Visualization Test on Spray Impingement of CTL Fuel

At present, most of the researches on spray characteristics are focused on free injection cases. This paper researches the spray impingement phenomenon of CTL fuel in a visualization test system by high-speed photograph technology and discusses the influences of ambient pressure and wall distance on impingement process. The results show that the wall diffusion radius increases linearly, the entrainment height increases firstly and then keeps stable gradually and the velocity of spray tip decreases rapidly with CTL continuation injection. When the ambient pressure increases, impingement wall time delays and initial impingement radius increases, and it is the same situation with increasing wall distance. Simultaneously, increasing ambient pressure can reduce the spray diffusion radius and raise the entrainment height, while it displays an opposite trend with increasing wall distance. The contrast test results of spray wall-impingement for both of two fuels show that CTL fuel exhibits a slightly later spray impingement wall, a shorter spray diffusion radius and a thinner entrainment height than No.0 diesel. The research results have a certain reference value to guide the application of CTL in diesel engines. Due to the restriction of combustion chamber geometry, the fuel spray impingement plays a leading role in the mixture formation which is the basis of thermodynamic process in the engine cylinder, especially for small and medium-sized diesel engines. Spray impingement shows significant advantages in enhancing the spray diffusion, accelerating the mixture forming and improving the engine performance. However, the film on the wall results from fuel impinging will cause the secondary atomization which is an important reason for the higher HC and PM emission. Therefore, the characteristic of fuel spray impingement directly determines the subsequent combustion quality and emissions quality [1 similar to 4]. The synthetic oil from coal (Coal-to-Liquids, CTL), is an excellent cleaning alternative fuel for diesel, produced by Fischer-Tropsch synthesis method in the early 20th century. Compared with the ordinary diesel fuel, the CTL has a higher cetane number, a lower process temperature, a lower density and a lower viscosity property, etc. International research for CTL as substitute fuel in a compression-ignition engine begins at the end of the 20th century. In recent years, the researches for application of CTL in engine include the fuel spray, combustion, emissions, applicability and life cycle assessment, etc. The different physical and chemical properties about CTL and ordinary diesel, including oil density, viscosity, surface tension and volatile, lead to a great different fuel spray process each other. At present, most of the researches on spray characteristics about CTL are focused on free injection cases[5 similar to 7], but on wall impinging related research is rarely. In the study on the basis of the free spray characteristics of CTL[8], the author further researches the spray impingement behavious of CTL in a spray visualization test system, focusing on ambient pressure (Pb) and wall impinging distance (Z) influence on vertical impingement characteristics of CTL fuel, and compares it with ordinary diesel fuel spray impingement. This research result will provide a useful theoretical foundation to the development of CTL fuel spray theory and will have a certain reference value to guide CTL application in diesel engine.