WHAT IS A DPF?
A diesel particulate filter (DPF) is a filter that is installed on the exhaust of a diesel engine and captures soot (PM) preventing the soot from being released into the atmosphere. Soot accumulates in the diesel particulate filter and is removed during a process called regeneration.
REGENERATION – 4 TYPES
During regeneration, the temperature in the DPF is increased to burn off the accumulated soot in the filter. There are 4 methods of regeneration.
Passive regeneration happens when the diesel engine is under enough load that the operating temperature is sufficient to prevent soot from accumulating in the filter. No other action is required to clean the DPF as there is minimal soot accumulation.
Active regeneration takes place when the engine needs to change the exhaust parameters in order to burn built up soot. At this point, there is still no user interaction required, but the engine will open and close valves to redirect exhaust and fresh air flows and/or add small amounts of diesel fuel to the exhaust stream to remove any accumulated soot. The engine will not, however, vary the operating speed during active regeneration.
Manual regeneration for Xylem diesel driven pumps can be done through the Godwin PrimeGuard. Manual regeneration will allow the engine to open and close valves to redirect exhaust and fresh air flows, add diesel fuel into the exhaust stream, and change the engine speed to remove the built up soot. During manual regeneration, load on the engine must remain constant.
The PrimeGuard is designed to shut the engine down in response to soot levels of 100% or greater. The 100% soot level as shown on the PrimeGuard is the maximum buildup of soot in the filter where the engine can no longer operate without damaging the diesel engine. If a manual regeneration fails to complete or is not done before the engine reaches a shutdown condition, a mechanic with laptop computer will be required to make the pump and engine operational again. This is a safety feature to prevent irreparable damage to your diesel engine.
WHAT DPF MEANS FOR OPERATION
In a perfect world, you would be able to size every job where the pump operates with sufficient load and cycle time so the diesel engine is constantly undergoing passive regeneration. But in the pumping world, this is sometimes difficult to accomplish. Most pumping jobs have variation in flow rates, and as flow rate changes, so does the load and cycle times on the diesel engine. While some variation in load is fine, below are a couple scenarios to avoid.
Short cycling occurs when the pump needs to turn on and off frequently with short periods of run time. If the pump is only required to run for a short period of time, the engine many not have enough time to build operating temperatures to a level that facilitates passive and active regeneration. This is the automatic process to remove accumulated soot. The soot will continue to build up to a point where manual regeneration will be required.
Automatic operation, similar to or a part of short cycling, could shut the engine down during active or passive regeneration and interrupt that process and cause continued soot buildup in the DPF. A stop command from floats or a transducer will override or cancel the regeneration command from the ECU. If active regeneration is interrupted frequently enough that the soot is allowed to accumulate, the engine will require a manual regeneration.
LOW FLOW CONDITIONS
Even when running continuously, the diesel engine may have trouble completing a successful regeneration if the engine is not under enough load.
The last regeneration impediment is ambient temperature. If ambient temperature is low, regeneration may still fail. Remember the main driver of DPF regeneration is the increased temperature in the exhaust flow and DPF to burn off soot. Low ambient temperatures can actually prevent the DPF from reaching the required temperature. Use the expertise of your Xylem sales representative to develop creative solutions to combat the cold temperatures.
DPF AND YOUR DIESEL DRIVEN PUMP
By being aware of what the flow conditions and operating requirements are, you can use interim and final Tier 4 engines with DPF appropriately and prevent problems down the road.
Consider using multiple pumps when you know there is a going to be a large variation in flows. Rather than running one large pump, use a lead, lag, and backup to make sure each pump has a high enough load on it that you are avoiding most of the problems from short cycling and insufficient loads.
Another thing you can do is monitor equipment closely during startup. Soot percentage is shown on the bottom of your PrimeGuard. If you are watching soot percentage consistently increase, see if there is something you can change in your application to help the engine complete regeneration, or use the PrimeGuard to manually regenerate the engine before the engine reaches the shutdown point.
It is also a great idea to consider putting FST on your pump. Using FST will help you monitor soot build up and the timing to take a proactive role in heading off issues before they become a problem. The FST will allow you to monitor and respond to the engine's soot level from anywhere in the world. You don't have to be on site. Contact your localXylem sales representative to discuss solutions for any issues or questions you may have.
NEXT TIME – HIGHLIGHT ON GODWIN HL225M FINAL TIER 4 PUMP OFFERING