Study of the Thermal Insulation and Flow Field of Vehicle Front Exhaust Pipe

Abstract

Exhaust is generated by engine flows through a turbocharger, front exhaust pipe, and selective catalytic reduction (SCR) post-treatment device. The structure of the front exhaust pipe affects the temperature, velocity, and turbulent kinetic energy of exhaust and the Sauter Mean Diameter (SMD) of urea water solution (UWS). A high temperature and turbulent kinetic energy in the exhaust will promote the decomposition of UWS, and further accelerate the evaporation and atomization effect of the UWS droplets. Therefore, in order for the exhaust to reach a high temperature and turbulent kinetic energy, a double-layered pipe structure with air insulation was designed. The flow field and the atomization of UWS in the double-layered pipe based on hydroforming processing was investigated through numerical simulation. The thermal insulation simulation was verified by the temperature measurement system and the temperature drops between the double-layered pipe and the volcanic rock-wrapped pipe were also compared. The results indicate that the temperature at the outlet of the designed double-layered pipe was 3.5% higher than that of a single-layered pipe with the same structure, and the velocity at the outlet of the exhaust of the double-layered pipe was 16.1% higher than that of a single-layered pipe. The maximum turbulent kinetic energy in the double-layered pipe was 71 times that of the single-layered pipe. The design is not only conducive to the mixing of UWS and exhaust, but can also improve the atomization performance of UWS.