Study of ECN Injectors’ Behavior Repeatability with Focus on Aging Effect and Soot Fluctuations 2016-01-0845

The Engine Combustion Network (ECN) has become a leading group concerning the experimental and computational analysis of engine combustion phenomena. In order to establish a coherent database for model validation, all the institutions participating in the experimental effort carry out tests at well-defined boundary conditions and using wellcharacterized hardware.

In this framework, the reference Spray A injectors have produced different results even when tested in the same facility, highlighting that the nozzle employed and its fouling are important parameters to be accounted for.

On the other hand, the number of the available Spray A injectors became an issue, due to the increasing number of research centers and simultaneous experiments taking place in the ECN community.

The present work has a double aim: on the one hand, to seek for an appropriate methodology to “validate” new injectors for ECN experiments and to provide new hardware for the ECN community. On the other hand, to investigate injector characteristics reproducibility, with particular focus on the effect of injector aging and on the data scattering observed in soot measurements.

In order to investigate these issues, a set of 10 new injectors with identical nominal Spray A specifications were purchased and characterized using ECN standard diagnostics. A full characterization of the injector-set was performed including nozzle orifice diameter, rate of injection, liquid/vapor phase penetrations, ignition delay, lift-off length, and high-speed 2D soot extinction.

The results outline a global agreement with the ECN dataset, also when parametric variations are applied. These results therefore validate this injector set which can be included in the ECN injector pool. Moreover, the analysis of the discrepancies observed among the injector set highlighted their causes. The differences observed in the vapor phase penetration and in liftoff length appeared to be related to slight differences measured in the average mass flow rate. A substantial impact of the nozzle aging on the liquid length measurements was observed and quantified. The injector aging showed a first order effect on the liquid length results, in particular on the first experiments performed on a brand new injector. The most likely aging agent detected in the present work is the pre-burn event performed in the high-temperature high-pressure vessel employed for the tests. This aging effect should be taken into account for future injector validations.

Finally, the lift-off length and the soot extinction measured during a single test appeared strictly depending on each other: factor two differences in soot KL were observed to be the consequence of minimal differences in lift-off length (10-20%).

These observations, based on a high number of measurements, underline the impact of the injector singularities on the spray/combustion characteristics, even when comparing nominal identical injectors.