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<div class="section abstract"<div class="htmlview paragraph"Ammonia, which is considered as an excellent hydrogen carrier, could potentially become a clean fuel for direct use in ICE.</div<div class="htmlview paragraph"An experimental setup with a strongly modified inline four-cylinder (I4) heavy duty Diesel engine was used to study different combustion modes of ammonia in ICE. The fourth cylinder of that engine was operated in a monovalent mode using either OME or Diesel fuel. Its complete exhaust stream was fed into the first cylinder of the same engine, which was operated on a dual-fuel mode by utilizing ammonia port injection and OME or Diesel pilot injection to ignite the mixture. The fourth cylinder of the I4 heavy duty engine can be operated at conditions between idle and full load and at different stoichiometries (λ) to impact both the temperature and the oxygen concentration at the exhaust of that cylinder. Since the first cylinder is fed by the complete exhaust stream of the fourth, the intake conditions of the first cylinder can be controlled appropriately and various ammonia combustion modes can be realized.</div<div class="htmlview paragraph"Emissions measurements at the intake and the exhaust of the first cylinder at different speeds and loads show the impact of the different combustion modes, especially due to temperature and oxygen content variations, on NOx and combustion efficiency. Chemical kinetics calculations have been elaborated to explain some of the main observations.</div</div
Finite control set model predictive control (FCS-MPC) is a promising method for the control of multi-phase machines, due to its capability to directly account for nonlinearities and multiple controlled variables. To overcome the drawback of high current ripples and excitation of harmonic currents in the so-called xy-subsystem, several methods have been proposed in the literature so far. This paper proposes an MPC-based method that achieves high granularity of switching by not only switching at the discrete time steps, but also within the sampling interval. In doing so, the discussed algorithm, referred to as variable switching point current control (VSP 2 CC), produces low current distortions, while still keeping the advantages of conventional FCS-MPC, such as fast dynamic behavior during transients. To highlight the above, VSP 2 CC is applied to a six-phase permanent magnet synchronous machine (PMSM) and compared with conventional FCS-MPC and MPC that employs virtual voltage vectors (VV-MPC).
Platinum dissolution in PEM fuel cells is an increasingly important indicator for the state-of-health and lifetime prediction of fuel cells in real applications. For this reason, portable online analysis tools are needed that can detect and quantify platinum with high sensitivity, selectivity, and accuracy in the product water of fuel cells. We validated the hanging mercury drop electrode (HMDE) and non-toxic bismuth film electrodes for the voltammetric determination of platinum for this purpose. Bismuth films were prepared by reductive deposition on both a glassy carbon solid state electrode and on a screen-printed electrode (film on-chip electrode). Both bismuth film electrodes could be successfully validated for the determination of platinum by adsorptive stripping voltammetry. An LOD of 7.9 μg/L and an LOQ of 29.1 μg/L were determined for the bismuth film solid state electrode, values of 22.5 μg/L for the LOD and of 79.0 μg/L for the LOQ were obtained for the bismuth film on-chip electrode. These numbers are still much higher than the results measured with the HMDE (LOD: 0.76 ng/L; LOQ: 2.8 ng/L) and are not sufficient to detect platinum in the product water of a fuel cell run in different load tests. The amount of dissolved platinum produced by a 100 W fuel cell stack upon dynamic and continuous high load cycling, respectively, was in the range of 2.9–4.1 ng/L, which could only be detected by the HMDE.
Depending on the application range, there are various recommendations in the literature which converter topology should be used. These are mostly based on experience or more or less deeper considerations. For DC/DC converters, which are operated over a wide input voltage range, such recommendations rarely exist. Therefore, this contribution shows the evolution of two input voltage dependent selection matrices, which should facilitate the selection of future topologies based on known publications and basic considerations. The focus here lies on converters for λ = V i_max /V i_min ≥ 3 with galvanic isolation. First, the data set is introduced, where a distinction is made between flyback converters, forward converters and other 1stage or 2stage converters before the evolution of the novel input voltage dependent matrices is carried out. These two matrices support the selection of a suitable topology and whether the energy transfer should be done by one or two stages.
This paper presents a comparative simulation analysis of an Interior Permanent Magnet Synchronous Machine (IPMSM) performance once fed by a traditional three-phase two-level inverter and then using a three-phase five-level Cascaded H-Bridges Multilevel Inverter (CHBMI). For this purpose, an enhanced mathematical model of the IPMSM, that take into account simultaneously saturation, cross-coupling, spatial harmonics and iron loss effects, has been employed. Furthermore, two different PWM modulation strategies have been considered. The study was conducted for several working conditions, evaluating the impact of CHBMI adoption on the IPMSM performance in terms of improved efficiency and torque ripple reduction.
The Be-Rex Engine-Generator
(2023)
Although electricity is necessary for a country's economic development, many countries lack suitable grid infrastructure. Portable generators offer a consistent electric supply in the event of a blackout.
Be-Rex B.V. develops and already assembled a revolutionary engine-generator prototype. It eliminates the use of camshafts, crankshafts and flywheels while integrating the generator parts into the same spherical housing. Thus, it constitutes a compact, lightweight and cost-efficient singular unit. There is no mechanical power output while the load of the engine is determined by the demanded load of the generator. The four combustion chambers are arranged in pairs on the north and south hemisphere and the magnets of the stator are placed circumferential at the equator of the spherical housing. The rotating disc and the joiner build the rotor of the generator. While developing the engine special emphasis has been put on its multi-fuel capability. Optimized gas exchange together with an efficient scavenging concept and the combustion system allow the atmospheric version of the prototype with a displacement volume of 400 cc to achieve 10 bar of indicated mean effective pressure (imep) when running on gasoline. Using 1-D WAVE simulations the same atmospheric version converted to ammonia fuel achieves 8 bar of imep.
First firing results of an engine generator prototype running on gasoline solidify the proof of concept. In the design section the main characteristics of the concept will be highlighted and the working principle will be explained. In the modelling approach section the methodology to tackle the leakage and the friction issues will be presented before the main results of the final design optimization will be discussed. Afterwards, the first experimental runs will be analyzed and finally some possible applications will be addressed.
The limited lifetime and severe degradation after long-term usage of polymer electrolyte membrane fuel cells (PEMFCs) are challenges that have to be overcome, if PEMFCs are to play the anticipated major role in a sustainable energy and transportation system based on green hydrogen. Therefore, analytical scanning methods to precisely characterize and understand the degradation and ageing mechanisms with high spatial resolution are essential. We are using and validating scanning electrochemical microscopy (SECM) as tool for detecting descriptors of the electrochemical performance of PEMFCs treated under different activation and ageing protocols. For this purpose, a pristine Nafion™ membrane, which is typically used as proton exchange membrane (PEM) in low temperature fuel cells, was activated and deactivated after well-defined protocols to demonstrate the fundamental suitability of SECM for investigating PEMFC components. Our results indicate that the impedance associated with the proton conductivity of the Nafion™ membrane as measured by SECM was dependent on the pretreatment of the membrane and increased in the following order: hot water < hydrochloric acid < sulfuric acid. The partial and complete deactivation of the membrane using Fenton’s reagent and barium hydroxide, respectively, could be spatially visualized with SECM as well. In addition, we investigated a PEM as part of a complete membrane electrode assembly in a fully functional PEMFC after accelerated ageing tests and could identify an increased local PEM impedance by SECM. All trends could be confirmed by electrochemical impedance spectroscopy (EIS). Moreover, we investigated a typical gas diffusion layer (GDL) of a PEMFC with SECM. As a result, the microporous side of the GDL showed a much lower impedance than its macroporous side, which is comprehensible since it agrees with the additional carbon black coating on the former side.
In this paper, a flux linkage-based direct model predictive current control approach is presented for small permanent magnet synchronous motor (PMSM) drives. The method aims to minimize the current ripples at steady state by deciding on the optimal switching instant, while exhibiting fast dynamic behavior during transients. To this end, the future trajectory of the stator current is not computed based on the machine inductances or inductance look-up tables, but on the changes of the magnetic flux linkage by utilizing flux linkage maps. As shown, the proposed method can be particularly advantageous for electric drives with a noticeable nonlinearity in terms of saturation and/or cross-coupling effects since it allows for a significantly increased prediction accuracy, which leads to an improved steady-state performance as indicated by the reduced current distortions.
A transformer with variable primary windings for wide input voltage range DC/DC converters is presented. This transformer structure allows three states of the primary winding to be converted by only two individual windings. Based on the evaluations of a two-switch flyback converter, the potential of DC/DC converters with variable structures, the implementation of such a transformer and the advantages and disadvantages are shown and discussed. Real measurement results demonstrate the noticeable increase in efficiency and the reduction in component stress, having a positive influence on the operation of the converter and the component selection during the design process.