● Setup - Constants - Fuel & Air
Information about the chemical composition (atom ratios) of the fuel is required to determine
the AFR. This information is entered into the AFRecorder after selecting "FUEL & AIR" in
the setup - constants menu.
The information requested is "H:C RATIO" (the hydrogen to carbon atom ratio of the fuel),
"O:C RATIO" (the oxygen to carbon atom ratio of the fuel), and "N:C RATIO" (the nitrogen
to carbon atom ratio of the fuel). The Input Specifications and Limits section on page 34
contains values for common fuels.
Information about the %O
2
in air is used during the “AIR CAL” of the AFR sensors. The
oxygen concentration in dry air (zero humidity) is 20.95% and decreases with increasing
humidity. The %O
2
in air can be calculated from the barometric pressure (P
b
), and the water
vapor pressure (P
w
) using the formula:
%O
2
= 20.95% x (P
b
- P
w
) / P
b
A psychrometric chart is used to determine the water vapor pressure (P
w
).
● Setup - Constants - ICC_L, ICC_R
Information pertaining to the engine's degree of combustion efficiency is entered after
selecting "ICC_L" (for the left AFR sensor) or "ICC_R" (for the right AFR sensor) from the
setup - constants menu. The three displays following this selection allow the entry of ICC
(incomplete combustion compensation) factors for lean (ICC LEAN), stoichiometric (ICC
STOICHIOMETRIC), and rich (ICC RICH) air-to-fuel ratios for the engine being tested.
This information is used to improve the accuracy of the AFR measurement. ICC values from
-10.0 to 10.0 may be entered with 5.0 (for each ICC) the recommended settings for typical
production engines. In general, the following engine conditions require an increase in the
ICC factors:
1. High degree of valve overlap
2. Low compression ratio
3. Cold engine operation
4. Spark timing advanced from MBT (minimum timing for best torque)
The ICCs must be activated (see Setup - Options - ICC on page 20) for them to influence
the reported AFR(s).
Stand-Alone Operation 21
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