Quantitative imaging of equivalence ratios in a natural gas SI engine flow bench using acetone fluorescence

Although compressed natural gas (CNG) is a gaseous fuel, the mixing process is quite different from air-liquid fuel mixing. The aim of this work is to understand the effect of the fuel feeding system on mixture homogeneity. Planar laser-induced fluorescence has been used to produce quantitative equivalence ratio maps in the intake manifold. Fluorescence results from excitation of doped acetone in natural gas. Its emission is proportional to the fuel mass. Collected images were post processed to obtain the equivalence ratio. This work shows the difference between continuous injection at low speed and sequential injection. In the first part, we present the behaviour of the injection jet in the intake manifold. The second part displays a smaller section of the duct upstream of the intake valve. The study shows clearly the stratification effect obtained with continuous injection at low speed. A very homogenous mixture is observed for sequential injection with fuel trapped for a cycle and aspirated in the next cycle.     

Destabilisation of a compressed vortex by a round jet

This paper presents data and analysis related to the compression and the breakdown of a tumbling motion after radial disruption in a simple geometry of the compression chamber of a model engine with large optical access. The disruption is a round jet injection perpendicular to the vorticity tube. Two configurations of injection are selected. They correspond respectively to a straight jet that competes with the tumble and an inclined jet that adds angular momentum to the large-scale rotating motion. The ratio between the angular momentum brought by the spray and the initial angular momentum of the tumble is of the order of 30% and is representative of the direct-injection engine situation at moderate rotation rate. The injection is performed at bottom dead centre (BDC) in a well-defined and well-known tumbling motion. The data are obtained in the symmetry plane of a square chamber by using particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF). A calibration is made in order to take account of acetone fluorescence yield during compression. The analysis of the injection phase at BDC shows that the mean topology of the flow after both injections differs significantly and that the vorticity tube is significantly distorted only in the vicinity of the injection plane. Strong transverse mean flows are detected by analysing the divergence of the mean velocity field. Although a mean rotation is still observed after injection during the compression phase, the authors show that no strong vortex core is evident. An important consequence of this finding, confirmed by the evolution of the global in-plane mean and fluctuating kinetic energy in the symmetry plane is that no vortex breakdown occurs during the compression after the injection event. Therefore, the global fluctuating kinetic energy at the end of the compression is much lower after an injection. During the first half of the compression, an inhomogeneous distribution of the jet fluid in the chamber is detected by the PLIF measurements. The transport of the jet fluid clearly results from both in-plane and out-of-plane motions triggered by the injection jet. This spatial repartition depends strongly on the injection strategy and can be very difficult to control accurately from cycle to cycle. The mixture is more homogeneous at top dead centre (TDC) with a low value of the spatial variance of the mean concentration field.     

FPIV study of gas entrainment by a hollow cone spray submitted to variable density

The gas entrainment in a hollow cone spray submitted to variable density is studied experimentally in order to better understand the effect on mixture formation. Particle image velocimetry on fluorescent tracers, associated with a specific processing of the instantaneous velocity fields have been applied to obtain measurement in the close vicinity of the spray edge. In the “quasi-steady” region of the spray, important effect of the ambient density on the mass flow rate of entrained gas have been pointed out. The axial evolution of is in good agreement with an integral model that takes the momentum exchange between phases into account.     

Measurements of concentration per size class in a dense polydispersed jet using planar laser-induced fluorescence and phase Doppler techniques

In dense two-phase flows, it is well known that phase Doppler anemometry is not well suited for the measurement of concentration and mass flux. Laser diagnostics based on fluorescence can provide the dispersed phase concentration but without discrimination between size classes. We present a new method of coupling the two techniques, in order to extract the local value of concentration and flux per size class. The method is applied to an axisymmetric turbulent jet, laden with polydispersed droplets 1–90 μm. Droplet concentration profiles are obtained in the development zone (x/d ₀ < 20) of the dense jet and are used to study droplet dispersion. The results are then introduced into the momentum transport equations to analyze the influence of droplets on the carrier phase. We show that the local decrease of the rate of variation of mean momentum with mass loading is due both to an increase in interfacial transfer rate and to a decrease in turbulent diffusion effects. Received: 20 November 2000 / Accepted: 3 April 2001     

Synthèse de dérivés O-substitués du (dihydroxy-3′,4′ phényl)-2 indole par utilisation de groupes protecteurs sulfonylés

O-Substituted derivatives of 2-(3,4-dihydroxyphenyl)indole have been synthesized from acetovanillone by various methods using hydroxyl protective groups such as benzene sulfonyl and methylsulfonyl. Thus these groups facilitate Fischer and Bischler indole synthesis. Moreover, selective O-demethylation and O-alkylation reactions are allowed. Finally, the already quoted protective groups may be easily removed to yield back the 2-(4-hydroxy-3-alkyloxyphenyl)indoles.     

NMR investigations into heterogeneous structures of thermosensitive microgel particles

The internal properties of submicron poly(N‐isopropylmethacrylamide) latex particles were investigated as a function of the methylene bisacrylamide (MBA) concentration used as a crosslinker. Two experimental approaches were performed. First, quasi‐electric light scattering measurements provided the size variation of the particles as a function of temperature, from which the swelling capacity of the particles as a function of MBA were estimated. In addition, the broadening and lowering effects of the volume phase transition temperature were detected from the turbidity of the solutions versus the MBA concentration. Second, observations of the transverse relaxation of protons gave evidence for heterogeneous structures inside the particles; several structural parts were discriminated from one another from different proton mobilities detected through magnetic relaxation rates. Corresponding to the concentration gradients of the crosslinker, the internal particle structures were looser and looser from the core to the shell. The state of the gelation of the polymer particles was governed by the initial amount of the crosslinker introduced into the latex recipe. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 889–898, 2000     

An efficient synthesis of the 4'-epimer of 2-fluoronoraristeromycin

The 4'-epimer of 2-fluoronoraristeromycin was synthesized by employing bis-t-butoxycarbonyl (Boc) protected 2-fluoroadenine as a superior substrate for the Mitsunobu reaction with the appropriate cyclopentenol. Unlike the unsubstituted counterpart 2-fluoroadenine, this substrate is completely soluble in THF and resulted in a very good yield in the Mitsunobu coupling reaction as well as subsequent steps.