a vehicle propulsion system
and an energy storage unit (Figure 9.8). Power units may include SI engines
CI direct injection engines
gas turbines
or fuel cells. Propulsion can result entirely from an electric motor in a series configuration
or the SI engine and electric motor in a parallel configuration. Energy storage may be achieved by use of batteries
ultracapacitors
or flywheels. Vehicles on the market at the time of this writing use SI engines with parallel configurations and battery storage. In a series configuration
an SI engine drives a generator that charges a battery that powers an electric motor. In a parallel configuration
the driveshaft is turned by either the SI engine or electric motor. The series hybrid is generally more efficient but less powerful and has a shorter driving range than a parallel HEV. The parallel configuration provides performance that is relatively similar to that of a conventional light-duty vehicle. An HEV is generally configured with the gasoline engine
electric motor
and electronic circuitry in the front and battery in the rear. As of 2003
three HEVs were marketed
the Toyota Prius
Honda Insight
and Honda Civic (Figure 9.9). These vehicles have been well accepted in Japan. In the U.S.
federal and state incentives have been applied to offset some HEV purchase costs. HEV technology can be applied to a variety of vehicles
including sport utility vehicles (SUVs) and small trucks. The HEV has the potential to receive widespread acceptance and use because it meets stringent emission limits for HCs
CO
and NOx and has high fuel efficiency. High fuel efficiency would result in a significant decrease in CO2 emissions
a major greenhouse gas. By increasing fuel economy and thus reducing CO2 emissions
HEVs have the potential to significantly reduce global emissions of CO2 in the coming decades. Air quality 336
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