The transition to electric vehicles in the transportation sector still faces multiple technological challenges and large investments as regards both vehicle design and vehicle charging infrastructure. Therefore, internal combustion engines still dominate such a sector, making the engine improvements, in terms of pollutant emissions and efficiency, essential to mitigate the impact of human activities on the environment. One of the possible approaches to improve the efficiency of internal combustion engines is the recovery of the engine exhaust heat, from both the hot exhaust gases and the engine cooling system. So far, several energy recovery approaches have been explored such as Stirling engines, thermoelectric generators, organic Rankine cycles or inverted Bryton cycles, with encouraging results. One energy recovery technique that has been explored in recent years involves the use of direct injection of H2O under supercritical and superheated conditions. Such a technique uses pressurized water recovered from the exhaust gases, heated to high temperature by using the engine waste heat and re-injected into the engine combustion chamber. This results in higher in-chamber pressure, which increases the engine work and efficiency. The injector geometry is a key component of the process, as it drives the direction of the resulting under-expanded jet and the in-chamber flow field, thus affecting the jet interaction with combustion. In this work, three different injector geometries have been considered in order to highlight the advantages and disadvantages of each of them. To this end, a CFD model of a 4-stroke spark ignition internal combustion engine has been considered and validated against experimental data. A detailed analysis of the turbulent flow field in the chamber has been carried out, with particular attention to the turbulent kinetic energy budget and the time required for the jet to reach the flame front and the cylinder wall. The three injectors are then compared to each other, and the implications on the jet-combustion interaction are discussed. The manuscript ends with suggestions for future developments.

On the direct injection of H2O under supercritical and superheated conditions into ICEs: the role of the injector geometry

Antonio Cantiani;Annarita Viggiano;Vinicio Magi
2022

Abstract

The transition to electric vehicles in the transportation sector still faces multiple technological challenges and large investments as regards both vehicle design and vehicle charging infrastructure. Therefore, internal combustion engines still dominate such a sector, making the engine improvements, in terms of pollutant emissions and efficiency, essential to mitigate the impact of human activities on the environment. One of the possible approaches to improve the efficiency of internal combustion engines is the recovery of the engine exhaust heat, from both the hot exhaust gases and the engine cooling system. So far, several energy recovery approaches have been explored such as Stirling engines, thermoelectric generators, organic Rankine cycles or inverted Bryton cycles, with encouraging results. One energy recovery technique that has been explored in recent years involves the use of direct injection of H2O under supercritical and superheated conditions. Such a technique uses pressurized water recovered from the exhaust gases, heated to high temperature by using the engine waste heat and re-injected into the engine combustion chamber. This results in higher in-chamber pressure, which increases the engine work and efficiency. The injector geometry is a key component of the process, as it drives the direction of the resulting under-expanded jet and the in-chamber flow field, thus affecting the jet interaction with combustion. In this work, three different injector geometries have been considered in order to highlight the advantages and disadvantages of each of them. To this end, a CFD model of a 4-stroke spark ignition internal combustion engine has been considered and validated against experimental data. A detailed analysis of the turbulent flow field in the chamber has been carried out, with particular attention to the turbulent kinetic energy budget and the time required for the jet to reach the flame front and the cylinder wall. The three injectors are then compared to each other, and the implications on the jet-combustion interaction are discussed. The manuscript ends with suggestions for future developments.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11563/156006
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