Yaw- and Trailer Dependence for Rear-Mounted Cooling Installations for Heavy Vehicles

Paper i proceeding, 2012

Due to stricter emissions legislation and increasing fuel prices vehicle efficiency must be improved. A trend that has been seen in recent years is increased engine power for heavy vehicles. Different exhaust gas after-treatment systems have also been introduced to be able to meet the emission demands. Though, these implementations do not only affect the engine power and the emission levels, they also tend to increase the cooling demand. Therefore, the cooling performance for vehicles has to be increased. At the same time the cooling installation in the front of the vehicle accounts for a substantial part of the total aerodynamic resistance of the vehicle. To reduce the fuel consumption the grill in the front could be covered and the cooling module could be relocated elsewhere. This would decrease the aerodynamic resistance; but a more frequent fan operation would most likely be needed to achieve the same cooling performance in different driving conditions. This paper presents a comparative study of front-mounted and rear-mounted cooling package installations, using three different configurations for the rear installation on a rigid truck. For each case the cooling performance, fan demand and aerodynamic resistance were compared for different operating conditions at both lower and higher vehicle speeds and engine loads. The study was based on Computational Fluid Dynamics (CFD), where the simulations were performed in zero and five-degree yaw conditions, with and without a trailer added behind the truck. It was seen that a relocation of the cooling module has a potential for fuel savings at higher vehicle speeds, due to the reduction in power to overcome the aerodynamic resistance. At lower vehicle speeds the cooling performance was increased since a lower system restriction was observed for the rear-mounted configurations. Results also showed that both the cooling performance and the aerodynamic drag was affected by the yawed air condition and when adding a trailer behind the truck. The mass airflow was increased when the air was directed towards the air intake, while it was decreased when the air intake was positioned at the leeward side of the vehicle. When the trailer was added behind the vehicle less air entered the cooling module at a higher vehicle speed. But for the critical cooling situation the trailer did not affect the amount of air entering the cooling module.