EXPERIMENTAL INVESTIGATION ON AN ICE COOLING SYSTEM UNDER NUCLEATE BOILING CONDITIONS

The paper presents the results of a test rig experimentation on a production model S.I. engine, whose cooling system is equipped with a 13 V - 60 W electrical pump and operates under Two-Phase Nucleate-Boiling conditions. Tests have been carried out for fixed engine load, speed and inlet coolant temperature while coolant flow rate was varied by means of pump supply voltage. The influence of coolant flow rate on cylinder head temperature, coolant expansion, coolant temperature and specific fuel consumption is preliminarily analyzed. Results indicate that reduced coolant flow rate combined with Nucleate Boiling regime achieves lower wall temperatures than standard cooling in many different engine operating conditions and that cylinder-to-cylinder temperature variations as well as temperature dependence on engine speed are significantly reduced. In addition, coolant expansion is moderate and specific fuel consumption difference with respect to the standard cooling configuration is negligible, as long as the coolant remains under Nucleate Boiling conditions. Engine performance and fuel consumption, on the contrary, deteriorate if Fully Developed sub-cooled Boiling conditions are set up. Finally, the issue of identifying the On-set of Nucleate Boiling is addressed. Results show that both coolant pressure pulsations and coolant expansion can be conveniently used to this purpose.