Development of in-use engine speed/torque heat maps across multiple heavy-duty commercial vehicle vocations

Abstract

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.

Delivering Clean Air in Denver: Propane Trucks and Infrastructure in Mail Delivery Application

“…The maps indicate that diesel (Figure 11) can achieve higher thermal efficiencies compared to propane (Figure 12), albeit over a smaller range of engine speed. It has been established that the high-frequency zone of engine operation for diesel trucks operating in the local delivery vocation is typically the engine speed range of 1,200-1,500 rpm and engine torque range of 100-500 Nm (Zhang, et al 2021). This high-frequency operating zone does not necessarily match the peak thermal efficiency zone for the engine.…”