GMUWCollaborative Research Lab Near-Nozzle Diesel Spray Imaging Using Visible Light T.E. Briggs & P. V. Farrell Diesel combustion systems must continue to evolve to meet future emissions regulations - aftertreatment will not be sufficient to meet the requirements Improving combustion requires understanding the spray physics well enough to design injection systems that will enable the required combustion performance It is not sufficient to know the downstream spray conditions such as drop sizes and mass fractions - we must know how the spray is behaving from the injector onward Strong light scattering in the dense spray near the injector has prevented typical spray measurement techniques from providing information on the spray structure or conditions X-ray imaging has been shown to be immune from the problems of scattering and has given mass and volume fraction data on the near-injector spray. The technique is expensive and only provides averaged results, however. By using two visible wavelengths of light and an absorbing dye in the fuel, sufficient redundant information about the light scattering can be obtained to remove the scattering signal from a spray image, yielding a purely absorption- based imaging technique. This provides equivalent results to the x-ray imaging method, but at a significant cost reduction and with instantaneous imaging capability. The area of interest is the burgundy zone at the left. The spray is beginning to break up and shed drops that will provide the initial combustion field. The rest of the combustion process is determined by what happens here. The diagnostic method is relatively simple. Two closely-spaced wavelengths are used to back-illuminate the spray. The light beams are separated spectrally and imaged side-by-side on a high speed camera. The scattering in each image is identical, so it may be removed by dividing one image by the other. The remaining information is due to the absorption of the light by the dye in the fuel. This signal is directly related to the mass of fuel that was along the path the light traveled. Once the mass is known, the volume fraction of the liquid fuel in the spray may be determined as well. 532 nm488 nm 23mm 100  s ASI This is what the camera sees. Approximately 20 frames are captured for each injection event. The images are separated and normalized using Matlab. They are then processed to generate an absorption image and a mass image of the spray at each timestep. Optical (mass in g) X-ray (mass in  g) 23 mm Beam diameter 100  s ASI Here is a comparison of the final mass image from the visible technique (on the right) with a corresponding image of the same spray using the x-ray technique (on the left). Note that the visible image captures much more detail of the spray due to the instantaneous nature of the measurement. Averaging temporally as the x-ray method does leads to lower-mass regions not being adequately imaged - the fuel is in a different location each injection, so the averages tend to give a zero result. Our current efforts are to obtain quantitative agreement with the x-ray measurement and to add volume fraction calculations to the processing code.