Diesel particulate filter (DPF) technology is becoming increasingly established as a practical method for control of particulate emissions from diesel engines. In the year 2000, production vehicles with DPF systems, using metallic fuel additive to assist regeneration, became available in Europe. These early examples of first generation DPF technology are forerunners of more advanced systems likely to be needed by many light-duty vehicles to meet Euro IV emissions legislation scheduled for 2005.
Aspects requiring attention in second generation DPF systems are a compromise between regeneration kinetics and ash accumulation. The DPF regeneration event is activated by fuel injection, either late in the combustion cycle (late injection), or after normal combustion (post injection), leading to increased fuel consumption. Therefore for optimum fuel economy, the duration of regeneration and/or the soot ignition temperature must be minimised. Both effects are strongly favoured by a higher treat rate of the metallic fuel additive. On the other hand, the more metal is added to the fuel, the more ash is produced and stored within the filter, implying reductions in engine performance over time. The objective of a 250,000 km lifetime for diesel car (with entire equipment, including DPF) leads to a desire to reduce metal treat rate while minimising regeneration duration, and soot ignition temperature.
Earlier work on a cerium fuel additive laid the foundations for the determination of influential parameters for regeneration rate. A bed engine test protocol was set up to optimise the treat rate of iron/strontium and iron based additives, in terms of kinetics and ash production. The final outcome of the test programme has resulted in overall improved performance for this second-generation DPF system.