Quantitative characterisation of diesel sprays using digital imaging techniques

In recent years, research in diesel engine technology has been motivated by the desire to meet increasingly stringent emissions standards without unacceptable compromise of performance and efficiency. An important way to achieve this goal is to enhance the performance of the fuel injection system so that fuel/air mixing and combustion are made more complete. Unfortunately, the mechanism of fuel spray formation and the influence of fuel injection parameters on the resulting spray structure are still not very clear. It is therefore highly desirable to develop a reliable and efficient means for the quantitative analysis and characterisation of diesel sprays. This paper presents the application of digital imaging and image processing techniques for the quantitative characterisation of diesel sprays. An optically accessible, constant volume chamber was configured to allow direct photographic imaging of diesel sprays. A high-resolution CCD camera and a flash light source were used to capture the images of the sprays. Dedicated image processing software has been developed to quantify a set of macroscopic, characteristic parameters of the sprays including tip penetration, near and far field angles. The spray parameters produced using the software are compared with those obtained using manual methods. The results obtained under typical spray conditions demonstrate that the software is capable of producing more accurate, consistent and efficient results than the manual methods. An application of the imaging processing software to the characterisation of diesel sprays for a VCO nozzle is also presented and discussed.