Hirohide Furutani

Controlling branching in streamer discharge by laser background ionization

Irradiation with a KrF laser controlled the positive streamer branching in atmospheric argon gas. This laser irradiation changed the amount of background ionization before the streamer discharge. Measuring the ionization current allowed us to evaluate the initial electron density formed by the KrF laser. We observed characteristic feather-like branching structure and found that it was only suppressed in the irradiated region. The threshold of ionization density which can influence the branching was evaluated to be 5 × 105 cm−3. The relationship between the size of avalanche head and mean distance between initial electrons explained this suppression behaviour. These experimental results support that the feather-like structure originates from the branching model of Loeb–Meek, a probabilistic merging of individual avalanches.

Lattice Boltzmann simulation on continuously regenerating diesel filter

To reduce particulate matter (PM) including soot in diesel exhaust gas, a diesel particulate filter (DPF) has been developed. Since it is difficult to observe the phenomena in a DPF experimentally, we have conducted a lattice Boltzmann simulation. In this study, we simulated the flow in a metallic filter. An X-ray computed tomography (CT) technique was applied to obtain its inner structure. The processes of soot deposition and oxidation were included for a continuously regenerating diesel filter. By comparing experimental data, a parameter of soot deposition probability in the numerical model was determined.

Micro Gas Turbine Firing Kerosene and Ammonia

A demonstration test with the aim to show the potential of ammonia-fired power plant is planned using a micro gas turbine. 50kW class turbine system firing kerosene is selected as a base model. A standard combustor is replaced by a prototype combustor which enables a bi fuel supply of kerosene and ammonia gas. Diffusion combustion is employed in the prototype combustor due to its flame stability. Demonstration test of co-firing of kerosene and ammonia gas was achieved to check the functionality of the each component of the micro gas turbine. The gas turbine started firing kerosene and increased its electric power output. After achievement of stable power output, ammonia gas was started to be supplied and its flow rate increased gradually. 21kW power generation was achieved with 30% decrease of kerosene by supplying ammonia gas. Ammonia gas supply increases NOx in the exhaust gas dramatically. However post-combustion clean-up of the exhaust gas via SCR can reduce NOx successfully.© 2015 ASME

Breakdown plasma and vortex flow control for laser ignition using a combination of nano- and femto-second lasers

The breakdown plasma and successive flow leading to combustion are controlled by the combination of a nano-second Nd:YAG laser and a femto-second Ti:Sapphire (TiS) laser. The behaviors are captured by an intensified charged coupled device (ICCD) camera and a high-speed schlieren optical system. The TiS laser determines the initial position of the breakdown by supplying the initial electrons in the optical axis of focusing YAG laser pulses. We show that the initial position of the breakdown can be controlled by the incident position of the TiS laser. In addition, the ignition lean limit of the flammable mixture changes depending on the TiS laser incident position, which is influenced by hot gas distribution and the flow in the flame kernel.

System Analysis of IGFC With Exergy Recuperation Utilizing Low-Grade Coal

Integrated Coal Gasification Fuel Cell Combined Cycle (IGFC) is expected to be the most efficient power generation system in coal fired power generation systems [1,2]. The Japanese project of the Strategic Technical Platform for Clean Coal Technology (STEP-CCT) aims a target efficiency of 65% (HHV) with exergy recuperation. We have been analyzing the processes of the exergy recuperated Integrated Coal Gasification Combined Cycle (IGCC) and the Advanced IGCC (A-IGCC) [3] which is expected to be realized in 2040. Previous studies have indicated a limitation of the quantity of high temperature steam in the case of auto-thermal reactions with the fluidized bed coal gasifier in the A-IGCC, in particular for TIT 1500 °C class gas turbine. The Advanced IGFC (A-IGFC) system can reduce the exergy loss resulting from combustion, and its ‘exergy recuperation’ is appealing. The waste heat exhausted from the fuel cells is recycled to the gasifier for steam reforming in an endothermic reaction with a low exergy loss and a high cold gas efficiency. Our current study focuses on the optimization of the unit configurations of the A-IGFC including gasifier, compressor, solid oxide fuel cell (SOFC), combustor, gas turbine, heat recovery steam generator (HRSG), and steam turbine. The process simulator HYSYS®.Plant (Aspen technology Inc.) is employed in order to express the gasifier, the SOFC and the other units. The optimum construction over the whole system by numerical simulation was examined for higher energy utilization efficiency. Under ideal conditions using bituminous coal, we verified the power generation efficiency to be 64.5% (HHV). However, utilizing low-grade coals, i.e., lignite and sub-bituminous coal, is deemed an important future energy resource to compensate for a decreasing supply of good-quality bituminous coal. For these low-grade coals, the power generation efficiency was as high as 53.6% (HHV) under the following conditions: Gasifier inlet: coal 23.6 Kg/s (667 MJ/s), steam 16.44 kg/s; Reactor reforming gas: 30.0, 8.7, 2.0, 0.8, 0.3, 0.05, 0.24, 0.14, 0.1 and 5.5 kg/s for CO, CO2 , H2 , CH4 , C2 H4 , C2 H6 , C3 H6 , HCN, N2 and H2 O respectively. The projected power outputs with this system were, SOFC: 214 MW; Gas turbine: 318 MW; Steam turbine: 86 MW.Copyright

Single-shot observation of growing streamers using an ultrafast camera

A recently developed ultrafast camera that can acquire 108 frames per second was used to investigate positive streamer discharge. It enabled single-shot evaluation of streamer evolution without the need to consider shot-to-shot reproducibility. This camera was used to investigate streamers in argon. Growing branches, the transition when a streamer forms a return stroke, and related phenomena were clearly observed.

Energy Flow of Advanced IGCC With CO2 Capture Option

Conventional IGCC (integrated gasification combined cycle) employs a cascaded energy flow with a high efficiency, yet it is difficult to achieve over 50% HHV (higher heating value). The current study proposes an alternative model of exergy recuperated Advanced IGCC (A-IGCC) to achieve higher plant efficiency by applying an autothermal reaction in the gasifier. This requires an additional heat supply from the gas turbine exhaust and the steam extracted from the steam turbine. System and performance analyses were studied on base IGCC and A-IGCC cases incorporating the heat (exergy) recuperation concept with an air-blown twin circulating fluidized bed gasifier for the gasification of sub-bituminous coal, both with and without the post combustion carbon dioxide (CO2 ) capture option. A-IGCC could deliver sufficient energy in the gasifier to the gas turbine without losing heat as resulted in IGCC. Chemical absorption methods using monoethanolamine (MEA) and methyldiethanolamine (MDEA) were selected as a CO2 absorbent. A-IGCC demonstrated a significantly higher system efficiency (51%) than IGCC (43%) without CO2 separation, provided the gas purification was at high temperature. The thermal efficiency penalty by CO2 capture was −8% using MDEA (56% absorption) and −11% using MEA (90% absorption).Copyright

Parametric Study of an Advanced IGCC

IGCC achieve high efficiency energy conversion from coal to electricity. However its efficiency is below 50% [HHV]. To achieve higher efficiency, Advanced IGCC was planned by using exergy-recuperation concept. Advanced IGCC requires many breakthroughs in technology. Advanced IGCC achieve high efficiency by using the heat of reformed gas and the application of the autothermal reaction in the gasifier. Authors try parametric study of Advanced IGCC to figure out the desirable consists of Advanced IGCC. The performance of Advanced IGCC depends on coal, gasifier condition, configuration of components, etc. The heat value of the supplied coal is 667MW [HHV]. Foreign subbituminous coal is selected as standard fuel. The adiabatic efficiencies of the compressor, the gas turbine, steam turbine and condensing turbine at standard condition were defined so that the efficiency of IGCC with 1500 °C class gas turbine is 48% [HHV] with high performance gasifier. The efficiency of IGCC reaches to 52% [HHV] by applying autothermal reaction in the gasifier. This system requires the extra heat supply in order to hold the autothermal reaction condition in the gasifier. Therefore the net efficiency of this system is about 44% [HHV]. The net efficiency of the advanced IGCC is 48% [HHV]. On the other hand, 1700 °C class advanced IGCC can achieve 51% [HHV] net efficiency and its gas turbine exhaust high temperature heat to hold autothermal reaction condition. Increase of the adiabatic efficiencies of the compressor and the gas turbine enables the high efficiency of the advanced IGCC. If the adiabatic efficiency of compressor reaches to 87% and adiabatic efficiency of the gas turbine reaches to 92%, 1700 °C class advanced IGCC has the potential of over 60% [HHV].Copyright

Control of pressure increase rate in compression ignition by pulsed plasma irradiation

Homogeneous charge compression ignition (HCCI) engines are potentially high-efficiency, low-polluting alternatives to conventional internal combustion engines. However, the usable operation range of these engines is limited by too rapid combustion for high-load operation. The combustion is brought by the simultaneous ignition over the cylinder volume. An attempt to suppress it has been tried by realizing stratified temperature or fuel distribution in the cylinder. In this paper, the possibility of pulsed dielectric-barrier discharge (DBD) irradiating the air/fuel mixture is discussed as the new stratified ignition method. A rapid compression and expansion machine (RCEM), which can simulate a single engine cycle, was used to investigate it. DBD was generated in the intake tube of the RCEM. The stratified distribution of the irradiated premixture was obtained by the discharge formation at the end of the induction period. By the pulsed DBD method, the rate of pressure increase was decreased and the characteristic oscillation at the top of the pressure waveform was suppressed. These behaviors were confirmed by observation using a high-speed camera.

Active Control of Flow Separation Over a NACA0024 Airfoil by DBD Plasma Actuator and FBG Sensor

Dielectric barrier discharge plasma actuators (DBD-PA) and fiber Bragg grating flow sensors (FBG-FS) have been investigated for active control of flow separation around a NACA0024 airfoil. Tangential jets were produced in the vicinity of the DBD-PA slightly aft of the leading edge of the airfoil. The flow separation control ability was evaluated at a low Reynolds number, Re = 5.0×104 , in an open-circuit wind tunnel. Analysis of instantaneous and time-averaged velocity distributions around the airfoil was achieved using a particle image velocimetry (PIV) system. The flow conditions induced by the DBD-PA to suppress the flow separation were found for angles of attack of α = 8°, 12°, and 16°. When unaided by the DBD-PA system, flow separations from NACA0024 airfoil are suppressed significantly for certain Reynolds numbers and angles of attack. FBG-FS attached a chord-wise cantilever near the trailing edge of the airfoil was used to measure strain fluctuations for its feasibility to detect flow separation in real time and construct feedback control system with DBD-PA. In this study, it was found that standard deviations of strain fluctuations increase obviously in cases of flow conditions at which the flow around NACA0024 airfoil separates.Copyright