DECS is now available at www.aeswave.com DECS is a compilation of diagnostic calculators, some already commonly used, to aid technicians in diagnosing driveability and emissions issues. These calculations have been improved upon and assembled in one application in order to streamline the diagnostic process.
For the complete manual/information click HERE.
All your diagnostic calculation needs in one application.
Designed by technicians, for technicians.
Written by: Scott Shotton
The following are bits of the DECS calculation platform. Most of these calculations are available on the main screen. They have been programmed this way for the technician's benefit. Additional calculations are included in additional windows.
Lambda / Combustion Efficiency Calculation
Lambda
Lambda is a measure of how well an engine was fueled. It calculates a rich, or lean, value in the form of a percentage. Since 1979 the Brettschneider equation has been used to determine this valuable information. A good lambda calculator can be a valuable diagnostic tool if a technician knows how to use the information provided. Some gas analyzers have this equation built in, but it usually applies to gasoline only. Lambda calculation software also uses this same equation in the same way. But the equation can do more.
Until recently, lambda calculations in the automotive industry have been based on gasoline, its chemical composition, and its 14.7 to 1 air fuel ratio. But with the introduction of alternate fuels (that have different compositions and air fuel ratios) the data from gas analyzers, or diagnostic software, may be incorrect.
The Brettschneider equation accommodates all carbon based fuels; therefore it can be used in situations other than common gasoline. The DECS lambda calculator is a fully functional lambda calculator equipped to report accurate results for multiple fuels. DECS default values are set for gasoline because it is still the most common fuel source for modern automobiles. But what happens if your exhaust analyzer reports a lambda number for gasoline, but the fuel being burned is really E85? Are the numbers you trust for accurate diagnosis correct? No.
DECS lambda calculator has been programmed with the appropriate values for multiple fuels. The fuels included in DECS lambda calculator are: USA gasoline, oxygenated gasoline, European gasoline, diesel, E85, CNG, and LPG. The lambda calculator also reports air fuel ratio and % rich or lean. Red text warns the user of a result that could be undesirable.
Exhaust leaks and secondary air injection can discredit lambda values. An additional calculation added to the DECS lambda calculator is oxygen dilution value. The oxygen dilution value is provided to warn of possible air leaks in the exhaust system (or the presence of secondary air injection) that could skew the lambda calculator’s results. If too much oxygen dilution could be present, DECS displays the oxygen dilution value in red and highlights any fields that could be incorrect due to the dilution in yellow.
Remember, the lambda calculator works for both pre and post catalytic converter gas samples. The results remain the same.
Combustion Efficiency
If lambda is a measure of how well an engine was fueled, combustion efficiency is a measure of how well the fuel introduced into the engine was burned.
Just like the lambda calculator, the DECS combustion efficiency calculation accounts for multiple fuels. Most gas analyzers, and software, report CE based on gasoline characteristics. DECS takes all of the same multiple fuels from the lambda calculation into account. The CE output of the calculator also appears in red when the value is poor.
Unlike a lambda calculator, a combustion efficiency calculation is different for pre and post catalytic converter gasses. If the catalytic converter is functioning further combustion occurs in the catalyst. Therefore, a post gas reading should show a higher CE result than a pre gas sample.
Volumetric Efficiency / Fuel Requirement Calculation
Volumetric Efficiency
The VE calculator determines the engine’s ability to pump air. By measuring VE a technician can be aided in diagnosing restricted intake systems, restricted exhaust systems, air metering problems, and/or mass airflow sensor issues.
Just like the previous calculations, the VE calculation highlights a questionable value in red.
Fuel Requirement
The fuel requirement calculator determines the amount of fuel required for specific driving conditions or the maximum amount of fuel required. These numbers are useful for determining specifications for fuel volume testing. The fuel requirement calculator also works for multiple fuels.
In the following example, the fuel specifications are reported for the conditions entered on the left.
DECS fuel report reflects the fuel required to maintain a stoichiometric air fuel ratio for current driving conditions. Since DECS does not have a throttle position input, a 120% figure has been added to account for the extra fuel required during acceleration enrichment.
If an engine size and its red line RPM have been entered without a MAF input. The end result is an invalid VE%, but the fuel volume numbers are the key. The fuel outputs in this situation are a good specification for a fuel volume test. DECS figures the minimum amount of fuel required for any operating condition. If your volume exceeds the DECS Stoich + 20% calculations, then fuel volume should be sufficient for any operating condition.
Note: fuel volume requirements have only been provided for liquid fuels. Currently CNG and LPG are not part of this particular equation.
Air Fuel to Lambda Conversion
The air fuel to lambda conversion calculator has been provided for your convenience. The user can enter an air fuel ratio, choose the appropriate type of fuel, and get a lambda value.
Just as the full lambda calculator does, this conversion calculator displays undesirable values in red.
Catalyst Efficiency Calculation
DECS catalyst efficiency calculation can be used to determine how well a catalytic converter does its job reducing each gas.
This calculation requires the measurement of pre and post converter gasses. Each gas is independently calculated and the results are a percentage output the represents the efficiency at which the catalytic converter reduces each gas.
Note: These results of this calculation could vary depending on engine operating conditions. For accurate results to be achieved the vehicle should be in good fuel control, and the catalytic converter should be fully warmed up, to insure proper catalyst operation.
Emissions Reduction Goal Calculation
The DECS emissions reduction goal calculation helps a technician equate constant sampling gas analyzer information to common exhaust gas analyzers. Constant sampling systems are sometimes used by state emissions inspection programs. Since the constant sampling systems actually weigh the gasses in the exhaust stream the outputs are often expressed in grams per mile. Common analyzers provide outputs in percent or parts per million. These two different readings make repair verification difficult. The goal calculator figures a goal based on the state’s readings and a before repair baseline test drive.
Conversion Calculators
DECS includes many conversion calculators for figuring items such as mass and volume. Many of the calculators included are incorporated in other DECS calculations. These conversion calculators have been provided, should the need arise, to assist technicians in performing basic calculations more rapidly and efficiently.
Help Files
DECS includes a range of help files to assist the user when using the software. The help files can be accessed from the main screen pull down menu. Many of the help files included examples.
DECS software is $40. For questions or ordering please email decs@driveabilityguys.com.
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Order online at www.aeswave.com
Direct link http://www.aeswave.com/Products/Product.asp?i=745
Order by mail: send a check payable to: The Driveability Guys ,PO Box 683, Wheaton ,Il 60187. Be sure to include a shipping address. Shipping is free.
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