Low Load Conditions Research Articles

Impact of dust aerosols on the Indian Summer Monsoon Rainfall on intra-seasonal time-scale

The Indian subcontinent is a major hotspot of aerosol loading and several studies have demonstrated the importance of interaction between Asian dust aerosols and the Indian Summer Monsoon Rainfall (ISMR). However, a few studies have suggested a declining trend in the pre-monsoon dust loading over the Indian region. The present study investigates how the decrease in dust emissions influences the intensity of the monsoon rainfall over the Indian region using a fully coupled Weather Research and Forecasting model coupled with chemistry (WRF-Chem). We have conducted two sets of simulation experiments for the June-July-August-September (JJAS) season of 2017: (1) a control experiment with the default dust aerosol emissions, and (2) a sensitivity experiment by reducing dust emissions by 60%. Our analyses show that the reduction in dust emissions significantly alters the spatial distribution of seasonal mean monsoon rainfall with enhanced rainfall over the Bay of Bengal (BoB) and eastern coastal regions, and decreased rainfall over the lower Indo-Gangetic Plain (IGP), and parts of Central India (CI). It is found that the low aerosol loading conditions alter the large-scale circulation patterns along the tropical/sub-tropical region centred between 15°N and 35°N and 40°E −130°E, and through dynamical feedback, strengthens the convective rainfall over the BoB region. As a result, the 10–20 days sub-seasonal mode of the ISMR strengthens, facilitating enhanced westward propagation of rain-bearing systems formed over northern BoB which provides substantial rainfall over vast regions of the Indian subcontinent.

“Reduction-aggregation” strategy to construct a low-cost and high-efficiency Ag/Al2O3 catalyst for NH3-SCO

Ammonia (NH3) is the main alkaline gas in the atmosphere and neutralizes acidic gases to form haze. Ag-based catalysts are widely used in the field of ammonia selective catalytic oxidation (NH3-SCO) due to their low cost and high efficiency. However, Ag-based catalysts with high activity at low temperatures are usually loaded with large amounts of Ag. To further reduce the cost of Ag-based catalysts, we used a “reduction-aggregation” strategy to aggregate isolated Ag atoms that were highly dispersed into Ag nanoparticles (AgNPs) so that more active centers could be exposed under low Ag loading conditions. Significant AgNPs size effects in the NH3-SCO reaction were found, including the effect of AgNPs size on catalyst activity and stability. Finally, novel Ag/Al2O3 catalysts with high efficiency and stability were developed at a low Ag loading of 1 wt % and achieved better NH3-SCO performance than 10% Ag/Al2O3, which significantly reduced the catalyst cost.

Influence of Fuel Oxygenation on Regulated Pollutants and Unregulated Aromatic Compounds with Biodiesel and n-Pentanol Blends

It is very important to determine the polycyclic aromatic hydrocarbon (PAH) emissions caused by the use of renewable fuels in diesel engines and to know the possible damages. This study investigates the emissions (regulated and unregulated) of biodiesel/n-pentanol mixtures, which are free of aromatic content, with emphasis on PAH formation and an examination of toxicity to public health and the environment. Engine failures caused by wetstacking are also discussed. Biodiesel/n-pentanol fuel mixtures with alcohol concentrations of 5%, 20%, and 35% by volume (v/v) served as test fuels in a compression ignition engine. A five-gas analyzer was used to measure hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx) emissions. Polycyclic aromatic hydrocarbons were detected and measured using gas chromatography-mass spectrometry (GC-MS). Against the baseline diesel fuel, the biodiesel/n-pentanol fuel blends and neat biodiesel reduced NOx emissions and produced significantly fewer PAHs and toxicity, confirming the significance of the aromatic content of the fuel. Biodiesel reduced total PAHs by 48.02% and the addition of 5% n-pentanol to biodiesel further decreased total PAHs by 21.26%. The total toxicity (BaPeq (benzo[a]pyrene equivalent)) as a result of biodiesel was 83.49% less than diesel. The addition of n-pentanol to biodiesel further reduced toxicity by 59.15%, 57.89%, and 48.33% for BPen5, BPen20, and BPen35 blends, respectively. In addition, n-pentanol was shown to be effective for reducing total PAH emissions, as well as heavier PAHs, which have greater carcinogenicity and pose a greater likelihood of engine damage from wetstacking when running in low-load conditions at cold temperatures.

Study on the acoustic characteristics of a heavy-duty gas turbine combustor

The acoustic characteristics of combustor are an important theoretical basis for determining whether a gas turbine will undergo thermoacoustic coupled oscillatory combustion. In this paper, the acoustic numerical model of a heavy-duty gas turbine combustor is established and its acoustic characteristics are studied using ANSYS simulation software. The results show that: 1) the acoustic pressure oscillation in the chamber primarily appears as the longitudinal mode below 705 Hz, while above 870 Hz, the transverse mode appears. 2) the effect of temperature on the acoustic natural frequency of the chamber enhances with the order of the acoustic mode. 3) the acoustic frequency of each order of the combustor varies considerably at low load conditions, and no longer varies when the gas turbine load is higher than 80 % rated power. 4) the variation of acoustic frequency with gas turbine load can be fitted by a third-order polynomial, and the acoustic frequency is proportional to the first and third orders.

An investigation of the effect of chamber temperature on macroscopic spray characteristic under GCI engine conditions

Spray characteristics play an important role in the application of gasoline compression ignition (GCI) engines because it affects engine performance as well as engine design. In this study, the influence of temperature on the non-vaporizing spray process was evaluated through the experimental process on the constant volume chamber (CVC) with simulated conditions of the GCI engine. The experimental matrix was constructed by varying key factors, including chamber temperature, fuel injection pressure, and chamber gas density. The CVC with built-in heaters allows for temperature variations at 323 K, 398 K, and 423 K. To accommodate low load conditions, the fuel injection pressure is varied between 50 MPa and 110 MPa. Simultaneously, chosen variations of gas density, including two levels of chamber density are selected at 15 kg/m3 and 30 kg/m3 respectively. In addition, the injector angles are arranged at 90° (vertical) and 180° (horizontal) to create an overview of the spray characteristics for the case study of GCI engine conditions, viable for future studies using a constant-volume combustion chamber (CVCC), or even rapid compression engine machine (RCEM) in which the injector is commonly set horizontally. The gasoline blended with biodiesel by volume percentage consisting of 80% gasoline and 20% biodiesel was used as the main fuel in this study, namely the GB20 blend. The results of the spray characteristics collected through the images of the spray process based on the Schlieren optical method and the highspeed camera, consisting of the spray evolution and penetration length, spray penetration rate, spray area, as well as the spray cone angle are investigated. The difference in the spray process is denoted as the chamber temperature is increased. The spray penetrates to the chamber wall limit more quickly at elevated temperatures. The results were recorded as a decrease in impingement time by 12% and 9.5%, respectively, at the injection pressure of 50 MPa together with an ambient gas density value of 15 kg/m3. The cone angle of the spray tends to reduce by approximately around 3° to 10° in all experimental cases when the chamber temperature is high. However, when entering the post-phase at 450–600 μs, cone angle differences are negligible during the injection reaching the stable phase.

Theoretical study on the effect of low-temperature reforming on gasoline compression ignition (GCI) at low-load conditions

In this paper, the influence of reforming conditions on the reforming products of gasoline, as well as the effect of main reforming products on GCI combustion at low-load conditions has been studied by experiment and numerical simulation. The results show CO, H2 and CH4 are the major reforming products, and their production is improved by higher reforming temperature, oxygen concentration and reforming time. The production of CO and H2 is mainly determined by the dehydrogenation reaction between fuel molecules and OH, while the one between iC8H18 and O2 is essential for the CH4 generation. The combustion efficiency rises sharply with more CO addition, but increases first and then decreases with increased H2, while the peak value of 96.71% is achieved. Besides, higher combustion efficiency is obtained with more internal exhaust gas recirculation (i-EGR) used. The increased OH and H radicals can be attained by adding CH4, which further improves combustion efficiency.

A systematic exploration of attentional load effects on the C1 ERP component.

The C1 ERP component reflects the earliest visual processing in V1. However, it remains debated whether attentional load can influence it or not. We conducted two EEG experiments to investigate the effect of attentional load on the C1. Task difficulty was manipulated at fixation using an oddball detection task that was either easy (low load) or difficult (high load), while the distractor was presented in the upper visual field (UVF) to score the C1. In Experiment 1, we used a block design and the stimulus onset asynchrony (SOA) between the central stimulus and the peripheral distractor was either short or long. In Experiment 2, task difficulty was manipulated on a trial-by-trial basis using a visual cue, and the peripheral distractor was presented either before or after the central stimulus. The results showed that the C1 was larger in the high compared to the low load condition irrespective of SOA in Experiment 1. In Experiment 2, no significant load modulation of the C1 was observed. However, we found that the contingent negative variation (CNV) was larger in the low compared to the high load condition. Moreover, the C1 was larger when the peripheral distractor was presented after than before the central stimulus. Combined together, these results suggest that different top-down control processes can influence the initial feedforward stage of visual processing in V1 captured by the C1 ERP component.

High visual perceptual load reduces prepulse inhibition induced by task-unrelated and task-related sound.

Prepulse inhibition (PPI) is an automatic and pre-attentive sensorimotor gating process. Several studies have shown that advanced cognitive functions can modulate PPI. This study aimed to further elucidate the modulatory effect of attentional resource allocation on PPI. We examined the differences in PPI between high and low attentional loads. First, we verified that the adapted feature versus combination visual search paradigm could produce high and low perceptual load differences according to the task demands. Second, we measured the participants' task-unrelated PPI during the visual search task and found that the PPI in the high-load condition was significantly lower than that in the low-load condition. To further elucidate the role of attentional resources, we tested task-related PPI using a dual-task paradigm in which participants were instructed to complete a visual task with an auditory discrimination task. We found a result similar to that of the task-unrelated experiment. The participants in the high-load condition had less PPI than those in the low-load condition. Finally, we ruled out the possibility that the working memory load explains the modulation of PPI. In line with the theory of PPI modulation, these results suggest that allocating limited attentional resources to the prepulse modulates PPI. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Benefits from prospective memory offloading depend on memory load and reminder type.

Prospective memory (PM) refers to the ability to remember to complete a task at the appropriate moment in the future. Past research has found reminders can improve PM performance in both laboratory and naturalistic settings, but few projects have examined the circumstances when and what types of reminders are most beneficial. Three experiments in the present study tested the influence of reminders in an event-based PM task under different cognitive loads. An additional study examined how effective reminders of different types were. In Experiments 1 (specific targets) and 2 (nonspecific targets), load was manipulated by having participants respond to a single (low load) or multiple (high load) targets. In Experiment 3, the association between target-action word pairs was manipulated by presenting strongly associated pairs (low load) or weakly associated pairs (high load). Experiment 4 used target-action word pairs and varied the type of reminder. Participants in the reminder conditions had target (Experiments 1 and 2), target and action (Experiment 3) or target and/or action (Experiment 4) reminders listed at the top of the screen throughout the PM task. Across the first 3 experiments, it was found that the benefit of reminders was greater under high load than low load conditions. Experiment 4 found that target-action reminders improved PM, while target-only or action-only reminders did not. Importantly, the improvements in PM from reminders occurred without cost to ongoing task performance. Together these results suggest that reminders can be beneficial for reducing PM failures, particularly under high load, without the potential downside of increased effort expenditure. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

A case analysis and treatment measures of high moisture content in wet desulphurization gypsum

China’s thermal power plant wet FGD (flue gas desulphurization) produces more than 80 million tons of gypsum each year. The factors affecting the quality of wet desulphurization gypsum are limestone quality, flue gas dust, gypsum slurry pH, slurry quality, gypsum water content, desulphurization system design features, and operating conditions, etc. There are many reasons for high gypsum moisture content, and the analysis and solution are particularly complex. Through a case analysis of a power plant with high moisture content of desulphurization gypsum, the main reasons are that the unit has been operating under low load conditions for a long time with low sulphur coal, limestone supply slurry is high, slurry pH is high, and the volume of gypsum crystals generated is small, resulting in gypsum dehydration difficulty and high moisture content. The measures were to add the crystal seeds into the slurry and to lower the operation pH. The slurry quality is improved, and the gypsum dehydration returns to normal. The design margin of the desulphurization system is large, even in a long-term low sulphur and low load operation. There are no similar cases, and this situation generally does not attract attention. It is worth further analysis and reference.

Research on Tunnel-Boring Machine Main Bearing Fatigue Damage and Vibration Response

Based on the damage evolution equation of bearing steel, a user subroutine was developed to simulate the fatigue damage behavior of the TBM main bearing under the condition of low speed and heavy load. In addition, the damage evolution law of the main bearing in the time domain and the space domain was studied. Then, a nonlinear spring element was introduced to simulate the interaction between the roller raceway, and the vibration response of the TBM after the main bearing damage was studied using the transient dynamic method. The research shows that the damage risk of the raceway is greater than that of the roller, and the damage risk of the main pushing raceway is greater than that of the other two raceways. The damage of the main bearing will not only lead to the increase in the peak vibration response of the TBM but also cause more frequency components of the response. By monitoring the time domain index of vibration signal, the damage degree to the main bearing can be mastered in real time, providing a reference for the maintenance of the main bearing.

Impact of waste-plastic-derived diesel on the performance and emission characteristics of a diesel engine under low load conditions

In recent years, hybrid (e.g. diesel-renewable) power systems have been implemented in many isolated regions (e.g. remote areas and islands) to reduce dependency on diesel generation. Nevertheless, low load (up to 30% of the maximum rated power) at variable speed operations is considered flexible and relevant for maximum renewable energy penetration because of the high cost and complexity of the conventional mode with fixed speed operation in the hybrid system. Given the increasing emphasis on fossil fuels in power generation sectors, plastic-derived diesel can be a suitable alternative. In this study, plastic-derived diesel was used for engine testing. It was produced from plastic crude oil from high-density polyethylene, polypropylene and polystyrene in a 1:1:1 ratio by using a vacuum distillation technique via the pyrolysis process. The pyrochemical properties of plastic-derived diesel were tested after distillation. The present work focused on validating the two-zone thermodynamic model for investigating engine performance and emissions at variable speeds (i.e. 1200, 1500, 1800 and 2100 rpm) at 5, 10, 15, 20, 25 and 30% load conditions fuelled with ultra-low sulphur diesel and plastic-derived diesel blends (5, 10 and 20). The simulation and experimental results showed good agreement. The maximum variation of 17.2% was found between the experimental and simulated results at mentioned speeds and loads for all tested fuels. Compared with ultra-low sulphur diesel, plastic-derived diesel showed a significant improvement in brake power, torque, brake thermal efficiency and brake-specific fuel consumption. The maximum brake power variation was 9.85% for plastic-derived diesel (20%) at 1200 rpm at 5% load. Moreover, the minimum brake specific fuel consumption variation was 4.15% for ultra-low sulphur diesel at 1500 rpm and 25% load. Compared with the commercial ultra-low sulphur diesel, 20% of plastic-derived diesel blends exhibited maximum reductions of 4.75, 5.95, 4.45 and 4.35% in NOx, CO2, CO, and HC emissions, respectively, under any tested conditions. Plastic-derived diesel blends showed less particulate matter emission compared to ultra-low sulphur diesel. Therefore, up to at least 20% of the plastic-derived diesel blends tested in this study can be used as an alternative fuel for ultra-low sulphur diesel. Further study should be carried out to test more than 20% plastic-derived diesel blends and reach a conclusion.

Impact of multi-scaled surface textures on tribological performance of parallel sliding contact under lubricated condition

Single-scale textured sliding contacts are effective for low-load and high-speed operating conditions. However, most machine-driven components operate under dynamic load and speed conditions. Therefore, to effectively counteract the dynamic operating conditions, the idea of multi-scale textures is devised. The present work describes the fabrication of multi-scale textured surfaces through Nd: YAG laser. Also, the effect of area density and texture depth of multi-scale textured surfaces on tribological parameters like frictional coefficient and wear rate was analyzed through a Pin-on-disc test rig. The results depict that in most loading conditions, the area density of 0.3 and the texture depth of 10 µm exhibit better tribological properties. Moreover, the obtained experimental results are in-line with numerical results.

A Second-Generation Palladacycle Architecture Bearing a N-Heterocyclic Carbene and Its Catalytic Behavior in Buchwald–Hartwig Amination Catalysis

Palladacyclic architectures have been shown as versatile motifs in cross-coupling reactions. NHC-ligated palladacycles possessing unique electronic and steric properties have helped to stabilize the catalytically active species and provide additional control over reaction selectivity. Here, we report on a synthetic protocol leading to palladacycle complexes using a mild base and an environmentally desirable solvent, with a focus on complexes bearing backbone-substituted N-heterocyclic carbene ligands. The readily accessible complexes exhibit high catalytic activity in the Buchwald–Hartwig amination. This is achieved using low catalyst loading and mild reaction conditions in a green solvent.

The transformations of cellulose after concentrated sulfuric acid treatment and its impact on the enzymatic saccharification

BackgroundThe dense structure of cellulose lowers its reactivity and hinders its applications. Concentrated sulfuric acid is an ideal solvent to dissolve cellulose and thus has been used widely to treat cellulose. However, the changes of cellulose after reaction with concentrated sulfuric acid at near-limit S/L ratio and its effect on enzymatic saccharification still need further investigation.ResultsIn this study, the interactions between cellulose (Avicel) and 72% sulfuric acid at very low acid loading conditions of 1:2 to 1:3 (S/L ratio) were studied for the enhanced production of glucose. The Avicel gradually transformed from cellulose I structure to cellulose II structure during the sulfuric acid treatment. Other physicochemical characteristics of Avicel also changed dramatically, such as the degree of polymerization, particle size, crystallinity index, and surface morphology. After acid treatment, both the yield and productivity of glucose from cellulose increased significantly under a very low enzyme loading of 5 FPU/g-cellulose. The glucose yields for raw cellulose and acid-treated (30 min) were 57% and 85%, respectively.ConclusionLow loadings of concentrated sulfuric acid were proven to be effective to break the recalcitrance of cellulose for enzymatic saccharification. A positive correlation between cellulose CrI and glucose yield was found for concentrated sulfuric acid-treated cellulose, which was opposite to previous reports. Cellulose II content was found to be an important factor that affects the conversion of cellulose to glucose.

Driving System Design and Power Source Parameter Optimization of Tractor with Dual-Motor Coupling Drive

For the poor working conditions of tractors, single-motor drive tractors usually choose a motor with large parameters, which leads to the lower efficiency of the motor under low-load conditions. Taking a wheeled tractor of YTO as the research object, a driving scheme of a dual-motor electric tractor was proposed, and the main components of the tractor electric drive system were matched. Based on MATLAB/Simulink, the electric tractor drive system model was established. On the premise of meeting the dynamic needs of the tractor, an optimization model was established with the tractor power consumption as the optimization goal and the power distribution coefficient of dual motors as the decision variable. The optimization model was solved by a genetic algorithm. The driving characteristics of the optimized electric tractor and the original tractor, as well as the instantaneous power consumption and total power consumption of the tractor before and after optimization, are compared and analyzed. The results show that the traction efficiency of the optimized electric tractor is about 2.7% higher than that of the original tractor, and the total power consumption of the electric tractor before and after optimization is reduced by 8.2%. The power performance and economy of the tractor after parameter matching and optimization are significantly improved.

Mitigating carcinogenic smoke opacity in a light-duty diesel engine by utilizing cyclohexanol, polyethylene glycol, and 2-methoxyethanol.

Diesel fuel reformulation is an attractive method to reduce hazardous smoke emissions because it does not require modifications to the existing engine infrastructure. As the concerns about global warming and air pollution are mounting, high-efficiency diesel engines with low smoke emissions have become more attractive. This study demonstrates that three alcohols, viz. cyclohexanol, polyethylene glycol, and 2-methoxyethanol, can be added to fossil diesel up to 3% by vol. to reduce carcinogenic smoke emissions in a one-cylinder, common rail direct injection (CRDI) diesel engine. The experimental investigations revealed that smoke could be reduced by up to 66.2%, 39.6% and 14% using 3% by vol. addition of cyclohexanol, polyethylene glycol, and 2-methoxyethanol to diesel, respectively, when compared to pure diesel operation. 1% addition by vol. of cyclohexanol and 2-methoxyethanol could reduce NOx and smoke emissions under all load conditions. CO emissions are slightly higher for all alcohol at high load conditions. HC emissions for the test fuels are lower than pure diesel operation at low load conditions, increasing at high loads. These emissions, however, can be reduced by using suitable after-treatment devices.

Working memory load modulates the processing of audiovisual distractors: A behavioral and event-related potentials study.

The interplay between different modalities can help to perceive stimuli more effectively. However, very few studies have focused on how multisensory distractors affect task performance. By adopting behavioral and event-related potentials (ERPs) techniques, the present study examined whether multisensory audiovisual distractors could attract attention more effectively than unisensory distractors. Moreover, we explored whether such a process was modulated by working memory load. Across three experiments, n-back tasks (1-back and 2-back) were adopted with peripheral auditory, visual, or audiovisual distractors. Visual and auditory distractors were white discs and pure tones (Experiments 1 and 2), pictures and sounds of animals (Experiment 3), respectively. Behavioral results in Experiment 1 showed a significant interference effect under high working memory load but not under low load condition. The responses to central letters with audiovisual distractors were significantly slower than those to letters without distractors, while no significant difference was found between unisensory distractor and without distractor conditions. Similarly, ERP results in Experiments 2 and 3 showed that there existed an integration only under high load condition. That is, an early integration for simple audiovisual distractors (240-340 ms) and a late integration for complex audiovisual distractors (440-600 ms). These findings suggest that multisensory distractors can be integrated and effectively attract attention away from the main task, i.e., interference effect. Moreover, this effect is pronounced only under high working memory load condition.

Experimental Investigation of Oil Transport during Low Load to High Load Transient in Internal Combustion Engines

Reducing the Lubricating Oil Consumption (LOC) has been a critical focus for engine manufacturers. LOC not only depends on engine operating condition but also the history of the operating condition variations. This work seeks to understand the oil transport in the ring pack during the low load to high load transient through experimental investigations. An optical engine with 2D Laser Induced Fluorescence (2D-LIF) technique, equipped with a modern low-tension Three-Piece Oil Control Ring (TPOCR), was applied to investigate the oil transport in the ring pack. It was found that, after the engine stayed under the blowby separation line long enough, a sudden increase to high load can result in a huge increase of oil ejection to the liner from the top ring groove in the expansion strokes. The mechanism behind it is that, when the load is increased, the oil accumulated inside the top ring groove during the low load condition is pushed out by the gas flow after the peak cylinder pressure is reached. Different combinations of load, speed, rate of change in load and time duration at low load were tested to examine their influence on this leakage mechanism. An operation with a gradual increase of engine load was found to be able to reduce the amount of oil leaked to the liner by releasing more oil to the second land. These findings can help the effort to reduce the oil emission (OE) generated from Spark Ignited (SI) engines equipped with TPOCR in the real-world transient driving conditions as well as the emission tests.

The Synergy Effect of Ignition Energy and Spark Plug Gap on Methane Lean Combustion with Addressing Initial Flame Formation and Cyclic Variation.

Controlling carbon emissions could be a win-win for both the environment and humans, and the use of low-carbon fuels is the key to being carbon-neutral in traffic transportation. Natural gas can achieve low carbon emissions and obtain high efficiency, but the poor lean combustion performance may result in large cycle-by-cycle variations. In this study, the synergy effect of high ignition energy and spark plug gap on methane lean combustion was optically studied under low-load and low-EGR conditions. High-speed direct photography combined with simultaneous pressure acquisition was used to analyze early flame characteristics and engine performance. The results show that high ignition energy can improve the methane engine's combustion stability, especially under high excess air coefficient conditions, and the main reason is that the initial flame formation is improved. However, the promoting effect may become marginal when the ignition energy increases above a critical value. As for the effect of spark plug gap, it varies with the ignition energy, and there exists an optimal spark plug gap for a given ignition energy. In another word, high ignition energy must combine with a large spark plug gap; thus, the promoting effect on combustion stability can be maximized and the lean limit can be extended. The statistical analysis of the flame area shows that the speed of initial flame formation is more important in determining combustion stability. As a result, a large spark plug gap (1.20 mm) can extend the lean limit to 1.4 under high ignition energy conditions. The current study shall give some insights into the spark strategies for natural gas engines.