Optimizing the NAHBE Piston Cap Design Utilizing Schlieren Photography Methods and Applications of the Helmholtz Resonator Theory

摘要

The Naval Academy Heat Balanced Engine (NAHBE) has been studied extensively for the last five years. Efforts to understand and predict the process occurring in the engine were complicated and difficult to verify experimentally. Optimization of the output of the engine, through possible, took much too long a time through parametric variation. An answer to the problem of predicting the time dependent reaction occurring in the engine was sought. Also, some easy design tool for optimizing the reaction was required. One possible solution to these problems was to model the NAHBE piston cap through the Helmholtz Resonator Theory. This theory generalizes the time dependent reaction of a volume of fluid in a chamber by the acoustic analog to the mechanical system forced oscillator. The theory enables one to predict or design the acoustic impedance of a cavity and its natural frequency by way of the cavity and inlet geometry. This study shows how the solution to the Helmholtz Theory may be obtained and the fluid mass displacement of NAHBE cap modeled by the Helmholtz Theory predicted. The solution of hte NAHBE cap reaction by the Hemholtz Theory, however, is only a hypothesis until it is substantiated. Conclusive evidence is shown in this study through a high-speed Schlieren film analysis of the actual combustion process in a NAHBE, that the theory holds true for and can predict reality. Thus, it is proven that the Helmholtz Theory, which can be used as a design tool, can model the real systems found in heat balanced engines today. (Author)