Stratification Zones Research Articles

Optimization of stratification combustion in a spark ignition engine by double-pulse port fuel injection

The potential of lean burn in a spark-ignition (SI) engine with optimized fuel injection was experimentally investigated and numerically simulated. The experiments were carried out on a production SI engine which has a port fuel injection (PFI) system. The previous port electronic fuel injection system was modified and the technique of double-pulse fuel injection (DFI) was employed. By regulating injection timings and proportions of DFI, the air-fuel mixture stratification was significantly improved and the expected lean burn was implemented. The experimental results showed that the reduction of fuel consumption with DFI could be above 10 per cent over quite a wide load range, compared to single fuel injection. With optimized fuel injection timings and double-pulse proportions, the ideal engine performance and emissions can be achieved with a two to three times higher air-fuel ratio (AFR) than single fuel injection. With numerical simulation, the effects of mixture stratification formed by different fuel injection amounts and timings were analysed using a phenomenological model. The mixture in the cylinder was divided into different regions that distribute spherically around the spark plug and consist of a central region of stoichiometric air-fuel mixture and a gradually leaner outside region. Simulation results demonstrated that the improvements in fuel economy and emissions with DFI were mainly attributed to increased stratification zones and a reduced AFR gradient in the stratification zones.

Pp´DDT and pp´DDE Accumulation in a Food Chain of Lake Maggiore (Northern Italy): Testing Steady-State Condition

Although pp'DDT usage was strongly limited or banned in most parts of the world during the last three or four decades, the parent compound, its homologues and their metabolites still occur at levels which might pose a risk for many ecosystem components. A case of DDT pollution of industrial origin was discovered in 1996 in Lake Maggiore, the second largest (212 km2) and deepest (370 m) lake in Italy, causing concern for wildlife and human health. The extensive monitoring of many biotic and abiotic compartments which followed from 1998 in order to assess the pollution level and its trend in time, provided a great availability of data referring to DDT contamination of the different fish species of the lake. In this study, the recent contamination levels in selected fish species were compared to those measured in 1998 to evaluate the temporal pollution trend of the lake and its natural recovery, given that no remediation measures were carried out on the contaminated soils and sediments in this time span. Moreover, a modelling approach to test the equilibrium condition between water and pelagic fish species was used. Analytical results of pp'DDT and pp'DDE concentrations in lake water were used as input data in the bioenergetic model by Connolly & Pedersen (1988) to calculate concentrations in two fish species and to compare the predicted and the measured contamination. Sampling and analytical determination of DDT homologues in lake water: Five water sampling campaigns were carried out from May 2002 to February 2004 in three sampling sites of Lake Maggiore. Suspended and dissolved pollutants were determined separately. Quantitative DDT homologue analyses were performed by HRGC coupled with ECD detection by the external standard method. Single water extracts were put together in correspondence with the stratification zones of the water column inferred on the basis of the temperature profile to improve analytical sensitivity. Selection of fish data: Concentrations of DDT and DDE in fishes were selected from recent literature (CIPAIS 2003, 2004). Bioaccumulation model: The bioenergetic model proposed by Connolly & Pedersen (1988) was used to assess the bioaccumulation of pp'DDT and pp'DDE of Alosa fallax (landlocked shad) and Coregonus spp. (whitefish), selected among the different species as representative of a secondary consumer level. The average concentrations of pp'DDT and pp'DDE in water to be used as input data in the bioenergetic model were obtained considering all the concentrations measured at the three sampling stations in the epylimnion where the fish species considered in this study spend most of their life. The resulting values were 0.05 and 0.16 ng/L for pp'DDT and pp'DDE, respectively. Average measured pp'DDT and pp'DDE concentrations in landlocked shad were 0.81 +/- 0.39 and 1.69 +/- 0.71 mg/kg lipids, respectively, and were 0.29 +/- 0.12 and 1.06 +/- 0.41 mg/kg lipids for the whitefish. Calculated and measured values turned out to be in quite good agreement for pp'DDT, while measured pp'DDE concentrations were higher than expected on the basis of the bioenergetic model in both species. Probably metabolic transformations of pp'DDT accumulated in fish tissues in the past are responsible for the observed differences between calculated and expected pp'DDE concentrations in fish. Pelagic fishes of Lake Maggiore seem to maintain the DDT accumulated during their life time and the most efficient mechanism responsible for the fish population recoveries is probably their generation changes; for this reason, equilibrium models cannot be used until negligible pp'DDT concentrations are reached in fish tissues. The limit proposed for pp'DDT in water by the EU Directive 2000/60, which will come in force in 2008, is 0.2 ng/L, four times higher than the average concentration measured in Lake Maggiore waters. Nevertheless, concentrations measured in Lake Maggiore fish were very close and sometimes exceeded the Maximum residue limits (MRLs) settled by the Italian legislation for foods (0.1 mg/kg w.w. for fish containing 5-20% lipid). It seems, therefore, that the 'environmental quality standard' of 0.2 ng/L cannot guarantee the suitability of fish for human consumption.

Numerical Modeling of Compartment Fires

A three-dimensional computer code FIRE3D for modeling heat and mass transfer in case of fire in a compartment with openings has been developed. The k−ε turbulence model and the model for disintegration of vortexes for turbulent combustion are used. Numerical solution of the system of gas mixture equations is based on the implicit method SIMPLE. The differential equations of transfer are solved in an orthogonal nonuniform staggered grid by a method of three-dimensional factorization: the equation of pressure adjustment is solved by the multigrid iteration method. The code FIRE3D has been verified against experimental data (Steckler et al., 1982). Development of a buoyant jet, its uplift and spreading over the ceiling, and formation of a hot area, exchanging mass and heat with the outside space through the doorway, have been obtained. In the calculations, the power of the source was changed; the time dependences of mass rates of flows incoming and outgoing through the opening as well as the characteristics of temperature stratification (the height of the interface, the average temperature in the upper and lower zones of stratification) have been determined. The calculation results are in satisfactory agreement with the experimental data.

Settlement of larvae of the giant scallop, Placopecten magellanicus, in 9-m deep mesocosms as a function of temperature stratification, depth, food, and substratum

In January and February 1992 an experiment was conducted in a 10.5-m deep tank (diameter: 3.7 m, volume: 117 m3) to examine the effects of food distribution with respect to a stable thermocline, depth, and substratum type on the settlement and metamorphosis of larvae of the giant scallop, Placopecten magellanicus (Gmelin). Polyethylene tube bags (diameter: 0.60 m) were used to enclose 9-m deep columns of seawater which were then used as treatment replicates. A sharp thermocline (i.e. 7 to 11°C gradient) was created between a depth of 4.0 and 5.0 m. At the beginning of the experiment, one million 6-d old larvae were added to the surface of each tube. Two or three replicate tubes of each of four feeding treatments were established: (1) food (Isochrysis galbana) added to the top 1 m of the water column (“top-fed”, n=3); (2) food added to the bottom 1 m of the water column (“bottom-fed”, n=3); (3) food added throughout the water column (“mixed”, n=3); and (4) no food added (“unfed”, n=2). Settlement collectors were placed in two replicate tubes of each treatment at depths of 0.1, 4, 5, and 9 m and contained two different substrata, Polysiphonia lanosa (a red filamentous alga) and aquarium filter-wool as an algal mimic. Spat settlement in the different feeding treatments was a function of larval growth rate. Most spat were collected in the mixed tubes. Fewer individuals were collected in the top-fed treatment and fewer still in the bottom-fed treatment; minimal numbers of spat were found in the unfed tubes. Filter-wool collected more spat than P. lanosa, but this was evident only in the 4-m deep collectors in the mixed tubes. Most spat were found in the 0.1-m or 4-m deep collectors; generally few were located below the thermocline in collectors at 5 or 9 m. We suggest that, in areas of intense stable stratification, spat collection of the giant scallop may be enhanced by the placement of collectors with appropriate substratum material at or above the zone of stratification, rather than near the bottom. Furthermore, we propose that natural settlement may be increased in areas where a stratification layer intersects with the sea floor or where the layer is disrupted by turbulent mixing.

Effect of the conditions of matrix curing on the tensile strength of a unidirectional organic plastic

1. Stratification of the material along the axis of the fibers is observed in extension of unidirectional organic plastics, and the length of the stratification zone is very sensitive to the matrix curing conditions. 2. A correlation was found between the length of the stratification zone and the strength of an organoplastic reinforced with fibers with an amorphous structure. 3. An increase in the degree of curing of the matrix in an organic plastic based on fibers with a crystalline structure results in organic plastic based on fibers with a crystalline structure results in splitting of neighboring fibers.

Antarctic Polar Front Zone in the Western Scotia Sea—Summer 1975

Abstract The component of the FDRAKE-75 data obtained by the R/V Conrad in the western Scotia Sea reveals a definite sequence of thermohaline stratification zones encountered on passing from Antarctic to Sub-antarctic waters. A Polar Front Zone, displaying multiple temperature minima, separates the Antarctic Zone, characterized by a single intense T-min above 200 m, from the Subantarctic Zone with its nearly isohaline layer from 100 m to over 400 m. The Antarctic Zones of the Weddell and the Scotia Seas aye separated by a cold, relatively homogeneous zone situated in the southern Scotia Sea called the Weddell-Scotia Confluence. The boundaries of the Polar Front Zone are highly meandered and isolated eddies of Subantarctic water may occur within the zone. The main axis of the Antarctic Circumpolar Current apparently lies close to the Subantarctic boundary of the, Polar Front Zone, while a secondary axis is associated with the southern limit of the Polar Front Zone. Inspection of the Islas Orcadas and Melvi...

Flow and Stress Near an Interface between Stratified Liquids

Observations are made of a density current system in which salt water flows turbulently under a pool of fresh water. The density and rate of flow of the salt water are varied, resulting in varying degrees of agitation of the interface. Measurements include the interface slope, the velocity and density profiles, and the rate of mixing. Profiles of stress and effective viscosity are developed from the observations and the equation of motion. In the zone of stable stratification the effective viscosity has a minimum equal to or greater than the molecular viscosity depending upon whether the interface is laminar or agitated. Dimensionless relationships between the observed or computed quantities and the given fluid properties and flow characteristics are investigated. The principal independent variables are a Reynolds number and a Froude number. An interfacial stress coefficient is found to depend upon both. With fair accuracy, the velocity profile can be related to the interfacial stress in a manner analogous to that for turbulent flow near a rigid boundary.

THE HYALINE ZONE OF THE CENTRIFUGED EGG OF CUMINGIA

1. The zones of stratification of the centrifuged egg of Cumingia have been redescribed.2. The relations of the presence of granules in the "broad clear zone" to previous work on (a) absolute protoplasmic viscosity, (b) the surface precipitation reaction, and (c) embryonic localization have been discussed.