As an alternative to the CRT® and CCRT® systems, it is possible in some applications to use a DPF system in which the catalyst is on the filter and no pre-catalyst is used. These systems are called catalysed soot filters (CSFs) or catalysed DPFs (CDPFs).
CSFs require higher exhaust gas temperatures for regeneration than CRT and CCRT systems, but note the emissions reduction performance of a CSF is similar to that for a CRT system.
CSFs require higher exhaust temperatures than CRT systems if they are to regenerate passively. These systems will be used in special cases only, for example, when the installation space is not big enough for the CRT and the required exhaust gas temperature is warranted >280°C catalyst temperature for at least 50% of the operating time.