Delphi Multec 3.5, Руководство по применению

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Fundamentals Multec 3.5 Fuel Injector Application Manual
2-26 Delphi Energy and Chassis Systems
Revision: 11/05-1
Figure 2-9 - Evaporative Emissions Regulations
2.4.3 Impact of Canister Purge on Engine Fueling
To reduce the amount of vehicle evaporative emissions, a contained fuel
storage and supply system is used to minimize the escape of fuel vapors
from the fuel tank to the atmosphere. This is accomplished by trapping
vapors formed in the fuel tank within a carbon canister connected to the
fuel tank. The amount of vapor to be contained increases with fuel
temperature and fuel volatility. The vapors trapped in the canister are then
drawn by engine vacuum through a hose to the intake manifold during
engine operation. This fuel must be accounted for in the combustion
process to prevent a rich air/fuel ratio and increased emissions. The
engine controller will reduce the amount of fuel being metered by the
injectors when canister purge is taking place, based on feedback from the
oxygen sensor. The impact of canister purge flow rates on the fuel injector
is greatest when purge is active at idle. Since the injector is normally at a
low pulse width at idle, canister purge can reduce the required flow rate of
the injector and lead to very small commanded pulse widths. These pulse
widths may be beyond the working flow range of the injector (see section
3.10.2.) The potential impact of these low pulse widths on flow variation
must be considered when setting up the fuel system calibration. Any
negative impacts of canister purge can be minimized by proper size
selection of the fuel injector and/ or use of a low pulse width correction
table.
See Section 3.9.1-
Minimum pulse-width
Note: Canister purge should not be so excessive as to lower the injector
commanded pulse-width to the point of inaccurate operation. Refer to
Section 3.9.1- Minimum Pulse-Width.
Evaporative Emissions Limits
0
0.5
1
1.5
2
2.5
LEV PZEV
HC emissions [g/test]
Fuel System and Vehicle
Vehicle Only
Fuel System Only
Evaporative emissions source: