Pre-catalyst engine emissions and detrimental injector deposits have been widely associated with the near-nozzle fluid dynamics during and after the injection events. Although the heating and evaporation of fuel films on the nozzle surface directly affects some of these processes, there are no experimental data for the transient evolution of nozzle surface temperature during typical engine conditions. In order to address this gap in knowledge, we present a non-intrusive approach for the full-cycle time resolved measurement of the surface temperature of production nozzles in an optical engine. A mid-wave infrared high-speed camera was calibrated against controlled conditions, both out of engine and in-engine to account for non-ideal in surface emissivity and optical transmissivity. A custom-modified injector with a thermocouple embedded below the nozzle surface was used to validate the approach under running engine conditions. Calibrated infrared thermography was then applied to characterise the nozzle temperature at 1200 frames per second, during motored and fired engine operation, thus revealing for the first time the effect of transient operating conditions on the temperature of the injector nozzle’s surface.
The temperature of fuel injectors can affect the flow inside nozzles and the subsequent spray and liquid films on the injector tips. These processes are known to impact fuel mixing, combustion and the formation of deposits that can cause engines to go off calibration. However, there is a lack of experimental data for the transient evolution of nozzle temperature throughout engine cycles and the effect of operating conditions on injector tip temperature. Although some measurements of engine surface temperature exist, they have relatively low temporal resolutions and cannot be applied to production injectors due to the requirement for a specialist coating which can interfere with the orifice geometry. To address this knowledge gap, we have developed a high-speed infrared imaging approach to measure the temperature of the nozzle surface inside an optical diesel engine. We investigated ways of increasing the emissivity of the nozzle surface with minimal intrusion by applying thin carbon coatings. We compare our measurements with those from a production injector that was instrumented with internal thermocouples. Our steady-state off-engine investigation showed that nozzle surface temperature measured by infrared imaging could yield data at 1200 fps with uncertainties of +20 K to -1 K compared to simultaneous thermocouple measurements. We applied this approach to an optical diesel engine to investigate the effect of injection duration and increased swirl ratio on injector nozzle temperature and surface homogeneity.
The accurate control of the the spray dynamics arising from the nozzle in GDI injectors is key in order to control the subsequent combustion process. In this work we present LES of in nozzle dynamics of gasoline direct injection and the resulting early development of spray plumes from an 8-hole injector (ECN Spray G). In order to do so a new three fluid solver within OpenFOAM has been developed. The objective is to evaluate the impact of the cavitation in a multihole gasoline injector, along with its influence on the flow field at the start of injection. It is shown how the interaction between the gaseous phases can influence the initial stages of the spray formation and the different pattern of cavitation across the injectors holes.
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