A Study of ECN ‘Spray B’ in a Light-Duty Optically Accessible Diesel Engine Based on High-Speed Imaging with LED Retro-Reflection 2019-01-0550

The Diesel-type three-hole Spray B (injector 211201) of the Engine Combustion Network (ECN) was used in a single-cylinder light-duty optically-accessible Diesel engine. A simple optical method was developed to quasi-simultaneously image both liquid and gas phase of the fuel spray as well as combustion at kHz rates by retro-reflection of pulsed LED light from the fire deck. From the images, liquid penetration length, fuel vapor penetration, spray dispersion angle, ignition delay, flame luminosity, and ignition location were determined. Wide-field imaging allowed for studying the nozzle hole-to-hole variation. In addition to a variation of ambient temperature and density to achieve the standard ECN condition, a variation of fuel rail pressure and swirl ratio was also investigated, under both non-reacting and reacting conditions. The results show physically reasonable variations with different operating conditions. At the same bulk temperature but a higher swirl ratio, the liquid length behaves slightly differently for different jets near the standard ECN condition; ignition occurs slightly later and temporally - but not spatially - more scattered and farther downwind in the swirl direction. Regarding hole-to-hole variation, jet 2 shows the greatest liquid length, fastest gas penetration, and longest ignition delay, even though hole 3 has the largest orifice outlet diameter. Previously, Spray B has been examined in pressure vessels as well as in large-bore and small-bore engines. Although the absolute values of liquid length cannot be compared with those in the ECN database because of different optical diagnostics, the slopes against ambient temperate can. Regarding ignition delay, two data consistencies were found in the ECN database, depending on the diagnostics used to determine the start of combustion. Some of the differences caused by facilities differing in chamber size and flow field still cannot be clarified at the moment.