Alternative fuelsBiofuels are a suitable alternative to reduce greenhouse gas emissions of the road traffic. Thus a valuable contribution to the climate protection is given. Furthermore, it is possible to gain a greater independence from fossil fuels. Due to their different fuel properties compared to conventional fuel, improvements can be achieved in engine efficiency and emissions behaviour.
In the course of several research projects different alternative fuels for gasoline- and diesel- engines, were investigated at the institute for powertrains and automotive technology of Vienna University of technology. Thereby a wide range of research topics is carried out.
Ethanol has predominantly positive effects for the operation in gasoline engines. Due to the higher knock resistance and enthalpy of vaporization, efficiency at full load can be increased sufficiently. At part load there is potential to decrease the limited emissions as well as unburned hydrocarbons and nitrogen oxides, because of the chemical properties of alcohol fuels. However lower wall heat dissipation leads also to an advantage in efficiency. Beside the advantages there are of course some problems when using alcohol fuels. High boiling temperature and enthalpy of evaporation as well as low vapour pressure and low stoichiometric air consumption leads to the well known cold start problem at low temperatures.
Other alcohols that includes one to four carbon atoms (methanol or the isomers of propanol or butanol) are also a suitable solution as blend components for conventional gasoline fuel. The number of carbon atoms and the chemical structure of the fuel have a significant influence on the performance of the operation in the engine. As example the boiling temperature increase by increasing carbon amount of the fuel, whereas the vapour pressure and the enthalpy of vaporization decrease.
In the range of the diesel engine there are pure vegetable oils or HVOs (Hydrotreated Vegetable Oil) but especially FAME (Fatty Acid Methyl Ester) main alternatives or blend components for minerally diesel fuel. Therefor the required oils glycerides (obtained from different crude materials) will be converted to fatty acids with methanol as catalyst. The main representatives are shown in the following overview:
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