There are many different alternatives of renewable fuels and Volvo is looking into all viable alternatives. They are evaluated based on seven different aspects: effects on climate, energy efficiency, land use effectiveness, fuel potential, vehicle adjustability, fuel cost and fuel infrastructure.
Bio diesel is made by transesterification of vegetable oils. The most common basis is rape seed or sunflower. It can be blended with conventional diesel, but the energy efficiency well-to-wheel is low, it also produces more NOx emissions with the present vehicle fleet and there is a limited potential for production of large quantities. Volvo's products are today compatible with bio diesel when blended into diesel.
Synthetic diesel is a mix of synthetically produced hydrocarbons made by gasification of biomass. It can be blended into conventional diesel and is compatible with existing Volvo engines. There are several sources and it has a variety of uses. It has however lower energy efficiency than other synthesis gas products and the current production is limited.
DME - dimethyl ether
Dimethyl ether is a gas handled in liquid form under low pressure. It is produced by gasification of biomass and it is a simpler chemical product than synthetic diesel and thus cheaper to produce. DME is also relatively easy to handle and distribute. Furthermore only modest modifications are required to convert a diesel engine to run on DME. If the fuel is produced from biomass, such as black liquor from the pulp industry, DME is CO2 neutral.
Methanol and ethanol are two types of alcohols. Methanol is produced by gasification of biomass, whereas most ethanol is produced by fermentation of sugar and other crops. They can be blended into gasoline and are available today.
The downside of ethanol is that it has a low energy efficiency well-to-wheel compared to biomass conversion routes. It also has a low boiling point and about 55% energy content compared to diesel.
Methanol has high energy efficiency well-to-wheel, low GWP (global warming potential) and cost. It can be produced from many sources and be used for a variety of purposes. But it is also toxic and corrosive and has about 45 % energy efficiency compared to diesel.
Biogas is a gaseous fuel that mostly consists of hydrocarbon methane. It has high energy efficiency well-to-wheel and low CO2. It can be produced locally and the emissions are low, with no soot. The energy efficiency compared to diesel is only 20% and currently only small volumes are produced.
Biogas + biodiesel
Biogas and biodiesel are combined with separate tanks and injection. A smaller amount of biodiesel or synthetic diesel is used to keep the compression combustion in a diesel engine.
Hydrogen is a gas that is compressed to 350-700 bar in vehicles. It is produced by reforming hydrocarbons using heat and steam, gasification of heavy hydrocarbons or biomass and electrolysis of water. The combustion or electrochemical reaction (fuel cell) is "emission free" and it can be used for a variety of purposes. But the well-to-wheel energy efficiency is low and delivery and storage is expensive. At 700 bar the energy content is about 22% compared to diesel. The current production is limited.