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To enhance the fuel-gas mixing and phase transition process, the fuel is injected by twin injectors in a large-bore low-speed two-stroke marine engine, while the cylinder condition has reached the transcritical and supercritical conditions. The twin-injector configuration has a great potential for further optimization, but the exploration on the outcome of collision and phase transition was still limited. Therefore, this work aims to study the effect of various collision angles (60°, 90°, 120°, 150°) and critical conditions (sub/trans/supercritical) on the twin-spray collision process using optical techniques. A wide range of experimental cases are conducted to provide an analysis and database for future modeling validation. The post-collisional spray structures, spatial distribution, and periphery features are analyzed to characterize the droplet’s collision. The results show that with the collision angle increasing, the higher collision velocity enhances the mass transfer while the minor vertical component results in a smaller axial dispersion. Because of the trade-off relationship between the vertical velocity component and pre-collision penetration, a higher reduction in droplet momentum results in a slighter collision behavior. At the collision angle of 150°, the subcritical condition tends to result in an off-axis collision. Under the transcritical (P) condition, the probability of head-on collision increases and presents a wider spatial distribution. But under the supercritical condition, because of the existence of the liquid collision, the thermal conversion among phases is accelerated, while the ambient resistance is reduced. Moreover, an exponential correlation of collision liquid length is formulated to predict the axial dispersion based on various critical conditions.

In a large-bore marine engine, the larger cylinder diameter and space correspond to more fuel injection in a limited time of each working cycle. The fuel injection of multiple injectors can achieve fast atomization and homogeneous fuel-gas mixing performance, which is liable to cause the spray collision problem, but the twin-spray collision phenomenon is rarely observed and studied. Therefore, this work aims to explore the effect of various collision angles (60°, 90°, 120°, and 150°) and injection pressures (60, 100, 140, and 180 MPa) on the combustion and soot emission of twin-spray collision process. Based on a large-bore constant volume chamber and two optical diagnostic techniques, the ignition delay time, initial ignition location, flame collision structure, and soot emission luminosity are obtained in a reactive atmosphere. The results show that near the collision point, there exists a fan-shaped flame structure. Due to the mutual entrainment from twin sprays, the ignition delay time of twin-spray collision is shorter than that of single free spray. As a result, at the constant diesel injection mass, the soot emission intensity of twin-spray collision becomes higher. With the collision angle increasing, the ignition delay time becomes shorter, and the initial ignition location gradually moves upstream, while the soot emission intensity becomes higher. The time integrated natural luminosity difference between 60 and 180 MPa gradually decreases and then reverses. Moreover, the wider collision angle also makes the ignition delay time less sensitive to the injection pressure.

The combustion and emission characteristics of a dual-fuel spark-ignition engine with direct injection of gasoline surrogates and port injection of ethanol were studied. Toluene reference fuel with different research octane number namely TRF#1, TRF#2, TRF#3, TRF#4 and TRF#5 were employed as gasoline surrogates, in which TRF#1 with high octane number was to simulate commercial gasoline under direct-injection spark-ignition mode as comparison. For dual-fuel spark-ignition mode, the ethanol port-injection ratios were 21%, 25%, 29%, 32% and 35%, respectively. The results demonstrated that with the increase of the ethanol ratio, the knock-limited spark timing was advanced gradually. The emissions of hydrocarbon, ethane, propylene, isopentane, cyclohexane and aromatic hydrocarbons reduced while CO, NOx, ethylene, acetaldehyde and ethanol increased. Compared to TRF#1 in direct-injection spark-ignition mode, the indicated thermal efficiencies of dual-fuel spark-ignition mode were slightly lower under most test conditions. When direct injection of TRF#3, TRF#4, TRF#5 and the ethanol ratio was higher than 29%, some of the indicated thermal efficiencies of the engine were consistent with or higher than that of TRF#1 in direct-injection spark-ignition mode. Based on dual-fuel spark-ignition mode and with the assistance of port injection of ethanol, the indicated thermal efficiency of low research octane number fuels was comparable to that of TRF#1 in direct-injection spark-ignition mode.

[EN] Computational fluid dynamics (CFD) modeling has many potentials for the design and calibration of modern and future engine concepts, including facilitating the exploration of operation conditions and casting light on the involved physical and chemical phenomena. As more attention is paid to the matching of different fuel types and combustion strategies, the use of detailed chemistry in characterizing auto-ignition, flame stabilization processes and the formation of pollutant emissions is becoming critical, yet computationally intensive. Therefore, there is much interest in using tabulated approaches to account for detailed chemistry with an affordable computational cost. In the present work, the tabulated flamelet progress variable approach (TFPV), based on flamelet assumptions, was investigated and validated by simulating constant-volume Diesel combustion with primary reference fuels - binary mixtures of n-heptane and iso-octane. Simulations were initially carried out to evaluate and compare the performance of two kinetic models in homogeneous reactors and laminar diffusion flames, followed by turbulent reacting spray simulations considering different fuels, ambient temperatures, and oxygen concentrations. The sensitivity study of the turbulent Schmidt number was then conducted, and results in terms of ignition delay and lift-off length were compared with experimental data to determine a more appropriate global constant. Finally, parametric variations of ambient temperature and oxygen concentration were performed for six fuel blends ranging from PRF0 (n-heptane) to PRF100 (iso-octane), confirming the validity of the TFPV model., Authors acknowledge the financial support from the China Scholarship Council (No. 201806230180) and Natural Science Foundation of China (No. 51961135105) for the first author's study in Politecnico di Milano, Italy

Multiple injection strategies are commonly used in conventional Diesel engines due to the flexibility for optimizing heat-release timing with a consequent improvement in fuel economy and engine-out emissions. This is also desirable in low-temperature combustion (LTC) engines since it offers the potential to reduce unburned hydrocarbon and CO emissions. To better utilize these benefits and find optimal calibrations of split injection strategies, it is imperative that the fundamental processes of multiple injection combustion are understood and computational fluid dynamics models accurately describe the flow dynamics and combustion characteristics between different injection events. To this end, this work is dedicated to the identification of suitable methodologies to predict the multiple injection combustion process. Two different approaches: Representative Interactive Flamelet model (RIF) and Tabulated Flamelet Progress Variable (TFPV) are compared and multiple n-dodecane Spray A injections from the Engine Combustion Network are simulated using the RANS methods with both standard k − ε and k − ω SST models. Evaluations of different turbulence and combustion models are carried out by comparing computed and measured data in terms of the mixing, penetration, first- and second-stage ignition characteristics, flame structures and soot formation.

Given the complexity and uncertainty of diesel compositions, it is of great challenges to study the fundamental combustion processes and mechanism of diesel fuel, in particular the gaseous and particulate pollutant formation mechanisms. A reasonably designed diesel surrogate is proved to be an effective way to study the fundamental combustion mechanism of diesel fuel. However, most existing diesel surrogates mainly adopt light hydrocarbon components, increasing the difficulty of accurately reflecting the physical and chemical properties of practical diesel fuel or the combustion and emissions characteristics of diesel engines. Therefore, in this study, a methodology to construct diesel surrogates with C10 ∼ C18 hydrocarbon components based on fuel properties and engine combustion and emissions characteristics was proposed. First, the key physical and chemical fuel properties that affect fuel injection, atomization, ignition, combustion, engine efficiency and emissions were discussed in detail. Second, 13 candidate components were chosen to represent n-alkanes, iso-alkanes, cycloparaffins and aromatics and blended with commercial diesel fuel in different proportions. Fuel injection, spray, ignition and combustion phase, engine efficiency and emissions versus changed blending component and proportion were systematically investigated. In particular, the effects of the cetane number and fuel volatility on combustion and emissions were investigated under fixed injection timing and fixed ignition timing conditions, respectively. Afterward, the key physical and chemical parameters of the surrogate fuels were defined, and the constraint equations were constructed for different parameters. Considered the uncertainties in the components and physicochemical properties of the actual diesel fuel, it is believed that the construction of surrogate fuel has only reasonable solutions and there is no optimal solution. Finally, three diesel surrogates were proposed from the feasible domains of constraint equations, including a 3-Components surrogate (41.3% n-hexadecane, 36.8% 2,2,4,4,6,8,8-heptamethylnonane (HMN), 21.9% 1-methylnaphthalene, by mol.), a 5-Components surrogate (21.6% n-hexadecane, 15.5% n-octadecane, 26.0% HMN, 20.7% 1-methylnaphthalene, 16.2% decalin, by mol.) and a 7-Components surrogate (21.5% n-hexadecane, 15.4% n-octadecane, 25.8% HMN, 13.7% 1-methylnaphthalene, 8.1% decalin, 8.1% n-butylbenzene, 7.4% n-butylcyclohexane, by mol.). It is found that the surrogates proposed in this study can accurately reproduce actual engine combustion characteristics. Also, the gaseous emissions of the 5-Components surrogate are closest to those of the target diesel fuel in the tested engine operation conditions.

[EN] The pre-blending of low- and high-reactivity fuels for a single direct injection system has been proven to be an effective way to control the reactivity of mixtures in compression ignition engines, having the potential to simultaneously reduce fuel consumption and pollutant emissions. However, there is not much knowledge about the complex physical-chemical phenomena in the turbulent sprays with fuels having widely different autoignition qualities, although this information is critical for the design and development of cleaner combustion systems based on this concept. For this reason, a computational analysis of ignition behavior, flame structure, and soot production for reacting sprays with five primary reference fuels (PRFs), from PRF0 (n-heptane) to PRF80 (20% n-heptane, 80% iso-octane) with 20% increment in iso-octane mass fraction, was first performed using the Tabulated Flamelet Progress Variable (TFPV) approach based on the tabulation of diffusion flamelets for different scalar dissipation rates. The temporal and spatial features of the flame structure and soot formation for different fuels were investigated with the so-called intensity-axial distance-time (IXT) plots. Then, ten PRFs, from RRF0 to PRF90 with 10% increment in iso-octane mass fraction, were investigated and compared in a heavy-duty Diesel engine operating at the conventional high-temperature, short-ignition delay (HTSID) condition. The injection timing was altered from -5 to -13 degrees ATDC to optimize the combustion phase and engine performance for different fuels. The results showed that PRF70 exhibited the best performance at the tested condition, which reduced the soot mass to 5% of the baseline value without sacrificing fuel efficiency., Authors acknowledge the financial support from the China Scholarship Council (No. 201806230180) and Natural Science Foundation of China (No. 51961135105) for the first author's study in Politecnico di Milano, Italy

Fast and high-fidelity combustion models including detailed kinetics and turbulence chemistry interaction are necessary to support design and development of heavy-duty diesel engines. In this work, the authors intend to present and validate tabulated flamelet progress variable model based on tabulation of laminar diffusion flamelets for different scalar dissipation rate, whose predictability highly depends on the description of fuel–air mixing process in which engine mesh layout plays an important role. To this end, two grids were compared and assessed: in both grids, cells were aligned on the spray direction with such region being enlarged in the second one, where the near-nozzle and near-wall mesh resolution were also improved, which is expected to better account for both spray dynamics and flame–wall interaction dominating the combustion process in diesel engines. Flame structure, in-cylinder pressure, apparent heat release rate, and emissions for different relevant operating points were compared and analyzed to identify the most suitable mesh. Afterwards, simulations were carried out in a heavy-duty engine considering 20 operating points, allowing to comprehensively verify the validity of tabulated flamelet progress variable model. The results demonstrated that the proposed approach was capable to accurately predict in-cylinder pressure evolution and NO x formation across a wide engine map.

Recently, as a kind of renewable fuel, low-grade biogas has been researched to apply in internal combustion engine. In this paper, an experimental study was conducted to study the influence of injection strategies on the efficient utilization of low-grade biogas in Reactivity Controlled Compression Ignition (RCCI) mode with port fuel injection of biogas and in-cylinder direct injection of diesel based on a modified electronic controlled high-pressure directly injected compression ignition engine. Considered the high proportion of inert gas in biogas, a four-components simulated gas (H2:CO:CH4:N2 = 5:40:5:50 vol%) has been selected as test fuels to simulate biogas. The effects of several injection control parameters such as pilot injection timing, main injection timing, common rail pressure and pilot injection ratio on the combustion and emissions are analyzed in detail. The research demonstrates that the main injection timing can effectively control the combustion phase and excessive early pilot injection timing leads to retard of combustion. CO emissions are relatively high due to homogenous charge of biogas. NOx and smoke emissions can be effectively controlled. In RCCI mode, the indicated thermal efficiency of biogas/diesel can reach 40%.

This paper presents a preliminary experimental study on the combustion and emission characteristics of Dual Fuel Sequential Combustion (DFSC) mode, in which port fuel injection of n-heptane combined with in-cylinder, directly injected ethanol, n-butanol and n-amyl alcohol are used in a single-cylinder engine at fixed directly injection timing. The results show that the heat release can be divided mainly into three stages: low temperature reaction, high temperature reaction of n-heptane and the directly injected fuel combustion stage. The amount of port injected n-heptane plays a key role in the maximum in-cylinder pressure (Pmax), maximum in-cylinder mass averaged temperature (Tmax) and the maximum pressure rise rate. For the high overall lower heating values (LHVs) per-cycle, the CO emissions decrease with the increase of the premixed ratio. By contrast, the CO emissions increase with the premixed ratio when the overall LHVs per-cycle are kept at medium and low levels. The NOx and soot emissions are all kept at low levels for the experimental conditions. In particular, the higher latent heat, lower cetane values and the shorter carbon chains associated with ethanol lead to lower NOx and soot emissions than those of n-butanol and n-amyl alcohol. When directly injection of n-butanol and at low loads, with optimized premixed ratio, the indicated thermal efficiency can be higher than 46% meanwhile maintaining low emissions.

Spark-ignition (SI) aviation piston engines are widely used on light helicopters and unmanned aerial vehicles (UAVs) because of the high-power density and ultra-high cost performance. Kerosene with high flash point is expected to improve safety of aforementioned aircrafts by replacing gasoline. However, in spark-ignition mode, kerosene is difficult to mix and is easy to knock. Short-chain alcohols have high volatility and octane number which can just make up for some defects of kerosene. In this paper, three kinds of alcohols including ethanol, n-propanol and n-butanol were blended with aviation kerosene (RP-3) by volume fraction of 30%, 50%, 70%, respectively. The combustion and emission characteristics of the blended fuels were deeply studied on a typical spark-ignition aviation piston engine. Meanwhile, engine performance fueled with commercial gasoline was also tested for comparison. Results indicated that alcohol/kerosene blends could reach higher brake thermal efficiency (BTE) (alcohol ratio ≥50%) compared to gasoline. Carbon monoxide (CO) and nitrogen oxides (NOx) emissions of blended fuels expressed dramatically descending. With the increase in alcohol ratio, the CO, hydrocarbons (HC) and soot emissions gradually decreased. The brake thermal efficiency showed an upward trend with the increase of alcohol ratios. The brake thermal efficiency of E70, P70 and B70 were increased by 2.15%, 3.52% and 6.51%, and the CO emissions of E70, P70 and B70 were reduced by 39.8%, 38.5% and 49.0%, respectively, compared to those of gasoline. Notably, n-butanol/kerosene blends exhibited the better combustion and emission characteristics, which had the higher efficiency and lower CO, HC and soot emissions.

Based on three-component gasoline surrogates and five-component diesel surrogates, the effects of fuel reactivity of port injection fuel and direct injection fuel on combustion and emission characteristics of reactivity controlled compression ignition (RCCI) mode were systematically studied. The research octane number of port injection fuels and cetane number of direct injection fuels were modulated by changing the proportions of n-alkanes and iso-alkanes in surrogates. The results show that both the cetane number of direct injection fuel and research octane number of port injection fuel played the key role in the combustion phase of RCCI mode. When port injection fuel with research octane number ≤ 90, the low temperature heat release would occur. For premixed ratio of 0.8 and with RON70/CN55 as fuel, the CO emissions were the lowest (as low as 1585 ppm). Increasing the premixed ratio was an effective solution for suppressing NOx and particulate matter emissions. For premixed ratio increased from 0.4 to 0.8, the peak value of nuclear mode particulates decreased from 109 to 107. Increasing the cetane number of direct injection fuels or lowering the research octane number of port injection fuels inhibited the emissions of formaldehyde, acetaldehyde, ethylene, propylene, acetylene and 1,3-butadiene effectively. Port injection of low research octane number was beneficial to reducing indicated specific fuel consumption. Fuel combination with port injection of RON70, direct injection of CN55 and premixed ratio of 0.8 was recommended taking into account of fuel consumption, and regulated/unregulated gas emissions.

Although the fabrication of SnS films by plasma-enhanced chemical vapour deposition (PECVD) has been reported by many researchers, to date there is no report available on the preparation of SnS films from solid source materials through the PECVD method. In the present work, SnS films are deposited from cost-effective and low-toxicity source materials (SnCl2·2H2O and Na2S2O3·5H2O) by a modified version of the PECVD technique. The X-ray diffraction (XRD) patterns demonstrate that the SnS films are successfully prepared. The field-emission scanning electron microscopy (FESEM) images reveal that the morphologies of the SnS films present mixed morphological features in accordance with the XRD results. The energy dispersive X-ray (EDX) analysis reveals that the stoichiometric ratios of the obtained SnS films are approximately the standard value of SnS, with slight deviations. The Raman spectra show that the Raman modes for the obtained SnS films are observed at 82, 109, 166, 195 and 226 cm−1. The optical properties are studied by UV–Vis–NIR spectrophotometry, and the results demonstrate that the optical band gap of the SnS film deposited on the soda-lime glass microscope slides is 1.5 eV. The absorption coefficient α is larger than 104 cm−1 in the photon energy range of 0.5–4 eV. Moreover, the morphology of SnS films changes with the deposition parameters, and a plate-like morphology can be deposited when the deposition temperature is decreased. Therefore, high-quality SnS films can be deposited by PECVD from solid source materials, and the distinct surface morphologies of the films can be attributed to the controllability of the PECVD deposition system.

In SiHa and CaSki cells, E6 and E7-targeting shRNA specifically and effectively knocked down human papillomavirus (HPV) 16 E6 and E7 at the transcriptional level, reduced the E6 and E7 mRNA levels by more than 80% compared with control cells that expressed a scrambled-sequence shRNA. E6 and E7 repression resulted in down-regulation of DNA methyltransferase mRNA and protein expression, decreased DNA methylation and increased mRNA expression levels of tumor suppressor genes, induced a certain apoptosis and inhibited proliferation in E6 and E7 shRNA-infected SiHa and CaSki cells compared with the uninfected cells. Repression of E6 and E7 oncogenes resulted in restoration of DNA methyltransferase suppressor pathways and induced apoptosis in HPV16-positive cervical carcinoma cell lines. Our findings suggest that the potential carcinogenic mechanism of HPV16 through influencing DNA methylation pathway to activate the development of cervical cancer exist, and maybe as a candidate therapeutic strategy for cervical and other HPV-associated cancers.

International audience; A novel method to produce strong and effective argon plasma jets in air is reported. By adjusting the structure and setting the location of a copper wire in the quartz tube, an intensive jet composed of two jets about 2.4 cm is produced with microwave power of 50 W. The microwave frequency is 2.45 GHz. Four twisty plasma jets about 2.0 cm for argon discharge are generated in four tubes at incident power of 120 W. A plasma ball of air discharge about 0.5 cm in radii is generated in the tube at the power of 100 W. The simulated distribution of electric field in the tube with a folded copper wire is consistent with the prediction of surface plasmon polaritons. Spectral diagnosis of the plasma jets is also discussed in this paper.

The production of surface microwave discharge is verified as a stable discharge excited by surface electromagnetic waves which is carried by surface plasmon polaritons. In order to achieve the purpose of coupling microwave energy efficiently and surface-wave discharge stably, in addition based on the dipole near-field radiation theory, we design the subwavelength diffraction grating. Moreover, the near-field radiation electric field distribution is studied by special proposed computation method and further the aim of design is achieved.

The generation mechanism of surface microwave discharge is studied by analyzing the simplified surface-wave plasma model, from which we show the spatial distribution characteristics of the surface electromagnetic waves. According to the characteristics of overdense plasma interacting with high-frequency electromagnetic waves, we get there is the surface plasmon polaritons (SPPs) phenomenon placed at the interface between overdense plasmas and dielectric. The characteristic parameters of SPPs in overdense plasmas are obtained by altering the plasma density and the collision frequency.

The determination method of the local electron density is shown based on millimeter wave interferometry and the electron density measuring is experimented on a cylindrical capacitively coupled plasmas (CCP) setup. Results show the excellent agreement between the radial density profiles in the central plane measured by interferometry with the proposed analysis method and by the Langmuir probe system.

Although surface-wave plasma (SWP) sources have many industrial applications, the ionization process for SWP discharges is not yet well understood. The resonant excitation of surface plasmon polaritons (SPPs) has recently been proposed to produce SWP efficiently, and this work presents a numerical study of the mechanism to produce SWP sources. Specifically, SWP resonantly excited by SPPs at low pressure (0.25 Torr) are modeled using a two-dimensional in the working space and three-dimensional in the velocity space particle-in-cell with the Monte Carlo collision method. Simulation results are sampled at different time steps, in which the detailed information about the distribution of electrons and electromagnetic fields is obtained. Results show that the mode conversion between surface waves of SPPs and electron plasma waves (EPWs) occurs efficiently at the location where the plasma density is higher than 3.57 × 1017 m−3. Due to the effect of the locally enhanced electric field of SPPs, the mode conversion...

In the present work, SnS2 films are deposited from solid source materials of S, Na2S2O3 ⋅ 5H2O and SnCl4 ⋅ 5H2O by the plasma-enhanced chemical vapor deposition (PECVD) method. Through controlling the deposition parameters, SnS2 films with nano-flower and nano-wall structure can be deposited without using any additives. By changing the deposition parameters, such as the molar ratio of S/Sn in source material, deposition temperature and the different kinds of sulfur source materials, SnS2 films with different morphology, building block and chemical composition can be produced. Furthermore, the formation mechanisms of the obtained morphologies have also been studied. It is mainly based on the crystal growth habit and the influence of the concentration of the sulfur radical in the vicinity of the growing surface. Moreover, the optical properties of SnS2 films have also been discussed. Due to the small size of SnS2 nanostructures, optical band gaps display the significant blue shift.

This paper describes a microwave plasma jet in an argon atmosphere capable of generating filamentary streamer discharges within the entire quartz tube excited by surface waves of surface plasmon polaritons (SPPs) located in the tube. Several discharge streamers are immediately produced at the end of the copper wire when incident power reaches 20 W. From simulations, the wavelength of the surface wave was found to be approximately 5.7 cm. Although the developing streamers induce E-field enhancements favoring discharging, more streamer bifurcations requiring additional energy to maintain discharging diminish the resonant enhanced E-field. The underlying mechanism of the proposed plasma jet is resonant excitation of SPPs and its interaction with plasmas.

Discharges in planar-type overdense plasmas caused by resonant excitation of surface plasmon polaritons (SPPs) are presented. The spatio-temporal evolution of surface waves of SPPs at the dielectric-plasma interface is reproduced numerically. It is found that different discharge light patterns are excited by different spatio-temporal wave fields. Moreover, the corrugation surface included in the proposed plasma sources plays a significant role in producing large-area uniform plasmas.

In this paper, the wave-mode conversion devices with three different structures have been devised for plasma heating. Surface-wave plasma (SWP) discharge analysis with or without considering the collision loss is presented theoretically. The comparative discharge experiments have been operated for obtaining the uniform stable microwave discharges. When a specially designed microwave appliance is selected as the proposed wave-mode conversion device, the discharges driven by resonant excitation with surface wave (SW) have yielded plasmas with density of about 1018 m−3 at the gas pressure larger than 10 Pa. By comparing the results, the production of large-area uniform stable overdense SWP is attributed to the resonant excitation with SW evenly on the whole dielectric-plasma interface by the application of the specially designed wave-mode conversion device.