1. Field of the Invention
This invention relates to a single shaft gas turbine engines and more particularly to a single shaft gas turbine engine which is advantageously arranged to permit mounting of the engine on the narrow 22 inch wide frame of a standard sized farming tractor while providing a particularly efficient engine configuration.
2. Description of the Prior Art
A single shaft gas turbine engine is an engine having a turbine mounted on a shaft and a compressor coupled to rotate with the turbine. The turbine receives, hot, high pressure gases and converts the energy of these gases to rotational torque which is applied to the shaft on which the turbine is mounted. The shaft torque is in turn applied to rotate the compressor which receives input gases at approximately atmospheric pressure and increases the pressure thereof before they are heated in a combustor and applied to drive the turbine. Approximately two-thirds of the rotational energy which is supplied to the shaft by the turbine is required to drive the compressor and the remaining one-third is available as useful power for driving apparatus external to the engine. A considerable amount of research and development has been conducted on the subject matter of single shaft gas turbine engines with research, inter alia, being particularly directed toward analyzing the effects of temperature and pressure changes at various points along the working fluid flow path, developing improved compressors, turbines, and combustors, and improving the efficiency with which the working fluid is handled as it is passed through an engine. While much progress has been made in this regard, the problems which have been encountered are extremely complex and much room for improvement remains. Because of the high temperatures and high velocities to which the working fluid is subjected, significant power losses are encountered in the fluid flow path of a present day gas turbine engine.
One technique which has been utilized to improve the efficiency of a gas turbine engine is to utilize a heat exchanger such as a counterflow recouperator or a regenerator to transfer heat from hot exhaust gases to cooler compressed gases prior to their entry into the combustor. One form of heat exchanger is an annular regenerator which is axially positioned between the compressor and turbine and mounted coaxially with the compressor and turbine with the annular regenerator extending circumferentially about the engine housing. While permitting engine efficiency to be increased by reducing the amount of energy that is wasted as exhaust heat, such a regenerator introduces additional losses into the working fluid flow path. In particular, the low pressure, high volume, high temperature exhaust gases must leave the turbine in an axially forward direction, be turned through 180.degree. and conducted a considerable distance in an axially rearward direction before they pass through the regenerator and are exhausted to the atmosphere. This rearward motion of the exhaust gases brings them into closer proximity to the inlet and reduces engine efficiency by increasing heat transfer either through engine components or through the atmosphere to the inlet gases. Furthermore, positioning a regenerator adjacent the side of an engine housing necessarily increases the width of the gas turbine engine. As presently known, such arrangements are too wide for mounting on a standard farm tractor frame.
Both conical and annular diffusers have been investigated for recovery of part of the kinetic energy of exhaust gases as they leave a turbine. However, conical diffusers have the disadvantage of greatly increasing engine length. With the pressure of the exhaust gases increasing as they flow through an exhaust diffuser, and with the exhaust gases exiting the diffuser to approximately atmospheric pressure, the pressure of the exhaust gases is necessarily below atmospheric pressure at the point where they leave the turbine and enter the diffuser. The working fluid pressure drop across the turbine is thus increased and greater power can be extracted from the turbine. The results of one study on the use of exhaust diffusers was presented to the "International Automotive Engineers Congress" in Detroit, Michigan, Jan. 13-17, 1969 by Charles A. Amann and David W. Dawson and has been published by the Society of Automotive Engineers in paper No. 690032.