Experimental and numerical studies of the ignition of ammonia/additive mixtures and dimethyl ether burning velocities

The incentive to limit global temperature rising and reduce man-made greenhouse emissions is driving the development and introduction of alternative fuels in current combustion engines. Ammonia and dimethyl ether (DME) both are considered as promising alternative fuels owing to their physical and chemical properties. This thesis focused on measuring the ignition delay times of ammonia and ammonia mixed with hydrogen, methane and DME, respectively, using rapid compression machine (RCM) and measuring the flame temperatures and burning velocities of DME/air mixtures using Raman scattering setup. The measurements were used to test the ability of chemical mechanisms describing the oxidation of these fuels. This study shows that all these additives show strong ignition-enhancing effect on NH3, while the effect of additives is non-linear. DME has the strongest ignition-enhancing effect on NH3, for instance, 5% DME addition decreases the ignition delay times of ammonia by 250K. During the course of this study a new NH3/DME mechanism that includes interactions between ammonia and DME species was developed, which predicts the ignition delay times of NH3/H2 and NH3/CH4 mixtures very well at the conditions studied. Kinetic analysis revealed that the ignition promoting effect of DME could be caused by its low temperature chain branching reactions. The measurements of DME/air flames were compared to predictions from one-dimensional flame calculations to assess the accuracy of different chemical mechanisms for DME oxidation. In some cases, the results permitted improved recommendations for the burning velocity of these mixtures

Fine root morphology and growth in response to nitrogen addition through drip fertigation in a Populus × euramericana “Guariento” plantation over multiple years

International audienceAbstractKey messageNitrogen addition through drip fertigation to a poplar plantation (Populus × euramericana“Guariento”) promoted fine root growth only in the early period. The relationship between root growth and soil N content was positive in the first 2 years, but became negative in the third year when the soil N availability had substantially increased.ContextNitrogen (N) deficiency is common in forest soils, and N addition is sometimes applied in the case of intensive plantations. There is a need to better document the impact of N addition through the high-efficiency fertilization technique on fine root morphology and growth, given their importance for the uptake of nutrients and for tree growth.AimsWe aimed to quantitatively investigate the responses of fine roots in morphology and growth to N addition through surface drip fertigation over multiple years in a Populus × euramericana “Guariento” plantation.MethodsA field experiment that included four drip fertigation treatments with N addition levels (0, 60, 120, and 180 kg N ha−1 year−1) was conducted for three successive years. A coring method was used to sample soils and quantify the root morphological traits and soil N content along 0–60-cm profiles.ResultsThe root biomass density, length, surface area, specific length, and tissue density were significantly higher in the N addition treatments than those in the control after the first year, but the positive effect decreased in the second year. In the third year, root biomass in the N addition treatments was even lower by 11–39% than that in the control. The relationship between root growth and soil N content was also positive in the first 2 years and negative in the third year.ConclusionN addition promoted fine root growth mainly in the shallow soil and in the early period of experiment. The relationship between root growth and soil N content became negative in the third year when the soil N availability had substantially increased. It is suggested that fine roots adjust their growth and morphology in response to N availability varying along the soil profile and with the fertilization duration

IMECE2004-59893 WAVE MOTION OF A NONLINEAR ELASTIC BAR SUBJECTED TO AXIAL EXCITATION

ABSTRACT This research intends to investigate the wave motion in a nonlinear elastic bar with large deflection subjected to an axial external exertion. A nonlinear elastic constitutive relation governs the material of the bar. General form of the nonlinear wave equations governing the wave motion in the bar is derived. With a modified complete approximate method, the asymptotic solution of solitary wave is developed for theoretical and numerical analyses of the wave motion. Various initial conditions and system parameters are considered for investigating the shape and propagation of the nonlinear elastic wave. With the governing equation of the wave motion of the bar and the solution developed, the characteristics of the nonlinear elastic wave of the bar are analyzed theoretically and numerically. Properties of the wave propagation and the effects of the system parameters of the bar and the influences of the initial conditions to the characteristics of the wave motion are investigated in details. Based on the theoretical analysis as well as the numerical simulations, it is found that the nonlinearity of the elastic bar may cause solitary wave in the bar. The velocity of the solitary wave propagating in the bar is related to the initial condition of the wave motion. This exhibits an obvious different characteristic between the nonlinear wave and that of the linear wave of an elastic bar. It is also found in the research that the solitary wave is a pulse wave with stable propagation. If the stability of the wave propagation is destroyed, the solitary wave will no longer exist. The results of the present research may provide guidelines for the wave motion analysis of nonlinear elastic solid elements

Effects of MWNT nanofillers on structures and properties of PVA electrospun nanofibres

In this study, we have electrospun poly(vinyl alcohol)(PVA) nanofibres and PVA composite nanofibres containing multi-wall carbon nanotubes (MWNTs) (4.5 wt%), and examined the effect of the carbon nanotubes and the PVA morphology change induced by post-spinning treatments on the tensile properties, surface hydrophilicity and thermal stability of the nanofibres. Through differential scanning calorimetry (DSC) and wide-angle x-ray diffraction (WAXD) characterizations, we have observed that the presence of the carbon nanotubes nucleated crystallization of PVA in the MWNTs/PVA composite nanofibres, and hence considerably improved the fibre tensile strength. Also, the presence of carbon nanotubes in PVA reduced the fibre diameter and the surface hydrophilicity of the nanofibre mat. The MWNTs/PVA composite nanofibres and the neat PVA nanofibres responded differently to post-spinning treatments, such as soaking in methanol and crosslinking with glutaric dialdehyde, with the purpose of increasing PVA crystallinity and establishing a crosslinked PVA network, respectively. The presence of carbon nanotubes reduced the PVA crystallization rate during the methanol treatment, but prevented the decrease of crystallinity induced by the crosslinking reaction. In comparison with the crosslinking reaction, the methanol treatment resulted in better improvement in the fibre tensile strength and less reduction in the tensile strain. In addition, the presence of carbon nanotubes reduced the onset decomposition temperature of the composite nanofibres, but stabilized the thermal degradation for the post-spinning treated nanofibres. The MWNTs/PVA composite nanofibres treated by both methanol and crosslinking reaction gave the largest improvement in the fibre tensile strength, water contact angle and thermal stability

DETC2005-84151 FINITE ELEMENT ANALYSIS FOR INTERIOR BOOMING NOISE REDUCTION IN A TRACTOR CABIN

ABSTRACT This paper presents a finite element approach to analyze the "boom" noise for a compact tractor cabin. The tractor cabin is initially designed to have a structure made up of steel beams and aluminum panels, as well as PMAA panels in windshield, backlight and windows. Cavity acoustic modes of the cab are evaluated and the acoustic resonant frequencies are identified. The study on the structural-borne noise from the cabin structural vibration generated by the engine of the vehicle is performed. A coupled-field finite element model, counting the interactions between the air fluid inside the cabin compartment and the cabin exterior structure, is presented for investigating the structural-borne noise in a low frequency range of 20 Hz to 80 Hz. This range has shown strong boom effects. The interior noise level at driver's right ear position is investigated. The peak noise levels at the position are determined. The effects of additional stiffeners and damping layers on the boom noise are also investigated

Directional water-transfer through fabrics induced by asymmetric wettability

Fabrics having an interesting unidirectional water-transfer effect have been prepared by a special coating technique to create a wettability gradient across the fabric thickness, and the treated fabrics also show considerably different breakthrough pressures on the two fabric sides

Experimental and numerical analysis of the autoignition behavior of NH3 and NH3/H2 mixtures at high pressure

Measurements of autoignition delay times of NH3 and NH3/H2 mixtures in a rapid compression machine are reported at pressures from 20–75 bar and temperatures in the range 1040–1210 K. The equivalence ratio, using O2/N2/Ar mixtures as oxidizer, varied for pure NH3 from 0.5 to 3.0; NH3/H2 mixtures with H2 fraction between 0 and 10% were examined at equivalence ratios 0.5 and 1.0. In contrast to many hydrocarbon fuels, the results indicate that, for the conditions studied, autoignition of NH3 becomes slower with increasing equivalence ratio. Hydrogen is seen to have a strong ignition-enhancing effect on NH3. The experimental data, which show similar trends to those observed previously by He et al. (2019) [28], were used to evaluate four NH3 oxidation mechanisms: a new version of the mechanism described by Glarborg et al. (2018) [29], with an updated rate constant for the formation of hydrazine, NH2 + NH2 (+M) = N2H4 (+M), and the literature mechanisms from Klippenstein et al. (2011) [30], Mathieu and Petersen (2015) [25], and Shrestha et al. (2018) [31]. In general, the mechanism from this study has the best performance, yielding satisfactory prediction of ignition delay times both of pure NH3 and NH3/H2 mixtures at high pressures (40–60 bar). Kinetic analysis based on present mechanism indicates that the ignition enhancing effect of H2 on NH3 is closely related to the formation and decomposition of H2O2; even modest hydrogen addition changes the identity of the major reactions from those involving NHx radicals to those that dominate the H2/O2 mechanism. Flux analysis shows that the oxidation path of NH3 is not influenced by H2 addition. We also indicate the methodological importance of using a non-reactive mixture having the same heat capacity as the reactive mixture for determining the non-reactive volume trace for simulation purposes, as well as that of limiting the variation in temperature after compression, by limiting the uncertainty in the experimentally determined quantities that characterize the state of the mixture