INTAKE-MANIFOLD TEMPERATURES AND FUEL ECONOMY

Supplementing a “more miles per gallon” movement in 1919, a series of experiments outlined by the S. A. E. Committee on Utilization of Present Fuels was undertaken by the Bureau of Standards, in May, 1920, which included measurements of engine performance under conditions of both steady running and rapid acceleration with different temperatures of the intake charge secured by supplying heated air to the carbureter from a hot-air stove, by maintaining a uniformly heated intake manifold and by using a hot-spot manifold, fuel economy being determined for both part and full-throttle operation. A typical six-cylinder engine was used, having a two-port intake manifold with a minimum length of passage within the cylinder block, an exhaust manifold conveniently located for installing special exhaust openings, rather high peak-load speed and conventional general design. The carbureter was selected with the requirements in view of securing definite and measurable conditions of the intake charge and accurate measurements of the behavior of the charge as indicated by fuel consumption in pounds per brake-horsepower-hour. Provision was made for an unusually complete series of measurements. These are described, the most unique being the construction of the tee portion of the manifold of Pyrex glass. Motion pictures of the manifold were taken during operation, but in only one run were the walls completely dry, and a surprising amount of directly applied heat was required to accomplish this.

The main series of runs was made with the exhaust-jacket manifold, in an attempt to determine how best to obtain low fuel consumption and rapid acceleration and how this result was influenced by changes in the amount of heat furnished the intake charge or in the method of supplying this heat. The fuel consumption tests were made at both full and half load at speeds of 650 and 1200 r.p.m. Full details of the tests are then stated, the results are presented in charts, and these are discussed. The results obtained are then summarized as follows:

1. (1)
   At constant speed, mixture ratio and power output fuel consumption in pounds of fuel per brake-horsepower-hour are independent of the temperatures and methods of heating the intake charge within the range tested
2. (2)
   The rate at which an engine will accelerate with a given mixture ratio, or carbureter setting, is markedly affected by the amount of heat supplied to the charge and its method of application. Within the limits of this work, the greater the amount of heat supplied to the charge and the higher its temperature at the intake port, the more rapidly the engine would accelerate