Development of a Heavy-Duty Diesel Modal Emissions and Fuel Consumption Model

There have been significant improvements in recent years in transportation and emissions modeling, in order to better evaluate transportation operational effects and associated vehicle emissions. In particular, instantaneous or modal emissions models have been developed for a variety of light-duty vehicles. To date, most effort has focused primarily on developing these models for light-duty vehicles with less effort devoted to Heavy-Duty Diesel (HDD) vehicles. Although HDD vehicles currently make up only a fraction of the total vehicle population, they are major contributors to the emissions inventory. Furthermore, it is generally believed that transit buses and heavy trucks will offer earlier opportunities for public implementation of automated operations compared to passenger cars. Thus, there is a critical need to have robust modal emissions and fuel consumption models for HDD vehicles. This report describes a HDD truck model that is now part of a larger Comprehensive Modal Emissions Modeling (CMEM) program developed at the University of California, Riverside. Within the CMEM framework, several HDD truck fuel consumption and emission sub-models have been developed, each corresponding to a distinctive vehicle/technology category. The developed models use a parameterized physical approach where the entire emission process is broken down into different components that correspond to physical phenomena associated with vehicle operation and emission production. As part of a parallel research program, UC Riverside has developed a Mobile Emissions Research Laboratory (MERL) that can be attached to a number of heavy duty rigs to measure instantaneous (i.e., modal) emissions and fuel consumption in-situ. Using MERL, a variety of trucks were extensively tested under a wide range of operating conditions. The collected data (along with other HDD truck data sources) were then used to calibrate the HDD models. Particular care was taken to investigate and implement the effects of varying grade and the effects of variable ignition timing. In this report, background material is provide on HDD vehicle fuel consumption and emissions research, followed by a description of the vehicle testing program. The HDD vehicle model development process is then described, along with the model validation process. The model was subsequently integrated with a variety of transportation simulation modeling tools for the purposes of evaluating several automation scenarios. Particular emphasis has been placed on simulating the truck platoon scenario, where aerodynamic drafting effects can provide a significant benefit in terms of fuel and emissions savings. In addition to the modeling, experimentation has been carried out with MERL in real-world tests, examining trucks traveling in tandem with close inter-vehicle spacings. Results of these tests are also described herein.