Noritsune Kawaharada

Evaluation of Mass Flow Rate Distribution in Diesel Fuel Spray by L2F

A laser 2-focus velocimeter (L2F) has been applied for measurements of velocity and size of droplets of diesel spray and an evaluation method of mass flow rate has been proposed. The L2F has a micro-scale probe which consists of two foci. The distance between two foci is 17μm. The data acquisition rate of the L2F has been increased to 15MHz in order to capture every droplet which appears in the measurement volume. The diesel fuel spray injected intermittently into the atmosphere was investigated. The orifice diameter of the injector nozzle was 0.113mm. The injection pressure was set at 40MPa by using a common rail system. Measurements were conducted on ten planes 5 to 25mm downstream from the nozzle exit. It was clearly shown that the velocity of droplet was the highest at the spray center. The size of droplet at the spray center decreased downstream within 15mm from the nozzle exit. The mass flow rate near the spray center was found to be larger than that in the spray periphery region. It was confirmed that the fuel mass per injection evaluated by the proposed method based on the L2F measurement was near to the injected mass in a plane further than 15mm from the nozzle exit. However, fuel mass was underestimated in a plane closer to the nozzle exit. The probability density of infinitesimal distance between surfaces of adjacent droplets increased remarkably near the spray center 5 and 12mm downstream from the nozzle exit. As infinitesimal distance can be thought as an indicator of a highly dense region, it is understood that underestimation of fuel mass near the nozzle exit is due to the highly dense region. The diameter of the region, where the highly dense region was observed, was estimated as an order of 0.2mm in a plane 5mm downstream from the nozzle.Copyright

Inhomogeneous Structure in High-Speed and High-Number-Density Sprays

A L2F (Laser 2-Focus velocimeter) was applied for the measurements of the velocity and size of droplets in diesel fuel sprays. The micro-scale probe of the L2F has an advantage in avoiding the multiple scattering from droplets in a dense region of fuel sprays. A data sampling rate of 15MHz has been achieved in the L2F system for detecting almost all of the droplets which passed through the measurement probe. Diesel fuel was injected into the atmosphere by using a common rail injector. Measurement positions were located in the planes 15, 20, and 25 mm apart from the injector nozzle exit. Measurement result showed that the integral time scale of turbulence in size was nearly the same as the one in frequency. And the integral time scale of turbulence in velocity was about two times larger than the time scale of size and frequency.Copyright