Bacterial contamination is known as a major cause of the reduction in ethanol yield during bioethanol production by Saccharomyces cerevisiae. Acetate is an effective agent for the prevention of bacterial contamination, but it negatively affects the fermentation ability of S. cerevisiae. We have proposed that the combined use of organic acids including acetate and lactate and yeast strains tolerant to organic acids may be effective for the elimination of principally lactic acid bacterial (LAB) contamination. In a previous study employing laboratory S. cerevisiae strains, we showed that overexpression of the HAA1 gene, which encodes a transcriptional activator, could be a useful molecular breeding method for acetate-tolerant yeast strains. In the present study, we constructed a HAA1-overexpressing diploid strain (MAT a/α, named ER HAA1-OP) derived from the industrial bioethanol strain Ethanol Red (ER). ER HAA1-OP showed tolerance not only to acetate but also to lactate, and this tolerance was dependent on the increased expression of HAA1 gene. The ethanol production ability of ER HAA1-OP was almost equivalent to that of the parent strain during the bioethanol production process from sugarcane molasses in the absence of acetate. The addition of acetate at 0.5% (w/v, pH 4.5) inhibited the fermentation ability of the parent strain, but such an inhibition was not observed in the ethanol production process using ER HAA1-OP.

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The geometric structure of a diesel fuel injector plays a significant role in the injected spray behaviours. Furthermore, the characteristics of diesel fuel spray are well known to have a crucial impact on the combustion process and the resulting engine performance. A single-hole diesel injector is usually applied in fundamental internal flow, spray and combustion research. On the contrary, under most realistic operating conditions, an axisymmetric multi-hole injector is used to couple with the combustion chamber. In the present paper, a detailed experimental investigation of the diesel fuel spray emerging from a single-hole nozzle and a multi-hole nozzle and a computational study of the internal flow inside these two kinds of configuration are reported. Globally, the analysis mainly focused on the different injection processes (the injection rate) and the spray structures of the single-hole nozzle and the multi-hole nozzle, keeping the same sac configuration, the same nozzle hole diameter of 0.1 mm and the same hole length of 0.8 mm for an injection quantity of 2 mm 3 per hole. High-speed images of the spray development were freeze captured by Mie scattering at 10,000 frames/s under the conditions where the rail pressure varies from 80 to 180 MPa, the ambient pressure is 1.5 MPa, the room temperature T = 298 K and there is an air environment. Image-processing algorithms were used to determine the fuel spray characteristics. The experimental results revealed that the spray of a multi-hole nozzle with 10 holes had a longer injection duration, a lower injection rate, a shorter spray tip penetration, a wider spray angle and a wider spray cone angle than those of a single-hole nozzle. The spray behaviours of the multi-hole nozzle were more sensitive to variation in the pressure than those of the single-hole nozzle. Moreover, aiming to correlate the observed spray properties to the internal flow phenomenon, computational fluid dynamics simulations were also carried out under the baseline conditions. The more complicated internal flow inside the multi-hole nozzle provided added insight into the different spray characteristics for these two nozzles.