The effect of fuel additives based on the alkali metals sodium and lithium on the regeneration behaviour of diesel particulate filters was studied. For this purpose the diesel fuel was doped with the lithium and sodium salts of an aliphatic alcohol. The efficiency of these additives was assessed by comparing it to ferrocene, which is, at present, the best studied additive for particulate filter regeneration.
The additives were tested on an engine test bench under steady state conditions, on a transient dynamometer and finally in a real driving test. As a result of the addition of the alkali metal salts, the ignition temperature of the soot trapped in the particulate filter is considerably lower than the ignition temperature without additives. The results with the alkali metal additives are similar to those of ferrocene or other additives with transition metals like manganese or copper. However, the regeneration range of the particulate filter is reached more frequently under real operating conditions. This avoids critical filter loading with soot, which can lead to filter damage during regeneration.
It is well known that compounds based on alkali metals are able to destroy the structure of cordierite at high temperatures. Therefore, one of the primary objectives of the study was to define some sort of reaction between the cordierite and the additive ash in normal driving cycles, particularly during regeneration.
As a result of ash accumulation within the particulate filter, the filter pressure drop increased during the driving test. Therefore, it is a very attractive additional feature of this type of additive that the produced ash is water soluble and can easily be removed by rinsing with water.