No subject

Thu May 30 05:48:45 GMT 2013

as a  
function of air-fuel-ratio (AFR).  
1.2.1 --- Constants and variables  
AFR: Air fuel ratio  
F_gal/hr: fuel flow rate in gal/hr  
Sg: specific gravity of gasoline  
     Sg = 0.74 gr/cc = 46 lb/ft^3  
1.2.2 --- Equation  
F_gal/hr = (air flow lb/hr) / (air fuel ratio) / (specific gravity  
of gas) X   
    (gal/cubic feet)  
F_gal/hr (gal/hr) = A_lb/hr (lb/hr) / AFR () / Sg (lb/ft^3) * 7.481  
F_gal/hr = 0.1626 * A_lb/hr / AFR  
Substituting the above equation for A_lb/hr gives,  
F_gal/hr = (107.6*Vd) * MAP * RPM * %VE / Ta / AFR  
where (107.6*Vd) is a constant and %VE is primarily a function of  
MAP and RPM.  
While this is the basic equation needed to control the injector  
duration, the  
terms should be grouped and normalized in such a way as to make  
the CPU easier (i.e., the terms MAP, RPM, and %VE could be combined  
into one  
lookup table as a function of MAP and RPM).  
1.2.3 --- Determination of AFR  
The air-fuel-ratio should be 14.7:1 whenever the system is operating  
closed-loop mode with the oxygen sensor. During conditions of  
starting, cold  
engine, cold O2 sensor, or power enrichment, the system should be  
open loop. Open loop AFR depends on coolant temperature, MAP, and  
RPM.  (need  
more info here --- need to define the controlling algorithm)  
1.3 --- Additional terms -- Acceleration Enrichment, Deceleration  
and Close-Loop Feedback  
1.3.1 --- Acceleration Enrichment (AE)  
In the prototype controller, AE should simulate the accelerator pump  
of a  
traditional carburetor. That would make it an additive term to the  
of (1.2.2) that would add a pre-set quantity of fuel as a function of 
throttle change. Additionally, it would have an adjustable "decay  
that would be similar to the hole diameter of the "shooter". In the  
it may be beneficial to include MAP and coolant temperature into this 
term. For now, I will just represent it as a yet to be defined  
function of AE. (need more info here --- need to define the  
1.3.2 --- Deceleration Enleanment (DE)  
I don't believe this term is necessary in the first prototype of our  
controller. Ultimately this term will lean the engine during  
much as the acceleration enrichment term adds fuel during  
acceleration. It  
should have the same inputs as the acceleration term.  
1.3.3 --- Close-Loop Feedback (CLF)  
This should be a multiplicative term representing the integrated  
error from  
the oxygen sensor. The conditions for when this term should be  
included are  
yet to be defined. Conditions to consider are cold O2 sensor, cold  
acceleration, deceleration, power enrichment. (others?) (need more  
info here,  
need to define the controlling algorithm)  
1.4 --- The overall fuel delivery equation.  
F_gal/hr = (107.6*Vd) * MAP * RPM * %VE / Ta / AFR * DE * CLF + AE  
In this equation, MAP, RPM, and Ta are engine parameters measured  
(107.6*Vd) is a constant. %VE is experimentally determined as a  
function of  
MAP and RPM. DE and AE depend on MAP, TPS, and coolant temperature.  
is a function of the O2 sensor input. AFR is a function of crank  
cold engine, and power enrichment.  
2 --- Idle Air Control  
3 --- Spark Timing  
This is getting lengthy...  
Will expanding this help anyone?  
Someone want to start an input/output description or a software  
                                       John S Gwynne  
                                          Gwynne.1 at  
               T h e   O h i o - S t a t e   U n i v e r s i t y  
    ElectroScience Laboratory, 1320 Kinnear Road, Columbus, Ohio  
43212, USA  
                Telephone: (614) 292-7981 * Fax: (614) 292-7292  
jsg at (John S Gwynne) Wrote:  
[article about injection equations deleted]  
instead of calculating mass airflow from rpm, shouldn't an airflow  
be used?  
> From: Steve=Ravet%Prj=Eng%PCPD=Hou at  
> Subject: re: basic fuel metering equations  
> [article about injection equations deleted]  
> instead of calculating mass airflow from rpm, shouldn't an airflow  
> be used?  
> --steve  
Thats a classic debate.  Mass-air based systems are generally easier  
tune than speed-density system.  However, a mass airflow sensor is a  
restriction in the intake path.  Traditionally, mass airflow sensor  
also been quite expensive.  The aftermarket scene for 5l mustang has  
changed that for some sizes of MAF sensors, though.  Still, the MAF  
needs to be roughly sized to the airflow requirements of the engine.  

More information about the Diy_efi mailing list