Special Section on Vehicle Power and Propulsions

P ERSONAL transportation offers people freedom, but this choice of freedom creates a conflict with growing environmental concerns and the sustainability of humanity's use of natural resources. Hybrid electric vehicles (HEVs) improve fuel efficiency by optimizing powertrain operation and recovering kinetic energy during braking, hence reducing liquid fuel consumption in the transportation sector. Electric vehicles (EVs) and plug-in HEVs (PHEVs) further reduce fuel consumption by using grid electricity. Electricity can be utilized more efficiently than the combustion process in a car. Well-to-wheel studies show that even if the electricity is generated from petroleum, the distance that can be driven when consuming one gallon of gasoline is 108 mi (equivalent) in an electric car compared with 33 mi in a conventional car that is driven by an internal combustion engine. Future electricity can be generated through renewable sources, such as hydroelectric, wind, sun, and biomass, which offer ultimate sustainability. High cost, limited driving range, and long charging time are the main challenges for battery-powered EVs. HEVs use both an internal combustion engine and an electric motor to drive the vehicle, thereby overcoming the cost and range issues of a pure EV with no need to be plugged in to charge. The fuel consumption of HEVs can be significantly reduced as compared with conventional gasoline engine-powered vehicles. However, the vehicle still operates on gasoline/diesel fuel. PHEVs are equipped with a larger battery pack and a larger sized electric motor compared with HEVs. PHEVs can be charged from the grid and driven for a limited distance (for example, 20–40 mi) using electricity, which is referred to as the charge-depletion mode operation. Once the battery energy has been depleted, it operates in a way that is similar to a regular HEV, which is referred to as the charge-sustain mode operation or the extended-range operation. Since most personal vehicles are for commuting and most of them are only driven for a limited range daily, a significant amount of fossil fuel can be displaced by deploying PHEVs. In an extended-range operation, a PHEV works similarly to an HEV by using the onboard electric motor and battery to optimize the engine and vehicle system operation to achieve higher fuel efficiency. Due to the larger battery power and energy capacity, a PHEV can recover more kinetic energy during braking, thereby further increasing the fuel efficiency. EVs, HEVs, and PHEVs provide many advantages and challenges. which is the heartland …