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Regular pyrometry techniques have been extensively used to infer the temperature field in sooting flames from soot luminosity. However, correction for soot self-absorption along the line-of-sight needs to be considered. The original contribution of the present paper is to assess both numerical and experimental uncertainties that can be attributed to the soot self-absorption effect on the soot temperature field measured by the two-color Modulated Absorption/Emission (2C-MAE) technique. Unlike for regular pyrometry techniques, the design of the 2C-MAE technique actually enables the direct measurement of the local spectral absorption coefficient field. The proportion of flame emission trapping caused by the soot along the line-of-sight is first simulated for different levels of soot loading ranges. The retrieved temperature error when self-absorption is neglected can then be quantified as a function of the level of soot loading and the detection spectral ranges of the technique. As a result, it is found that the proportion of the flame emission attenuation due to self-absorption is directly proportional to the soot volume fraction $$f_\mathrm{v}$$ and hardly depends on the temperature field to be retrieved. These trends are emphasized as the lower spectral range of detection is shifted towards the smaller wavelength. In addition, a linear correlation between the absolute temperature error and the peak $$f_\mathrm{v}$$ in the flame can be extracted and confirmed by experimental results. Eventually, it is also found that selecting detection spectral ranges centered at 645 nm and 785 nm offer the minimum temperature deviation when soot self-absorption is neglected for any conditions of soot loading level within the three studied spectral combinations. This finding is especially relevant for the identification of the optimal operating conditions required by regular 2C-pyrometry for the sooting flames considered.

International audience; A dynamic model using the bond graph formalism of the expansion cylinder of an open Joule cycle Ericsson engine intended for a biomass-fuelled micro-CHP system is presented. Dynamic phenomena, such as the thermodynamic evolution of air, the instantaneous air mass flow rates linked to pressure drops crossing the valves, the heat transferred through the expansion cylinder wall and the mechanical friction losses, are included in the model. The influence on the Ericsson engine performances of the main operating conditions (intake air pressure and temperature, timing of intake and exhaust valve closing, rotational speed, mechanical friction losses and heat transfer at expansion cylinder wall) is studied. The operating conditions maximizing the performances of the Ericsson engine used in the a biomass-fuelled micro-CHP unit are an intake air pressure between 6 and 8 bar, a maximized intake air temperature, an adjustment of the intake and exhaust valve closing corresponding to an expansion cycle close to the theoretical Joule cycle, a rotational speed close to 800 rpm. The heat transfer at the expansion cylinder wall reduces the engine performances.

IF=1.743; International audience; In this paper, a comparison of exergetic models between two hot air engines (a Gamma type Stirling prototype having a maximum output mechanical power of 500 W and an Ericsson hot air engine with a maximum power of 300 W) is made. Referring to previous energetic analyses, exergetic models are set up in order to quantify the exergy destruction and efficiencies in each type of engine. The repartition of the exergy fluxes in each part of the two engines are determined and represented in Sankey diagrams, using dimensionless exergy fluxes. The results show a similar proportion in both engines of destroyed exergy compared to the exergy flux from the hot source. The compression cylinders generate the highest exergy destruction, whereas the expansion cylinders generate the lowest one. The regenerator of the Stirling engine increases the exergy resource at the inlet of the expansion cylinder, which might be also set up in the Ericsson engine, using a preheater between the exhaust air and the compressed air transferred to the hot heat exchanger

International audience; In an optimization process, models are applied to simulate different design behaviors in order to determine the most suitable one. However, this requires the use of a structured methodology to correctly explore the design space and truly converge to the best solution. It is therefore necessary to test and validate the optimal design. For engines, two ways are essentially used: building and testing a real cylinder, or simulating the new design with Computational-Fluid-Dynamics (CFD) models. These two techniques are both expensive and time consuming. An alternative way is proposed to test new designs with a fast simulation based on a kriging method. The exploration of the design space is based on 27 cylinder configurations and the results of their CFD models. It converged to an optimal design depending on the objective function. A kriging method was used to interpolate the behavior of the optimal design just found. In this paper we present the β-NTF model reduction (to define the data set used by the kriging method) and the principle of the kriging technique. We then briefly discuss the results. The results underline the method's advantages despite the small gap between the expected results and those for kriging.

We present the fabrication of a vapor–liquid–solid grown silicon nanowire array solar cell with a radial heterojunction. Lithography defined Cu catalyst patterning is used to grow a periodic array of 300 nm diameter nanowires with a center-to-center distance of 800 nm. A conformal a-Si:H layer is deposited on the nanowire surface to create the heterojunction and passivate the nanowire surface. Transparent conductive oxide and Ni–Al metal grid are then deposited to complete the solar cell fabrication. With a nanowire height of 1.6 µm, the solar cell has an open-circuit voltage of 467 mV. This clear improvement of the open-circuit voltage compared to previous works may be due to the conformal deposition of a-Si:H and to the use of a Cu catalyst. The parameters limiting the solar cell performances are discussed and explained. This work opens up the possibility to fabricate silicon nanowire array solar cells on low-cost substrates.

The micro combined heat and electrical power systems (micro-CHP) with hot air engines are well adapted for solid biomass upgrading, in particular, the Ericsson engines working with an open cycle and an external combustion. This paper presents a model of an Ericsson engine with a compression and an expansion cylinder which allows a thermodynamic optimization of the engine performances in a global approach. A sensitive analysis on the influent parameters is carried out in order to determine the optimal working conditions of the engine: temperature and pressure range, expansion cycle shape with a late intake valve closing or an early exhaust valve closing, heat transfers through the wall of the cylinders. This study, focused on thermodynamic aspects, is a first step in the design of an Ericsson engine.

International audience; This paper presents the development of a new scavenging model to optimize cylinder design. The developed model explicitly integrates some of the cylinder’s design and environmental variables to describe flows during the scavenging process. Then, based on the reduced model, an optimization phase was carried out in order to determine the optimal values of cylinder variables. From computational fluid dynamics (CFD) models to optimal cylinder design, all method steps used are described in this paper. Adaptable to any type of engine, here it is applied to the particular two-stroke diesel engine with ports only. In order to fully understand fluid flow, the methodology integrates a number of CFD calculations with different cylinder configurations to provide data. The CFD results are used as neural network outputs during the training phase, whereas the cylinder variables plus the crankshaft angle are the inputs. The trained network provides the analytical reduced model for gas composition transiting through ports, which characterize the scavenging process. Thanks to these, genetic algorithms are run to define the most suitable values of cylinder variables in order to improve scavenging. The entire process for establishing the reduced model and the optimal design of the chamber is presented in this paper

International audience; Advanced combustion processes induced by self-ignition mechanisms in piston engines, such as Homogeneous Charge Compression Ignition (HCCI), especially need an accurate spatio-temporal temperature information because their phenomenology therefore their performances highly depend on the thermal conditions. The objective of this study is to measure the temperature distribution inside a rapid compression machine (RCM) using anisole planar laser induced fluroescence. The present paper gives a new insight into the interpretation of RCM autoignition data. It also brings useful information for kinetics-related combustion research and combustion modeling. The anisole planar laser-induced fluorescence (PLIF) technique is applied, in order to observe the formation and the evolution of temperature heterogeneities in the combustion chamber prior to the auto-ignition process. Anisole is used as a novel tracer species, and the fluorescence signal's dependence on parameters, such as temperature, pressure and bath gas composition, is quantified in a high-pressure, high-temperature facility. Calibration of the fluorescence signal is defined under RCM-related temperature and pressure conditions and a protocol is proposed for post-processing of the PLIF image sequences, allowing the quantitative field temperatures to be determined at successive instants following compression. In order to gain a better understanding of the mixture process, Particle Image Velocimetry (PIV) measurements are analysed under the same conditions. The correlation between thermal and aerodynamic phenomena is determined. The temperature field is found to be non-uniform, with hot and cold centre positions resulting from recirculation inside the chamber, combined with heat transfer effects from the chamber wall.

The combustion initiation by auto-ignition demonstrates benefits in NOx reduction and in process stability for both spark-ignited and compression ignited engines. Based on the better thermodynamic particularities of the auto-ignition, which have been presented in the first part, the characteristics of this process are demonstrated in the second part by experimental analysis. For comparison with similar studies, the analyses have been carried out in base of a two stroke loop scavenged spark-ignition single cylinder engine.

A Laser Extinction Method has been set up to provide two-dimensional soot volume fraction field time history at a tunable frequency up to 70 Hz inside an axis-symmetric diffusion flame experiencing slow unsteady phenomena preserving the symmetry. The use of a continuous wave laser as the light source enables this repetition rate, which is an incremental advance in the laser extinction technique. The technique is shown to allow a fine description of the soot volume fraction field in a flickering flame exhibiting a 12.6 Hz flickering phenomenon. Within this range of repetition rate, the technique and its subsequent post-processing require neither any method for time-domain reconstruction nor any correction for energy intrusion. Possibly complemented by such a reconstruction method, the technique should support further soot volume fraction database in oscillating flames that exhibit characteristic times relevant to the current efforts in the validation of soot processes modeling.

The objective of this study is to investigate 3-pentanone fluorescence experiments in a constant volume vessel at high temperature and high pressure to underline the influent parameters in conditions close to those encountered in internal combustion engines. To obtain quantitative analysis, measured fluorescence signals must be corrected by considering the influence of preponderant parameters such as temperature, pressure and gas composition. Quantitative dependences of fluorescence on thermodynamic parameters are measured and compared with the predictions of a photophysical model, which combines the effects of temperature, pressure, excitation wavelength on fluorescence quantum yield. The increase of 3-pentanone fluorescence with pressure is due to the vibrational relaxation of energy levels. The fluorescence decreases with increasing temperature, except at low temperature where the fluorescence increase is due to an activation of intersystem crossing between triplet toward singlet levels. The influences of thermodynamic parameters are based on an increase of the non-radiative decay rate with the vibrational energy level of excited electronic state and the important collisions to remove the excess vibrational energy. Experimental and calculated results show a satisfactory agreement.

International audience; The purpose of this work is to get fundamental knowledge and to understand experimentally the fluorescence phenomenon usually used in laser-based imaging diagnostics. A complete review of thermodynamic effects (pressure, temperature, oxygen and tracer concentration) on biacetyl fluorescence is presented for a wide range of temperature and pressure. Biacetyl fluorescence increases with pressure and then levels off at high pressure when the relaxation is complete. The influence of the temperature is explained by a competition between the intersystem crossing and fluorescence. The effect of oxygen fluorescence quenching is important at high pressure and is discussed.

International audience; The fuel concentration in a pressurized and heated gas mixture flow was measured by LIF (laser induced fluorescence) technique. Diacetyl was used as the fluorescence tracer of fuel and was excited at a wavelength of 355 nm. Influent parameters on the LIF intensity among the equivalence ratio, the environment temperature and pressure, the flow velocity were determined from a parametric study. The technique of plans of experiments with statistical tests and analysis was investigated to determine exactly the preponderant parameters and their influence on the LIF intensity. For the experimental conditions explored in this work, the value of the LIF intensity was calculated by developing a quadratic model. By inversion of the transfer function, the equivalence ratio was deduced with a low mean relative error.