Fischer-Tropsch Diesel Fuels – Properties and Exhaust Emissions: A Literature Review

Natural gas, coal, and biomass can be converted to diesel fuel through Fischer-Tropsch (F-T) processes. Variations of the F-T process and/or product work-up can be used to tailor the fuel properties to meet endusers needs. Regardless of feedstock or process, F-T diesel fuels typically have a number of very desirable properties.
This review describes typical F-T diesel fuel properties, discusses how these fuel properties impact pollutant emissions, and draws together data from known engine and chassis dynamometer studies of emissions.
The comparison of fuel properties reveals that F-T diesel fuel is typically one of two types – a very high cetane number (>74), zero aromatic product or a moderate cetane (~60), low aromatic (=15%) product. The very high cetane fuels typically have less desirable low temperature properties while the moderate cetane fuels have cold flow properties more typical of conventional diesel fuels. The lubricity of both types of F-T diesel fuels is poor, but can be improved with additives. The effects of long-term use of F-T diesel fuel on engine durability have not been documented.
Fischer-Tropsch diesel fuel can be used neat without engine modification or can be blended in any proportion with conventional diesel fuel. A number of studies have collected emissions data from F-T diesel and F-T/ conventional diesel fuel blends in engine and chassis dynamometers. In almost every case, NOx, CO, and PM emissions are reduced with neat F-T diesel fuel. The impact of F-T diesel fuel on HC emissions is more variable, although the HC emissions are very low in any case. Average NOx reductions are 13% and average PM reductions are 26% compared to conventional diesel fuel.