Final answer:
The charge-depleting operating mode in PHEVs represents the period when the vehicle uses the energy from its battery pack, aiming to reduce fuel consumption and emissions until the battery reaches a certain level.
Step-by-step explanation:
The charge-depleting operating mode (CD) refers to the phase in a plug-in hybrid electric vehicle (PHEV) when the car is primarily using the energy stored in its battery pack for propulsion. Typically, this is the initial mode when a fully charged PHEV starts to operate. The vehicle will continue to drive in this mode until the battery level reaches a predetermined threshold, at which point it will switch to charge-sustaining (CS) mode where the internal combustion engine or another charging mechanism keeps the battery at a constant level.
CD mode aims to maximize the use of electrical energy, thus reducing fuel consumption and emissions. The duration of CD mode depends on various factors including battery capacity, vehicle efficiency, and driving habits.