Etude expérimentale de la combustion de biogaz dans un chambre de turbine à gaz

L'utilisation de combustibles gazeux issus de la biomasse dans les chambres de combustion LPP est généralement difficile car ces gaz ont un faible PCI, ainsi qu une forte variabilité dans leur composition. L'objectif de ce travail est d'étudier le domaine de stabilité ainsi que la structure de flamme d'un biogaz issue de la méthanisation des déchets (CH4+CO2+N2) dans une chambre de combustion de turbine à gaz. Les profils de vitesses radiales et axiales ont été obtenus par ADL. La structure et l'intensité de la zone de réaction ont été étudiées par chimilumunescence sur le radical CH*. Lorsqu'on passe du gaz naturel à du biogaz, le domaine de stabilité se décale vers des richesses plus hautes, la structure de la flamme est modifiée, et les amplitudes des instabilités sont atténuées. Le rôle joué par le CO2 dans ces évolutions est expliqué par une étude numérique, en particulier par la modification de la vitesse de flamme laminaire lorsque le méthane est dilué par du CO2

Thermal Structure of Laminar Methane/Air Flames: Influence of H 2 Enrichment and Reactants Preheating

International audienc

A pragmatic approach to assess the exposure of the honey bee (Apis mellifera) when subjected to pesticide spray

Plant protection spray treatments may expose non-target organisms to pesticides. In the pesticide registration procedure, the honey bee represents one of the non-target model species for which the risk posed by pesticides must be assessed on the basis of the hazard quotient (HQ). The HQ is defined as the ratio between environmental exposure and toxicity. For the honey bee, the HQ calculation is not consistent because it corresponds to the ratio between the pesticide field rate (in mass of pesticide/ha) and LD50 (in mass of pesticide/bee). Thus, in contrast to all other species, the HQ can only be interpreted empirically because it corresponds to a number of bees/ha. This type of HQ calculation is due to the difficulty in transforming pesticide field rates into doses to which bees are exposed. In this study, we used a pragmatic approach to determine the apparent exposure surface area of honey bees submitted to pesticide treatments by spraying with a Pottertype tower. The doses received by the bees were quantified by very efficient chemical analyses, which enabled us to determine an apparent surface area of 1.05 cm2/bee. The apparent surface area was used to calculate the exposure levels of bees submitted to pesticide sprays and then to revisit the HQ ratios with a calculation mode similar to that used for all other living species. X-tomography was used to assess the physical surface area of a bee, which was 3.27 cm2/bee, and showed that the apparent exposure surface was not overestimated. The control experiments showed that the toxicity induced by doses calculated with the exposure surface area was similar to that induced by treatments according to the European testing procedure. This new approach to measure risk is more accurate and could become a tool to aid the decision-making process in the risk assessment of pesticides

Distribution of the deposit during preliminary calibrations and experimental controls.

<p>The preliminary calibrations were performed before the experiment, and the experimental calibrations were performed during the experiment. The deposit was expressed in µL/cm² of the disc. T-test preliminary vs. experimental calibrations; (t = 0.0739, df = 148, p-value = 0.9412).</p

Determination of the exposure surface area per bee for each active substance.

<p>S.D.: Standard Deviation (n = 3).</p><p>g a.s./ha: gram of active substance per hectare.</p><p>ng a.s./ha: nanogram of active substance per hectare.</p><p>ng a.s./bee: nanogram of active substance per bee.</p>a<p>The application rate was corrected with the measured concentration (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0113728#pone-0113728-t003" target="_blank">Table 3</a>) and the experimental control deposit.</p>b<p>This corresponds to the concentration of active substances found in the bees frozen just after contamination.</p>c<p>The exposure surface area is the ratio between the residues (ng a.s./bee) and the corrected application rate (ng a.s./cm²).</p><p>For each treatment, the bees from the 6 replicates were counted, pooled, and weighed; the mean bee weight was determined by dividing the weight of bees by the actual number of bees.</p><p>Determination of the exposure surface area per bee for each active substance.</p

Comparison of the commercial and measured concentrations.

<p>S.D.: Standard Deviation.</p><p>The concentrations of commercial products are expressed according to their nature, liquid or solid.</p><p>The quantification of the active substance was performed in triplicate from the phytopharmaceutical preparation used for the spray application.</p><p>The differences were expressed as percentages of the commercial concentrations.</p><p>Comparison of the commercial and measured concentrations.</p

Correlation between mortality induced by spraying and mortality induced by topical treatment.

<p>Each dot represents one substance among the 15 tested on bees by thorax topical contact and spraying. The mortality elicited at 48 hours by spraying was given for the chosen field application rate (g a.s./ha) (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0113728#pone-0113728-t001" target="_blank">Table 1</a>). On the basis of the mean exposure surface area (1.05 cm²/bee), the application rate (g a.s./ha) was converted into an individual dose (ng a.s./bee) to treat the bees topically. The dose-mortality relationship at 48 hours was modeled for each of the 15 active substances, which enabled assessing the mortality that could be induced at a given field exposure.</p

Determination and comparison of the HQ and the revisited HQ.

<p>g a.s./ha: mass of active substance per hectare expressed in grams.</p><p>µg a.s./bee: mass of active substance per bee expressed in micrograms.</p><p>ng a.s./bee: nanogram of active substance per bee.</p><p>E.D.: Experimental Data.</p><p>LD₅₀: Median Lethal Dose.</p><p>HQ: Hazard Quotient (field rate (g/ha)/LD₅₀ (µg/bee)).</p><p>Revisited HQ (exposure (ng/bee)/LD₅₀ (µg/bee)).</p><p>N.C.: Not Calculated because of the low toxicity of the active substance.</p><p>DAR EFSA: Draft Assessment Report of the European Food Safety Authority.</p><p>PED US EPA: Pesticides Ecotoxicity Database of the United States Environmental Protection Agency.</p>a<p>Time at which the LD₅₀ was determined. The LD₅₀ values resulting from the experimental data were calculated at the time corresponding to a stabilized mortality.</p>b<p>For each active substance, 2 scenarios of exposure are presented: the lowest and the highest homologated application rate.</p>c<p>For each active substance, the highest and the lowest known LD₅₀ values were compared to the lowest and highest homologated application rates, respectively.</p>d<p>HQ is the ratio between the application rate (g a.s./ha) and the LD₅₀ (µg a.s./bee).</p>e<p>The exposure was calculated from the application rate (ng a.s./cm²) and the mean exposure surface area determined with the 20 active substances (1.05 cm²/bee).</p>f<p>The LD₅₀ values from the experimental data were calculated with the BMD software from the US EPA.</p>g<p>The revisited HQ is the ratio between the exposure (ng a.s./bee) and the LD₅₀ (ng a.s./bee).</p>h<p>For each active substance, the dose-mortality relationship was modeled at the time corresponding to a stabilized mortality.</p><p>Determination and comparison of the HQ and the revisited HQ.</p

Comparison of preliminary calibrations and experimental controls of the deposit.

<p>S.D.: Standard Deviation.</p><p>Nc: Number of calibrations.</p><p>C.I. 95%: Confidence Interval at 95%.</p>a<p>Sprayed volume corresponds to the deposit in field conditions.</p><p>Comparison of preliminary calibrations and experimental controls of the deposit.</p

Comparison of the exposure and physical surface area of a bee.

<p>Mean exposure surface area (± S.D.) of a bee (average of the 20 commercial products) and mean physical surface area (± S.D.) of a bee (sum of the mean body and wing surface area).</p