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Regulations for Emissions from Vehicles and Engines

Advanced Light-Duty Powertrain and Hybrid Analysis (ALPHA) Tool

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Overview of ALPHA Model

EPA’s ALPHA model is a full vehicle simulation model which estimates the greenhouse gas (GHG) emissions from light-duty vehicle sources. It is a physics-based, forward-looking, full vehicle simulator, capable of simulating various vehicle types and powertrain technologies. 

ALPHA was used by EPA to inform the 2016 Draft Technical Assessment Report of light-duty vehicle greenhouse gas standards for model years 2022-2025, as well as the 2016 Proposed Determination under the Midterm Evaluation.  ALPHA is an in-house vehicle simulation model used by EPA, and is not intended to be a commercial product.

The ALPHA model shares an underlying structure with EPA's Greenhouse Gas Emissions Model (GEM) used for medium- and heavy-duty vehicle compliance calculations. ALPHA is under active development and the versions of the model presented below represent the state of the package at particular points in time.

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Response Surface Model

Because operating the ALPHA model in real time to conduct full vehicle simulations is cost and time prohibitive, EPA developed a method of reproducing ALPHA model effectiveness values using an industry standard statistical methodology known as a Response Surface Model (RSM). The RSM is used to computationally access a complete set of ALPHA model results using a collection of response surface equations (RSEs). The RSEs can then be used to reproduce the ALPHA model results in real time for determining the effectiveness of vehicle technologies.

EPA commissioned RTI International to conduct an independent peer review of the Response Surface Equations methodology.

Peer Review of EPA’s Response Surface Equation Report (PDF) (125 pp, 2.09 MB, EPA-420-R-18-006, May 2018)

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ALPHA v2.2 Technology Walk Samples

In response to stakeholder comments on the MTE Proposed Determination, EPA utilized a version of ALPHA capable of executing this sample technology walk analysis to further corroborate EPA’s assessment that vehicles equipped with conventional technologies can support compliance with the MY2025 targets without the need for extensive electrification. These ALPHA runs are referenced in the Response to Comments for the 2017 Final Determination on the Appropriateness of the Model Year 2022-2025 Light-duty Vehicle Greenhouse Gas Emissions Standards under the Midterm Evaluation.

ALPHA v2.2 Technology Walk Samples (ZIP)(31 MB, January 2017)
This file contains a series of ALPHA V2.2 simulations (as of 2017.01.12) used to support a sample technology walk analysis. Running this version of ALPHA requires Matlab/Simulink with StateFlow 2016b. For convenience, a plaintext form of the workspace for each ALPHA run is provided in an m-file format. Further details are in the readme.txt file.

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ALPHA v2.1 Calibration Samples

EPA used ALPHA simulation results to inform its calibration of the Lumped Parameter Model (LPM), an EPA desktop computer application that estimates the effectiveness (CO2 reduction) of various technology combinations. A subset of the numerous ALPHA simulation results studied during the MTE process were identified as key simulations used to inform the calibration of the LPM.

ALPHA v2.1 Calibration Samples (ZIP)(30 MB, November 2016)
This file contains a series of ALPHA V2.1 simulations (as of 2016.11.18) used to inform the calibration of the Lumped Parameter Model. Running this version of ALPHA requires Matlab/Simulink with StateFlow 2016b. For convenience, a plaintext form of the workspace for each ALPHA run is provided in an m-file format. Further details are in the readme.txt file.

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ALPHA v2.0 Simulation Samples

EPA used ALPHA simulation results to inform its calibration of the Lumped Parameter Model (LPM), an EPA desktop computer application that estimates the effectiveness (CO2 Reduction) of various technology combinations. A subset of the numerous ALPHA simulation results studied during the MTE process were identified as key simulations used to inform the calibration of the LPM.

  • ALPHA v2.0 Simulation Samples (ZIP)(1 pg, 4 MB, July 2016)
    This file contains a series of ALPHA V2.0 simulations (as of 2016.07.07) of the same type used to inform the calibration of the Lumped Parameter Model.
    Running this version of ALPHA requires Matlab/Simulink with StateFlow 2014a. For convenience, a plaintext form of the workspace for each ALPHA run is provided in an m-file format. Further details are in the readme.txt file

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ALPHA v2.0 Peer Review

EPA engaged ICF International to perform a peer review of the ALPHA Full Vehicle Simulation Model. This peer review process was carried out under EPA’s peer review guidelines. The entire model and all subsystems were unlocked for complete transparency. A number of independent subject matter experts provided reviews and comments on the methodologies used in the model.

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Publications Concerning ALPHA v2.0

Throughout the MTE process, EPA’s goal was to publish as much of our research as possible in peer-reviewed technical papers and journals. These publications describe in more detail the development and use of the ALPHA model.


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Overview of Testing and Integration with Modeling

NCAT has integrated benchmarking and modeling activities to ensure robust data. The following presentation highlights the benchmarking and modeling activities relating to light-duty GHG emissions.


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Engine Mapping Process Documents

Integrating Test Data for Light-duty GHG Technology and modeling results for engines into the ALPHA model requires a process for translating test results into a full map representing all phases of engine operation. The following documents explain the process for creating ALPHA engine maps for key engine packages.

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ALPHA v1.0

The initial version of ALPHA, used for off-cycle technology evaluations, is provided for historical purposes. The software is a freely-distributed, desktop computer based application, built on MATLAB/Simulink. EPA is no longer using this version of ALPHA.

The downloadable installation file below (in a zip format) contains the ALPHA v1.0 tool. The model documentation provides details on how to launch and run the simulation tool.

  • ALPHA User's Guide for Off-Cycle Credit Evaluation v1.0 (PDF)(22 pp, 1.27MB, EPA-420-B-12-051, August 2012)
    This document contains descriptions of how to launch and use the ALPHA tool for off-cycle technology evaluation.
  • ALPHA v1.0 Installation File (ZIP)(1 pg, 203 K)
    This file contains the ALPHA v1.0 application files written in MATLAB/Simulink. This version was used in EPA’s Model Year 2017-2025 Final Rulemaking for Light-Duty Vehicle Greenhouse Gas Emission Standards. 

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