To increase the output of a gasoline engine, it is the general practice to supercharge the engine. ln this case, however, the suction temperature increases as the boost pressure increases, to find the engine causing knock phenomena. To avoid this, it is necessary to inject fuel or liquid having large values of latent heat of vaporization, such as methanol or water, into the induction manifold to reduce the suction temperature.
The engine, however, does not always operate at full power, and when at partial power, i. e. when the suction temperature is relatively low, methanol or water injection is unnecessary. Therefore, it is preferable to install the engine with the injection pump having automatic temperature control mechanism, such that, injection begins automatically when the suction temperature exceeds some definite value, but ceases injection when the suction temperature descends below this value.
Experiments were made with such a injection pump of geared type installed with automatic temperature control unit. This temperature control unit has temperature sensible element using ether as a medium, and the pressure variations of ether caused by temperature variations are transmitted by bellows and links to the plunger valve controlling the overflow area, thus controlling the injected amount of methanol or water. In this case, experiments using water were performed to find the effect of revolutions of the pump, the effect of the springs which control the opening of the above-mentioned overflow area upon injection pressure, amount of injected water and further the temperature at which the injection begins or ceases.