• Energy Research

AbstractAdditively manufactured nano-MEH systems are widely used to harvest energy from renewable and sustainable energy sources such as wind, ocean, sunlight, raindrops, and ambient vibrations. A comprehensive study focusing on in-depth technology evolution, applications, problems, and future trends of specifically 3D printed nano-MEH systems with an energy point of view is rarely conducted. Therefore, this paper looks into the state-of-the-art technologies, energy harvesting sources/methods, performance, implementations, emerging applications, potential challenges, and future perspectives of additively manufactured nano-mechanical energy harvesting (3DP-NMEH) systems. The prevailing challenges concerning renewable energy harvesting capacities, optimal energy scavenging, power management, material functionalization, sustainable prototyping strategies, new materials, commercialization, and hybridization are discussed. A novel solution is proposed for renewable energy generation and medicinal purposes based on the sustainable utilization of recyclable municipal and medical waste generated during the COVID-19 pandemic. Finally, recommendations for future research are presented concerning the cutting-edge issues hurdling the optimal exploitation of renewable energy resources through NMEHs. China and the USA are the most significant leading forces in enhancing 3DP-NMEH technology, with more than 75% contributions collectively. The reported output energy capacities of additively manufactured nano-MEH systems were 0.5–32 mW, 0.0002–45.6 mW, and 0.3–4.67 mW for electromagnetic, piezoelectric, and triboelectric nanogenerators, respectively. The optimal strategies and techniques to enhance these energy capacities are compiled in this paper.Graphical Abstract

A numerical wave energy converter (WEC) similar to the Wavestar WEC with eight units, each comprising an I-shaped power take-off (PTO), was studied with the cylindrical-hemispherical (C-HS) and S-shaped floaters. Efforts were made to examine the effects of the floater-geometry change on the PTO power performance and to study the significance of replacing a C-HS with an S-shaped floater of the same size and resonance characteristics using a hybrid algorithm based on ANSYS AQWA and MATLAB Simscape. The pure floater-shape-change effects on their heave responses were evaluated through the time-domain simulations in ANSYS AQWA and imported into a MATLAB-Simscape-based algorithm of the PTO to investigate the performance of the PTO and the overall WEC model under those effects. The buoys on the model scale were tested in a lab-scale facility, followed by a CFD analysis to study how the surrounding fluid interacts with the C-HS and the S-shaped floaters. The spectral modeling showed that the S-shaped floater could achieve a 5.5% greater RMS heave response than the C-HS in irregular waves. Replacing a C-HS with an S-shaped floater, the maximum increase in the PTO force was recorded to be 14%. A PTO integrated into an S-shaped floater attained 26% greater input power than one integrated into a C-HS floater. At an energy conversion efficiency of 55%, the PTO output power with an S-shaped floater tends to be 25–26% greater than with a C-HS floater. Replacing a C-HS with an S-shaped floater in the Wavestar-like WEC could be an optimal choice.

Abstract Increased menacing engine emissions and threat to human health from metallic combustion catalysts demand a shift towards the application of non-metallic fuel additives. Therefore, the current study is an effort, conducted to introduce a new, less toxic and non-metallic graphite (G) nano diesel-fuel additive, by investigating its effects on the performance and regulated gaseous emissions of a four-cylinder, water-cooled, compression ignition (CI) engine. The experiments were also repeated with Iron oxide (Fe2O3) nanoparticles and statistical analyses were implemented to have a comparison with graphite nanoparticles. The G and Fe2O3 nanoparticles, in concentrations of 50, 100 and 150 mg per litre (mg/l), were mixed with neat diesel by magnetic stirring to prepare homogeneous fuel blends. The physicochemical properties of the fuel blends were determined. A maximum decrease of 4.9% in viscosity and an increase of 3.26% in Cetane index was observed for graphite blends. The investigated parameters include torque (T), brake power (BP), brake specific fuel consumption (bsfc), brake thermal efficiency (BTE), carbon monoxide (CO) and nitrogen oxides (NOx) emissions at engine speed varying from 1500 to 3000 rpm with an interval of 300 rpm at full load. The results revealed that at a confidence level of 95% (significance level α = 0.05), G-blends indicated a higher increase in torque, power, BTE and a greater decrease in bsfc than Fe2O3 blends. Graphite blends produced significantly lower NOx emissions than Fe2O3 treated blends. The increase in T, BP and BTE was 2.4%, 8.9% and 3.9% respectively, with 150 mg/l Fe2O3 blends and 2.9%, 9.6% and 4.1% respectively, with 150 mg/l G-blends. Graphite blends resulted in a 2.6% reduction in bsfc. The increase in NOx emissions was 34.7% with Fe2O3 and 29.2% with G at concentrations of 150 mg/l. The CO increased by 14.2% with G blends. A negative statistical correlation was observed for CO emissions between G and Fe2O3 blends. We conclude that G nanoparticles are more environmentally friendly fuel additives than Fe2O3; however, their application is more recommended for large turbocharged CI engines with improved oxygen density in inlet compressed air.

The autonomous underwater vehicle has widespread applications in marine resource exploration, seabed search and rescue, underwater military reconnaissance, and marine environmental monitoring. Owing to the limited battery capacity, autonomous underwater vehicles usually only operate for several hours or days at a time. This article presents an extended-range wave-powered autonomous underwater vehicle (WPAUV) for underwater wireless sensor networks. Through theoretical analysis, simulation, dry and field experiments, the power generation performance of the extended-range WPAUV was evaluated. Under different wave amplitudes and wave frequencies, the mechanical efficiency of the extended-range WPAUV ranges from 20.41% to 81.56%. The average efficiency is 45.35%. In the field experiments, under calm ocean conditions, the maximum instantaneous power can reach 67.74W with an average of 10.18W. This high performance manifests that the extended-range WPAUV can effectively scavenge wave energy and converts it into electrical energy for expanding the cruising mileage.