A Parametric Analysis Microcomputer Model for Evaluating the Thermodynamic Performance of a Reciprocating Brayton Cycle Engine

Abstract

A novel Brayton open-cycle engine is under development. It operates similarly to a gas turbine engine, but uses reciprocating piston compressor and expander components. The design appears to have a number of advantages, including multifuel capability, the potential for lower cost, and the ability to be scaled to small sizes without significant loss in efficiency. An interactive microcomputer model has been developed that analyzes the thermodynamic performance of the engine. The model incorporates all the important irreversibilities found in piston devices, including heat transfer, mechanical friction, pressure losses, and mass loss and recirculation. There are 38 input parameters to the model. Key independent operating parameters are maximum temperature, compressor rpm, and pressure ratio. While the development of the model and its assumptions are outlined in this paper, the emphasis is on model applications. The model has demonstrated itself to be a powerful tool for evaluating engine thermal efficiency, net specific work, and power. It can be used to analyze the performance of individual engine designs, to generate performance “maps” that graphically represent engine operating characteristics, and to perform sensitivity analysis to compare the relative effects of various input parameters. Examples of each of these model applications are discussed. Recommendations for model improvements and for further engine development work are made. The need for better experimental data to verify some critical model assumptions is stressed.