Analysis of spray structure characteristics

The paper deals with numerical and experimental analyses of mixture formation and combustion processes in diesel engines. Numerical simulations are quick, accurate and cost efficient and are good compensation to experiments, which are usually longer lasting and more expensive. Numerical analyses were made using the computation fluid dynamic (CFD) program FIRE and 1D simulation program AVL Hydsim. In the present paper the influence of different mixtures of commercial diesel fuel, D2, with biodiesel fuel B100 has been studied. Numerical analysis results are compared to the experimental observations of the two-phase flow available from the literature and to the experimental measurements made in our laboratory. Experiments were made on injection system test bed Friedmann-Maier type 12 H 100-h. This type of test bed allows for measurements of the needle lift and the amount of injected fuel. The penetration length and the spray cone angle of injected fuel were measured by taking photos. Experimental results were compared with numerical results from FIRE and Hydsim. Due to the limited options in the experimental measurements, only the needle lift, spray cone angle, and penetration length of spray were compared. A comparison of the Sauter mean diameter has been done between both numerical programs FIRE (3D) and Hydsim. The results obtained from numerical simulations agree well with experimental results and confirm possible use of biofuels in diesel engines. Introduction Global atmosphere pollution has become a serious problem of today. The emissions from the combustion of fossil fuels contribute a notable part to this pollution. Biodiesel fuels, an alternative for petroleum fuel, are the acid esters of triglycerides that originate from vegetable or animal sources. This renewable source significantly reduces exhaust emissions. While biodiesel fuel has similar physical properties, no major engine modifications are necessary. Nevertheless, the differences in physical properties may result in spray anomalies causing an unnecessary increase of pollutive emissions. Fuels with a higher density and viscosity show shorter penetration lengths and greater spray cone angles [4–8]. Applicative research based on the fundamental knowledge of twophase flows is used for the investigations of the fuel spray characteristics in individual industrial devices. They result in numerous empirical correlations, which are common in today’s practice and deliver important data for the development of spray mathematical models. Experimental details For simulating spray formations, fuel physical properties and necessary injection characteristics were measured. Experiments were made on injection system test bend Friedmann-Maier Type 12 H 100-h. This type of test bend allows measurements of the needle lift, injection pressure and injection rate, at three different camshaft speeds (550, 800 and 1100 rpm) at full load. Injection characteristics at 1100 rpm for diesel and biodiesel fuel are shown in Figures 1 and 2. Figure 1: Diesel injection process characteristics at 1100 rpm Figure 2: Biodiesel injection process characteristics at 1100 rpm In order to validate numerical result, spray development was filmed using a high-speed camera.