NACA-TN-2069

Abstract

INTRODUCTION <br>A knowledge of the cooling characteristics of reciprocating aircraft engines is essential for the prediction of engine performance at extreme conditions of operation. Consequently, a research program was conducted at the NACA Cleveland laboratory in 1943to investigate the cooling characteristics of liquid-cooled aircraft engines. The initial phase of this research program consisted of an investigation conducted on two single-cylinder engines to provide data for a fundamental study of the heat-transfer processes involved. These data, which isolate the effects of the various engine and coolant variables on the cylinder-head temperatures, are presented in reference 1. A semiempirical method based on the theory of heat transfer by nonboiling forced convection and used for correlating the cylinder-temperature data of reference 1 with the engine and coolant variables is presented in reference 2. <br>Concurrent with the investigation on the single-cylinder engines, the cooling characteristics of a multicylinder engine of 1710-cubic-inch displacement were investigated over wide range of engine and coolant conditions. The results of this investigation are reported in reference 3, which presents the variation of both the cylinder temperatures and coolant heat rejection data of reference 3 with the pertinent engine and coolant variables in presented in reference 4. The method of correlation is based on the theory of nonboiling forced-convection heat transfer and is similar to that developed in reference 2. <br>In order to determine if the trends presented in reference 3 are generally applicable to liquid-cooled multicylinder aircraft engines, a similar investigation of the cooling characteristics of an engine of 1650-cubic-inch displacement was conducted during 1946 and is reported herein. The cylinder-head temperatures and the coolant heat rejection were determined for power outputs up to 2000 brake horsepower over wide ranges of engine speed, manifold pressure, fuel-air ratio, inlet-air temperature, ignition timing, exhaust pressure, and for various conditions of coolant flow, composition, temperature, and pressure. Runs were made for coolant flows as low as 49 gallons per minute in order to investigate the cooling characteristics of this engine under boiling coolant conditions. The variation of the cylinder-head temperatures and the coolant heat rejection with the engine and coolant variables is presented and a comparison is made of the results of this investigation with those of the investigation of the engine of 1710-cubic-inch displacement (reference 3). These cylinder-head-temperature and coolant-heat-rejection data were correlated by means of the NACA correlation method, which is fully illustrated in reference 4, and the final results of the correlation are presented to aid in the application of the data. An example of the use of the correlation method for the prediction of cylinder-head temperatures and the coolant heat rejection is also included.