A novel dosing system for fuel borne catalyst (FBC), used to assist regeneration with a diesel particulate filter (DPF), has been developed. The system was designed for on-board vehicle use to overcome problems encountered with batch dosing systems. Important design features were simplicity, to minimise system cost, and the use of in-line dosing rather than batch dosing linked to tank refuelling.
The paper describes the development of the dosing system which continuously doses FBC into the fuel line feeding the engine injection pump. The theoretical considerations behind the concept are explored, together with the realities imposed by fuelling regimes in which a variable proportion of the fuel flowing through the injection pump is passed back to the fuel tank. Two types of system are considered, ie where 1) FBC is added to the fuel in direct proportion to the flow rate of fuel and 2) FBC is added at a constant time-based rate. Modelling of changes in the concentration of FBC in the fuel over time indicated significant non-linearity with both approaches.
Bed testing with a diesel engine equipped with a DPF assessed both flow-based and time-based dosing concepts. The test work demonstrated that the in-line FBC dosing concept could achieve reliable regeneration with either system. The averaging effect of soot accumulation over time on the ratio of metal to soot within the DPF apparently accounts for successful regeneration despite big variations in FBC concentration.
The paper describes the application of the system to light duty vehicles such as Black Cabs used in central London. Data loggers indicated successful operation on several vehicles over distances ranging from 12,000 to 20,000km. An in-line FBC dosing system was also fitted to a heavy duty fire appliance support vehicle for additional tests. Data to date suggest that this application has produced acceptable DPF regeneration performance. Test work on this vehicle continues.