An Engine and Powertrain Mapping Approach for Simulation of Vehicle CO ₂ Emissions 2015-01-2777

Simulations used to estimate carbon dioxide (CO₂) emissions and fuel consumption of medium- and heavy-duty vehicles over prescribed drive cycles often employ engine fuel maps consisting of engine measurements at numerous steady-state operating conditions. However, simulating the engine in this way has limitations as engine controls become more complex, particularly when attempting to use steady-state measurements to represent transient operation. This paper explores an alternative approach to vehicle simulation that uses a “cycle average” engine map rather than a steady state engine fuel map. The map contains engine CO₂ values measured on an engine dynamometer on cycles derived from vehicle drive cycles for a range of generic vehicles. A similar cycle average mapping approach is developed for a powertrain (engine and transmission) in order to show the specific CO₂ improvements due to powertrain optimization that would not be recognized in other approaches. While a related paper [1] focuses primarily on simulation results, this paper summarizes the associated experimental results and development of the concept. Test results for an engine and a powertrain demonstrate the cycle average map is a smooth, continuous surface. The paper also compares accuracy of using the steady-state engine map versus the cycle average engine map. Considerations for using the cycle average map for vehicle simulation in the context of CO₂ regulations are also discussed with the conclusion that the cycle average map appears to be a technically viable approach to utilizing engine fuel consumption performance in a vehicle regulation.