Concept of “Temperature Swing Heat Insulation” in Combustion Chamber Walls, and Appropriate Thermo-Physical Properties for Heat Insulation Coat

Abstract

The aim of this work is to investigate the possibility of heat insulation by "Temperature Swing", that is temperature fluctuation, on combustion chamber walls coated with low-heat-conductivity and low-heat-capacity materials.Adiabatic engines studied in the 1980s, such as ceramic coated engines, caused constantly high temperature on combustion wall surface during the whole cycle including the intake stroke, even if it employed ceramic thermal barrier coating methods. This resulted in increase in NOx and Soot, decrease in volumetric efficiency and combustion efficiency, and facilitated the occurrence of engine knock.On the other hand, "Temperature Swing" coat on the combustion chamber walls leads to a large change in surface temperature. In this case, the surface temperature with this insulation coat follows the transient gas temperature, which decreases heat loss with the prevention of intake air heating, and also which is expected to prevent NOx and Soot from increasing. In our calculations, the increase of the surface temperature fluctuation, "Temperature Swing" results from the coat of lower heat conductivity and lower heat capacity. Particularly in Gasoline engines, the coat with the appropriate thickness can reduce the heat flux from the wall to the working gas during intake stroke and can avoid engine knock.Based on our calculations, it is clarified that both the prevention of intake air heating and the low heat rejection were successfully possible with the material of appropriate thermo-physical properties.In addition to the calculations, a preliminary test-piece experiment was executed. It was demonstrated that the surface temperature of a porous coat, that is a candidate of "Temperature Swing" coat, immediately follows the transient gas temperature, and also the proposed insulation coat can exactly reduce the heat flux in the single-cylinder engine.

Effect of wall heat insulation on wall heat transfer mechanism in rapid compression and expansion environment

“…Keywords : ICEs, Heat insulated coating, Wall heat transfer, Modeling, Thin-film thermocouple, PIV (Assanis and Badillo, 1987), ( Fujimoto et al, 2011), (Yamashita et al, 2012, (Kosaka et al, 2013) Initial wall temperature (K) 298…”

“…In addition, non-dimensional velocity distribution in wall boundary layer was not changed drastically by wall temperature behavior. In terms of modeling under heat insulated condition, wall heat flux was able to be predicted well by wall heat transfer model taking into account of density change in wall boundary layer.Keywords : ICEs, Heat insulated coating, Wall heat transfer, Modeling, Thin-film thermocouple, PIV (Assanis and Badillo, 1987), ( Fujimoto et al, 2011), (Yamashita et al, 2012, (Kosaka et al, 2013) Initial wall temperature (K) 298Initial gas pressure Atmospheric Pressure (Han and Reitz, 1997)(Harada et al, 2017) Harada, Y., Uchida, K., Tanaka, T., Sato, K., Qianjin, Z., Fujimoto, H., Yamashita, H. and Tanahashi, M., Wall heat transfer of undeveloped turbulent flow in internal combustion engines, COMODIA2017 (2017), A204. …”

Analytical and Experimental Investigation of Temperature-Swing Insulation on Engine Performance

“…This consideration is necessary especially in materials that contain low volumetric heat capacity which would allow fast changes in temperature, and low thermal conductivity which would enable a reduction in overall heat transfer and an increase in surface temperature during combustion and expansion. In both analytical (Wallace, Way, & Vollmert, 1979) (Morel, Fort, & Blumberg, 1985) (Anderson & Prakash, 1985) (Kosaka, et al, 2013) and experimental (Furuhama & Enomoto, 1987) (Harder & Anderson, 1988) (Aoki, et al, 2015) studies, a non-negligible swing in surface temperature throughout the engine cycle was observed with increasing insulation. This poses unique possibilities and challenges over the concept of a steady, elevated temperature and was fundamentally different from the net-zero heat transfer model with respect to the processes occurring in-cylinder.…”

“…There has been considerable recent activity to minimize heat losses and improve engine efficiency through in-cylinder temperature-swing insulation (Kosaka, et al, 2013) (Kogo, et al, 2016) (Kumar & Nagarajan, 2012) (Hoffman, Lawler, Guralp, Najt, & Filipi, 2015). The capability for surface temperature swing is dictated in part by the intrinsic material properties of the material in contact with the gas.…”

“…The capability for surface temperature swing is dictated in part by the intrinsic material properties of the material in contact with the gas. Figure 1-1 depicts the thermal properties of a variety of materials, overlaid by lines representing the surface temperature swing predicted by (Kosaka, et al, 2013). The surface temperature swing is dependent on the material properties, but is also a strong function of engine operating parameters such as load, combustion phasing, engine speed, and any others that affect the gas temperature, heat transfer coefficient, and time for heat transfer.…”