Passive or Active DPF's for Construction Equipment?

 

Will the retrofitting of construction equipment with diesel particulate filters (DPF) be as easy as retrofits on school or transit buses? I seem to think that retrofitting construction equipment with DPF's will be more difficult than anyone anticipates. The exhaust temperatures are critical for DPF regeneration. If the filters become clogged, a buildup of backpressure can damage the engine. Extensive testing must be done to determine proper exhaust temperatures. The following are some issues that should be given some thought:

•  Since busses, both school and transit, run continuously without long periods of idle time, there most likely will not be a issue with exhaust temperatures. If a bus was border line, a passive catalyzed DPF could be used. A catalyzed DPF uses catalyst coated filter fibers to increase exhaust temps for proper regeneration of the filter. The catalyzed filter coverts NO to NO2 which then reacts with more trapped particulate matter.

 

•  The issue with construction equipment DPF retrofits are exhaust temperatures. My experience with the operation of construction equipment leads me to believe that passive DPF's will not be the proper device for this industry. Most equipment will have periods of intermittent heavy use and idle time. Therefore, exhaust temperatures will not be sufficient for the use of passive DPF's. Construction equipment will require the use active DPF's. Active DPF's regenerate when engine backpressures reach a minimum threshold or at the end of an eight hour workday. The regeneration can be completed in one of three ways.

1. The injection and burning of diesel fuel upstream of the filter to generate proper exhaust temperatures. A draw back of this method is additional fuel  consumption.
2. Electric regeneration through which a current is passed though conductive resistant filter material, thus creating heat which burns the particulate matter.
3. The filter can physically be removed from the housing and placed in a regeneration system which burns off the particulate matter.

Construction equipment will have to use one of the above mentioned three methods for proper filter regeneration.