A novel technique for measuring droplet temperatures has been demonstrated. Laser-induced phosphorescence from thermographic phosphors, seeded to distilled water and iso-octane, was used to measure temperatures of single falling droplets. The phosphors were excited by the fourth and third harmonics of a Nd:YAG laser. The subsequent emission was evaluated by spectral and temporal investigations of the thermographic phosphors Mg4FGeO6:Mn and La2O2S:Eu, respectively. The spectral and the temporal methods permitted temperature measurements of free-falling droplets up to 433 K. Results from both methods, which show an estimated accuracy of better than 1%, are presented.
To study the effect of different injection timings on the charge inhomogeneity, planar laser-induced fluorescence (PLIF) was applied to an operating engine. Quantitative images of the fuel distribution within the engine were obtained. Since the fuel used, iso-octane, does not fluoresce, a dopant was required. Three-pentanone was found to have vapour pressure characteristics similar to those of iso-octane as well as low absorption and suitable spectral properties.A worst case estimation of the total accuracy from the PLIF images gives a maximum error of 0.03 in equivalence ratio. The results show that an early injection timing gives a higher degree of charge inhomogeneity close to the spark plug. It is also shown that charge inhomogeneity gives a more unstable engine operation. A correlation was noted between the combustion on a cycle to cycle basis and the average fuel concentration within a circular area close to the spark plug center. The correlation coefficient when a second order polynomial was fitted reached a value of -0.8 when the engine operated with a high degree of inhomogeneity. The highest correlation coefficient between the duration of 0-0.5% heat released and the average fuel concentration was obtained within a radius of approximately 5-10 mm from the spark plug. When the standard disc-shaped combustion chamber was replaced with a turbulence generating geometry, the inhomogeneity of the charge became very low, independent of injection timing. No cycle to cycle correlations between fuel/air equivalence ratio and combustion were then noted.
A tunable KrF excimer laser operating at 248nm is used for visualization of water vapor (H 2 0 ) at engine-like conditions by two-photon laser-induced fluorescence (LIF). The effects of twophoton absorption in water, laser sheet focusing and two-dimensional fluorescence imaging conditions are discussed, and an estimation of the reliability of the image data is given. The water vapor content measured close to the spark plug prior to ignition in a high-pressure combustion cell is correlated to the ensuing combustion rate, which is determined from the evolving pressure during combustion. The combustion rate is shown to be dependent on the water vapor concentration close to the spark plug prior to ignition, where a high water concentration yields a slow combustion. Using two-photon LIF of water vapor, the influence of residual gases on cycle-to-cycle variations is also investigated in a running spark-ignition (SI) engine. With a low inlet manifold pressure, a correlation coefficient of 0.6 is found between the combustion rate and the residual gas concentration close to the spark plug at the time of ignition. Further, a fast combustion in one cycle is found to yield more residual gases in the subsequent cycle.
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