45 research outputs found
An Architecture for Distributed Energies Trading in Byzantine-Based Blockchain
With the development of smart cities, not only are all corners of the city
connected to each other, but also connected from city to city. They form a
large distributed network together, which can facilitate the integration of
distributed energy station (DES) and corresponding smart aggregators.
Nevertheless, because of potential security and privacy protection arisen from
trustless energies trading, how to make such energies trading goes smoothly is
a tricky challenge. In this paper, we propose a blockchain-based multiple
energies trading (B-MET) system for secure and efficient energies trading by
executing a smart contract we design. Because energies trading requires the
blockchain in B-MET system to have high throughput and low latency, we design a
new byzantine-based consensus mechanism (BCM) based on node's credit to improve
efficiency for the consortium blockchain under the B-MET system. Then, we take
combined heat and power (CHP) system as a typical example that provides
distributed energies. We quantify their utilities, and model the interactions
between aggregators and DESs in a smart city by a novel multi-leader
multi-follower Stackelberg game. It is analyzed and solved by reaching Nash
equilibrium between aggregators, which reflects the competition between
aggregators to purchase energies from DESs. In the end, we conduct plenty of
numerical simulations to evaluate and verify our proposed model and algorithms,
which demonstrate their correctness and efficiency completely
A Platinum Nanowire Network as a Highly Effective Current Collector for Intermediate Temperature Solid Oxide Fuel Cells
We report the fabrication and evaluation of a platinum nanowire network as a highly efficient current collector for solid oxide fuel cells (SOFCs). The ink of carbon-black supported platinum nanoparticles was sprayed onto the cathode. After firing, the carbon black was oxidized and disappeared as carbon dioxide gas while the platinum nanoparticles connect with one another, forming a tree-branch-like nanowire network. The diameters of the nanowires range from 100 nm to 400 nm. Compared to a conventional platinum paste current collector, the polarization resistance of the PrBaCo2O5+δ (PBCO) cathode with a nanowire current collector was reduced by 44% at 650 °C (from 0.18 Ω cm2 to 0.1 Ω cm2). The peak power density of the button cells was improved at different degrees of 31.8–59.6% under temperatures 650–550 °C for typical cathode materials of PBCO, La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF), and Ba0.5Sr0.5Co0.8Fe0.2O3−δ(BSCF). The nanowire network did not show obvious changes after long term testing (400 h)
A Double Auction for Charging Scheduling among Vehicles Using DAG-Blockchains
Electric vehicle (EV) is becoming more and more popular in our daily life,
which replaces the traditional fuel vehicles to reduce carbon emissions and
protect the environment. The EVs need to be charged, but the number of charging
piles in a charging station (CS) is limited and charging is usually more
time-consuming than fueling. According to this scenario, we propose a secure
and efficient charging scheduling system based on DAG-blockchain and double
auction mechanism. In a smart area, it attempts to assign EVs to the available
CSs in the light of their submitted charging requests and status information.
First, we design a lightweight charging scheduling framework that integrates
DAG-blockchain and modern cryptography technology to ensure security and
scalability during performing scheduling and completing tradings. In this
process, a constrained double auction problem is formulated because of the
limited charging resources in a CS, which motivates the EVs and CSs in this
area to participate in the market based on their preferences and statuses. Due
to this constraint, our problem is more complicated and harder to achieve the
truthfulness as well as system efficiency compared to the existing double
auction model. To adapt to it, we propose two algorithms, namely the truthful
mechanism for charging (TMC) and efficient mechanism for charging (EMC), to
determine the assignments between EVs and CSs and pricing strategies. Then,
both theoretical analysis and numerical simulations show the correctness and
effectiveness of our proposed algorithms
A Ceramic-Anode Supported Low Temperature Solid Oxide Fuel Cell
We report the fabrication and evaluation of a ceramic-anode supported button cell LSCM-SDC/SDC/PBSC (thickness 400 μm/20 μm/20 μm). The anode/electrolyte assembly LSCM-SDC/SDC was co-fired at low temperature of 1250°C, where a slight amount of CuO was mixed with LSCM. The CuO (20.3 wt%) were impregnated into the porous substrate to enhance current collecting effect. The cell exhibited power density of 596 mWcm−2 and 381 mWcm−2 at 700°C with wet hydrogen and methane as the fuel respectively, where the silver paste was used as current collectors, the highest performance up to date for the cells with metal oxide anodes at this temperature
Flow Dynamics of a Dodecane Jet in Oxygen Crossflow at Supercritical Pressures
In advanced aero-propulsion engines, kerosene is often injected into the
combustor at supercritical pressures, where flow dynamics is distinct from the
subcritical counterpart. Large-eddy simulation combined with real-fluid
thermodynamics and transport theories of a N-dodecane jet in oxygen crossflow
at supercritical pressures is presented. Liquid dodecane at 600 K is injected
into a supercritical oxygen environment at 700 K at different supercritical
pressures and jet-to-crossflow momentum flux ratios (J). Various vortical
structures are discussed in detail. The results shown that, with the same
jet-to-crossflow velocity ratio of 0.75, the upstream shear layer (USL) is
absolutely unstable at 6.0 MPa (J = 7.1) and convectively unstable at 3.0 MPa
(J = 13.2). This trend is consistent with the empirical criterion for the
stability characteristics of a jet in crossflow at subcritical pressures (Jcr =
10). While decreasing J to 7.1 at 3.0 MPa, however, the dominant Strouhal
number of the USL varies along the upstream jet trajectory, and the USL becomes
convectively unstable. Such abnormal change in stability behavior can be
attributed to the real-fluid effect induced by strong density stratification at
pressure of 3.0 MPa, under which a point of inflection in the upstream mixing
layer renders large density gradient and tends to stabilize the USL. The
stability behavior with varying pressure and J is further corroborated by
linear stability analysis. The analysis of spatial mixing deficiencies reveals
that the mixing efficiency is enhanced at a higher jet-to-crossflow momentum
flux ratio