Planar Visualization of Vapor and Liquid in a Spray Plume

In liquid fueled combustion systems it is necessary for the fuel to vaporize prior to combustion. As a result, a method to quantify the amount of vapor that exists in the spray plume is desired in order to help understand the evaporation process. Such results are also useful in validating detailed computer models of this same process. Unfortunately, such a measurement is very difficult in practice due to the complex interaction of the spray droplets with any method applied. The objective of the proposed effort is to develop a robust diagnostic method to quantify the planar concentration of fuel vapor, fuel liquid, and gas phase temperature in a spray plume. The method proposed is to use multi-angular light extinction using collinear laser beams of specific wavelengths generated by tunable diode lasers. The wavelengths selected will allow differences in the absorbed light to be used to quantify fuel vapor, fuel liquid and gas temperature. Laser extinction is a very robust reliable method and the use of differential absorption eliminates challenges with windows, droplets effects, and dense spray issues that tend to plaque laser sheet imaging methods typically used. In Phase I, laser absorption was successfully applied to determine fuel vapor concentration within a gasoline spray plume using existing lasers and available wavelengths. Several wavelength pairs were evaluated for performance and some limitations were identified with the existing lasers. This led to identification of other available lasers/wavelengths that should be pursued to optimize the system performance in Phase II. In addition, laser absorption was demonstrated for determining the gas phase temperature. A concept for doing these measurements simultaneously was developed which is straightforward. The framework for applying tomography (to generate planar images of the vapor and temperature fields) for multi-path, multi-wavelength TDLAS was established. Initial coding was carried out to allow planar reconstruction of an asymmetric spray. An initial opto-mechanical design (lasers, controllers, fiber optics, detectors) for a fully integrated system including the strategy to gather results from multiple angles was developed. In addition, light scattering models were developed in MatLab to simulate and account for known wavelength dependent scattering when using multiple wavelengths. In Phase II, the wavelengths for optimum simultaneous probing for fuel vapor and temperature will be finalized and procured. This step will be done in conjunction with establishing the necessary temperature dependent spectroscopy of gasoline for these wavelengths along with consideration for any interfering species (e.g., water, carbon dioxide). The expected improved performance using these wavelengths will be verified in gasoline sprays under non-reacting and reacting conditions and at high pressure conditions. The initial opto-mechanical design developed in Phase I will be refined and optimized for the recommended wavelengths. The tomography framework will be further evolved to incorporate the finalized opto-mechanical design. System software with an initial graphical user interface will be developed for a prototype instrument that will be assembled in Phase II. The overall system will be sufficiently refined such that it can be used for trade show demonstrations as well as for demonstration at potential customer locations. A number of OEM supporters have been identified and have provided letters indicating interesting in the instrument and allowing access to practical automotive research facilities with optical engines. A major instrument vendor has indicated support for helping ERC evolve the prototype to a commercial product and to provide appropriate licensing options. The proposed instrument fills a significant niche in the diagnostics market for spray characterization. If successful this instrument will be of great interest to a wide range of OEMs and component suppliers for fuel injectors for many applications. The data generated can be used to gain insight into the fuel injection process and also provide important validation data for models. With validated models, fuel injector and combustion designers can more efficiently develop higher efficiency, clean burning liquid fueled engines which will reduce fuel costs and reduce pollutant emissions.