Scheduling simulators are useful in the design exploration phase of the development of reactive embedded real-time computer systems. However, most conventional scheduling simulators do not fulfill all the requirements needed for the modeling of application functionality and system environment. Other system modeling approaches exist for this purpose, but these usually do not deal with scheduling aspects.This paper proposes a new approach to the modeling and simulation of both functional and scheduling aspects of real-time systems. The new approach is based on Petri nets and uses a principle called delegated execution. The main idea is to associate time progress with an explicit scheduler subnet instead of the task structure. Advantages of this approach are the ability to model preemptive scheduling, to combine an application with several schedulers, and to reuse standard scheduler models. The modeling methodology is demonstrated using the well known mine drainage system case study.