Hybrid Vehicle

Hybrid Vehicle

A hybrid vehicle (HV) is a vehicle that uses two distinct power sources such as:

* An on-board rechargeable energy storage system (RESS) and a fueled power source for vehicle propulsion
* Human powered bicycle with battery assist
* A sail boat with electric power[1]

The term most commonly refers to petroleum electric hybrid vehicle, also called Hybrid-electric vehicle (HEV) which use internal combustion engines and electric batteries to power electric motors.

The term hybrid when used in relation with cars also has other uses. Prior to its modern meaning of hybrid propulsion, the word hybrid was used in the United States to mean a vehicle of mixed national origin; generally, a European car fitted with American mechanical components. This meaning has fallen out of use. In the import scene, hybrid was often used to describe an engine swap. Some have also referred to flexible-fuel vehicles as hybrids because they can use a mixture of different fuels — typically gasoline and ethanol alcohol fuel.

Gasoline

Gasoline engines are used in most hybrid designs, and will likely remain dominant for the foreseeable future. A 2006 article, "Hybrid Vehicles Gain Traction", in Scientific American (April 2006), co-authored by Joseph J. Romm and Prof. Andrew A. Frank, argues that hybrid cars that can be plugged into the electric grid (Plug-in hybrid electric vehicles) will soon become standard in the automobile industry.[1]

While petroleum-derived gasoline is the primary fuel, it is possible to mix in varying levels of ethanol created from renewable energy sources. Like most modern ICE-powered vehicles, hybrids can typically use up to about 15% bioethanol. Manufacturers may move to flexible fuel engines, which would increase allowable ratios, but no plans are in place at present.

Nowadays petroleum gasoline engines can use directly biobutanol (see direct biofuel).

Diesel

One hybrid vehicle combination uses a diesel engine for power generation. Diesels have advantages when delivering constant power for long periods of time, suffering less wear while operating at higher efficiency. The Diesel engine's high torque, combined with hybrid technology, may offer performance in a car of over 100 mpg US (2.35 litres/100 km). Most diesel vehicles can use 100% pure biofuels (biodiesel), so they can use but do not need petroleum at all; if diesel-electric hybrids were in use, this benefit would likely also apply. For passenger vehicles, no diesel-electric hybrids are currently commercially available, although demonstration vehicles have been shown.

As with regular diesel engines, diesel-electric hybrids may be more appropriate for high-mileage, intensive-use applications, such as buses, trucks, and delivery vehicles, and less appropriate for passenger vehicles. Diesel-electric vehicles are increasingly being used for applications with high usage profiles, such as city buses, where the significantly higher mileage and lower emissions may be important. Both parallel and serial hybrids are in use.

Diesel-electric hybrids with parallel drivetrains like the Prius may have a substantial cost disadvantage to other options for use in passenger cars. Diesel engines are generally more expensive than gasoline equivalents, due to the demands for higher compression (although this also makes diesels more durable). If this "diesel premium" is added to any additional expense for the hybrid, the diesel-electric combination may make the payback period for such vehicles even longer and less feasible for many consumers. In addition, the higher torque of diesel engines may obviate one of the advantages of the electric motors.In addition, regular diesel vehicles may get similar mileage to gasoline-electric hybrids, for a smaller premium, and the marginal benefit of "hybridization" may not be viable.

Diesels are not widely used for passenger cars in the United States, as US diesel fuel has long been considered very "dirty", with relatively high levels of sulfur and other contaminants in comparison to the Eurodiesel fuel in Europe, where greater restrictions have been in place for many years. Despite the dirtier fuel at the pump, the US has tough restrictions on exhaust, and it has been difficult for car manufacturers to meet emissions levels as higher sulfur levels are damaging to catalytic converters and other emission control systems. However, ultra-low sulfur diesel was mandated and became widely available in the U.S. in October 2006 for highway vehicles, which will allow the use of newer emissions control systems.

Diesel-electric motors are common for use as locomotives, but using a serial hybrid design. In locomotives, the diesel engine is used to generate electricity for the electric drivetrain. This configuration allows the internal combustion engine to be operated at more efficient operating parameters, while removing the need for a separate transmission for the ICE unit and allowing the efficient delivery of torque from the electric motors. Such a system may need a smaller diesel engine and allow for better emissions controls, since the operating range of the diesel engine would be optimized for electric generation rather than power delivery through the mechanical transmission and wheels. There have been studies of this type of diesel-electric hybrid, but there are no confirmed attempts to commercialize such a vehicle for passenger use.

PSA Peugeot Citroën has unveiled two demonstrator vehicles featuring a diesel-electric hybrid powertrain: the Peugeot 307 and Citroën C4 Hybride HDi (PDF). VW made a prototype diesel-electric hybrid car that achieved 2 litres/100 km (118 mpg US) fuel economy, but has yet to sell a hybrid vehicle. General Motors has been testing the Opel Astra Diesel Hybrid. There have been no concrete dates suggested for these vehicles, but press statements have suggested production vehicles would not appear before 2009.
Hybrid Orion VI Metrobus
Hybrid Orion VI Metrobus

So far, production diesel-electric engines have mostly just appeared in mass transit buses. Current manufacturers of diesel-electric hybrid buses include New Flyer Industries, Gillig, Orion Bus Industries, and North American Bus Industries. In 2008, NovaBus will add a diesel-electric hybrid option as well.

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