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The FST sensors are basically metal antennas mounted inside the exhaust system of vehicles that use diesel particulate filters (DPF). In 2007, the Environmental Protection Agency introduced strict emissions limits for diesel engines, resulting in the widespread use of these large ceramic filters, which capture more than 95 percent of soot and other particles emitted from diesel engines.
A downside to DPFs, however, is they become saturated frequently, sometimes every eight hours — depending on engine use — and must be cleaned. With diesel trucks, for instance, the engine “regenerates” the filter by using some fuel to heat up the exhaust to high temperatures and burn the soot, like a self-cleaning oven. Conventional technologies use pressure-drop measurements and predictive models to roughly estimate buildup. If the estimates are off, soot and ash can also exceed the filter’s limit, impacting the pressure-drop response, service life, and fuel consumption.
With no way to accurately measure buildup in real time, OEMs generally program a diesel truck’s control system to regenerate the filter more frequently than necessary, regardless of actual contamination, Sappok says. “Trucks are burning a lot more fuel than they need in order to heat up and clean off this filter,” he says.
FST sensors transmit a radio frequency signal very similar to those used for cell phones, through part of the vehicle’s emissions-control system. As soot and ash accumulate in the filter, the signal strength decreases — the weaker the signal, the more buildup. “It’s the same concept as going through a tunnel on your phone and losing a signal,” Sappok says.
These data re received by the onboard engine-control system, so the engine only initiates self-cleaning when needed and cuts off when the filter is cleaned, saving fuel and cutting costs for operators.
The sensors have so far proved effective in field and engine tests. In a two-year study with heavy-duty trucks operated by the New York City Department of Sanitation, funded in part by the Department of Energy, the sensors demonstrated the potential to cut the frequency and duration of filter regeneration in half in some cases, which may enable a 1 to 2 percent fuel savings. This can be significant for fleets of trucks such as those in the study, which use roughly 5,000 to 8,000 gallons of diesel fuel annually.
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