SUPPLEMENTING the results of an investigation at the Massachusetts Institute of Technology on supercharging a single-cylinder automobile engine which were presented at the 1928 Annual Meeting, this paper reports a study that was made to determine whether the mechanical action of a high-speed centrifugal supercharger improves engine performance by increasing the degree of atomization and vaporization of the fuel in the inlet manifold. While changes in the degree of fuel atomization and vaporization might be measured directly by sampling the gases as they pass to each cylinder, an indirect evaluation of these changes by measuring their effect on engine performance was considered more practicable.
Tests were made on a six-cylinder automobile engine connected to an electric cradle-dynamometer. The usual exhaust jacket was removed from the intake manifold to avoid any possibility of obscuring the desired results and a normal and a supercharged carbureter of identical design were connected to the intake manifold by passages of as nearly identical length and shape as possible. Comparative runs with the two carbureters were made at four speeds and three loads, engine conditions, including the inlet-manifold pressure and temperature, being kept as nearly the same as possible in each pair of runs.
The conclusions drawn from these tests are that the mechanical-mixing effect of the high-speed centrifugal blower at approximately full load causes increased brake mean effective pressure, decreased specific fuel-consumption and a slightly increased mixture-ratio range. With increasing blower-speed, other conditions being held constant, a tendency toward increased maximum brake mean effective pressure, reduced fuel-consumption and an increased firing range was observed. These improvements are more pronounced with a less-volatile fuel. At three-quarter and lower loads, when commercial gasoline was used as fuel, no improvement in engine performance was obtained.
In the discussion of the paper, the statement is made that no diffuser was used and the question is raised whether design constants of the wheel, such as the shape of the blades, were properly adapted to the conditions in the apparatus used by Professor Taylor. The actions in an efficient supercharger with smooth flow are then outlined.