Active Diesel Particulate Filter (Photo credit: Massachusetts Dept. of Environmental Protection)
The D.C. fire department is trying to determine why one of its newer diesel ambulances broke down as crews were transporting a patient in cardiac arrest.
It happened on I-295 Wednesday afternoon as Ambulance 19 was taking a shooting victim to the hospital. Then it took several minutes for a second ambulance to arrive.
The driver of Ambulance 19 is telling investigators the indicator lights on the emission control system suddenly and unexpectedly jumped from a warning to shut down in a matter of seconds, and as the engine died, she was able to pull the rig to the side of the road.
It turns out that due to an EPA regulation, active regeneration is required to clear particulate matter from the filter.
Sensors tell the engine when excessive particulate matter has built up in the DPF, and active regeneration mode is triggered. During active regeneration, the engine idle is increased to help heat the DPF, and diesel fuel is injected during the exhaust stroke, allowing fuel to enter the exhaust system and burn in the DPF. The combusition of diesel fuel in the DPF generates the heat necessary to burn off soot within the filter, essentially cleaning it. During active regeneration, the DPF can exceed temperatures of 1,000 degrees F. The main downfall of active regeneration mode is that it dramatically decreases fuel economy.
Another downfall is that if active regeneration doesn't occur (i.e., the engine is not allowed to idle), the engine simply shuts off. In patient care, minutes are important. In this case, the patient had to be transferred into a second ambulance in order to get him to the hospital, where he was determined to be in the process of assuming ambient temperature. But at least the air's cleaner.
