Hydrogen is recognised as an attractive solution to reduce greenhouse gases emissions and urban pollution, to which road transport is a great contributor. But there are still today numerous barriers before introducing hydrogen in the current vehicle fuel pool. The blend of natural gas and hydrogen, sometimes referred to under the name Hythane®, represents a relevant and pragmatic transition solution to massively introduce hydrogen in the public transportation system (buses), by taking advantage of the synergies with the NGV technology and infrastructure.

This paper presents the ALT-HY-TUDE project lead by the Research Division of Gaz de France, which intends to demonstrate the use of Hythane® as an environmental friendly fuel. The objectives are to:

- assess the relevance of Hythane® as a short term transition towards hydrogen,
- provide immediate benefits with reduction of urban pollution and greenhouse gases,
- take advantage of synergy with NGV infrastructure and vehicle technologies.

The project is developed in two cities in France that have a strong environmental policy and wish to lead the path of innovation towards hydrogen: Dunkerque and Toulouse.

The subjects and results of the project deal with:

- on-site H2 production and Hythane® refuelling station design,
- improvement of the NGV engine and buses for hydrogen/natural gas blend: bench tests were carried on in order to find the best engine performance trade-off in term of emissions, efficiency and reliability, for several hydrogen contents in the blends,
- administrative approval processes,
- technico-socio-economic assessment of Hythane® as clean fuel.