5.4 Conclusion

In order to study macroscopic spray characteristics and autoignition properties of different type of nozzles, a constant volume combustion chamber was manufactured and diesel engine conditions were obtained in the experimental setup. Four different kind of nozzle and three different kind of fuel were tested in the test facility. A CCD camera was used to obtain spray images and a digital imaging program was used to obtain corrected images. Digitalization allows objectively determining spray characteristics. Experimental results were compared with well-known spray correlations published in the literature. From the analyses of the exper-imental study, the following conclusions are revealed.

1. Conicity and hydrogrinding increase discharge coefficients. Convergent nozzle has higher and divergent nozzle has smaller discharge coefficients. All the nozzles orifices experience supercavitation condition. However, the convergent nozzles may retard the onset of cavitation to the higher injection pressures.
2. The spray liquid penetration starts from zero velocity at the nozzle exit and reaches maximum velocity at around breakup time.
3. Spray liquid penetration decreases as the ambient pressure or temperature increases. Higher injection pressure, lower injection quantities have increasing effect and conical nozzles (divergent and convergent) have decreasing effect on spray liquid penetration.
4. Spray cone has wider angles at the initial stages of spray evolution. Cone angle decreases as the spray penetrates, and, after the spray developed enough, the spray cone angle settles to constant value.
5. Spray cone angle increase as the ambient pressure increase. Injection pressure and conicity have incon-siderable effect on developed spray cone angle.
6. Generally, autoignition observed at unsettled down-stream part of the injected fuel spray. The indefinite location of autoignition gets closer to the injector tip