Abstract
The three foundational elements that determine mobile source energy
use and tailpipe carbon dioxide (CO2) emissions are the tractive
energy requirements of the vehicle, the on-cycle energy conversion
efficiency of the propulsion system, and the energy source. The
tractive energy requirements are determined by the vehicle's mass,
aerodynamic drag, tire rolling resistance, and parasitic drag. Oncycle
energy conversion of the propulsion system is dictated by the
tractive efficiency, non-tractive energy use, kinetic energy recovery,
and parasitic losses. The energy source determines the mobile source
CO2 emissions. For current vehicles, tractive energy requirements
and overall energy conversion efficiency are readily available from
the decomposition of test data. For future applications, plausible
levels of mass reduction, aerodynamic drag improvements, and tire
rolling resistance can be transposed into the tractive energy domain.
Similarly, by combining thermodynamic, mechanical efficiency, and
kinetic energy recovery fundamentals with logical proxies,
achievable levels of energy conversion efficiency can be established
to allow for the evaluation of future powertrain requirements.
Combining the plausible levels of tractive energy and on-cycle
efficiency provides a means to compute sustainable vehicle and
propulsion system scenarios that can achieve future regulations.
Using these principles, the regulations established in the United
States (U.S.) for fuel consumption and CO2 emissions are evaluated.
Fleet-level scenarios are generated and compared to the technology
deployment assumptions made during rule-making. When compared
to the rule-making assumptions, the results indicate that a greater
level of advanced vehicle and propulsion system technology
deployment will be required to achieve the model year 2025 U.S.
standards for fuel economy and CO2 emissions.