Resumen de Study of the gasoline direct injection process under novel operating conditions
Fuel injection is among the engine research topics one of the critical pieces to obtain an efficient engine. The role is even more significant when a direct injection strategy is pursued. The internal geometry and pintle movement determine the injector flow behavior, which is known to hugely affect the external spray development and, ultimately, the combustion performance inside the chamber. Climate change and pollutants awareness has been growing, pushing forward the effort on cleaner engines. In this regard, gasoline en- gines have a wider margin to improve than diesel engines. The evolution from old Port Fuel Injectors to modern direct injection strategies, which are used in new generation engines, demonstrates this trend. GDI systems have the potential to comply with stringent emissions and increase fuel economy, however, it still faces many challenges. This work involves the use of two injectors, one is a modern research GDI nozzle appointed by the Engine Combustion Network (ECN), and the other is a production injector unit (PIU) with the same technology and slightly different geometry. Both hardware's undergo a complete characterization (internal and external flow) covering the state- of-the-art techniques in various experimental facilities. Furthermore, a new facility is designed and built to perform experiments under flash boiling conditions (when the fuel injected's vapor pressure is higher than the pressure in the discharge volume).
The developed facility is designed to simulate a discharge ambient at certain engine conditions in which flash boiling phenomena could occur. Thus, due to typical gasoline fuel properties, it was a requirement to operate from chamber pressures from 0.2 bar to 15 bar. Also, the ambient temperature was controlled by implementing a resistor that can heat the ambient gas. The facility operates in an open loop, being able to renovate the gas volume between injections. Finally, three wide optical accesses were built to accommodate many optical diagnostic techniques such as DBI, MIE, shadowgraphy, or PDA, among others.
For the internal flow description, it was determined the nozzles geometry and holes orientation, the pintle movement, and finally, the characterization of the rate of momentum (ROM) and rate of injection (ROI) of both nozzles. The nozzles geometry and needle lift were measured using advanced optical x-ray techniques at Argonne National Laboratory (ANL). The ROI and ROM measurements were performed using CMT-Motores Térmicos facilities follow- ing the know-how applied in diesel injectors and adapting it to GDI nozzles. The ROI allowed us to compare the nozzles, whose orifices number and geometry were different, although they deliver approximately the same amount of fuel. It was tested their response to typical boundary conditions such as rail pressure, discharge pressure, fuel temperature, etc. For the research nozzle "Spray G", it was developed a 0-D model of the rate of injection allowing to obtain the signal for different injection duration and conditions, which is useful in engine calibration and CFD validation. Furthermore, for the ROM characterization, the plastic deformation technique methodology was developed to obtain spray cone orientation and adequately guide the fuel jets for measuring ROM. The hydraulic analysis combined the data to study the low discharge coefficient and area coefficient values, which could result from low needle lift combined with novel hole designs in both nozzles that promote cavitation and air interaction from inside the orifice.
In the external flow characterization, it was used the new developed vessel to study the external spray covering flash boiling conditions. It was employed four surrogate fuels to simulate different volatility properties of gasoline com- pounds and ultimately reproduce more extreme flashing conditions. It was used lateral visualization using DBI and Schlieren in addition to frontal MIE visualization. Some of t
