Alternative propulsion

Alternative propulsion is a term used frequently for powertrain concepts differing from the internal combustion engine concept used in only petroleum fueled vehicles.

Definition

The term alternative propulsion or "alternate methods of propulsion" includes both
* alternative fuels used in standard or modified internal combustion engines (e.g. combustion hydrogen).
* alternative propulsion systems (alternative motoring), that is to say, those not based on internal combustion, such as those based on electricity (for example, electric or hybrid vehicles) , compressed air, or fuel cells (e.g. hydrogen fuel cells). Under certain conditions they can be more efficient than petroleum propulsion. However, while some are hoping for spectacular breakthroughs such as bubble fusion or cold fusion (currently discredited), at the moment no technology yields significantly higher fuel efficiency than traditional methods.

Today's cars can be classified in three main groups:

* Petroleum fueled vehicles, which use petroleum derived fuels (such as gasoline or diesel exclusively (though many such vehicles can also be run on biofuels).
* Hybrid vehicles, which use petroleum fuels in conjunction with other energy sources, generally electricity.
* Petrofree cars, which do not use petroleum, such as battery electric cars, 100% biofueled vehicles, hydrogen vehicles, and compressed air vehicles.

Motivation and petro-free
The motivation for the research in alternative propulsion in transport is primarily to achieve more sustainable methods of transportation than those relying on fossil fuels.

Petrofree is a term to indicate that is not used or sold (i.e. petrofree fuel station, petrofree vehicle).

Application fields
Most work in alternative propulsion concepts is focused on replacing traditional internal combustion engines in automobiles. Several contenders, such as Michelin's Challenge Bibendum and the North American Solar Challenge, are designed to provide motivations for effective concepts utilizing alternative propulsion. Hybrid vehicles, which combine an internal combustion engine with an alternative system, are perhaps the most visible example of alternative propulsion systems in use today.

Alternative propulsion is not limited to automobiles, however; it can also apply to types of spacecraft propulsion beyond solid- or liquid-fueled rockets. Propulsion methods such as the ion thruster and solar sail are examples of alternative propulsion options for spacecraft.

Criteria for successful application of alternative propulsion
In order to supplant traditional propulsion systems, alternative propulsion systems must be able to equal or exceed the performance and convenience of traditional systems in several areas:
* operating radius (range)
* acceleration and top speed
* stability of the stored energy (degradation over time, losses or leakages).
* refueling or recharge procedure.
* environmental effects (minimizing odor, noise, vibrations, radiation, emission of noxious substances, etc.).

Misuse of alternative propulsion for promotion

Because of failure to come one the market with Fuel cells in due time, the automakers tend to introduce hydrogen for internal combustion engines. This has several setbacks:
* moderate reduction in NOx
* same noise
* approx. same efficiency in the engine
Though depending on the hydrogen reduction the CO2 emission might be reduced. This requires renewable sources for the electrolysing power or a production out of biogas. Comparing the yield of those production paths with the consumption or better wasting of energy with today's cars, this path seems like utopy.

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