a b s t r a c tIn this research, two Engine Combustion Network (ECN) mono-orifice nozzles, referred to as Spray C and Spray D respectively, were analyzed by performing visualization tests through Schlieren and Diffused Backlight Illumination (DBI) techniques under a wide range of ambient conditions in a non-reactive atmosphere. Spray C presents a straight nozzle designed with a sharp fillet in opposition to Spray D that has similar hydraulic properties, but with a convergent nozzle construction and a smoother corner. The experiments were carried out injecting two distinct fuels at different injection pressure ranges, from 50 MPa to 150 MPa with n-dodecane and to 200 MPa for diesel. The images were processed with Matlab home-built routines to calculate parameters as spray penetration, spreading angle, quasisteady liquid length, as well as the spray penetration derivative respect to the square root of time, presented in this document as R-parameter. The results showed a clear influence of nozzle geometry in all measured parameters, due mainly to the nature of Spray C to cavitation, which increase the spreading angle and consequently a reduction in vapor penetration. On the other hand, fuel properties also affected spray penetration due to its dependency on viscous forces expressed in terms of the Reynolds number and its volatility in case of liquid length. This last parameter was calculated employing two processing methodologies, finding a good general agreement between them.

a b s t r a c tThe second part of this experimental analysis, presented in this paper, seeks to go deep on the characterization of the Spray C and Spray D nozzles from the Engine Combustion Network, investigating the penetration of fuel spray at reacting conditions alongside characteristic parameters of combustion such as ignition delay and lift-off length. Both ECN mono-orifice injectors have similar nozzle flow capacity but different conicity degrees and corner sharpness, being Spray C more susceptible to cavitate. Schlieren imaging technique was employed to quantitatively measure reactive penetration and ignition delay, while lift-off length was identified through OH ⁄ chemiluminescence. As in the inert part of this research, n-dodecane and commercial diesel were selected for the tests, thereby the effect of the fuel properties in the measured parameters was analyzed. Also, once again the concept of R-parameter, defined as the penetration derivative respect to the square root of time was calculated to delve into the penetration behavior. The experiments were performed in a constant pressure-flow facility able to reproduce engine-like thermodynamic conditions. Results revealed that R-parameter evolution can be divided in four stages: an inert zone, a 'bump', a 'valley' part and a quasi-steady one that overlaps the previous inert part. Those stages are highly governed by ambient temperature and oxygen concentration. Nozzle geometry and fuel properties demonstrated to have a noteworthy influence on all measured parameters.

One of the test boundary conditions whose control is necessary for both experimental and numerical studies about the automotive engines research field is the temperature of the fuel inside the injector body during the injection. However, it is a difficult parameter to be directly measured in a non-intrusive way due to the injector architecture and the nature of the standard experiments that are done to characterize sprays. An experimental analysis is performed in this work employing a continuous flow test chamber, normally used in the optical diagnosis of diesel sprays, in order to compare and characterize two different designs for the nozzle holder of the test rig. The first one consisted in an aluminum holder that coats the nozzle until its tip, while the second one is made of steel and only supports the nozzle without covering it from the environment. The employed methodology was to set the test rig at a wide range of thermodynamic conditions inside the vessel such as ambient temperature and density, and also the coolant temperature at the outlet of the injector casing for both cooling pieces. In this case, a dummy injector provided with a thermocouple was used to measure the tip temperature. In this way, correlations are obtained to estimate the injector body temperature out of the measurement points. Further experiments with a real single-hole diesel injector, controlling its tip temperature according to the previous results, are also discussed in this manuscript in order to analyze the effect of this parameter on the spray evaporation process. Liquid length at inert conditions and both ignition delay and lift-off length at reactive ones were measured employing the same test vessel. All those parameters showed to be shortened with an increment of injected fuel temperature, and the lower the ambient temperature, the stronger this influence is.

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