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6.2.1 Ignition at Idle
Ignition during engine idling is calibrated using the parameters available in
the RPM Control RPM Control Ignition RPM folder.
6.3 Calibrating Fuel
NIRA i7x controls the amount of injected fuel based on two tables;
Volumetric Efficiency Table (VE) and Fm Lambda Target. In NIRA rk, you find
these tables in the Mappings tab under All Parameters -> 1.Fuel -> 1.Basic
Calibrate these tables by following the steps below.
6.3.1 Engine Start Fuel
For the engine to start, the correct amount of fuel has to be injected. The
settings for start fuel are adjusted in the tables found under Engine Start
Injection control. How much extra fuel that is needed depends on a number
of parameters and varies from engine to engine. Start with the default values
and iterate changes until you are happy with the result.
In the beginning of the start sequence, an additional fuel squirt is added. This
additional fuel is injected from all injectors at the same time, as soon as NIRA
i7x detects crankshaft rotation. The appropriate amount of fuel depends on
the engine temperature and is programmed in Start Primer table. The
amount of fuel is given in mg per cylinder and the Start Primer table is
independent from the values in the Choke Enrichment table and the other
tables in the Engine Start folder.
6.3.2 Volumetric Efficiency Comp Table
This table sets up the compensation table for VE as a function of MAT.
When the MAT increases, the intake air volume expands, which in turn means
the engine requires less fuel. Using the ideal-gas equation, we get
k=273/(MAT+273)
where the MAT is given in degrees Kelvin (K). 273K = 0°C.
When the fuel is injected and vaporized in the intake manifold, it cools the
intake air, which increases VE. In addition, the cooling effect increases with
MAT.
Based on experiments, a good approximation, when using gasoline, is the
square root of k, which gives the final formula for VE compensation as:
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