An overview of the fundamentals of droplet evaporation and combustion calculation at pressures above the critical values for the pure fuel or propellant injected in the liquid phase is provided. The basic methodologies for determining highpressure phase equilibria are outlined first, and the issues concerning the mutual diffusion coefficient in the critical state of a binary mixture are discussed. Then, the importance of a scheme to switch from the subcritical to the supercritical evaporation mode in the numerical simulation of droplet evaporation and combustion in a supercritical environment is stated. Finally, the condition under which the droplet undergoes transition from the sub-to-supercritical evaporation regime is identified in terms of the initial parameters such as temperature, density, heat capacity, and thermal conductivity of ambient gas and droplet.
Fluid dynamics and numerical simulation on cryogenic jets under supercritical pressures is reviewed in this paper. First of all the mechanism of cryogenic jets under a supercritical pressure is discussed through the recent study. Then the evaluation of thermal and transport properties of gases is described. The recent important tasks of the combustion models and numerical methods are discussed. Finally the examples of the numerical simulations are presented to show the mixing feature of the planar and coaxial jets under supercritical pressures.
In this article, large-eddy simulation (LES) is conducted for a liquid oxygen (LOX) and gaseous hydrogen (GH2) shear-coaxial jet flame at supercritical pressure. In this LES framework, the laminar flamelet approach is employed for turbulent combustion modeling, and the real-fluid thermodynamics and transport are considered. The present LES framework is applied for simulating LOX/GH2 combustion experiment under supercritical pressure (6 MPa), which is conducted by the high-pressure test facility P8 at DLR Lampoldshausen. By analyzing the obtained LES results, the flowfield features of a cryogenic shear-coaxial jet flame are explored. The integral length scales of turbulent coherent structures are calculated from the present LES framework and show fair agreement when compared with available experimental data. The effects of the numerical dissipations inherent in interpolation schemes are also investigated and recommendations are provided for future studies.
Carbon dioxide (CO2) emissions from thermal power plants are one of the primary causes of global warming. As global demand for energy increases while environmental regulations tighten, novel power generation cycles are being developed to meet market needs while accommodating green requirements. To meet this demand in the global market, Toshiba has been engaged in the development of an environmentally conscious thermal power generation system applying a supercritical CO2 cycle (Allam cycle) developed by 8 Rivers in cooperation with U.S. companies: 8 Rivers Capital, NET Power, LLC; Chicago Bridge & Iron Company; and Exelon Corporation. The Allam cycle is an approach (with high pressure, low pressure ratios, oxy-fuel combustion and CO2 as a working fluid) that efficiently produces power in a compact plant, avoids NOx emissions, makes efficient use of clean-burning natural gas and can generate high-pressure carbon dioxide for enhanced oil and gas recovery in the field. We have been engaged in the development of a 25 MW-class pilot plant. In this project, Toshiba has been assigned the development of key equipment, including a high-temperature and high-pressure turbine and a combustor, for this thermal power generation system aimed at realizing a 295 MW-class commercial plant.
In this review, development and future plan of IHI original gasifier TIGAR® (Twin Ihi GAsifieR) are described. IHI has developed gasification technology for lignite coal, TIGAR® is applied the Circulating Fluidized Bed technology, operated under atmospheric pressure and the steam gasification agent. TIGAR® gasifier features a simple coal feed system with coarse particle & high moisture, and slag free gasifier because of low gasification temperature. Furthermore TIGAR® has the advantage to utilize a various kinds of feedstock such as a biomass not only the coal because of the atmospheric pressure which is not required the pressurized and dry feeding. Through various fundamental researches, the design concept of gasifier has been obtained. And 6 tons/day pilot plant was built for the verification of the process in IHI factory. Those results showed that syngas with high calorie and high hydrogen content can be produced. After successful operation of pilot plant, IHI has built 50 tons/day prototype plant at Fertilizer factory of Indonesia in 2014 and is ongoing the demonstration operation from 2015. IHI will have a plan to carry out the demonstration of TIGAR® process for about 4,000 hours until 2017. IHI is targeting a highly efficient use of unused energy by TIGAR® technology.
An experimental study has been performed for comparing the atomization behavior during spheroid-type evaporation on a heated surface between oil-in-water (O/W) and water-in-oil (W/O) emulsion droplets. The base fuel of the emulsions was n-dodecane, and the water content set to 20 % in volume. The effect of the initial droplet size on the atomization behavior was examined as well as that of the surface temperature. For the O/W emulsion, phase separation occurred at the early stage of evaporation and a water-based fluid was enveloped by a shell of the base fuel. Disruptive microexplosion, which corresponds to intense secondary-atomization, took place earlier due to explosive boiling of the fluid. Both the minimum waiting time and the waiting time for the disruptive microexplosion decreased with increasing the surface temperature. The waiting time was scarcely affected by the initial droplet size, while the minimum waiting time increased with increasing the size. For the W/O emulsion, intermittent puffing microexplosion and/or the disruptive microexplosion occurred. Aggregation and coalescence of water and the phase separation appeared to occur prior to the disruptive microexplosion at higher surface temperatures, while the phase separation hardly occurred and the droplet disappeared after the intermittent puffing microexplosion at lower surface temperatures. The occurrence of the disruptive microexplosion was delayed due to longer time period until the phase separation than that for the O/W emulsion. The intermittent puffing microexplosion retarded the phase separation. The waiting time was either scarcely affected by the initial droplet size, while the minimum waiting time increased with increasing the size.