Thu May 30 05:48:45 GMT 2013
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
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
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
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
engine, cold O2 sensor, or power enrichment, the system should be
open loop. Open loop AFR depends on coolant temperature, MAP, and
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
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
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
the oxygen sensor. The conditions for when this term should be
yet to be defined. Conditions to consider are cold O2 sensor, cold
acceleration, deceleration, power enrichment. (others?) (need more
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
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 osu.edu
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
Telephone: (614) 292-7981 * Fax: (614) 292-7292
jsg at coulomb.eng.ohio-state.edu (John S Gwynne) Wrote:
[article about injection equations deleted]
instead of calculating mass airflow from rpm, shouldn't an airflow
> From: Steve=Ravet%Prj=Eng%PCPD=Hou at bangate.compaq.com
> Subject: re: basic fuel metering equations
> [article about injection equations deleted]
> instead of calculating mass airflow from rpm, shouldn't an airflow
> be used?
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.
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