Research and trials are taking place all over the world on alternatives to petroleum-based/fossil vehicle fuels.
Many alternative fuels are being tested, but few are yet produced in large quantities. This is partly because demand is still limited, partly also because petroleum is still available.
ZEUS is not focused on picking a "best fuel", but rather on testing a variety of fuels in "real world" conditions. ZEUS will monitor the performance of the fuels listed below, and share its experience with European Comission Programmes and networks engaged in larger-scale demonstrations and tests.
Within the ZEUS project we have chosen to test fuels that we believe will be sustainable for the future in environmental and energy terms. Here you can read more about the fuels and their environmental impacts and how they are produced.

RME–RapeMethylEster
RME is a gaseous fuel fuitable for diesel engines. RME is produced from rapeseed oil, which is extracted from rapeseed. Pure rapeseed oil has a higher viscosity and a higher freezing termperature than regular diesel. This makes it less suitable as a fuel in a diesel engine. However, by estering rapseed oil with an alcohol a rape-ester is produced, the most common form called RME. This produce has the properites of diesel and few adjustments are necessary to a diesel engine for its use. Because this product is produced from biomass, it has a low impact on biological life and low carbon dioxide emissoins. The energy content is about 6% less than diesel, so fuel consumption is 6% higher when using RME.

In the ZEUS project, pure RME is used in Luxembourg.

DME–DiMethylEther
DME is a gaseous fuel suitable for diesel engines, originally a derivative of methanol. DME may be produced from either fossil fuels (natural gas or a gasification of crude oil) or of biomass (such as peat or wood chips.) Moderate changes to the fuel injection system are necessary for a diesel engine to operate on DME. DME has lower emissions than diesel, and if produced from biomass, far lower emissions of carbon dioxide.

In the ZEUS project, DME is used for buses in Copenhagen.

CNG–Compressed Natural Gas
CNG is a methane gas for otto-engines. GNG is a fossil fuel stored in the earth’s crust. CNG, when used as a vehicle fuel, has far lower emissions of carbon and nitrogen oxides than petrol. Because of the low coal content of CNG, emissions of carbon dioxide are also lower.

In the ZEUS project, CNG is used for buses and cars in Athens/Amaroussion, Bremen, Helsinki, London/Coventry, and Palermo.

LPG–Liquefied Petroleum Gas
LPG, commonly referred to as propane, is a gas in its natural state. It liquefies under moderate pressure it is stored in vehicles in large tanks. However, it is burned in the vehicle in large tanks. Propane has lower emissions as compared to gasoline, and is used in a wide variety of vehicles.

In the ZEUS project, LPG is used for buses in Helsinki.

Biogas
Biogas is a gaseous fuel for petrol (otto) engines. It contains mostly methane but also a small amount of inert gases such as carbon dioxide. Biogas is produced through a bacterial breakdown of biomass deprived of oxygen. Before the biogas can be used as a vehicle fuel, it is purified of carbon dioxide and humidity and upgraded to yield a higher energy content. Biogas is a renewable resource with very low emissions and no emission of carbon dioxide.

In the ZEUS project biogas, produced from residual sludge from wastewater treatment, is used for cars in Stockholm.

Electricity
An engine powered by electricity stored in batteries drives electric vehicles. Electric vehicles have zero emissions and make hardly any noise. Electricity in Europe is produced from a variety of sources–coal, oil, biomass, nuclear power, solar energy, or hydro power–so the total environmental benefit of EV depends on the source of electricity. Batteries used today are mostly either lead-acid or nickel-cadmium, though several more powerful batteries are in development. Electric vehicles have a shorter driving range than other vehicles due to the limited power capacity of the batteries in current use.

In the ZEUS project electric vehicles are used in Athens/Amaroussion, Copenhagen, London/Coventry, Palermo, and Stockholm. In Bremen electric-hybrid (electric/diesel) buses are used.