Date of Graduation

1997

Document Type

Dissertation/Thesis

Abstract

The three chamber (3C) engine concept was evaluated using computer programs with thermodynamic emphasis. This 3C engine utilizes pistons to perform compression and expansion of the working gas. These cylinders are connected by a combustion chamber. By separating the compression and expansion processes, it is possible to have a larger expansion displacement thus introducing the displacement ratio which is the quotient of expansion to compression displacement. Initially an algebraic analysis of the air-standard cycle was completed. Following this an ideal computer model was developed and used to verify that the 3C engine deviated from the Diesel cycle and approached that of the Brayton cycle. The ideal computer model was also used to choose an expansion cylinder intake valve closing time of 40 degrees after top-dead-center and a displacement ratio of 1.1. Next, an ideal transient model was developed which required choosing a piston phase angle of 20 degrees with the expansion cylinder leading. The transient model was then used to show that there were large pressure fluctuations in the combustion chamber when the volume was small, but these fluctuations diminished rapidly as the size increased. Another form of the transient computer model was used to show that the response times increased linearly with combustion chamber volume and a value of twice the size of the compression cylinder was chosen. A final computer model was developed to represent a more realistic 3C engine. This model included losses due to the dependence of the specific heat on both temperature and gas composition, flow through the valves, blowby, convective and radiation heat transfer, and friction. These non-idealities introduced several new variables and a parametric study was completed. It was seen that the thermal efficiency increased as the amount of blowby, the cylinder wall temperature, and the fuel emissivity decreased and as the combustion chamber wall temperature increased. A comparison to a diesel engine using the realistic computer model indicated that the thermal efficiency of the 3C engine was lower and thus further exploration of other possible benefits such as emission characteristics should be performed. It has been concluded that although high pressures are experienced, the 3C engine concept is thermodynamically viable and an appropriate design has been presented for a locomotive application.

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