Coupled Simulations of Cooling and Engine Systems for Unsteady Analysis of the Benefits of Thermal Engine Encapsulation

Licentiatavhandling, 2015

A well-designed engine encapsulation can extend engine cool-down time significantly - on the order of 500 - 700%. This is expected to have a sensitive influence on the fuel consumption due to the increased probability for high oil temperatures at the following engine start, reduced length of the initial warm-up period and consequently, reduced friction losses. This work aims to set up and develop a simulation platform for investigations of the potential effect of thermal engine encapsulation on fuel consumption of commercial and passenger vehicles. It documents the development and validation of the methods and tools used for this purpose, and apply them to estimate the effect of various initial oil temperatures on the fuel consumption of a commercial vehicle during a cold start drive cycle. Presented is a comprehensive 1D unsteady model verified against experimental data and supported with parallel 3D simulations. The model contains predictive representations of engine, cooling system, oil circuit and utilizes a temperature dependent model of engine friction losses. A number of steady-state and transient simulations are performed for a 13L Volvo FM commercial vehicle and results are compared with physical measurements. The developed 1D and 3D methodologies were validated and achieved satisfactory accuracy both in steady and unsteady mode of operation. Predictions of oil sump temperature development were compared to measured values to conclude that the model is fit for further use in a temperature dependent friction model. As a last step all models were unified to perform a complete vehicle simulation of a cold start drive cycle at different initial oil temperatures in order to evaluate the influence of reduced warm-up phase on fuel consumption. The simulations indicated that there is a potential of up to approx. 3% decrease of fuel consumption as a result of increased initial engine temperatures.