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[June 2007]
Ceramic Coating From Nuclear Industry Keeps Particulate Filters up to Temperature
Zircotec thermal coating reduces heat loss in diesel exhaust systems, offering more precise temperature control, helping particulate filters reach optimum operating temperature more quickly and improving system performance.A high-technology ceramic coating originally developed for the nuclear industry and already used by five Formula One teams could help vehicle and engine manufacturers reach Euro 5 emission standards with proven technologies. By significantly reducing heat loss from the exhaust system, Zircotec's coating retains high exhaust gas temperatures, reducing warm-up times for aftertreatment systems, reducing the need for close coupling and allowing more consistent control of exhaust gas temperatures.
The technology is expected to be particularly useful for keeping particulate filters (increasingly important with rising EGR ratios) at their operating temperature, particularly in applications with a stop-start drive cycles such as off-highway, delivery vehicles and busses. EGR engines can produce more particulates than other NOx control technologies, so rely on efficient particulate filtration. Plasma-sprayed thermal barriers provide a durable, affordable thermal barrier that keeps the heat where the designers need it.
“Maintaining sufficient heat in the aftertreatment system is an increasing challenge, especially as catalysts and filtration stack up,” says Andy McCabe, Zircotec's technical director. “Zircotec's coating technology substantially reduces heat loss in exhaust streams, allowing efficient working temperatures to be maintained. Superior temperature control will also allow reductions in the precious metal content in some catalyst applications.”
The problem with particulate filtration is that regeneration (the burning of collected soot) can only occur efficiently at very high temperatures. “Typically this occurs during periods of high load,” explains McCabe. “In a vehicle with a mixed drive cycle the gaps between periods of full load can be far greater than is required, leading to reduced efficiency of the trap and of the engine due to filter choking. Our coating can assist in solving this problem.”
Zircotec's thermal coating also makes it easier to find a suitable location to house the filter in a vehicle since, taking into consideration space, accessibility, operator safety and the impact on other vehicle components, the distance of the filter from the engine can be increased without any significant additional heat loss from the exhaust stream. Keeping the thermal energy in the exhaust stream can also significantly improve turbo response.
Zircotec's zirconia-based ceramics have a thermal efficiency of less than 1.7 W/m K, providing an excellent thermal barrier, inhibiting the radiation of heat from the surface of the material and holding the heat inside. Unlike other ceramic paint and coating application techniques that can burn off, become brittle and lead to flaking, Zircotec's plasma-spray coating process is proven to be highly durable, withstanding even the harshest applications. It can also resist local impacts like minor knocks during maintenance and is neater, more compact and more durable than traditional exhaust wraps, making it ideal for Original Equipment (OE) applications.
Almost eliminating the escape of exhaust heat around the powertrain also increase the durability and effectiveness of engine and transmission oils, improves engine cooling and helps to protect ancillaries such as regulators, wiring and ignition systems from the degrading affects of excessive heat. This also makes the coating ideal for selective catalytic reduction (SCR) diesel exhaust systems, for protecting surrounding components from the high temperatures reached in the catalyst converter, removing the need for separate heat shields.
ENDS