Reo Kai

• Kyushu University

Furan groups play significant roles in the combustion of low-rank coal. We employed ReaxFF MD to investigate the pyrolysis and oxidation processes of furan (FR) and benzofuran (BFR) under various oxygen contents and temperatures. The results show that the initial reaction of FR groups pyrolysis is FR/BFR → R-unstable carbon chain + CO, with all oxy...

A thorough understanding of the Differential Diffusion (DD) effect is necessary for properly predicting combustion processes fueled by NH3/H2, especially because of the higher diffusivity of H 2 compared with thermal diffusivity and diffusivities of O2 and NH3. It is a common practice in turbulent combustion simulations to ignore the effects of DD...

In this study, a semi-implicit pressure-based scheme which can suppress the spurious pressure oscillations is developed for real fluid flows. Conservation properties relevant to the proposed scheme are investigated through one-dimensional numerical simulations of the nitrogen interface advection. The efficiency and validity of this scheme are caref...

Preferential diffusion plays an important role especially in hydrogen flames. Flame stretch significantly affects the flame structure and induces preferential diffusion. A problematic phenomenon occurring in real combustion devices is flashback, which is influenced by non-adiabatic effects, such as wall heat loss. In this paper, an extended flamele...

One-dimensional numerical simulations of an unstretched propagating hydrogen/air premixed flame and two-dimensional numerical simulations of outwardly propagating hydrogen/air laminar premixed flames are performed using a flamelet-generated manifold (FGM) method. The effects of considering preferential diffusion and flame stretch in the FGM method...

To design a low-emission hydrogen-fired gas turbine combustor, prevention of flashback is one of key issues. However, the detailed measurement of flashback is difficult and expensive, especially at the actual operation condition. Therefore, the high-precision numerical simulation technology is important to study the mechanism and countermeasures of...

A new semi-implicit pressure-based solver considering the real gas effect is developed and tested. The advantage of the semi-implicit solver is that it can take a large time step, which makes the calculation speed faster than the classical density-based explicit solver. The comparison of the calculation speed between the explicit density-based solv...

Large-eddy simulation (LES) coupling with a non-adiabatic flamelet progress variable (NA-FPV) approach with reconstructed flamelet chemistry states is employed to simulate the hot coke oven gas (HCOG) reforming process. In the NA-FPV model, the chemistry states are first computed based on the correction factor for enthalpy defects and then modified...

Direct numerical simulation is conducted to address the detonation–turbulence interaction in a stoichiometric hydrogen/oxygen/argon mixture. The argon dilution rate is varied so that the mixture composition is 2H 2 + O 2 + 7Ar and 2H 2 + O 2 + Ar to discuss the effects of cell regularity on the sensitivity to turbulence. Turbulent Reynolds number a...

Effects of species diffusion models on the laminar burning velocity SL of lean hydrogen-air premixed flame are investigated by performing one-dimensional numerical simulations of lean hydrogen-air premixed flames at an equivalence ratio of 0.5. Maxwell-Stefan (MS) diffusion, mixture-averaged (MA) diffusion, and unity Lewis number diffusion are comp...

A flamelet-generated manifold (FGM) method that explicitly considers the preferential diffusion effect, referred to as FGM-PD method, is employed for large-eddy simulations (LESs) of a lean-premixed H2/air low-swirl lifted flame, and the validity is examined by comparing with the experiment. First, the applicability of the FGM-PD method is investig...

The flame–turbulence interaction and statistical behavior of the surface density function (SDF; i.e. magnitude of the reaction progress variable gradient) in the vicinity of the wall for a stoichiometric methane-air flame are investigated using a three-dimensional direct numerical simulation of a turbulent premixed V-flame interacting with an isoth...

Large eddy simulation (LES) employing a flamelet model coupled with an artificial neural network (ANN), namely the LES/flamelet/ANN is developed for supercritical oxy-fuel combustion and its validity is investigated in detail. An ANN is introduced to reduce the size of the flamelet library for non-adiabatic three gas-stream conditions of a real sup...

This work presents a detailed numerical investigation of dilute spray lifted flames experimentally studied by O’Loughlin and Masri at the University of Sydney (O’Loughlin and Masri, Combust. Flame 2011), with a focus on understanding the mechanism that governs flame stabilization under the influence of sprays. Two ethanol flames with varied spray m...

Large-eddy simulation (LES) employing a flamelet/progress-variable approach that considers the real gas effect is applied to liquid oxygen/ gaseous hydrogen (LOX/GH2) supercritical combustion, and the breakup mechanism of the LOX core is investigated in detail by comparing it to that in the inert case. The results show that in the reactive case, O2...

Design of Compression Ignition (CI) engines with improved thermal efficiencies needs better understanding of the heat transfer mechanism from spray flame to the combustion chamber wall. In this regard, heat transfer occurring during the interaction between impinging spray flame and wall, under CI engine-like conditions, is investigated in this stud...

To realize further low carbon monoxide (CO) emissions for industrial gas turbine combustors, the elucidation of the CO formation and reduction mechanism for lean premixed combustion is crucial. In this study, one-dimensional numerical simulations using a detailed reaction mechanism approach and two-dimensional numerical simulations using a detailed...

Owing to the increasing worldwide demand for natural gas, the development of a large submerged combustion vaporizer is required. Its burner is equipped with a water spray nozzle to reduce nitrogen oxides, and a practical simulation method is required for the optimal design. The non-adiabatic flamelet approach can predict the combustion emissions an...

In this study, the applicability of the flamelet approach to numerical simulations of hydrazine (N2H4)/nitrogen tetroxide (NTO, N2O4) combustion, in which hypergolic ignition and thermal decomposition occur, is investigated in terms of two-dimensional numerical simulations of two types of N2H4/NTO jet flames, namely, the gaseous N2H4/NTO jet flame...

To design a gas turbine combustor for low emissions, carbon monoxide (CO) generated near the cooled wall is one of the important indexes. However, the measuring of CO concentration is difficult in experiments in actual conditions of high pressure and temperature. In this study, in order to take the heat loss effect on the cooled wall into account,...

Conjugate heat transfer analyses of methane/air premixed flames propagating toward walls are performed without employing any wall model in terms of one- and two-dimensional numerical simulations, and the flame-wall interaction is investigated in detail. To describe the combustion reaction of methane, a two-step global reaction model is used. In one...

The applicability of Large-Eddy Simulation (LES) for analyzing the phenomenon of turbulent spray flame impinging on a wall, under compression ignition (CI) engine-like environment is assessed in this paper. The LES results are compared with those of Direct Numerical Simulation (DNS), and it is demonstrated that LES can be successfully applied for r...

Conjugate heat transfer analyses of premixed flames propagating toward the insulation or Al alloy wall are performed for C1 to C3 alkanes and H2 flames at different equivalence ratios of φ = 0.6, 0.8, 1.0 and 1.2 under a high pressure condition of 2MPa in terms of one-dimensional numerical simulations with detailed reaction mechanisms (70 species a...

Spray reactive flow finds application in various technical devices, and due to the complex nature, their optimization is very challenging, requiring proper modeling of turbulence/chemistry interactions as well as of the contribution from spray evaporation. This work presents a study of sub-grid scale combustion models, where relevant assumptions on...

In order to meet the increasing demand of natural gas worldwide, the development of large-scale and environmentally friendly submerged combustion vaporizer (SCV) burners, which can vaporize massive liquefied natural gas (LNG), is strongly desired. One of good solutions to reduce nitrogen oxides emissions is the installation of water spray system in...

A large-eddy simulation (LES) employing a non-adiabatic flamelet generated manifold approach, which can account for the effects of heat losses due to radiation and cold walls, is applied to NH3/CH4/air combustion fields generated by a swirl burner, and the formation mechanisms of NO and CO for ammonia combustion are investigated in detail. The amou...