•The merits and demerits of the different combustion modes are comprehensively discussed.•Effective strategies are systematically reviewed to overcome the limitations of the HCCI engine.•Ignition ...timing and combustion phase are still the main challenges for the HCCI engine application.•Combination strategies are proposed to optimize the auto-ignition timing and combustion phase.
Generally, the homogeneous charge compression ignition (HCCI) engine presents superior fuel economy and ultra-low NOx and particle matter emissions compared with the traditional combustion engine. However, the HCCI engine is essentially decoupled from the spark plug and fuel injection. That means the HCCI engine has no direct control mechanism for the auto-ignition timing and subsequent combustion phase. Without effective strategies to control the auto-ignition timing on time according to the operating conditions, the HCCI engine will be limited in a small operation range due to the cold start problem, high pressure rate and combustion noise, and even knocking combustion at the high-load. Generally, the properties of physical–chemical kinetics of fuels, as well as the mixture temperature spatial and temporal changing histories in the cylinder, strongly determine the ignition timing and affect the combustion phase in HCCI engine. Some effective techniques and controlling strategies, such as fuel management, homogeneous charge preparation, exhaust gas recirculation, etc. are widely used in the HCCI engine. These techniques and controlling strategies are used solely or conjunctively with each other to control the compressed gas temperature, pressure and mixture distribution in the cylinder at the end of the compression stroke so that the charge mixture could be auto-ignited at the desired crank angle, and thereby obtaining optimal combustion phase and heat release rate on a wide operation range for the HCCI engine. Thus, this paper comprehensively reviews different effective techniques and controlling strategies used in the HCCI engine, and also summarizes in the tables.
Neuromorphic computing has been extensively studied to mimic the brain functions of perception, learning, and memory because it may overcome the von Neumann bottleneck. Here, with the light‐induced ...bidirectional photoresponse of the proposed Bi2O2Se/graphene hybrid structure, its potential use in next‐generation neuromorphic hardware is examined with three distinct optoelectronic applications. First, a photodetector based on a Bi2O2Se/graphene hybrid structure presents positive and negative photoresponsibility of 88 and −110 A W−1 achieved by the excitation of visible wavelength and ultraviolet wavelength light at intensities of 1.2 and 0.3 mW cm−2, respectively. Second, this unique photoresponse contributes to the realization of all optically stimulated long‐term potentiation or long‐term depression to mimic synaptic short‐term plasticity and long‐term plasticity, which are attributed to the combined effect of photoconductivity, bolometric, and photoinduced desorption. Third, the devices are applied to perform digital logic functions, such as “AND” and “OR,” using full light modulation. The proposed Bi2O2Se/graphene‐based optoelectronic device represents an innovative and efficient building block for the development of future multifunctional artificial neuromorphic systems.
All‐optical synapses based on a 2D Bi2O2Se/graphene hybrid structure can yield positive photoresponses under visible light and negative photoresponses under 365 nm illumination without the extra electrical control. Contributing to this unique optoelectronic property, the single two‐terminal device with fully optical operations is demonstrated for the photodetector, optoelectronic synapses, and optical logic functions.
•The detailed 1D simulation model of the hydrogen-enriched natural gas SI engine was built and validated.•The LP EGR, HP EGR, their combinations, and the internal EGR systems were investigated on the ...detailed 1D model.•The positive and negative waves played a crucial role in the exchange process and volumetric efficiency.
In this study, a detailed 1D simulation model of the hydrogen-enriched natural gas SI engine was built according to realistic engine layout in the lab with practical boundary conditions, and validated against the experimental data. Four different types of EGR systems were comprehensively investigated, including a low-pressure (LP) EGR, a high-pressure (HP) EGR, their combinations, and an internal EGR, using the validated 1D simulation model of the hydrogen-enriched natural gas SI engine for their combustion, performance, and emissions characteristics. The results indicated that the peak combustion pressure of the in-cylinder pressure decreased with increase in EGR ratio either using the HP, LP, or combined HP-LP systems. The NOx emissions with the HP EGR were observed to be lowest of all types of EGR systems. Combined the 10% HP EGR ratio with the 5% LP EGR ratio (total 15% EGR ratio) was predicted to achieve the highest indicated thermal efficiency compared with other EGR strategies. As for the internal EGR, the peak combustion pressure and the heat release rate slightly increased with decrease in the valve overlap. Moreover, the indicated thermal efficiency firstly increased with decrease in overlap and then slightly declined. The internal EGR was mainly determined by the timing of the exhaust valve closing; However, it was not the only influence factor. The positive and negative waves in the intake and exhaust systems also played a crucial role in the gas exchange process and volumetric efficiency.
This paper focuses on the design of a dynamic Petri recurrent fuzzy neural network (DPRFNN), and this network structure is applied to the path-tracking control of a nonholonomic mobile robot for ...verifying its validity. In the DPRFNN, the concept of a Petri net and the recurrent frame of internal-feedback loops are incorporated into a traditional FNN to alleviate the computation burden of parameter learning and to enhance the dynamic mapping of network ability. Moreover, the supervised gradient-descent method is used to develop the online-training algorithm for the DPRFNN control. In order to guarantee the convergence of path-tracking errors, analytical methods based on a discrete-type Lyapunov function are proposed to determine varied learning rates for DPRFNN. In addition, the effectiveness of the proposed DPRFNN control scheme under different moving paths is verified by experimental results, and its superiority is indicated in comparison with FNN, RFNN, Petri FNN, and PRFNN control systems.
Here we demonstrate that the photoactivity of Au-decorated TiO2 electrodes for photoelectrochemical water oxidation can be effectively enhanced in the entire UV–visible region from 300 to 800 nm by ...manipulating the shape of the decorated Au nanostructures. The samples were prepared by carefully depositing Au nanoparticles (NPs), Au nanorods (NRs), and a mixture of Au NPs and NRs on the surface of TiO2 nanowire arrays. As compared with bare TiO2, Au NP-decorated TiO2 nanowire electrodes exhibited significantly enhanced photoactivity in both the UV and visible regions. For Au NR-decorated TiO2 electrodes, the photoactivity enhancement was, however, observed in the visible region only, with the largest photocurrent generation achieved at 710 nm. Significantly, TiO2 nanowires deposited with a mixture of Au NPs and NRs showed enhanced photoactivity in the entire UV–visible region. Monochromatic incident photon-to-electron conversion efficiency measurements indicated that excitation of surface plasmon resonance of Au is responsible for the enhanced photoactivity of Au nanostructure-decorated TiO2 nanowires. Photovoltage experiment showed that the enhanced photoactivity of Au NP-decorated TiO2 in the UV region was attributable to the effective surface passivation of Au NPs. Furthermore, 3D finite-difference time domain simulation was performed to investigate the electrical field amplification at the interface between Au nanostructures and TiO2 upon SPR excitation. The results suggested that the enhanced photoactivity of Au NP-decorated TiO2 in the UV region was partially due to the increased optical absorption of TiO2 associated with SPR electrical field amplification. The current study could provide a new paradigm for designing plasmonic metal/semiconductor composite systems to effectively harvest the entire UV–visible light for solar fuel production.
An indoor photovoltaic (PV) energy harvester using a time-based maximum power point tracking (TBMPPT) circuit and an on-chip PV cell is presented. The TBMPPT circuit selects one of three ...switched-capacitor DC-DC converters and adjusts the switching frequency to achieve the maximum power. This TBMPPT circuit can also track the light intensity variations. When the TBMPPT circuit is locked, a duty-cycle control technique is used to lower the power. This indoor PV energy harvester is realized in a 0.18μm CMOS process. Its total active area is 2.89mm 2 wherein the area of the PV cell is 1.436mm 2 . The measured peak power conversion efficiency (PCE) is 68.3%. This energy harvester can cover the wide input power range of 5μW-500μW and maintain the PCE>50% over the input power range of 10μW-500μW.
In daily life, we usually make materials with certain colors via dyes or pigments. However, there is a methodology for making specific nanostructures that reflect light under certain wavelengths, and ...this is considered structural color. In this study, we demonstrate novel sliced polymeric films exhibiting reflected purple, blue, cyan, and red colors via Bragg reflection. The pitch of the cholesteric liquid crystal was changed by altering the ratio of chiral dopant inside the liquid crystal mixture. It was confirmed that the reflected colors remained stable and did not change as the size and thickness of the sliced films were decreased. Furthermore, colorful patterns were easily achieved by using CLC slices as colorants, and these were fixed with transparent glue for image production. Theoretically, nanosized structural colorants could be prepared via a femtosecond laser. It is anticipated that these sliced polymerized cholesteric liquid crystal films can be applied in the surface coating and painting industries.
Damage detection is one of the primary purposes of structural health monitoring to inform catastrophic risks of structures right after extreme loadings such as earthquakes and hurricanes. In ...structural design codes, story drifts are considered as an indicator to estimate the damage states of structures. For instance, when the story drift ratios achieve 0.2‐0.4%, light damage may be present in a building. In addition, the remaining stiffness ratios can also reveal the damage levels of a structure. Previous studies have shown that structural stiffness changes can affect the frequency responses of structures, for example, changing the locations of poles in frequency response functions. In this research, two multi‐target neural network models are developed to concurrently estimate story drifts and remaining stiffness ratios using floor accelerations under seismic excitation. One of the multi‐target neural network models focuses on developing a physics‐guided loss function with a parallel model combination. Meanwhile, the other neural network model sequentially integrates two deep learning approaches by transfer learning. For example, the long short‐term memory units estimate story drift responses from floor accelerations. Then, the short‐time Fourier transform layers of floor accelerations yield the remaining stiffness ratio estimation. The proposed models are numerically investigated and experimentally verified. As a result, both models can estimate story drift and remaining stiffness ratio using the proposed neural network models.
•The mechanisms of chemical, thermal and dilution effects of diluents quantitatively analyzed.•The artificial species of FCO2, FH2O, FN2 and FEGR used to separate chemical and physical effects.•The ...chemical amplifier of the methane/hydrogen/air was improved with the hydrogen enrichment.
In this study, the mechanisms of the chemical, thermal and dilution effects of the CO2, H2O, N2 and EGR quantitatively analyzed on the laminar flame speed, laminar flame structure and key radicals profiles of the premixed methane/air mixture. Moreover, the artificial species of the FCO2, FH2O, FN2 and FEGR were used to separate the combined chemical and physical effects. Furthermore, the impacts of the hydrogen enrichment coupled with the EGR on the laminar flame speed, the laminar flame structure and key radicals profiles of the premixed methane/air mixture was also studied in detailed. The results indicated that the chemical effect of the CO2 dilution gas produced the greatest impacts on the laminar flame speed, adiabatic combustion temperature and key radicals formation of the methane/air, and followed by the H2O vapor, EGR and N2. In addition, the dilution limitation of the CO2 in the methane/air was smallest, followed by the H2O vapor, EGR and N2. Moreover, the thermal effect of the CO2 in the methane/air was strongest due to its highest specific heat capacity, followed by the H2O vapor, EGR and N2. The laminar flame speed and adiabatic combustion temperature of the methane/hydrogen/air increased with increasing the hydrogen. Furthermore, the lean-burn limitation of the methane/air was extended with the increase of the hydrogen. The radical pool, such as H, O, OH, accelerated the chain branching reactions and the chain propagation reactions, and thereby increasing the effect of the chemical amplifier during the combustion of the premixed methane/air mixture.
•Control strategies for mixture activity and chemical reaction pathway were achieved.•Hydrogen addition and EGR strategy were studied on the performance of the NG SI engine.•Better performance was ...achieved by using the late DI hydrogen in the NG SI engine.
The excellent physicochemical properties of the hydrogen make it a promising fuel in the clean energy systems, including engines. In this study, the performance of a heavy-duty lean-burn natural gas (NG)-fueled spark ignition (SI) engine with hydrogen addition are examined through experiments. Then, a full-size one-dimensional (1D) GT-Power simulation model of the SI engine is established, and the feasibility of the model is validated by comparing the experimental and simulation results. In addition, control strategies for mixture reactivity and chemical reaction pathway are realized by using various exhaust gas recirculation (EGR) ratios and hydrogen injection timings, which applied in this validated simulation mode. The results reveal that the in-cylinder pressure, peak heat release rate (HRR), and in-cylinder averaged temperature of the hydrogen-enriched NG-fueled SI engine decrease with the increase in the EGR ratio by using the port fuel injection (PFI), early direct injection (DI), or late DI strategy. In addition, the volumetric efficiency, combustion efficiency and NOx emissions are reduced, while the ignition delay period is prolonged with the increase of the EGR ratio if the three strategies are used. Specifically, under the same operating conditions and EGR ratio of 18%, the volumetric efficiency the NG SI engine is obtained to be 66.6% and 70.9% by using the PFI strategy and late DI strategy, respectively. Obviously, compared to the PFI strategy, the volumetric efficiency of the NG SI engine is increased by using the late DI strategy. In addition, the combustion efficiency of the NG is 92.7% by using the PFI strategy, while it is 95.4% by using the late DI strategy. This suggests that the late DI strategy is also more conducive to enhancing the combustion efficiency of the NG SI engine. Furthermore, the NOx emissions are reduced by introducing the EGR strategy due to the control of the chemical reaction pathway. Overall, compared to the PFI and early DI strategies, by adopting the late DI strategy in the simulation model of the hydrogen-enriched NG-fueled SI engine, the in-cylinder pressure, peak HRR, and in-cylinder averaged temperature can be effectively increased based on the control of the mixture reactivity.
