Development of In-Use Engine Speed/Torque Heat Maps Across Multiple Heavy-Duty Commercial Vehicle Vocations

Research output: Contribution to journalArticlepeer-review


The U.S. Department of Energy (DOE) established the SuperTruck program with the goal of achieving brake thermal efficiency (BTE) greater than or equal to 55% as demonstrated in an operational heavy-duty (HD) diesel engine at a 65-miles-per-hour (mph) cruise point. Beyond the line-haul application, HD engines operate in a wide range of speed and torque conditions that are unlikely to yield the same efficiency under real-world operation. Thereby, the in-use engine heat maps described in this paper are a valuable tool to illustrate whether the engine-efficiency “sweet spot” matches the most frequent operating conditions. In this study, NREL developed engine heat maps to quantify the important operating points for various vocations using our Fleet DNA database of commercial fleet vehicle operations data. These heat maps clearly show that high-frequency operating points vary significantly according to vehicle vocation, while only a few of them match the sweet spot. Beyond the illustration, engine in-use heat maps can also be leveraged to build up reduced-order engine-efficiency models, needed by many rapid powertrain simulations. As case studies, nine reduced-order models – including line-haul truck, transfer truck, transit bus, transit bus with compressed natural gas (CNG) engine, drayage, refuse pickup, local delivery, utility truck, and school bus with CNG engine – using a trust-region reflective algorithm to fit the on-road data extracted based on the engine in-use heat maps.

Original languageAmerican English
Pages (from-to)1717-1731
Number of pages15
JournalInternational Journal of Engine Research
Issue number10
StatePublished - Oct 2022

Bibliographical note

Publisher Copyright:
© IMechE 2021.

NREL Publication Number

  • NREL/JA-5400-80150


  • Commercial vehicles
  • engine efficiency
  • engine model
  • on-road data
  • operational heat maps


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