A Novel Tank Heater Based on PTC (Positive Temperature Coefficient) Plastic Nanomaterial

The emission reduction in gasoline and diesel engines is driving the introduction of systems implementing additives in liquid form: in particular water for injection systems in gasoline engines and urea solutions (AD-blue) in SCR (Selective Catalytic Reduction) systems in diesel engines. Owing to water and AD-Blue can freeze in the car operative temperature range, the tanks must be equipped with heaters to guarantee a sufficient amount of additives in liquid form. Currently used technologies are ceramic PTC (Positive Temperature Coefficient) elements and distributed metal resistors. Ceramic PTC based heaters concentrate all the power in small volumes. They need thermally conductive elements distributing the power over a wide area. The assembly is complex and the cost of the metal parts and related packaging technologies used to insulate the heater from the environment (water or urea) is typically high. Metal resistors are cheaper but must be controlled in current. Besides, the simple resistor cannot guarantee that in the parts of the heater not immersed in the liquid (when the tank is partially empty) the temperature is limited at an acceptable value. The solution we propose is based on a plastic nanocomposite with PTC effect (in the following nanoPTC). The heater can be moulded in any shape, following the specific tank needs, in carpet like shapes for a distributed heating of the tank, or in bulky components integrating sensors housings, pipes, pumping systems or in the packaging of other components. The PTC effect is distributed avoiding overheating in parts with poor thermal exchange (dry condition). The advantages can be summarized as follows: higher efficiency, safer operation, no additive damage (urea is decomposed if overheated), arbitrary shape design, low cost. Some examples of the developed heaters will be presented and the performances compared with currently used technologies.