"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 Martensson, environmental director Volvo Trucks. "As a result, this truck consumes considerably less energy than traditional gas trucks do."
The venture was initially spawned in August 2007, when the company introduced seven driveable demo trucks adapted for different biofuels. The company has now decided to focus its efforts on DME and a combination of methane gas and diesel.
"Methane gas is by far the most accessible fuel as an alternative to diesel," Martensson 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."
While typically a truck with a spark-ignited engine has a lower range of operation, Volvo tackled this issue by combining methane gas with diesel and using this fuel in a diesel engine, boosting the operating range by over 50 percent, the company claims.
The solution is based on Volvo's Euro 5 diesel engines. When the engines are converted for gas operation, special tanks are added for either liquid volume-efficient methane gas (LNG/LBG) or pressurised 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 driveability are identical to that of a conventional diesel truck.
"Processors continuously calculate fuel ratio according to the driver's current driving pattern," said Martensson. "The optimum - i.e. the highest - proportion of gas is achieved during smooth, stable driving."
If the gas runs out, the truck can continue operating on only diesel, Volvo says. 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 Franzen, manager of engine strategy and planning, 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."