researchers in the us say liquid nitrogen-fuelled vehicles could help reduce carbon dioxide emissions and possibly reverse global warming. The vehicle works on the same principle of an old-fashioned steam engine, but uses nitrogen in place of water. A team of researchers led by Abe Hertzberg at the University of Washington in Seattle has converted an old van into a prototype ( New Scientist , Vol 155, No 2095).

In a steam engine, coal is burned to heat water in a boiler, which generates high-pressure steam. The steam is used to power a piston engine. However, liquid nitrogen boils at a temperature of -196