Multec 3.5 Fuel Injector Application Manual Software
Delphi Energy and Chassis Systems
Revision: 11/05-1 5-1
5.0 Software
5.1 General
Refer to Section 2.2.1.1
An ideal air fuel (A/F) ratio provides minimum emissions and maximum
fuel economy and driveability. For any given engine and vehicle
operating condition, there is an optimum A/F ratio. It is the function of
the engine controller’s software to calculate the optimum A/F ratio for the
existing conditions. The engine controller monitors the output of the
engine and vehicle sensors, and uses this data to determine the correct fuel
delivery requirements for the existing conditions. An injector pulse width
is calculated from the fuel delivery requirements through a series of look-
up tables and modifiers based on the injector flow performance at the
current engine operating state. Pulse-width is a function of the following:
• Desired air/fuel ratio
• Air flow
• Corrections, sensor inputs (i.e., TPS, O2S, ECT, MAF, etc.)
• Injector flow characterization
Desired Air/Fuel Ratio
The desired air/fuel ratio is stoichiometric for steady state operation and
normal operating temperatures during the emission test procedure for a
closed loop system. As previously mentioned, stoichiometric is dependent
on fuel — for gasoline it is approximately 14.7 to 1 (See Table 2-1). At
this ratio, the fuel and air are in correct theoretical proportion for complete
combustion, providing optimum fuel efficiency and a minimum of
emissions. Stoichiometric operation provides the optimum trade-off in
catalytic conversion efficiency for HC, CO and NOx (refer to Figure 2-2).
Air Flow
Airflow must be determined in order to achieve the desired air/fuel ratio
and calculate pulse-width. The two methods used by the engine
management system to determine airflow are speed density and mass
airflow.
•
The speed density system estimates airflow by calculating the amount
of air through the cylinders. It uses Manifold Absolute Pressure
(MAP) to determine density, engine speed (rpm), temperature of the
A/F mix, volume per cylinder, calculated EGR flow, and volumetric
efficiency (see section 5.2.3.1).
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