FVV 1349: Beeinflussung Wandwärmeverluste Ottomotor

Autoren

J. Achenbach - TME, RWTH Aachen University, D. Weßling - Universität Magdeburg, T. Fischer - FZ Jülich

Zusammenfassung

Further increasing efficiency is a major development focus in modern gasoline engines. Wall heat losses are a primary contributor to the engine’s process losses. So-called "temperature swing" coatings on the combustion chamber walls are intended to ensure that the surface temperatures approximate the course of the gas temperatures. This type of coating is characterized by low thermal conductivity and low heat capacity. The adapted surface temperature is intended to reduce the wall heat transfer at any time during the engine cycle.

In the FVV research project 1349, the efficiency potential of an yttrium-stabilized zirconium oxide (YSZ) coating on the piston surface in gasoline engines was investigated. By optimizing the coating process and increasing the porosity, it was possible to reduce the thermal conductivity to 0.7 W/(mK). The effect of the thermal piston coating on the combustion process was shown in 3D-CFD simulations of the engine cycle to be an increase in the knock tendency, requiring to retard the spark timing by 0.75 °CA.

In addition, 3D-CFD was used to develop a thermal coating model for the engine pro-cess simulation. The thermal coating model showed very good predictive power and was used for various sensitivity studies. The potentials for increasing the effective efficiency were found to be at a relatively low level of 0.2...0.3 %. Experimental investigations with a single-cylinder engine confirmed the low influence of the coating on the efficiency. The tests also showed an increase in nitrogen oxide emissions and a 4K rise in the exhaust gas temperature, so that an increased process temperature in the combustion chamber can be assumed. The associated reduction in HC emissions suggests an increase in efficiency. However, this is in contrast to the dynamic measurement of the piston temperatures, which showed an increase in the structure temperatures of 2 K in the coated case.