STOCKHOLM, Sweden Volvo Group, parent company of Prevost Car and Nova Bus, says it can readily produce diesel engines that use a wide variety of renewable fuels and do not emit any environmentally harmful carbon dioxide.

But before it can put these engines into production, public policy makers and petroleum makers must decide what fuels make the most sense on a long-term basis, says Volvo.

Earlier this month, Volvo demonstrated seven on-highway diesel engines that operate on a number of renewable fuels and/or combinations of fuels, including biodiesel, biogas combined with biodiesel, ethanol/methanol, dimethyl ether, synthetic diesel, and hydrogen gas combined with biogas.

Since all of these fuels are produced from renewable raw materials, they produce no carbon dioxide when combusted and, accordingly, do not impact the environment, says Volvo.

Getting rid of carbon dioxide is the last major pollutant emitted by diesel engines that environmental regulators have targeted. By the time 2010 emission standards in the United States, Europe and Japan are in force, particulate matter and nitrogen oxide pollution from diesel engines will be close to zero, leaving carbon dioxide as the primary pollutant.

However, a side effect of removing other pollutants from vehicles that burn petroleum-based diesel fuel is that carbon dioxide emissions rise.

But Volvo contends the technology exists to produce heavy-duty vehicles that are carbon-dioxide neutral - that is, the combustion of bio-fuels generate no more carbon dioxide than the vegetation and bacteria that make the fuel absorb while growing.

"With these vehicles, we have shown that Volvo is ready, that we possess the technology and the resources for carbon-dioxide-free transport, but we cannot do this alone," said Volvo Group CEO Leif Johansson.

"We also require large-scale production of renewable fuels and putting such production in operation requires extensive investments in research and development, and also well-defined, common guidelines from authorities in as many countries as possible."

Volvo said it has conducted extensive analysis of renewable fuels, considering such critical aspects as the impact on the environment, energy efficiency, the efficiency level in the use of the land for cultivating crops for fuels, the amounts of the different fuels that can potentially be produced, the level of vehicle adaptation required in purely technical terms to use the fuels, the costs of the fuels, and how easy it is to distribute them.

"We know that in the foreseeable future there will be insufficient biomass or renewable fuels to fully replace fossil fuels," said Jan-Eric Sundgren, Volvo Group senior vice president for public and environmental affairs.

"That is why it is important that decisions on the production of future fuels are preceded by such comprehensive assessments - otherwise there is the risk that we focus on too many and quite simply unsuitable alternatives, which will delay the introduction of carbon dioxide-free transport."

"As one of the world's largest manufacturers of heavy trucks, diesel engines and buses, the Volvo Group is part of the climate problem," said Johansson. "But environmental issues are one of the areas which we have assigned the very highest priority, and based on our resources and knowledge, we both can and will be part of the solution."

Added Sundgren: "The diesel engine is an extremely efficient energy converter that is perfectly suited to many different renewable fuels, liquid or gaseous. With our know-how in engine technology and our large volumes, we can manufacture engines for several different renewable fuels," creating possibilities for carbon-dioxide-free trucks, buses, construction equipment and boats, he noted.