Investigation of Rear-Mounted Cooling Module Installations for Heavy Vehicles

Licentiate thesis, 2011

Due to stricter emissions legislations and increasing fuel prices vehicle efficiency must be improved. A trend that has been seen during recent years is increased engine power for many vehicle segments. 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 the fan would most likely be needed to operate more frequent to achieve the same cooling performance. This thesis presents a comparative study of front-mounted and rear-mounted cooling package installations, using four different configurations for the rear installation. For each case the cooling performance and aerodynamic resistance were compared for different operating conditions at both lower and higher vehicle speeds and engine loads. The results show that the cooling performance was favourable, at the same time the total power demand was lowered for two of the rear-mounted cooling package installations. The grill design and the inlet duct shape were shown to be of great importance to avoid separation, and to assist air entering the inlet duct at higher vehicle speeds. The power required due to aerodynamics and cooling performance was lowered by 1.9 percent for a rear-mounted compared to the front-mounted one seen on the vehicles today. For equivalent cases, at 90km/h, the rear-mounted installations only received approximately 50 percent of the mass airflow compared to the front-mounted one, when the fan was not operating. In critical cooling situations the cooling performance was higher for three of the rear installations, compared to the front-mounted installation. The main reason for this result was due to the high fan operating speed and the lower system restriction. Hence, a rear-mounted installation can result in higher cooling performance and lower power demand due to aerodynamics and fan operation. Therefore, such an installation has potential for fuel savings.