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In this paper, the effects of direct water injection (WI) on characteristics of combustion and emission for a hydrogen (H2)-fueled spark ignition (SI) engine were experimentally investigated. The experiments conducted under different amounts of water injection (AWI) and varied water injection timing (WIT). The experimental results showed that in-cylinder pressure decreased, indicated thermal efficiency (ITE) increased, and the flame development (CA0-10) and propagation (CA10-90) periods prolonged when AWI raised. When AIW grew to 4.5 mg/cycle, Nitrogen oxides (NOx) expelled from the original engine decreased by 53.7% when excess air ratio (λ) was 1.15. Early WIT had positive effects on the reduction of NOx emissions. When WIT retarded, in-cylinder pressure increased, ITE decreased and CA0-10 and CA10-90 shortened, NOx emissions rapidly increased.

Dimethyl ether (DME), as a sustainable fuel, could be used as an ignition improver in spark ignition engines to improve the performance under lean conditions. Direct injection engines could gain higher thermal efficiency than the port fuel injection engines. To study the effects of second injection (SOI2) timing on the engine combustion characteristics, experiments were conducted on an engine with independent DME port injection and gasoline direct injection systems. Tests were performed at a constant engine speed of 1400 rpm and manifolds absolute pressure of 60 kPa under excess air ratios of 1.2 and 1.3. The start of injection during intake was kept constant at 300 oCA BTDC and the SOI2 timing was varied from 90 to 150 oCA BTDC. Split injection ratio was 1:1. Results showed that a higher brake thermal efficiency (BTE), lower cyclic variation, HC and particle emissions were obtained for DME-gasoline blends engines. Moreover, the ideal SOI2 timing could make the heat release more concentrated and ease the cyclic variation, which enhance BTE and reduce HC, NOx and particle number emissions. In addition, when more fuel was obtained, the combustion temperature was increased, improving BTE and reducing HC emissions under lean combustion conditions.

The influences of wall are important in practical combustion devices. In present study, the propagating processes of near wall ignited laminar methane/hydrogen/air flame were explored under different hydrogen fractions in a constant volume combustion vessel mimicking engine geometry. Results showed that both effects of heat losses and wall compression cause difference of local flame speed at different directions. The flow inside burned zone induced by compression accelerates local flame speed at direction opposing to the wall, makes the local flame speed higher than freely propagating laminar flame speed. Meanwhile, flame shape changing process was quantified by fitted ellipses. It was found that flame shapes are strongly affected by the wall compression but not obviously influenced by hydrogen addition. Hydrogen addition exacerbated flame instabilities, notably improved the local and global flame speeds due to both increase of laminar flame speed and flow velocity inside burned zone. The maximum local speed increase from 258 cm/s for 20% hydrogen fraction to 695 cm/s for 80% hydrogen fraction. Maximum combustion pressure and maximum pressure rise rate were slightly increased by hydrogen addition. On contrary, the combustion duration notably decreased nearly 3 times when hydrogen fraction increased from 20% to 80%.

It has been shown that identifying the structural holes in social networks may help people analyze complex networks, which is crucial in community detection, diffusion control, viral marketing, and academic activities. Structural holes bridge different communities and gain access to multiple sources of information flow. In this paper, we devised a structural hole detection algorithm, known as the Conductance&ndash, Degree structural hole detection algorithm (CD-SHA), which computes the conductance and degree score of a vertex to identify the structural hole spanners in social networks. Next, we proposed an improved label propagation algorithm based on conductance (C-LPA) to filter the jamming nodes, which have a high conductance and degree score but are not structural holes. Finally, we evaluated the performance of the algorithm on different real-world networks, and we calculated several metrics for both structural holes and communities. The experimental results show that the algorithm can detect the structural holes and communities accurately and efficiently.

Supported carbon quantum dots (CQDs), used as fluorescent sensors for the detection of metal ions, have rarely been used to remove heavy metals from water. Nitrogen-doped CQDs immobilized in hydrophilic silica hydrogels exhibited a more superior sensitivity and selectivity for the detection of Re(VII) and Cr(VI) than other metal ions, including Fe(III), Fe(II), Zn(II), Cu(II) and Mn(II). For the first time, low limits of detection (LOD) of 2.3 μM for Re(VII) detection and 65 nM for Cr(VI) detection were reported by a facile method. Based on the high selectivity of fluorescent silica hydrogels for Re(VII) and Cr(VI) detection, the removal of Re(VII) and Cr(VI) by graphene oxide (GO) in water was monitored with the hydrogels used as a turn-off fluorescent sensing platform. The consistent results of the sorption isotherms of each metal on GO, which were obtained from the fluorescence spectra and by UV absorption, further verified the possibility of monitoring metal removal by fluorescence detection. Remarkably, GO removed 1186 mg/g of Re(VII) but only 178 mg/g of Cr(VI). The density functional theory (DFT) calculations indicated that both Re(VII) and Cr(VI) formed stable bonds with silica hydrogels, confirming that the interactions between the metal ions and the substrate would promote the fluorescence quenching of the supported CQDs. On the other hand, Re(VII) interacted more strongly with the carboxyl groups of GO than Cr(VI). In addition, a real-time detection system was designed to alarm the service life of a GO filter used for Re(VII) removal.

Wood-based plastics obtained via chemical modifications are usually dark and opaque, which limits their potential applications. All-wood plastics (AWPs) derived from ball-milled mulberry wood (BMMW) via an efficient heterogeneous esterification for 2 h in dimethyl sulfoxide (DMSO)/1-butyl-3-methylimidazolium chloride (BMIMCl) with the molar ratios of DMSO to BMIMCl at 5.9:1 exhibit a highly translucent appearance. With desirable thermoplasticity and tensile strength, AWPs can be processed into light-permeable specimens and transparent film. FT-IR and solid-state 13 C NMR spectra provide evidence for successful substitution of hydroxyl groups of BMMW by carboxybenzoyl groups. The darkness of AWPs arising from the oxidation of phenolic lignin into benzoquinone indicates that reaction time plays a critical role for controlling the transparency of AWPs. AWPs represent composite structures, including cellulose I and cellulose II. Different degradation mechanisms are observed among AWPs differently esterified. Moreover, the SEM and AFM images demonstrate the self-reinforcement of AWPs specimens and the heterogeneous surface of a transparent AWP film, respectively.

In this paper, the effects of direct water injection (WI) on characteristics of combustion and emissions for a hydrogen (H2)-fueled spark ignition (SI) engine were experimentally investigated. The experiments were conducted under different excess air ratios (λ) and ignition timing (IT). In each test, the water to air ratio (α) was varied, and the results were compared with baseline data without WI. The experimental results showed that in-cylinder pressure decreased, indicated thermal efficiency increased, and the flame development and propagation periods prolonged when WI was used. When α increased to 1.87%, NOx emissions expelled from the original engine separately decreased by 36.9% and 55.4% when IT were 5°CA BTDC and 15°CA BTDC at λ of 1.15.