Three Types of Power Units in HEVs

Hybrid Electric Vehicles (HEVs) offer consumers the opportunity to drive vehicles with a combination of different power units. These vehicles can be powered by any combination of spark ignition engines or compression ignition engines, and fuel cells. Using alternative power sources to supplement internal combustion engines in the HEV reduces emissions, as well as lowering dependence on fossil fuels.

Spark Ignition

A spark ignition engine is the type of engine found in most gas-powered cars and trucks. In a HEV with spark ignition, fuel and air are mixed in the carburetor, and sent into combustion chambers called cylinders. A spark plug generates a spark, igniting the mixture, and setting off a small explosion. The explosion forces a piston out of the end of the cylinder, which turns the engine's crankshaft, producing mechanical energy for the engine.

Compression Ignition

An engine that uses compression ignition does not require the use of a spark plug. In an HEV with a compression ignition, the carburetor also ensures that the correct amount of fuel is sent into the cylinder to mix with the air. This type of ignition, however, is achieved by quickly compressing the air in the cylinder. The repeated compression of the air generates heat from friction, which ignites the fuel as it is sent into the cylinder by the carburetor.

Fuel Cell

A fuel cell uses a chemical reaction to create electricity, and is also known as an electrochemical energy conversion device. Typically, fuel cells use hydrogen as their fuel source. When hydrogen is combined with oxygen, and exposed to an electrolyte, the hydrogen and oxygen are turned into water. The process of converting the two elements into water produces electricity, which is then used to power the motor of the HEV.

Advantages

While HEVs currently sell at higher up-front prices than comparable gas-engine vehicles, efficiency in production and advancements in technology are lowering prices. Many HEVs are currently being offered at prices competitive with gas-engine vehicles. In addition, money saved on fuel, and received as tax incentives, can offset the increased purchase price of an HEV.

Disadvantages

The use of a fuel cell to generate electricity can cause excess heat due to the chemical reaction. In addition, a portable source of enough hydrogen to fuel the cell for an appreciable amount of time is not in evidence. Until hydrogen refueling stations become available to consumers, an HEV will be unable to travel long distances without relying heavily on the alternate power source.