Céline Morin

Droplet vaporisation characteristics of vegetable oil derived biofuels at high temperatures

To characterise the mechanisms occurring in the deposit formation during the combustion of vegetable oils used as biofuels in Diesel engines, it is necessary to investigate the vaporisation of vegetable oil droplets under various flow, pressure and temperature conditions. In the current work, experimental results about the vaporisation of rapeseed and sunflower oil methyl ester droplets are presented. The fibre-suspended droplet technique is used and the time evolution of droplet diameter during vaporisation is observed by imaging technique. Average and instantaneous vaporisation rates have been estimated from the d 2 (t) curves at temperatures between 473-1020 K and at atmospheric pressure. The droplets of vegetable oil methyl esters evaporate like mono component droplets with a very significant heating phase. A comparison with experimental results obtained with n-alkanes droplets (from n-pentane to n-decane) and prediction of the quasi-steady theory is also presented and discussed.

Soot volume fraction fields in unsteady axis-symmetric flames by continuous laser extinction technique.

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.

Comparison Based on Exergetic Analyses of Two Hot Air Engines: A Gamma Type Stirling Engine and an Open Joule Cycle Ericsson Engine

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.

Experimental Spectroscopic Studies of Carbon Monoxide (CO) Fluorescence at High Temperatures and Pressures

Two-photon excitation laser-induced fluorescence of carbon monoxide (CO-LIF) is investigated experimentally in order to determine the applicability of this technique for imaging CO concentration in aeronautical combustors. Experiments are carried out in a high temperature, high-pressure test cell, and in a laminar premixed CH4/air flame. Influence of temperature and pressure on CO-LIF spectra intensity and shape is reported. The experimental results show that as pressure increases, the CO-LIF excitation spectrum becomes asymmetric. Additionally, the spectrum strongly shifts to the red with a quadratic dependence of the collisional shift upon pressure, which is different from the classical behavior where the collisional shift is proportional to pressure. Moreover, pressure line broadening cannot be reproduced by a Lorenztian profile in the temperature range investigated here (300–1750 K) and, therefore, an alternative line shape is suggested.

Auto-ignition generated combustion@@@Verbrennungssteuerung durch Selbstzündung: Part 2: Thermodynamic fundamentals@@@Teil 2: Experimentelle Analyse

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.