Illustration of the Use of an Instructional Version of a Thermodynamic Cycle Simulation for a Commercial Automotive Spark-Ignition Engine

The development and use of an instructional version of a thermodynamic engine cycle simulation for classroom use is described. This simulation is based on well-established features, but which are not necessarily the most advanced. The major simplification of this instructional simulation is the use of constant specific heat capacities as opposed to the use of variable composition and properties. The cycle simulation was developed with an elementary set of conventional sub-model components. To account for the unsteady flow dynamics, an empirical adjustment factor was used. With the exception of this empirical adjustment factor, all of the constants associated with the sub-models are used as suggested by the original publications. Students, therefore, are readily able to develop and use this simulation. This paper then demonstrates the usefulness of such a basic simulation in describing the overall performance of a commercial automotive spark-ignition engine for a range of engine speeds and operating conditions. A modern, four-valve per cylinder, two-camshaft engine was selected for this study. Although the cycle simulation was based on elementary conventional features, a number of important engine characteristics were correctly obtained. These included the overall performance for engine speeds up to 7000 rpm, and details such as the time (crank angle) of peak pressure for optimum performance.