Induction Ramming Effects in Single-Cylinder Four-Stroke Engines

The paper describes a series of experiments carried out to determine how the fluctuations of pressure, which occur in the induction pipes of four-stroke engines, may be best employed to improve the charging of the engine cylinder. Two single-cylinder engines were used during the tests, the first being a medium-sized water-cooled unit running at speeds between 1,000 and 2,000 r.p.m., the second a smaller air-cooled engine capable of higher rotational speeds. The effects of changes in diameter and length of induction pipe were explored with both engines, the valve timing remaining fixed; and, using the water-cooled unit, extensive trials were carried out at three standard engine speeds to find what valve timing gave maximum air consumption for each of a number of induction pipe lengths. Finally, the influence of several sizes of carburettor Venturi tubes in damping out the pressure fluctuations and reducing the ramming effect was investigated. Information is given, based on the results of the experiments, enabling a suitable length and diameter of induction ramming pipe to be chosen for engines running at any constant speed, as well as for those covering a wide range of speeds.