Combustion Engine Characterization and Development by Means of Laser Diagnostics

Sammanfattning: Planar laser induced fluorescence (LIF) has been utilized for two-dimensional imaging in combustion environments. By using tracer LIF the fuel distribution prior to ignition has been monitored in a GDI-engine. The results obtained were used to determine the influence from various engine parameters such as nozzle type, spray angle, duration of injection, start of injection, piston shape, etc. Two fundamentally different concepts for controlling the stratification was evaluated and compared. In addition, the results were compared with CFD-modelling performed at Volvo Car Corporation. Hence, the results from the performed laser diagnostics were in direct use in the work of developing a new engine concept. Due to the strictly limited optical access of the GDI-engine an endoscopic detection system was developed and used for monitoring the distribution of gaseous fuel inside the combustion chamber. The endoscope provided an unrestricted view in areas of special interest that could not be reached by conventional through the piston detection. Raman spectroscopy has been applied to perform cycle-resolved measurements of the air/fuel-ratio in a running engine. The technique proved capable of providing quantitative data from single-shot measurements. Demonstrations of such measurements have been performed in both GDI- and HCCI-engines. In addition, a technique for making in-situ absolute calibration of fuel tracer LIF images using Raman scattering is outlined in detail. Different optical techniques have been utilized for primarily investigations of the mixture preparation and combustion in HCCI-engines. Fuel tracer LIF was used to make two-dimensional, cycle resolved, measurements of the fuel distribution. From this data the degree of homogeneity of the charge could be determined for different mixing strategies. Raman scattering provided cycle resolved absolute values of the air/fuel-ratio. Spontaneous emission from the flame was collected through various filters with an image intensified CCD-camera and with a high speed framing camera. Absorption measurements using a continuos light source revealed useful information for future diagnostics. A high-speed laser and imaging system has been adapted and used for true single-cycle resolved measurements in combustion engines. This technique provided a unique ability to study various combustion parameters with a high temporal resolution and without any averaging effects caused by cycle-to-cycle variations. The in-cylinder spray and fuel distributions were investigated in a GDI-engine by means of fuel tracer LIF. The early flame development in the same engine was visualized by high-speed imaging of OH-radicals. The highly stochastic ignition and combustion characteristics of HCCI engines were thoroughly studied. The high-speed imaging technique proved to be a crucial tool for mapping the fuel concentration distribution during the short combustion events. Both two- and three-dimensional concentration maps were generated to visualize the gradual consumption of the fuel that is unique to HCCI combustion. Primary investigations of two-photon laser-induced fluorescence for detection of carbon monoxide have been performed in the laboratory. The applicability of the technique in a LPP gas turbine combustor was briefly investigated at Volvo Aero Corporation.