Diesel exhaust particle number concentrations and size distributions, as well as gaseous and particulate mass emissions, were measured during steady-state tests on a US heavy-duty engine and a European passenger car engine. Two fuels were compared, namely a Fischer-Tropsch diesel fuel manufactured from natural gas, and a US D2 on-highway diesel fuel.
With both engines, the Fischer-Tropsch fuel showed a considerable reduction in the number of particles formed by nucleation, when compared with the D2 fuel. At most test modes, particle number emissions were dominated by nucleation mode particles. Consequently, there were generally large reductions (up to 93%) in the total particle number emissions with the Fischer-Tropsch fuel. It is thought that the most probable cause for the reduction in nucleation mode particles is the negligible sulphur content of the Fischer-Tropsch fuel.
In general, there were also reductions in all the regulated emissions with the Fischer-Tropsch fuel. A notable feature of the test results was the substantial reduction in both the regulated emissions as well as particle number emissions at the idle and low load test modes. This indicates that significant benefits may be derived from the use of the Fischer-Tropsch fuel in congested city centers, where such engine operating conditions are prevalent.