1. General

1.1 Environmental context

The world's known reserves of natural gas are of the same order of magnitude and geographically more diversified than those of oil. The use of gas as an alternative motor fuel initially developed in regions with natural resources, but its use, which remains highly dependent on tax incentives, is very unevenly distributed from country to country. In Europe, Italy and Benelux alone account for the largest share of the European car fleet, and the estimated number of gas-powered stationary and propulsion engines worldwide exceeds four million units.

Gas is attracting renewed interest as a clean-burning fuel, whose combustion reaction in the air results in minimized engine exhaust emissions compared with conventional liquid hydrocarbons....