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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.

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What is Lambda? Lambda is Oxygen Balance

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**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.

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**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

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Engine-Out Gas Values

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**CAT Oxidation and Reduction Efficiency vs Lambda**

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CAT Out Gases

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**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.

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**Brettschneider Equation - a balance equation that calculates Lambda**

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**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

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**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.

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**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.

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**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.

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**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.

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**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.

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**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.

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**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.

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**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.

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

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