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In the U.S., most retrofit applications have employed passive systems, while most OEM’s have verified active units. Regardless of the regeneration strategy employed, the oxidation process leaves a layer of fine ash inside the filter. Over enough time, even a perfectly operating filter will plug with this oxidized ash. It is crucial for every application installed with a DPF to have some way of indicating the filter is becoming loaded. This is accomplished by measuring the backpressure with an electronic monitoring device. This device is discussed in more detail below. |
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Monitoring System Performance |
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A backpressure monitor/alarm component is a critical part of a DPF system. If the DPF is not effectively destroying all of the PM collected on the filter during normal engine operation, PM (ash and other constituents) will build up over time on the surfaces of the filter. If there is an engine problem (worn fuel injectors or turbocharger failure) that results in elevated levels of PM entering the filter, the PM build-up will occur far more rapidly. Increased levels of PM on the DPF filter surfaces will result in increased backpressure. If the backpressure level increases are high enough, it could result in a DPF failure and/or adverse impact on vehicle/equipment performance and fuel economy. If the backpressure monitoring system shows a sudden drop in engine backpressure, the cause may be a mechanical failure of the filter such as cracks or attrition. If the backpressure drops, the filter should be inspected. |
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A back pressure monitor/alarm system tracks the backpressure levels, and warns the vehicle/equipment operator or technician that a problem exists before significant problems occur. It can also be used to help plan for and schedule filter cleaning. A variety of backpressure monitors exist using both audible and visual alarms to signal elevated backpressure levels. DET’s BackTraker system employs a three-light dashboard indicator panel which is installed within the line of sight of the driver of the vehicle. The indicator has a series of light-emitting diodes (LEDs) that serve two functions. The uppermost single LED, denoted as the “diagnostic LED” serves to notify the driver of the overall state of filter soot loading through green, orange and red lights. A green light denotes the system is working efficiently. A yellow light is illuminated to signal that the backpressure is it a level at which the DPF should be checked and cleaned as soon as possible. The red light is illuminated to signal that backpressure has reached a level that vehicle/equipment operation should cease. The lower series of four LEDs, denoted as the “Level LED”, indicates the approximate PM loading by displaying in percent the number of passages that remain open as the filter accumulates PM. The advantage of an alarm visible to the operator is that the operator can take corrective action immediately, and in doing so may salvage a filter before it becomes damaged. |
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The BackTraker™ monitoring device is one of the most sophisticated units available and records not only backpressure, but information such as the history of control parameter settings, operating hours, exhaust temperature, as well as a soot loading index which corresponds with the aforementioned “level LED’s.” The BackTraker™ and similar monitoring systems not only alert the operator/technician to possible backpressure problems, but also provide data that can help identify the source of problems with either the DPF or engine components that can be addressed, subsequently. |
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