Electron microscopy of lignocellulosic biomass following high-temperature pretreatment revealed the presence of spherical formations on the surface of the residual biomass. The hypothesis that these droplet formations are composed of lignins and possible lignin carbohydrate complexes is being explored. Experiments were conducted to better understand the formation of these "lignin" droplets and the possible implications they might have on the enzymatic saccharification of pretreated biomass. It was demonstrated that these droplets are produced from corn stover during pretreatment under neutral and acidic pH at and above 130 degrees C, and that they can deposit back onto the surface of residual biomass. The deposition of droplets produced under certain pretreatment conditions (acidic pH; T > 150 degrees C) and captured onto pure cellulose was shown to have a negative effect (5-20%) on the enzymatic saccharification of this substrate. It was noted that droplet density (per unit area) was greater and droplet size more variable under conditions where the greatest impact on enzymatic cellulose conversion was observed. These results indicate that this phenomenon has the potential to adversely affect the efficiency of enzymatic conversion in a lignocellulosic biorefinery.

This paper presents results of a study to investigate the effect of leading edge erosion on the aerodynamic performance of a wind turbine airfoil. The tests were conducted on the DU 96-W-180 wind turbine airfoil at three Reynolds numbers between 1 million and 1.85 million, and angles of attack spanning the nominal low drag range of the airfoil. The airfoil was tested with simulated leading edge erosion by varying both the type and severity of the erosion to investigate the loss in performance due to an eroded leading edge. Tests were also run with simulated bugs on the airfoil to assess the impact of insect accretion on airfoil performance. The objective was to develop a baseline understanding of the aerodynamic effects of varying levels of leading edge erosion and to quantify their relative impact on airfoil performance. Results show that leading edge erosion can produce substantial airfoil performance degradation, yielding a large increase in drag coupled with a significant loss in lift near the upper corner of the drag polar, which is key to maximizing wind turbine energy production.

Transgenic down-regulation of the Pt4CL1 gene family encoding 4-coumarate:coenzyme A ligase (4CL) has been reported as a means for reducing lignin content in cell walls and increasing overall growth rates, thereby improving feedstock quality for paper and bioethanol production. Using hybrid poplar (Populus tremula 3 Populus alba), we applied this strategy and examined field-grown transformants for both effects on wood biochemistry and tree productivity. The reductions in lignin contents obtained correlated well with 4CL RNA expression, with a sharp decrease in lignin amount being observed for RNA expression below approximately 50% of the nontransgenic control. Relatively small lignin reductions of approximately 10% were associated with reduced productivity, decreased wood syringyl/guaiacyl lignin monomer ratios, and a small increase in the level of incorporation of H-monomers (p-hydroxyphenyl) into cell walls. Transgenic events with less than approximately 50% 4CL RNA expression were characterized by patches of reddish-brown discolored wood that had approximately twice the extractive content of controls (largely complex polyphenolics). There was no evidence that substantially reduced lignin contents increased growth rates or saccharification potential. Our results suggest that the capacity for lignin reduction is limited; below a threshold, large changes in wood chemistry and plant metabolism were observed that adversely affected productivity and potential ethanol yield. They also underline the importance of field studies to obtain physiologically meaningful results and to support technology development with transgenic trees.Composed of diverse layers of cellulose microfibrils and amorphous hemicelluloses within a matrix of pectins, proteins, and lignin, the secondary cell walls of plants are diverse in their morphology, chemistry, and physiological functions. Lignification is of particular interest, as it exhibits highly predictable temporal and spatial patterning and is the last major step in the structural reinforcement of cell walls before the protoplast is dissolved (Donaldson, 2001

The glycoside hydrolase family 5 endocellulase, E1 (Cel5A), from Acidothermus cellulolyticus was transformed into both Nicotiana tabacum and Zea mays with expression targeted to the cell wall under a constitutive promoter. Here we explore the possibility that in planta expression of endocellulases will allow these enzymes to access their substrates during cell wall construction, rendering cellulose more amenable to pretreatment and enzyme digestion. Tobacco and maize plants were healthy and developed normally compared with the wild type (WT). After thermochemical pretreatment and enzyme digestion, transformed plants were clearly more digestible than WT, requiring lower pretreatment severity to achieve comparable conversion levels. Furthermore, the decreased recalcitrance was not due to post-pretreatment residual E1 activity and could not be reproduced by the addition of exogenous E1 to the biomass prior to pretreatment, indicating that the expression of E1 during cell wall construction altered the inherent recalcitrance of the cell wall.

Most design and analysis methods widely used for horizontal axis wind turbine performance prediction, such as the PROP code, are based on the traditional 2-D blade element/momentum theory (BEMT) methods, which are inadequate and underpredict the wind turbine rotor power output in the high-wind/peak-power condition, owing to effects of rotation on the wind turbine blade boundary layer. Although the deficiencies of the methods have been known for some time, this area has been neglected. The continued development of viable and well-established stall-regulated wind-turbine technology makes this research topic timely and particularly relevant to reducing the cost of wind energy.The main aim of the present paper is to describe and analyze the fundamental flow phenomena that characterize the boundary layer on rotating blades, and to develop a preliminary stall-delay model that modifies the 2-D airfoil data so as to simulate the 3-D stall-delay effects. The following steps were taken in the development of the model: 1) analysis of the 3-D integral boundary-layer equations for a reference system rotating with the blade, 2) description of the effects of rotor rotation on the separation point and its causes, and 3) determination of a simple correction formula to obtain rotating rotor lift coefficient Ci(a) and drag coefficient Cd(a) data from measured 2-D airfoil data. The preliminary 3-D stall-delay model consists of two key parameters (the ratio of local chord to local radius c/r the ratio of rotation speed to freestream velocity A) and three empirical correction factors (a, b, d}. The stall-delay model is consistent with the blade element/momentum theory method and the Viterna/Tangler model, and the 3-D stall-delay model can be incorporated into the state of the art performance prediction codes, such as PROP. Through comparison with the field test data, the new model for 3-D stall-delay shows good agreement between predictions and experiments. The new model should be of great use in existing codes for horizontal axis wind turbine design and analysis. 1 Nomenclature a = correction factor in stall-delay model b = correction factor in stall-delay model c = blade chord Cd = drag coefficient Cf = skin friction coefficient Ci = lift coefficient d = correction factor in stall-delay model H = boundary layer shape factor k = velocity gradient p = air pressure r,9,z = cylindrical coordinates R = blade radius Re = Reynolds number s = separation point on airfoil surface u, v, w = velocity components u e = boundary layer edge velocity Woo = freestream velocity V w = wind speed a = angle of attack 0 W = stream angle p -air density 01,62 = boundary-layer momentum thickness 61,62 = boundary-layer displacement thickness Downloaded by MONASH UNIVERSITY on September 19, 2013 | http://arc.aiaa.org |