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In view of limited crude oil resources, alternative fuels for internal combustion engines are currently being intensively researched. Synthetic fuels from natural gas offer a promising interim option before the development of CO2-neutral fuels. Up to a certain degree, these fuels can be tailored to the demands of modern engines, thus allowing a concurrent optimization of both the engine and the fuel. This paper summarizes investigations of a Gas-To-Liquid (GTL) diesel fuel in a modern, post-EURO 4 compliant diesel engine. The focus of the investigations was on power output, emissions performance and fuel economy, as well as acoustic performance, in comparison to a commercial EU diesel fuel. The engine investigations were accompanied by injection laboratory studies in order to assist in the performance analyses.

A Mercedes E320 CDI vehicle has been modified for more optimal operation on Gas-To-Liquids (GTL) diesel fuel, in order to demonstrate the extent of exhaust emission reductions which are enabled by the properties of this fuel. The engine hardware changes employed comprised the fitment of re-specified fuel injectors and the reduction of the compression ratio from 18:1 to 15:1, as well as a re-optimisation of the software calibration. The demonstration vehicle has achieved a NOx emission of less that 0.08 g/km in the NEDC test cycle, while all other regulated emissions still meet the Euro 4 limits, as well as those currently proposed for Euro 5. CO2 emissions and fuel consumption, were not degraded with the optimised engine. This was achieved whilst employing only cost-neutral engine modifications, and with the standard vehicle exhaust system (oxidation catalyst and diesel particulate filter) fitted.

World wide, energy policy makers are increasingly keen to move away from petroleum based fuels to more diverse and renewable sources of energy for reasons of environmental protection, energy security and continued economic development. A well-known example is Gas-To-Liquid (GTL) diesel fuel which is derived from natural gas and thus provides a diversification away from crude oil, which is the feedstock for 97% of the world transport fuels. Towards the same goal, Fatty Acid Methyl Esters (FAME), from vegetable oils, recycled oils, or animal fat, are being used with increasing frequency as blends with diesel fuel, even at a concentration of 30% in some captive fleets (B30). In this paper, the impacts on engine pollutant emissions and performance are evaluated.