Abstract
In state of the art internal combustion engines less than fifty per cent of the fuel energy is transformed into useful mechanical energy. Most of the fuel energy is dissipated to the environment as thermal energy. Because of limitations in oil production and rising fuel prices, the total efficiency of the internal combustion engine as a system needs to be increased. Due to their mission profile with continuous long-haul driving cycles commercial vehicles provide a very high potential for thermal recovery systems.
The dynamic vehicle simulation model of a truck considered here is called FasiSteam and is a combination of three different simulation tools. The longitudinal dynamic model is calculated in Matlab/Simulink, the thermal management part is modeled in Flowmaster. The third tool, the waste heat recovery model, is built in the multi-engineering simulation software Dymola. The thermal and longitudinal dynamic models are in-house simulation systems of MAN Truck & Bus AG. The waste heat recovery model is connected to these two parts to yield the overall system FasiSteam. This holistic simulation tool enables transient vehicle simulations with respect to the interactions between these three subsystems. FasiSteam allows detailed simulations under various boundary conditions. Thus, for example, different dynamic driving cycles under different ambient conditions can be simulated. Both individual subsystems as well the complex interactions in the entire system can be analyzed.
In this paper the results of a dynamic vehicle model for waste heat recovery concepts for commercial vehicles will be presented. The simulation models are based mainly on physical correlations and are compared with test bench results. Both stationary and transient validations are performed. The main focus is on predicting and optimizing fuel efficiency. However, the results can be used to design the individual system components as well as for controlling and optimizing the overall system operation. With the object-oriented modeling it is possible to change certain components in the Rankine cycle with little effort. Simulation results for different types of expansion machines, e. g. piston expanders or steam turbines, will thus be shown. Furthermore, the thermal inertia in the Rankine cycle and the resulting effects are presented.
The design and the validation of models are based on prototypes, which means that the results do not represent the optimum: with adjusted components and optimized controllers the fuel economy can be further improved. This paper shows only one possible configuration of the Rankine cycle, and the interaction with the engine's combustion process is not yet considered. The results from a transient co-simulation of a dynamic commercial vehicle in combination with a Rankine cycle are new. Beside this, the different types of expansion machines have not yet been compared and the influence of thermal inertia effects on the system is still unknown. A validated dynamic commercial vehicle simulation model combined with a Rankine cycle has been developed. With this simulation tool viable conclusions can be drawn about the effects of thermal recuperation measures in commercial vehicles.
KEYWORDS – Waste Heat Recovery; Rankine Cycle; Commercial Vehicle; Dynamic Vehicle Simulation; Fuel Efficiency;