Experimental Analysis of the After-Boiling Phenomenon in a Small I.C.E.

An experimental investigation was conducted on a production 4-cylinder, MPI small S.I. engine, 1.2 dm³ displacement, which was operated at 4000 rpm full load, then brought to idle for a short period and finally switched off. As the coolant flow stops while the metal temperature is quite high, a fraction of coolant vaporizes, pressure and temperature increase and part of the coolant is lost through the radiator pressure relief valve. This phenomenon is often known as after-boiling.

Tests were carried out for different values of the idle operation time, while coolant conditions and metal temperature at 26 points of the engine head and liner were monitored for 2 mins before and 15 mins after engine switch-off. The volume of leaked coolant as well as the start and finish of the expulsion process were also recorded.