24 research outputs found
Measurement of global polarization of {\Lambda} hyperons in few-GeV heavy-ion collisions
The global polarization of {\Lambda} hyperons along the total orbital angular
momentum of a relativistic heavy-ion collision is presented based on the high
statistics data samples collected in Au+Au collisions at \sqrt{s_{NN}} = 2.4
GeV and Ag+Ag at 2.55 GeV with the High-Acceptance Di-Electron Spectrometer
(HADES) at GSI, Darmstadt. This is the first measurement below the strangeness
production threshold in nucleon-nucleon collisions. Results are reported as a
function of the collision centrality as well as a function of the hyperon
transverse momentum (p_T) and rapidity (y_{CM}) for the range of centrality
0--40%. We observe a strong centrality dependence of the polarization with an
increasing signal towards peripheral collisions. For mid-central (20--40%)
collisions the polarization magnitudes are (%) = 6.0 \pm 1.3
(stat.) \pm 2.0 (syst.) for Au+Au and (%) = 4.6 \pm 0.4 (stat.)
\pm 0.5 (syst.) for Ag+Ag, which are the largest values observed so far. This
observation thus provides a continuation of the increasing trend previously
observed by STAR and contrasts expectations from recent theoretical
calculations predicting a maximum in the region of collision energies about 3
GeV. The observed polarization is of a similar magnitude as predicted by 3D
fluid dynamics and the UrQMD plus thermal vorticity model and significantly
above results from the AMPT model.Comment: 8 pages, 4 figure
Inclusive ee production in collisions of pions with protons and nuclei in the second resonance region of baryons
Inclusive ee production has been studied with HADES in + p,
+ C and reactions, using the GSI pion beam at
= 1.49 GeV. Invariant mass and transverse momentum
distributions have been measured and reveal contributions from Dalitz decays of
, mesons and baryon resonances. The transverse momentum
distributions are very sensitive to the underlying kinematics of the various
processes. The baryon contribution exhibits a deviation up to a factor seven
from the QED reference expected for the dielectron decay of a hypothetical
point-like baryon with the production cross section constrained from the
inverse n p reaction. The enhancement is attributed
to a strong four-momentum squared dependence of the time-like electromagnetic
transition form factors as suggested by Vector Meson Dominance (VMD). Two
versions of the VMD, that differ in the photon-baryon coupling, have been
applied in simulations and compared to data. VMD1 (or two-component VMD)
assumes a coupling via the meson and a direct coupling of the photon,
while in VMD2 (or strict VMD) the coupling is only mediated via the
meson. The VMD2 model, frequently used in transport calculations for dilepton
decays, is found to overestimate the measured dielectron yields, while a good
description of the data can be obtained with the VMD1 model assuming no phase
difference between the two amplitudes. Similar descriptions have also been
obtained using a time-like baryon transition form factor model where the pion
cloud plays the major role.Comment: (HADES collaboration
The effect of alternative fuels injection timing on toxic substances formation in CI engines
The present study describes selected issues associated with the emission level in toxic exhaust gases and fuel injection timing. The study was focused on the following types of fuels: Diesel oil (the base fuel) and the other fuels were the mixture of fatty acid methyl ester with Camelina (L10 – diesel fuel with 10% V/V FAME of Camelina and L20 – diesel fuel with 10% V/V FAME of Camelina) was used. Fuel injection advanced angle was set for three different values – the factory setting – 12° before TDC, later injection – 7° and earlier injection – 17°. The most important conclusion is that in most measurement points registered in the same engine operating conditions, the concentration of fuel NOx in L10 and L20 increased but PM emissions decreased which is caused by active oxygen located in the internal structure of the fuel. This fact contributes to the rise in temperature during the combustion process. At the same time factory settings of the angle makes NOx emissions lower and close to reference fuel
Hydroxyl radicals as an indicator of knocking combustion in the dual-fuel compression-ignition engine
The occurrence of knocking combustion is one of the basic problems of dual-fuel compression-ignition engines supplied with diesel oil and gaseous fuel. In order to detect this phenomenon and evaluate its intensity, several methods are commonly used, including the analysis of pressure of working medium in the combustion chamber of the engine or vibrations of certain engine components. This paper discusses the concept of using mass fraction of hydroxyl radicals as the indicator of the occurrence of knocking combustion. Current knowledge on the conditions of hydroxyl radical formation in the engine combustion chamber has been systematized and the results of research on this subject have been presented. Theoretical considerations are illustrated by exemplary results of simulation studies of the combustion process in a dual-fuel compression-ignition engine supplied with diesel oil and methane. The conclusions drawn may be useful for the development of dual-fuel engine control systems
Evaluation of emission level of biofuels from waste-free production in compression-ignition engines
This article presents the impact of biofuel for compression-ignition engines, produced with the use of innovative production technology, on the emission of toxic substances.
The innovative production technology of biodiesel does not generate by-products, eliminating the need for development glycerol fraction and toxic methanol, substances inconvenient for environment. This technology is not currently well known and not used on an industrial scale. The essence of this technology is to carry out the transesterification of triglycerides and methyl acetate in special conditions and with using an alkaline catalyst. The only product of this technology is a mixture of fatty acid methyl esters and glycerol triacetate (no by-products). In the first part of the article, selected physical and chemical properties of such biofuel in comparison to the limits specified in the standard quality requirements for this type of products (EN 14214) were discussed.
In the next part, the results of empirical studies were evaluated, showing the influence of speed and load conditions in test engine Perkins 1104C-E44TA on concentrations of harmful components in the exhaust gases such as carbon monoxide, nitrogen oxides, hydrocarbons, particulates. Engine tests were performed with using biofuels selected by the authors. The measurement system, consisted of an AVL CEB II gas analyser and MEXA-1230PM device for measure of particulate matter in real time, to measure the concentrations of toxic exhaust components was used. Based on the concentration of toxic components of exhaust gases according to Test C1 according to ISO 8178, the emission of the above-mentioned normalized toxic components of exhaust gases was determined. In the final part of the article, the results of empirical studies on the concentrations of toxic exhaust gases in the linear-point diagrams, and emission in the bar chart diagrams were presented
EVALUATION OF EMISSION LEVEL OF BIOFUELS FROM WASTEFREE PRODUCTION IN COMPRESSION-IGNITION ENGINES
This article presents the impact of biofuel for compression-ignition engines, produced with the use of innovative production technology, on the emission of toxic substances.
The innovative production technology of biodiesel does not generate by-products, eliminating the need for development glycerol fraction and toxic methanol, substances inconvenient for environment. This technology is not currently well known and not used on an industrial scale. The essence of this technology is to carry out the transesterification of triglycerides and methyl acetate in special conditions and with using an alkaline catalyst. The only product of this technology is a mixture of fatty acid methyl esters and glycerol triacetate (no by-products). In the first part of the article, selected physical and chemical properties of such biofuel in comparison to the limits specified in the standard quality requirements for this type of products (EN 14214) were discussed.
In the next part, the results of empirical studies were evaluated, showing the influence of speed and load conditions in test engine Perkins 1104C-E44TA on concentrations of harmful components in the exhaust gases such as carbon monoxide, nitrogen oxides, hydrocarbons, particulates. Engine tests were performed with using biofuels selected by the authors. The measurement system, consisted of an AVL CEB II gas analyser and MEXA-1230PM device for measure of particulate matter in real time, to measure the concentrations of toxic exhaust components was used. Based on the concentration of toxic components of exhaust gases according to Test C1 according to ISO 8178, the emission of the above-mentioned normalized toxic components of exhaust gases was determined. In the final part of the article, the results of empirical studies on the concentrations of toxic exhaust gases in the linear-point diagrams, and emission in the bar chart diagrams were presented