STOCKHOLM --- Sweden's Volvo recently debuted a line of truck engines designed to run on renewable fuels. Seven types of fuel --- ranging from synthetic diesel to a mixture of hydrogen and biogas --- power the engines, Reuters reported. These fuels are made from renewable raw materials. During a press conference, Volvo Chief Executive Leif Johansson said that politicians and energy companies need to do more to make sure renewable fuels become widely available to consumers. At present, none of the new Volvo engines are being produced for the market, he said, but manufacturing could begin within a few years if the necessary fuels become available. To make that happen, he added, there must be more public investment in renewable fuel research and development.