With high oxygen content and cetane number, polyoxymethylene dimethyl ether 3 (PODE3) is favorable as a fuel to be used in internal combustion engines. In this study, PODE3/diesel/gasoline blends in a homogeneous charge compression ignition engine are numerically studied for the first time. The effects of fuel blend ratio as well as equivalence ratio (ER) are investigated. It is noticed that high temperature heat release depends largely on blend ratio. Furthermore, indicated thermal efficiency is observed to be better with higher ER and is generally higher with increased PODE3. As for emissions, higher ERs show trends of less CO and more NOx. Moreover, similar trends are seen when diesel addition to PODE3 is made comparison with gasoline addition to PODE3, potentially putting CO and NOx in a trade-off relationship.
A skeletal mechanism with 133 species and 877 reactions for MOD9D (one of the main unsaturated methyl esters in biodiesel fuels) is constructed by using decoupling methodology. The obtained skeletal mechanism consists of four parts: high temperature decomposition, low temperature oxidation, ester group reactions and detailed chemistry of small species. Extensive validations are firstly performed against available experimental data in shock-tube for autoignition delay. The predicted results by the skeletal mechanism matches well with the experiment results. The comparison has been conducted between the detailed mechanism and a semi-detailed mechanism. Good agreement or even better predictions at some initial conditions has been observed. Further validations are conducted against the experimental data of fuel species’ conversion rate and species concentration in PSR at varying initial temperatures. The results indicate that the developed skeletal mechanism is capable of predicting the combustion characteristics of MOD9D.
Vehicle to grid (V2G) is a technology which is receiving much attention as a method for achieving an efficient energy management system by connecting electric vehicles (EVs) to an electric power grid. In recent years, the amount of EV and renewable energy, such as photovoltaic (PV), increases rapidly. To make full use of energy, the relationship between self-consumption rate (SCR) of PV and EV penetration rate (EVPR) is a valuable issue. In addition, the stability of micro grid (MG) with different EVPR is also considered. This paper aims to find how the EVPR influence the stability of MG and SCR of PV. To achieve the main objective of this paper, a typical PV installed capacity is adopted and several scenarios with different EVPR are compared in MATLAB programming environment. The result shows that under a stable MG environment, with the growth of EVPR, remarkable increase occurs in both the stability of MG and SCR of PV. But there is an ultimate capacity for EV. Under ultimate capacity, stable load curve and fewer dump energy can be achieved simultaneously.
The objective of this work is to analyze two different solutions to the energy demand of the Tucuruí Locks. A photovoltaic power station is compared to a hybrid power generation system composed by photovoltaic and small hydraulic turbine, with pumped storage. The alternatives are discussed technically and economically: the annual energy costs of the scenarios are calculated based on the evolution of the expenses and the related energy payback time are found. The water resource is exploited responsibly, keeping balanced the volume of water in pumping and generating mode. The grid works as an intermediate storage and allows the operations with a single Pump As Turbine (PAT). The installation site is adjacent to the boat-lift structure of the Tucuruí dam. Its specific location lowers down the initial investment in favor of the hybrid system as the more viable alternative to the considered conditions.
Membrane distillation (MD) utilizes low-grade thermal energy and alternative energy to drive vapor transport through hydrophobic membrane pores for the application of water desalination, aroma compounds recovery, waste water treatment and concentration of thermo-sensitive solutions. In this work, to overcome commonly observed trade-off problems between thermal efficiency, water flux and water productivity, the simulation and optimization of a series of key objective parameters of MD were conducted by proposing a novel modeling approach. The heat and mass transfer across membrane is synchronously enhanced on account of the interaction effects of operational and module configuration variables to achieve a global optimization of MD.
The deep borehole heat exchanges (DBHEs) use a coaxial tube to obtain deep geothermal energy, avoiding the problem of groundwater corrosion and recharge, which have great application value. In this paper, a heat transfer model of a DBHE with a depth of 2000m and an outer diameter of 177.8mm is established by Fluent. The effects of various inlet temperature (5~20℃), inlet velocity (0.5~1m/s), thermal conductivity of rock (2.5~3.5W/(m·℃)) and geothermal gradient (0.035~0.045℃/m) on the heat transfer performance in a heating season are studied. The results show that the heat transfer performance of DBHEs decays with time. The rock temperature field is basically invariant outside the radius of 15m. Decreasing the inlet temperature, increasing the inlet velocity, increasing the thermal conductivity of the rock, and increasing the geothermal gradient can increase the heat extraction rate of DBHEs. Under the condition of constant geometric parameters, for every increase of 0.005℃/m in geothermal gradient, the heat extraction rate of the DBHE studied increases by an average of 22.76kW, and for every increase of 0.5W/(m·℃) in the thermal conductivity of the rock, it increases by an average of 26.44kW.
The safety issues of lithium-ion batteries, i.e. thermal runaway, have attracted abroad attention and become more critical with the increase of battery energy density. In this study, the thermal runaway behaviors of high-energy-density lithium-ion batteries with nickel-rich cathode are investigated considering the effects of cathode morphology and state of health. The results show that the safety behaviors of batteries with single crystal cathode is almost same as that with the poly crystal cathode. However, after cycling, the battery with single crystal showed worsen thermal stability after cycling at 45oC, as the onset temperature of thermal runaway decrease, while the battery with poly crystal cathode exhibited opposite changes.
In this paper, liquid-separation is attempted to plate condenser to improve the condensation of plate heat exchangers. Liquid-separation plate condenser (LPC) with two paths, three paths and four paths are proposed. The model exhibits good accuracy in predicting heat transfer coefficients (HTC). LPCs show superior performance to conventional plate condenser (CPC). There exists optimum configuration for each LPC, and they are selected for further study. It is found that the more paths LPC has, the higher HTC and heat load (Q) it would be. LPC with three paths and path length ratio (PLR) of 4:3:3 is recommended.
Due to the integration of distributed photovoltaic (PV) and access of electronic devices, power systems are suffering from serious voltage problems, and therefore they require greater flexibility. By using appropriate methods, a PV cluster can autonomously regulate reactive power output in a distributed manner to improve voltage profile. In this paper, a distributed Newton-based reactive power control method to realize distributed voltage control for high penetration of PV generation is introduced, which can fast respond to voltage mismatch and address the robustness issues of (de-)centralized approaches against communication delay and noises. The proposed distributed control scheme for PV clusters can coordinate PV to provide voltage regulation in a more efficient, reliable and flexible way than existing decentralized methods.
An oval-tube structure is used as the new generation aero-engine recuperator, which has a wide range of application prospects in aerospace, marine and other important industrial fields. The heat transfer performance of this structure directly determines the energy efficiency of the aero engine. However, the enhanced heat transfer mechanism of oval-tube recuperator is not clear due to the lack of internal flow field information. Based on the standard k-ε model, shell-side heat transfer and resistance performance are conducted by using commercial CFD software FLUENT. The influences of structural parameters and tube arrangement on heat transfer and resistance performance are further studied. Then the mechanism on heat transfer augmentation is discussed according to the fluid flow characteristics and the field coordination principle. The results show that the standard k-ε and periodicity model is feasible and accurate to simulate the fluid flow on shell side of oval-tube recuperator. The heat transfer and resistance performance increase with the ratio of major and minor axes and longitudinal spacing of oval-tube. With the increase of horizontal and longitudinal spacing of oval-tube, the performance increases at first and then decreases. The maximum velocity appears at the minor axis, and the minimum value of fluid temperature, velocity and pressure appears at the major axis. The amplitude of field synergy angle is small in the inlet section, but the fluctuation amplitude in the recuperator is large.