New fuels

New fuels in vehicles might also involve new risks. SP offers both evaluation of such risks and how to eliminate these.

New fuels as e.g. E85 and different gases do not have the same fire and explosion properties as gasoline. Since most components and safety systems on vehicles are designed either for gasoline or diesel it is important to know that the properties of these new fuels do not affect the overall safety. Two of the most important factors are the fuel vapour composition and the flammability properties. A fuel tank containing gasoline at room temperature has a too “rich” fuel mixture, i.e. the air/fuel mixture in the tank has an excess of fuel vapours.

In the corresponding way, the fuel vapours a tank with diesel contains too little fuel and is designated as “lean”. In both cases it means that a fire in for instance the filling neck cannot propagate into the fuel tank. Other liquids, for instance pure ethanol creates flammable fuel vapours at a room temperature and a fire outside the tank can therefore propagate into the tank.

 

The explosion chamber used to determine the flammability range.

Since vehicle fuels often is a mixture of different products to fulfil existing fuel specifications it is important to evaluate the actual properties of such mixture. SP has the resources and the competence to evaluate new fuels, i.e. to determine the flammability range and the composition of the fuel vapours in a tank at various temperatures. Specific knowledge about the fire and explosion properties of different fuel alternatives enables you to discover any risks and take appropriate measures to avoid an accident. The largest risk for ignition of the fuel vapours in the tank is during filling. There are several possibilities to reduce such a risk by the design of the tank and the refuelling pipe and SP can help you with such an evaluation.

Ignition test at the opening of the refuelling pipe connected to a fuel tank in order to evaluate a protective system against flame propagation.


An example of an evaluation of a new fuel is given in SP report 2008:15 where the fuel E85, which is a mixture of ethanol and gasoline, was examined. E85 of both summer and winter quality was conditioned and the fuel vapour composition was determined at different temperatures. Samples of the fuel vapours were also taken and introduced into an explosion chamber, where these were ignited. The tests showed for instance that the fuel vapours does not have the same relative composition as the liquid phase and contained a larger amount of petrol fractions. This is positive from safety point of view as the fuel vapours of E85 is more similar to those from ordinary petrol. The temperature range where the fuel vapours from E85 (summer quality) is flammable was determined to about +5˚C down to about -18 ˚C. As a comparison, fuel vapours from petrol are flammable at about -20 ˚C or lower. E85 could therefore be considered to create a somewhat higher risk compared to petrol, especially during cold weather conditions. Also different kinds of fuel tanks and refuelling pipes were examined and significant differences observed.

Sampling of fuel vapours outside the refuelling opening in order to evaluate fuel vapour emission during refuelling and how this was influenced by the design of the refuelling pipe, the opening and the fuel nozzle.

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SP Technical Research Institute of Sweden, Box 857, SE-501 15 Borås Phone +46 10-516 50 00, E-mail info@sp.se