Engine Thermal Management in Heavy Duty Vehicles
Licentiate thesis, 2007
Future regulations on noise and exhaust emissions have a large impact on heavy duty engine installations. Cooled EGR is used for NOx abatement. Better sealed engine encapsulations are used to meet new noise regulations. Engine thermal management is therefore becoming an increasingly important discipline.
In order to meet those challenges, improvements are needed in several areas. Steady state performance is always important for trucks due to low power to gross cargo weight ratio. Two major steady state situations are climbing of a very long hill with full load in extreme heat and cruising at constant road speed on a flat road with average load at average temperature. In the first case cooling performance requirements has to be met. In the second case parasitic losses has to be minimised.
The cooling system can be reduced to three sub systems: The hot side (coolant pump), the heat exchanger (radiator) and the cold side (cooling air fan). The key components for steady state performance are the cooling fan and the radiator. The key to good fan performance is the optimisation between fan and installation. The limiting factor for radiator development on the other hand is fouling resistance.
The requirement for coolant flow is very fluctuating. Usually only a small fraction of the available flow is routed through the radiator by the thermostat. Coolant pump speed control would reduce parasitic losses significantly. An innovative compromise, a way of controlling the pump performance with the thermostat is presented.
Electronic control systems make advanced control strategies possible. A comprehensive model for transient engine thermal management simulation has been developed in order to fully utilise this potential. The aim was to implement a model where several aspects like heat flow, mechanical systems and control can be simulated simultaneously. A general tool that can be used interdisciplinary was required to achieve this. SIMULINK was chosen for this task.