Il Thermal Management nei Motori a Combustione Interna. Analisi teorica e sperimentale di pompe innovative per il raffreddamento del motore.

The road transport sector is one of the main contributors to anthropogenic CO2 emissions, being it widely based on Internal Combustion Engines (ICEs). Progressively stringent regulations have been implemented over the years to limit these emissions. A valid contribution in this sense can be given by electric vehicles, but costs and operability concerns still make necessary solutions to improve the efficiency of ICEs. In this context, the optimization of the Engine Thermal Management (ETM) represents one of the most promising strategies. In fact, the engine cooling system still uses basic fail-safe components, that do not allow any optimization of the engine performance under many common driving conditions, such as during the warm-up phase. Advanced ETM systems require high-efficiency pumps to reduce the energy spent to cool the engine. Volumetric pumps can offer a valid contribution in this sense, due to their high efficiency also when operating far from the design point, as usual on-board of a vehicle. In this thesis, screw-type volumetric pumps have been studied when used as cooling pumps in ICEs. A novel zero-dimensional mathematical model capable to predict the volumetric, indicated and mechanical performances of triple-screw pumps has been developed. The experimental validation of the model showed a mean error equal to 0.6% and 6.1% for flow rate and mechanical power, respectively. Once validated, the model has been used to optimize the design of screw pumps for engine cooling applications. After identifying a suitable design point for a specific engine cooling system, the performances of a wide set of screw pump’s geometries have been studied, to identify the geometric proportions which maximize the pump efficiency. Thus, an optimized screw pump has been designed and compared with the standard centrifugal one when operating on a reference driving cycle. The results showed a strong energy reduction (about 56%), and thus a significant CO2 emissions saving (2.08 gCO2/km). These promising results suggested to build a physical prototype of the so-designed triple-screw pump, and to compare its performances with those of an equally optimized centrifugal pump. Even in this case, significant energy (-21%) and emissions (-0.28 gCO2/km) savings were found. The prototyped triple-screw pump introduced also an innovative idler screws’ axis support, designed to reduce friction and wear. Hence, the mathematical model has been refined to catch these new friction conditions, as well as blow-hole backflows. Then, this model has been used to calculate the performances of the prototyped pump when operating under extreme conditions, difficult to measure experimentally. Furthermore, the availability of a screw pump prototype allowed to investigate experimentally also the indicated cycle of this type of machine. Finally, the thermal management of a passenger vehicle propelled by a spark ignition engine has been investigated experimentally. The vehicle was equipped with a Portable Emissions Measurement System (PEMS), and with additional sensors to characterize completely the thermal dynamics of coolant, oil and engine block. Hence, the same road test has been realized staring with different engine initial temperatures. The results showed a significant reduction of fuel consumption (-3.9%), CO2 (-5.9%) and CO (-30.6%) emissions when starting with the engine already warmed up. Instead, higher NOx emissions (+21.6%) have been measured. Moreover, the thermal dynamics of the block’s metallic masses was found to evolve almost simultaneously with that of the coolant, which is of great scientific interest if a variable-speed cooling pump wants to be implemented. In conclusion, this study offers a deep understanding of the potential benefits related to the use of screw pumps for engine cooling applications. Moreover, it provides useful information to develop advanced cooling pumps for the optimization of the engine thermal management.