Numerical investigation of heat retention and warm-up with thermal encapsulation of powertrain

Powertrain thermal encapsulation has the potential to improve fuel consumption and CO2 via heat retention. Heat retained within the powertrain after a period of engine-off, can increase the temperature of the next engine start hours after key-off. This in turn reduces inefficiencies associated with sub-optimal temperatures such as friction. The Ambient Temperature Correction Test was adopted in the current work which contains two World-wide harmonised Light duty Test Procedure (WLTP) cycles separated by a 9-hour soak period. A coupled 1D - 3D computational approach was used to capture heat retention characteristics and subsequent warm-up effects. A 1-D powertrain warm-up model was developed in GT-Suite to capture the thermal warm-up characteristics of the powertrain. The model included a temperature dependent friction model, the thermal-hydraulic characteristics of the cooling and lubrication circuits as well as parasitic losses associated with pumps. A 23°C WLTP cycle was run via the 1D model, key fluids and solids temperatures around the engine bay calculated at the end of the 1st WLTP cycle were then imported into a 3D heat retention model, in which the transient 3D computational fluid dynamics and heat transfer coupled simulation was initiated to model the full-geometry vehicle for a 9 hours static soak period. The cool-down behaviors of the coolant and oils were predicted from the 3D model and the temperatures at the end of the soak were fed back to the 1D warm-up model to carry out the second WLTP cycle simulation at 14°C ambient condition.

A coupled 1D-3D heat retention modelling method predicted both warm-up and cooldown characteristics to within circa ±3 °C of vehicle test data over the entire ATCT test. The impact of thermal encapsulation was clearly shown, whereby coolant and oil temperatures at the end of the 9 hour soak period were 6°C and 10°C higher with encapsulation respectively, which led to a fuel consumption improvement in the order 1% over the post-soak 14°C WLTP through retaining heat.