Experimental determination of the hydrogenation/dehydrogenation - Equilibrium of the LOHC system H0/H18-dibenzyltoluene

Liquid organic hydrogen carrier (LOHC) systems store hydrogen through a catalyst-promoted exothermal hydrogenation reaction and release hydrogen through an endothermal catalytic dehydrogenation reaction. At a given pressure and temperature the amount of releasable hydrogen depends on the reaction equilibrium of the hydrogenation/dehydrogenation reaction. Thus, the equilibrium composition of a given LOHC system is one of the key parameters for the reactor and process design of hydrogen storage and release units. Currently, LOHC equilibrium data are calculated on the basis of calorimetric data of selected, pure hydrogen-lean and hydrogen-rich LOHC compounds. Yet, real reaction systems comprise a variety of isomers, their respective partially hydrogenated species as well as by-products formed during multiple hydrogenation/dehydrogenation cycles. Therefore, our study focuses on an empirical approach to describe the temperature and pressure dependency of the hydrogenation equilibrium of the LOHC system H0/H18-DBT under real life experimental conditions. Because reliable measurements of the degree of hydrogenation (DoH) play a vital role in this context, we describe in this contribution two novel methods of DoH determination for LOHC systems based on ¹³C NMR and GC-FID measurements.     

Fuzzy control of hydrogen pressure in fuel cell system

Precise control of hydrogen pressure is crucial for the performance and durability of fuel cell systems. With the widely used common-rail injection system, traditional PID controller still dominates. For a long time, the hydrogen pressure fluctuates acutely when hydrogen purge valve switches or load sharply changes with using PID controller. In recent studies, several new control strategies are presented. However, mostly of them are theoretical and experimental. In this study, an improved common-rail injection system, hydrogen injector/ejector assembly is introduced. Based on a real fuel cell system, a Mamdani fuzzy controller is designed to regulate the hydrogen pressure. The algorithm of fuzzy controller is explained in detail. A comparative study is carried out between fuzzy controller and PID controller. According to the results, the stability of hydrogen pressure with using fuzzy controller is better than using PID controller. This research could be useful for the control of fuel cell system.     

Analysis of the uncertainties in gas uptake measurements using the Sieverts method

An analysis of the uncertainties in the calculation of the amount of gas absorbed or desorbed by a sample has been made for the manometric or Sieverts technique, commonly used for the determination of hydrogen uptake on potential hydrogen storage materials. The analytical derivations provide a means to calculate the uncertainty in each step of a hydrogen absorption isotherm. In addition, a Sieverts system is modelled to allow a detailed investigation of the effect of volumes and other parameters as well as the relative impact of the different measurement uncertainties. Reliable uncertainty estimates are especially important for authoritative measurements of gas uptake by carbons and other nanostructured materials used for hydrogen storage.     

Kinetic limitations in the Mg-Si-H system

Magnesium silicide (Mg₂Si) has attracted interest as a hydrogen storage material due to favorable thermodynamics (ΔH_desorption = 36 kJ/mol H₂) for room temperature operation. To date, direct hydriding of Mg₂Si under hydrogen gas to form MgH₂ and Si has only been attempted at low pressure and has been hindered by poor kinetics of absorption. In this paper we study the dehydrogenation reaction with in-situ neutron powder diffraction and present results of our attempts to hydrogenate Mg₂Si under both hydrogen and deuterium gas up to temperatures of 350 °C and pressures of 1850 bar. Even under these extreme absorption conditions Mg₂Si does not absorb any measureable quantity of hydrogen or deuterium.     

An effective method for hydrogen production in a single-chamber microbial electrolysis by negative pressure control

In this study, we construct a scalable tubular single-chamber microbial electrolysis cell that using negative pressure (40.52 kPa) to enhance the hydrogen production. The impact of negative pressure on current production, hydrogen recovery, and microbial community of microbial electrolysis cells are investigated. Negative pressure could effectively enhance the hydrogen recovery and inhibit the growth of methanogens. Consequently, the microbial electrolysis cell operated under negative pressure achieves a maximum hydrogen production rate of 7.72 ± 0.06 L L^?1 d^?1, which is more than four times higher that of reactor running under normal pressure (1.51 ± 0.41 L L^?1 d^?1). Energy quantification shows that the electrical energy recovery under negative pressure is 146.98%, which is much higher than 95.00% under normal pressure. Therefore, negative pressure control is as effective for increasing hydrogen production and energy recovery in the scalable MEC, and has a great practical application prospect. However, negative pressure cannot knick out methanogens. Once negative pressure is removed, methanogens will quickly take over and after that applying negative pressure again can only partly inhibit methane production.     

高压共轨燃油系统喷油诱导的压力波特征试验研究

在油泵试验台架上开展喷油为主动量诱导的高压压力波动特征的试验研究,分析靠近嘴端的高压油管内以及高压油轨的轨压传感器处压力波动规律。研究表明:柴油机高压共轨燃油喷射系统中,喷油引起的压力波不受油泵引起的压力波影响;喷油引起的嘴端压力波动比轨端要显著;嘴端压力波呈现明显的波动衰减,其压力波的频率与燃油属性有关,波动的最大振幅主要与喷射压力、喷孔大小有关;高压油轨处的压力波动特征不明显,单次喷油引起的轨压下降总量不仅与喷射压力、喷孔大小有关,还与喷射脉宽有关。     

系统性方法在12V180型柴油机机油压力低故障判断上的应用

介绍应用系统性方法准确判断12V180型柴油机机油压力低故障发生点并及时进行处理的情况。     

Prediction of the capacity of a heat exchanger by a thermal network method: Modified effective specific heat model considering the influence of static pressure distributions of refrigerants

In this paper, we proposed a method to predict the capacity of a heat exchanger by considering static pressure distributions of refrigerants. The thermal network method was modified by adding an equivalent heat generation term into a heat balance equation that was connected with calculated 1D static pressure distributions of refrigerants. An experiment was performed with a heat exchanger having two rows and two passes to verify the accuracy of the proposed method. The result showed the error of the predicted capacity to be less than 1% for an evaporator and less than 2% for a condenser. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(5): 376–390, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10039     

Effect of Ni content on the hydrogen storage behavior of ZrCo1−xNix alloys

ZrCo_1−xNi_x (x = 0, 0.1, 0.2 and 0.3) alloys were prepared and their hydrogen storage behavior were studied. ZrCo_1−xNi_x alloys of compositions with x = 0, 0.1, 0.2 and 0.3 prepared by arc-melting method and characterized by X-ray diffraction analysis. XRD analysis showed that the alloys of composition with x = 0, 0.1, 0.2 and 0.3 forms cubic phase similar to ZrCo with traces of ZrCo₂ phase. A trace amount of an additional phase similar to ZrNi was found for the alloy with composition x = 0.3. Hydrogen desorption pressure–composition–temperature (PCT) measurements were carried out using Sievert's type volumetric apparatus and the hydrogen desorption pressure–composition isotherms (PCIs) were generated for all the alloys in the temperature range of 523–603 K. A single sloping plateau was observed for each isotherm and the plateau pressure was found to increase with increasing Ni content in ZrCo_1−xNi_x alloys at the same experimental temperature. A van't Hoff plot was constructed using plateau pressure data of each pressure–composition isotherm and the thermodynamic parameters were calculated for desorption of hydrogen in the ZrCo_1−xNi_x–H₂ systems. The enthalpy and entropy change for desorption of hydrogen were calculated. In addition, the hydrogen absorption–desorption cyclic life studies were performed on ZrCo_1−xNi_x alloys at 583 K up to 50 cycles. It was observed that with increasing Ni content the durability against disproportionation of alloys increases.     

Dissolution,diffusion, and penetration of H in the group VB metals investigated by first-principles method

The group VB metals (V, Nb, Ta) are referred to as one of the most valuable hydrogen separation membrane materials because of their advantages over Pd. To evaluate the hydrogen-permeation performance of the three metals, their structure stability, H-solubility, H-diffusivity, H-permeability, and elastic stiffness tensors have been investigated using the first-principles method. Our results reveal that the tetrahedral interstitial site (TIS) is favorable position for H-occupying, but mainly because H-solution enthalpy is the lowest. H-diffusion coefficient follows the order of V > Nb > Ta, H-permeability and H-permeation flux follow the order of Nb > V > Ta. The attractive interactions between H atoms are weak, so it is impossible to form H₂ molecules inside the metals, and all metal hydride phases present good ductility. The calculated Debye temperature is basically consistent with the experimental value. These results provide fundamental data for the further design of alloy membranes based on VB metals.     

The effects of fuel-injection timing at medium injection pressure on the engine characteristics and emissions of a CNG-DI engine fueled by a small amount of hydrogen in CNG

The experiments to determine the effect of fuel-injection timings on engine characteristics and emissions of a DI engine fueled with NG-hydrogen blends (0%, 3%, 5% and 8%) at various engine speeds were conducted. Three injection timings namely 120°, 180° and 300° CA BTDC with a wide open throttle at relative air-fuel ratio, λ = 1.0 were selected. The ignition advance angle was fixed at 30° CA BTDC, while the injection pressure was fixed at 1.4 MPa for all the cases. The tests were firstly performed at low engine speed of 2000 rpm to determine the engine characteristics and emissions. The results showed that the engine performance (e.g. Brake Torque, Brake Power and BMEP), the cylinder pressure and the heat release have the highest values at the injection timing of 180° CA BTDC, followed by the 300° CA BTDC and the 120° CA BTDC. The NO_x emission was found to be highest at the injection timing of 180° CA BTDC. The THC and CO emissions were found to decrease while the CO₂ emission increased with the advancement in the injection timing. The addition of a small amount of hydrogen to the natural gas was found to increase the engine performance, enhance combustion and reduce emissions for any selected injection timings. Secondly, the tests were carried out at variable engine speeds (i.e. 2000 rpm-4000 rpm) in order to further investigate the engine performance. The injection timings of 180° and 300° CA BTDC with CNG-H₂ blends were only selected for comparisons. The injection timing of the 300° CA BTDC was discovered to yield better engine performance as compared to the 180° CA BTDC injection timing after a cutoff engine speed of approximately 2500 rpm.     

A novel decentralized method based on the system engineering concept for reliability‐security constraint unit commitment in restructured power environment

In the deregulated power environment, including Central operator (CO) and Micro Grids (MGs), different parts of the network are dedicated to the private sector, and each of them seeks to increase their profits independently. The CO and MGs should cooperate and collaborate in terms of operating, security and reliability in the whole power system. This article proposes a new method based on a System of System (SoS) concept for the secure and economic hourly generation scheduling to find optimal operational point. The main methodology includes three steps. In the first step, the power system is divided into several subsystems by using a spectral clustering partitioning technique to reduce converge time by decentralizes methods. And also load forecasting based on a Gaussian probability distribution function to avoid conventional calculation and considering uncertainty of the loads has been presented. To find a similar scenario, and reduction scenario with low probability, the probabilistic method has been addressed. The main contribution of this method is removing scenarios with low value of probabilities and scenarios which are similar to each other. In fact, the reduced set must include scenarios which are scattered appropriately in the uncertain space while holding high probabilities. In order to estimate the similarity (distance) between two scenarios the Kantorovich distance is implemented. In the second step, the hierarchical Bi‐level optimization approach is used to execute the decentralized decision making to solve the Security Constraints Unit Commitment (SCUC) problem between CO and MGs. Regarding all physical relations and shared data among CO and MGs, the SoS concept and Bi‐level optimization are presented to find the optimal operating point of autonomous systems. In the third step, a random number of generators will be select. Hence, the initial iteration number is set. In this step, sampling from state space to classifying reliability object achieved (The expected energy not supplied and loss of load probability are the reliability criterion). The presented method is evaluated using a 6‐bus, the RTS 24‐bus, 118‐bus, and 4672‐bus as an IEEE test systems. The suggested structure has been implemented by GAMS, and the results illustrate the usefulness of the presented methodology. To comparing proposed approach with the centralized method, the results illustrate improving total operational costs and security (in RTS‐24($603,209), 118 bus ($2 562 154) and 4672‐bus ($9 185 168)) in scenario 3 near to 9%, 10% and 8% respectively. Similarly, by comparison (in three test systems) with genetic algorithm these improvements are near to 23%, 22% and 13% respectively.