Lambda Calculation from Exhaust Gas Measurements

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Lambda Calculation from Exhaust Gas Measurements
Determining how close the A/F ratio is to the stoichiometric point using exhaust gas analysis. Presented to East Bay ATA, Hayward, CA May 5, 2004 By: Robert J. Schrader President, Bridge Analyzers, Inc.

What is Lambda? Lambda is Oxygen Balance

Why is Lambda Important?
Lambda control is necessary for peak combustion efficiency in the Engine. Lambda control is necessary for peak CAT efficiency. Lambda Control Improves Reliability, Fuel Economy and Lowers Emissions.

Combustion Efficiency (CE)
Engine out CE for Gasoline Fuel is no better than 95%. Tailpipe-out CE for CAT equipped vehicles improves to %. Factor of 10 improvement Required for Current Emission Standards CAT CE is very Lambda-Dependent

Engine-Out Gas Values

CAT Oxidation and Reduction Efficiency vs Lambda

CAT Out Gases

3-Way CAT vs Lambda NOx Reduction Bed CO/HC Oxidation Bed
Requires Lambda to be not greater than CO/HC Oxidation Bed Requires Lambda to be not less than Modulation Depth Cycles Rich and Lean Between the Limits Above.

Brettschneider Equation - a balance equation that calculates Lambda

Calculating A/F Ratio from Lambda
Lambda = when the Oxygen available and Combustible Oxygen demands are in balance. This is the point of perfect stoichometric balance. At this point the A/F ratio is to 1.00 for Gasoline. Thus, A/F = x Lambda

Sensitivity to Combustion Efficiency (Pre CAT vs Post CAT)
Brettschneider Lambda uses all the oxygen-bearing and combustible-bearing gases. Balance Equation - Calculation not affected by the degree of oxidation. Method is insensitive to combustion efficiency. Either Pre-CAT or Post-CAT gases may be used.

Lambda for Emissions Control
 = when Oxygen available and Combustible demands are in balance. ECM controls =1.000 at Cycles/Sec using ‘lambda sensor’ input. 3-Way CAT operation requires   to 1.020 Lambda can be confirmed by exhaust gas measurement, either pre or post CAT.

Lambda for Fuel Control Diagnostics
 calculated from exhaust gas indicates air-fuel mixture independent of the engine controls.  calculated from exhaust gas indicates air-fuel mixture independent of combustion efficiency. Cold (Open Loop) vs Hot (Closed Loop) vs CAT light-off operation can be evaluated.  can be used to tune systems which do not have closed-loop control.

Qualifying EGA gas tightness prior to Lambda Calculation
High Combustion Efficiency: Measure O2 post CAT - every 5% air leak adds 1.0% O2 to gases. Low Combustion Efficiency: Add CO and CO2 - should equal 15% for Gasoline. Compare both Methods. If O2 indicates air dilution - then confirm this with low CO and CO2 sum. They should agree.

iATN Lambda Calculator
Created by iATN Tech Support staff, and available to iATN members on-line at Plug and Play either 4 or 5 gas values. Can select either US or European gasoline constants. Operates in Java - can be saved and run off-line by any Java-equipped net browser.

Bridge Excel Worksheet
Available as attached Excel file by contacting: Plug and Play either 4 or 5 gas values. Can select either US or European gasoline constants. Operates on any PC with Excel - can be saved and run off-line using Microsoft Excel.

iPaq Palm Computer Worksheet
Written by Miles Wada using the Brettschneider equation - a’la Bridge. Available for download at: Operates on the iPaq using CE Excel. Can operate on other CE-based units.

Palm Computer Worksheet in Excel.
Written by Greg Meyer using the Brettschneider equation - a’la Bridge. Available from Greg via at: Operates on Palm OS computers in Excel.

A/F Ratio From Lambda A/F = x Lambda