GOTHENBURG, SWEDEN --- Volvo Trucks said it will be the first truck manufacturer with an efficient diesel engine fueled by a mixture of methane gas and diesel. 

The engine meets the strict Euro 5 exhaust emission standards introduced in 2009. Field testing will start in Sweden and the U.K. in 2010. 

"This unique technology allows us to combine the advantages of gas with the diesel engine's high efficiency rating, which is about 30-40 percent superior to that of the spark plug engine," said Lars Mårtensson, environmental director of Volvo Trucks. "As a result, this truck consumes considerably less energy than traditional gas trucks do." 

In August 2007, Volvo Trucks presented seven demo trucks adapted for different biofuels. Following further analysis, the company is now focusing on two renewable fuels: DME and methane gas plus diesel. 

"Methane gas is by far the most accessible fuel as an alternative to diesel," Mårtensson said. "There are larger reserves of natural gas than oil. But above all, production of climate-neutral biogas is gaining momentum in many countries, which solves the most urgent problem -- reducing CO2 emissions." 

It used to be difficult to use methane gas for long-haul transportation. A truck with a spark-ignited engine usually has a restricted range of operation. Volvo Trucks said it solves this problem by combining methane gas with diesel and using this fuel in a diesel engine. This increases the operational range by over 50 percent, but when a liquefied gas is used, with higher energy density, the range will double. In addition, the diesel engine's drivability is better compared to a spark-ignited engine, the company said. 

The solution is based on Volvo's Euro 5 diesel engines, the company said. When the engines are converted for gas operation, special tanks are added for either liquid volume-efficient methane gas (LNG/LBG) or pressurized methane gas (CNG/CBG). In addition, a separate fuel system is added with gas injectors in the inlet manifold. 

A small amount of diesel is injected and ignited by the compression, which in turn ignites the methane gas/air mixture. This saves the need for a spark plug and allows Volvo to make full use of the efficient diesel technology. As a result, the power and drivability are identical to that of a conventional diesel truck. 

"Processors continuously calculate fuel ratio according to the driver's current driving pattern. The optimum -- i.e. the highest -- proportion of gas is achieved during smooth, stable driving," said Mårtensson. 

If the gas runs out, the truck can continue operating on only diesel. The amount of diesel required during operation varies, but Volvo Trucks aims to minimize the proportion of diesel. 

"We expect to be able to run on up to 80 percent methane gas once the technology has been refined and tested," said Mats Franzén, manager of engine strategy and planning for Volvo Trucks. "Our field tests in 2010 will start with a mixture containing up to 70 percent methane gas. The remainder will consist of bio-mix diesel, i.e. fossil diesel mixed with diesel produced from renewable raw materials." 

Calculated over the whole fuel chain, from production to use on roads, the new technology could reduce carbon dioxide emissions by up to 80 percent in the long term compared to traditional diesel operation, if biogas and 100 percent biodiesel are used, Volvo Trucks said.