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Figure 1 Comparison between a pure internal combustion engine and a 2x hybrid vehicle.
Figure 1 Comparison between a pure internal combustion engine and a 2x hybrid vehicle.

Hybrid vehicles offer superior efficiencies over both petrol and electric vehicles because they are operated at their most efficient modes and they can recover some energy through regenerative braking. For example, to double the fuel efficiency (2X hybrid-electric), we can use an engine only half the size and supplement the power through recovering much of the losses during braking. Let’s consider two cars, one conventional and another hybrid as depicted in Figure 1. The conventional car (1X) consumes 100 units of fuel, losing 73 units through the exhaust, radiator, friction, and other accessories and another 11 units during standby, thereby delivering 16 units of energy to propel the car. The hybrid car (2X or two times efficiency) deploys an internal combustion engine half the size using 50 units of fuel and losing 38 units to the ambient. The standby losses are eliminated because the vehicle operates as an electric vehicle when the car stops and no motor is left running. An additional 4 units of energy can be recovered through regenerative braking as the vehicle decelerates. Like the gas-powered car, the net useful energy is 16 units.

Table 1. Specifications of most popular hybrid
vehicles available in the US in 2005
Honda Insight Honda Civic Toyota Prius
Engine/Electric Motor Power
Engine compression ratio
Fuel economy (city/highway)
Emission rating
Passenger capacity
65 h.p./9.7 kW
57/56 mpg
1975 lb
528 miles
85 h.p./9.7 kW
48/47 mpg
2736 lb
554 miles
76 h.p./50 kW
60/51 mpg
2890 lb
589 miles
* Super Ultra Low Emission Vehicle
Source: Manufacturers published data.

In 1993, the US government, partnered with national laboratories and three major US automakers, Daimler-Chrysler, Ford, and General Motors, ventured the Partnership for New Generation of Vehicles (PNGV), whose long term goal is to come up with a 3X car that can triple fuel economy to 80 mpg. A similar program called FreedomCAR is also being undertaken to develop new and alternative technologies that improve fuel efficiency and reduce the US dependence on imported foreign oil.


(1) Toossi Reza, "Energy and the Environment:Sources, technologies, and impacts", Verve Publishers, 2005

Further Reading

Tillman, D., Fuels of Opportunity: Characteristics and Uses In Combustion Systems, Academic Press, 2004.

Sorensen, K., Hydrogen and Fuel Cells: Emerging Technologies and Applications, Academic Press, 2005.

Dhameia, S., Electric Vehicle Battery Systems, Academic Press, 2001.

Hussain, I., Electric and Hybrid Vehicles: Design Fundamentals, CRC Press, LLC. 2003.

Jefferson, C.M., and Barnard, R. H., Hybrid Vehicle Propulsion, WIT Press, 2002.

Spelberg, D. The Hydrogen Energy Transition: Moving Toward the Post Petroleum Age in Transportation, Academic Press, 2004.

Fuel, Direct Science Elsevier Publishing Company, Fuel focuses on primary research work in the science and technology of fuel and energy fuel science.

Transportation Research Part C: Emerging Technologies, Direct Science Elsevier Publishing Company; this journal focuses on scholarly research on development, application, and implications in the fields of transportation, control systems, and telecommunications, among others.

Fuel Cells Bulletin, Direct Science Elsevier Publishing Company, Fuel Cells Bulletin is the leading source of technical and business news for the fuel cells sector.

International Journal of Hydrogen Energy, Direct Science Elsevier Publishing Company, Quarterly journal covering various aspects of hydrogen energy, including production, storage, transmission, and utilization, as well as economical and environmental aspects.

External Links

US Department of Transportation (http://www.dot.gov).

US Department of Energy (http://www.doe.gov).

US Environmental Protection Agency (http://www.epa.gov).

National Energy Renewable Laboratory Hybrid Electric &Fuel Cell Vehicles (http://www.nrel.gov/vehiclesandfuels/hev).

FreedomCar (http://www.eere.energy.gov/vehiclesandfuels).