Fleet-Level Modeling of Real World Factors Influencing Greenhouse Gas Emissions Simulation in ALPHA

Paper #:
  • 2017-01-0899

  • 2017-03-28
The Environmental Protection Agency’s (EPA’s) Advanced Light-Duty Powertrain and Hybrid Analysis (ALPHA) tool was created to estimate greenhouse gas (GHG) emissions from light-duty vehicles. ALPHA is a physics-based, forward-looking, full vehicle computer simulation capable of analyzing various vehicle types with different powertrain technologies, showing realistic vehicle behavior, and auditing of internal energy flows in the model. In preparation for the midterm evaluation (MTE) of the 2017-2025 light-duty GHG emissions rule, ALPHA has been updated utilizing using newly acquired data from model year 2013-2015 engines and vehicles. As part of its engine and vehicle benchmarking work to support ALPHA validation efforts, EPA has been careful to look at all aspects of vehicle and engine operation that affect fuel consumption, such as steady state fuel consumption to meet road load and driver demands, increased fuel usage due to engine transients during vehicle acceleration, operational limits to meet NVH and emissions requirements, and consumption associated with accessory loading. A model that accounts for these various types of fuel consumption will provide better estimates of the effectiveness of future low-GHG technologies. This paper discusses updates made to the ALPHA to reflect vehicle benchmarking data for tire slip, electrical system, accessory loads, driver behavior, transmission gear selection, and torque converter lockup. To allow general modeling of various car classes in ALPHA, generic calibrations for driver behavior, transmission gear selection and torque converter lockup were created based on benchmarking data observed across a range of vehicles and transmissions. The paper also shows the derivation of correction factors needed to estimate cold start emission results from the modeled FTP hot test results.
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