Boiling detection in an internal combustion engine cooling system

A study was undertaken to characterize nucleate boiling occurring in the coolant passages of an internal combustion engine cylinder head for both pool boiling and forced convection boiling. First, a bench top study was conducted to investigate pressure based detection techniques in a simplified pool boiling environment. Dynamic signal processing techniques were employed to analyze the data, and an optimal frequency range for boiling detection was determined. The RMS of the fluctuation pressure component, p', provided an excellent boiling identification signature.; Next, an engine study using a 5.4L gasoline V8 was initiated. A separate computer controlled coolant supply system was utilized to provide precise control of the flow rate and temperature of the coolant supplied to the engine. The engine was instrumented with thermocouples to measure bulk coolant temperatures, and two pairs of embedded thermocouples to measure metal temperatures and calculate heat flux. In addition, high sensitivity pressure transducers were installed in the cooling passages of the cylinder head to test a novel pressure based boiling detection technique. Data was taken for no-flow (pool boiling) conditions and forced convection flow boiling conditions over a range of speed and load settings. The RMS of p' again provided a distinct boiling signature for pool boiling identification. A local measurement of DeltaT = Tsat - Tf,vb, where Tf,vb is the local fluid temperature at the valve bridge, provided the best boiling detection signature during forced convective conditions.