air) is required for best power.  Let us assume for an
instant, that we have a device to measure the amount of air passing by.  By
measuring the temperature of the air, the device may more accurately measure
the mass of the air.  If we know the mass of air flowing into the engine per
unit time, then we may calculate the amount of fuel needed to obtain the
correct ratio of fuel and air.  We cannot just squirt the fuel into the
engine as we please, so we decide to inject a specified amount of fuel each
revolution or portion of a revolution into the engine.  To determine the
amount of fuel the engine requires each injection event we can measure the
RPM of the engine and know the amount of air that enters the engine in one
revolution by dividing the total amount of air by the rpm.  With the amount
of air known to enter a cylinder per designated event, we can calculate the
amount of fuel required for that amount of air.  Now that we know the amount
of fuel required for a 100% effecient engine, we can look up a map that
tells us the REAL effeciency of the engine at a specific operating point and
offset the calculated fuel.  We will also need to add in amounts of fuel for
choke, acceleration and what not.  Now with this fuel quantity, we multiply
it by the magical constant that will give a time value.  This time value is
the time the injector must be open in order to deliver the amount of fuel
desired.  Now all you have to do is determine when to inject the fuel.  And
that is a different story.

I can also give the same basic type of description of speed density if
anyone wants.


David J. Doddek                                          |pantera at pobox.com
Owner SGD Electronics & Development Engr for Caterpillar |h 309 685-7965
Formula SAE Team Sidewinder 94-95                        |w 309 578-2931
89 T-bird SC,  69 Fairlane w/SGD EFI                     |fx 217 428-4686
74 Pantera w/Electromotive Tec-II Twin turbos and Nitros |
Hey, If you are going to go fast, go REEEAAL FAST.       |