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 Engine Combustion Network (ECN) is a worldwide collaboration on engine spray combustion with a common set of standardized injectors and spray conditions. We report a set of optical measurements of spray and combustion images and derived parameters of “Spray B”, a three-hole Diesel injector in a small-bore optical engine. In addition to the standard ECN conditions, a variation of ambient temperature and density, fuel rail pressure, and swirl ratio were also investigated. We developed a simple optical method to quasi-simultaneously image both liquid and gas phase of the fuel spray as well as combustion at 56 kHz by retro-reflection of pulsed LED light from the firedeck. From the image data, liquid penetration length, fuel vapor penetration, spray spreading angle, flame luminosity, ignition delay, and ignition location were extracted. The results show a physically reasonable variation with different operating conditions and match well with existing results from vessels and engines in the ECN database. Under standard ECN conditions, the liquid length stabilizes shortly after the gas phase impinges on the bowl wall (diameter 47.4 mm), while ignition occurs at almost the same time as impingement near the bowl wall. Under different conditions, ignition may occur before or after gaseous spray impingement, depending on the ambient gas temperature and density. With decreasing ambient temperature, ignition delay is longer, and ignition location moves downstream, first towards the bowl wall and then in the direction of swirl. With a higher swirl ratio, ignition occurs later and is located more downstream in the direction of swirl. Also, shortly before impinging on the bowl wall, the vapor penetration is decreased while liquid length is nearly not affected.