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In this study, the authors analyze the concentration distribution of an evaporative spray mixture with LIEF (Laser induced exciplex fluorescence) method, which is a type of optical measurement. LIEF method is one of the optical measurements for obtaining the spray concentration distribution for separating vapor/liquid phases based on the fluorescence characteristics. In this paper, a quantitative concentration distribution analysis method for wall impingement spray in heterogeneous temperature field has been proposed. Then, a series of experiments were performed in varying injection pressure and ambient density. As a result, a two-dimensional concentration distribution was obtained for the free spray and wall impingement spray.

n-Tridecane is a low boiling point component of gas oil, and has been used as a single-component fuel for diesel spray and combustion experiments. However, no reduced chemical kinetic mechanisms for n-tridecane have been presented for three-dimensional modeling. A detailed mechanism developed by KUCRS (Knowledge-basing Utilities for Complex Reaction Systems), contains 1493 chemical species and 3641 reactions. Reaction paths during ignition process for n-tridecane in air computed using the detailed mechanism, were analyzed with the equivalence ratio of 0.75 and the initial temperatures of 650 K, 850 K, and 1100 K, which are located in the cool-flame dominant, negative-temperature coefficient, and blue-flame dominant regions, respectively.

Methyl butanoate (MB) and methyl decanoate (MD) are surrogates for biodiesel fuels. According to computational results with their detailed reaction mechanisms, MB and MD indicate shorter ignition delays than long alkanes such as n-heptane and n-dodecane do at an initial temperature over 1000 K. The high ignitability of these methyl esters was computationally analyzed by means of contribution matrices proposed by some of the authors. Due to the high acidity of an α-H atom in a carbonyl compound, hydroperoxy radicals are generated out of the equilibrium between forward and backward reactions of O₂ addition to methyl ester radicals by the internal transfer of an α-H atom in the initial stage of an ignition process. Some of the hydroperoxy methyl ester radicals can generate OH to activate initial reactions. MB has an efficient CH₃O formation path via CH₃ generated by the β-scission of an MB radical which has a radical site on the α-C atom to the carbonyl group.

Three-dimensional large eddy simulation (LES) has been conducted for a diesel spray flame using KIVALES which is LES version of KIVA code. Modified TAB model, velocity interpolation model and rigid sphere model are used to improve the prediction of the fuel-mixture process in the diesel spray. Combustion is simulated using the Eddy-Dissipation model. CIP method was incorporated into the KIVALES in order to suppress the numerical instability on the combustible flow. The formation of soot and NO was simulated using Hiroyasu model and KIVA original model. Three different grid resolutions were used to examine the grid dependency. The result shows that the LES approach with 0.5 mm grid size is able to resolve the instantaneous spray with the intermittency in the spray periphery, the axi-symmetric shape and meandering flow after the end of injection as shown in the experimental results.

Large Eddy Simulation (LES) is applied to non-evaporative and evaporative diesel spray simulations. KIVALES, which is LES version of KIVA code, is used as the LES computational code. Modified TAB model is used as breakup model, and interpolated donor cell differencing scheme is employed to calculate convective terms. To validity LES simulation, LES results using KIVALES are compared with experimental results and simulated results with conventional RANS approach using KIVA3V res.2. The results show that the LES simulation of non-evaporative spray depends on the grid size in comparison with RANS simulation, and good agreement is obtained between experimental results and the LES results with fine grid (720,000 cells). Furthermore, asymmetric non-evaporative spray which has intermittency at the outer edge of sprays is simulated, since instantaneous turbulent flow field can be predicted directly in LES case.

It is significant for understanding the phenomena in a stratified charge engine and an SI engine with direct injection system to carry out the fundamental research. The experiments were conducted in a constant volume chamber with atmospheric condition. The pre-mixed charge composed of ethylene and air was charged with various equivalence ratio, the second charge with the same composition was injected into the chamber, thereafter, the combustion started by a spark plug. The phenomena were analyzed by use of the experimental results of shadowgraph, [OH] natural emission, pressure history and NOx and UHC in the exhaust gas.

This paper confirms a structure for the soot formation process inside a burning diesel jet plume of oxygenated fuels. An explanation of how the soot formation process changes by the use of oxygenated fuel in comparison with that for using a conventional diesel fuel, and why oxygenated fuel drastically suppresses the soot formation has been derived from the chemical kinetic analysis. A detailed chemical kinetic mechanism, which is combined with various proposed chemical kinetic models including normal paraffinic hydrocarbon oxidation, oxygenated hydrocarbon oxidation, and poly-aromatic hydrocarbon (PAH) formation, was developed in present study. The calculated results are presented to elucidate the influence of fuel mixture composition and fuel structure, especially relating to oxygenated fuels, on PAH formation. The analysis also provides a new insight into the initial soot formation process in terms of the temperature range of PAH formation.

Diesel sprays injected into a combustion chamber of a small sized high-speed CI engine impinge surely on a piston surface and a cylinder wall. As a consequence, their vaporization, mixture formation and combustion processes are affected by impingement phenomena. And the other important factors affecting on the processes is the injection pressure. Then, the distribution of the vapor concentration in a single diesel spray impinging on a flat and hot wall was experimented by the exciplex fluorescence method, as a simple case. The injection pressure was varied in the range from 55 MPa to 120 MPa. It is found that the distribution of the vapor concentration in this case is much leaner than that in the case of the low injection pressure of 17.8MPa.

This paper deals with the particle distribution in Diesel spray under the non-evaporating condition from the analytical aspect based on our experimental results. In the analysis, TAB method of KIVA II code and the k-ε turbulent model were used, and the mono-disperse distribution of the initial parcel's diameter, whose size equals to the nozzle hole diameter, was utilized in conjunction with the breakup model. The size distribution of atomized droplets (i.e. the χ-squared distribution function) is justified with the degree of freedom. It is shown that the ambient gas, which is initially quiescent, is induced and led to a turbulent gas jet. The turbulent gas jet which has a equivalent momentum with the Diesel spray was also examined by Discrete Vortex method. The quantitative jet growth was shown to be possible for the estimation and determination in its initial boundary values at the nozzle.

The purposes of this study are to clarify the atomization mechanism, the change over time in droplet size distribution, and the change in spray characteristics dependent on back pressure on diesel fuel spray. Diesel spray injected into a quiescent gaseous environment under high pressure is observed by taking direct microscopic photographs varying the moment of exposure, the back pressure, and the ambient density. The results show that the mechanism of spray atomization is divided into 4 processes, and spatial distribution of breakup droplets and a droplet volume rate are assessed for the whole spray region. Total and local distributions of droplet size are expressed by empirical equations as a function of time elapsed from the moment of injection. It is confirmed that the uniformity of the distribution, Sauter mean diameter of droplets, and droplet production rate change with time. Mean droplet diameter is further described in relation to the pressure drop and the ambient density.