Benefits Of Electronic Fuel Injection Over Other Types Of Fuel Systems; Impact Of Transient Conditions On Combustion - Delphi Multec 3.5 Applications Manual

Multec 3.5 Fuel Injector Application Manual
2.2.4

Benefits of Electronic Fuel Injection Over Other Types of Fuel Systems

2.2.5

Impact of Transient Conditions on Combustion

See Section 3.9.1
Delphi Energy and Chassis Systems
Electronic fuel injection has enabled engines to meet tighter exhaust
emissions standards through improved fuel control. Engine calibration
software can be programmed to deliver the precise amount of fuel required
by the engine under all operating conditions. Typical A/F ratio
distribution requirements are +/- 1.0 cylinder to cylinder
In addition, evaporative emissions standards require closed fuel systems
using seal rings and minimal tip leakage. The Multec 3.5 injector is a dry
coil design. There are no internal seal rings, eliminating possible sources
of evaporative emissions.
Purging the evaporative canister during engine operation requires better
control of lower fuel rates, placing greater demands on the low pulse
width capability of the injector (see section 2.4.3).
The term "transient conditions" is used to describe a change in engine load
and/or operating conditions. The primary focus is in response to driver-
commanded vehicle acceleration or deceleration maneuvers, but other
changes in state, such as transmission gear changes, torque converter lock
condition (automatic transmissions) and air conditioning compressor
engagement can impact fueling requirements. The impact of transient
conditions on combustion and emissions are typically magnified during
cold engine operating conditions.
During these transient conditions, the amount of fuel required and the
amount of fuel delivered may be different as there is likely to be some
"lag" between the actual change in state and the response of the fuel
injection system to these changes. In addition, fuel that builds up on
manifold walls or in crevices during steady state engine conditions may be
suddenly forced into the engine due to rapid changes in engine pressure
and airflow. This can be detrimental to driveability and emissions. These
differences in fuel delivery can be accounted for by software corrections
such as wall wetting compensations, deceleration enleanment and
acceleration enrichment.
When the vehicle is in a coasting (overrun) condition with the throttle
closed, the fuel supply to the cylinder can be stopped by shutting off the
injectors. This aids in further reducing the power output of the engine and
conserves fuel. Transitions into and out of this mode often require very
small amounts of fuel delivered in rapid fashion to minimize the impact on
vehicle performance and stability.
Fundamentals
Revision: 11/05-1 2-9