| 1. |
- Berglund, Svante, et al.
(författare)
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Identifying local spatial association in flow data
- 1999
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Ingår i: Journal of Geographical Systems. - : Springer Science and Business Media LLC. - 1435-5930 .- 1435-5949. ; 1:3, s. 219-236
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we develop a spatial association statistic for flow data by generalizing the statistic of Getis-Ord, Gi (and Gi*). This local measure of spatial association, Gij, is associated with each origin-destination pair. We define spatial weight matrices with different metrics in flow space. These spatial weight matrices focus on different aspects of local spatial association. We also define measures which control for generation or attraction nonstationarity. The measures are implemented to examine the spatial association of residuals from two different models. Using the permutation approach, significance bounds are computed for each statistic. In contrast to the Gi statistic, the normal approximation is often appropriate, but the statistics are still correlated. Small sample properties are also briefly discussed.
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| 2. |
- Bernhardsson, Anders, et al.
(författare)
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Direct self-consistent reaction field with Pauli repulsion : Solvation effects on methylene peroxide
- 1996
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 251:3-4, s. 141-149
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Tidskriftsartikel (refereegranskat)abstract
- The properties of methylene peroxide in the gas phase and water have been examined. The solution effects have been modeled with a cavity. To make it possible to optimize the geometry of the cavity, we have added an approximate description of the Pauli repulsion between the solvent and the solute. An efficient direct implementation of the calculation of multicenter multipole operators is also described. We have applied the method to calculate the electric properties of methylene peroxide, a system that is characterized by its near degeneracy between a biradical and a zwitterionic state. As expected, it is shown that solvent effects will stabilize the ionic configuration, resulting in a considerably weakened OO bond and an increased double bond character in the CO bond. The theoretical study has been performed using the multiconfigurational (CAS) SCF method and second-order perturbation theory (CASPT2).
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| 3. |
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| 4. |
- Burgdorf, Klaas, 1966, et al.
(författare)
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Using multi-rate filter banks to detect internal combustion engine knock
- 1997
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; , s. 971670-
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Tidskriftsartikel (refereegranskat)abstract
- The wavelet transform is used in the analysis of the cylinder pressure trace and the ionic current trace of a knocking, single-cylinder, spark ignition engine. Using the wavelet transform offers a significant reduction of mathematical operations when compared with traditional filtering techniques based on the Fourier transform. It is shown that conventional knock analysis in terms of average energy in the time domain (AETD), corresponding to the signal's energy content, and maximum amplitude in the time domain (MATD), corresponding to the maximum amplitude of the bandpass filtered signal, can be applied to both the reconstructed filtered cylinder pressure and the wavelet coefficients. The use of the filter coefficients makes possible a significant additional reduction in calculation effort in comparison with filters based on the windowed Fourier transform. A knock classification system based on the duration of the knocking process, defined as the time during which the signal exceeds an energy threshold, is presented using different scales. An advantage of this method is that the relation of the duration between different frequency bands can be used to draw conclusions about the presence of multiple knock.
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| 5. |
- Engkvist, Ola, et al.
(författare)
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On the relation between retention indexes and the interaction between the solute and the column in gas-liquid chromatography
- 1996
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Ingår i: Journal of chemical information and computer sciences. - : American Chemical Society (ACS). - 0095-2338 .- 1520-5142. ; 36:6, s. 1153-1161
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Tidskriftsartikel (refereegranskat)abstract
- Gas-liquid chromatography retention indexes for organic molecules are determined by the interaction between the molecule and the column liquid phase. In this article, a model for calculating the interaction energy between a molecule and a dielectric wall is developed. The model is at least to our knowledge the first attempt to predict retention indexes from the interaction between the molecules and the column. This approach to predict retention indexes is radically different from methods proposed before. Earlier predictions of the retention indexes have been done by a large number of descriptors, which were Linearly correlated to the retention indexes. The developed model has been tested for polycyclic aromatic hydrocarbons mainly with a molecular weight of 302. For the molecules with MW 302 the obtained correlation coefficient is 0.92. A somewhat simpler model is used to fit PAH with different MWs. A correlation coefficient of 0.998 is obtained if the retention indexes were fitted to the logarithm of the interaction energies between the PAHs and the column.
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| 6. |
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| 7. |
- Engstrand, Per, et al.
(författare)
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The impact of chemical addition on refining parameters
- 1995
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Ingår i: International Mechanical Pulping Conference 1995, Ottawa/St Paul, Canada. - Ottawa, : Ontario Technical Section, CPPA. - 1895288843 ; , s. 281-286
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 8. |
- Gjirja, Savo, 1945, et al.
(författare)
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Considerations on Engine Design and Fuelling Technique Effects on Qualitative Combustion in Alcohol Diesel Engines.
- 1998
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Ingår i: SAE, Society of Automotive Engineers, Inc. 400 Commonwealth Drive Warrendale, PA 15096-0001 USA, October 1998. - 0768003059 ; :982530, s. 175-187
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Konferensbidrag (refereegranskat)abstract
- The paper depicts the main topics of the experimental investigation on alcohol engine development field, aiming at the engineering targets for the emission levels. The first part of this study was focused on engine design optimization for running on ethanol mexed with poly-ethylene glycol (PEG) as ignition improver. It was shown that some design changes in compression ratio, turbine casing, injector nozzle configuration and exhaust pressure governor (EPG) activation, lead to a better engine thermodynamics and thermochemistry. The second objective of this study was the investigation of engine performance and enmission levels, when the ignition improver diethyl ether (DEE) would be generated on board via catalyticallly dehydration of ethanol, and used directly as soluble mixture or separately fumigated. Both alternatives: ether fumigation technique and dissolved ether in alcohol fuel application were conceptually analyzed, and a stand up system based on DEE fumigation was used to determine the optimum DEE-ethanol ratio at any engine operating range. The heat release investigation, when the engine was run on neat ethanol and optimum fumigated DEE, has been indicated earlier combustion, and very short ignition delay. Verified possibilities for using DEE as ignition improver, would lead to a proper version of the on board ether reactor design, which would bring to another solution for ethanol fuelled engines.
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| 9. |
- Gjirja, Savo, 1945, et al.
(författare)
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Ether Fumigation, a New Alternative for the Neat Ethanol Diesel Engine
- 1998
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Ingår i: 31st ISATA, International Symposium on Automotive Technology and Automation, 2nd-5th June 1998 Duseldorf, Germany. ; 31:98EL008, s. 301-309
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Tidskriftsartikel (refereegranskat)abstract
- The main purpose of this study has been to investigate the possibilities off using diethylether (DEE) as ignition improver in an ethanol (EtOH) fuelled Volvo AH10A245 diesel engine, previously optimized to run on ethanol with a polyethylene-glycol ignition improver of trade mark "Beraid".Comparisons between DEE and Beraid is included in the study and it is shown that DEE can be used as excellent cetane enhancer due to the low autoignition temperature.A special fuel system based on DEE-EtOH-H2O fumigation, i.e. a small amount of DEE,EtOH and water fed directly into the inlet air duct, has been designed in order to overcome the problems associated with longer ignition delay when running the engine on DEE-EtOH mixture.The optimum enhancer content during the fumigation tests has been determined according to the engine economy and emission levels. The heat release investigation has indicated earlier combustion, and very short ignition delay. The engine runs smoothely and the peak of the heat release is lower than that obtained when the EtOH-Beraid mixture is used. Extensive increase of the negative work during compression stroke, has been avoided by the fumigation technique. Since the NOx formation rate depends strongly on combustion temperature, the DEE-EtOH mixture has been optimized in respect to low NOx level. It has been observed that HC and CO increase with the fumigation flow and engine load due to overlapping time. It is shown that a reduction of the overlapping time by optimizing the camshaft configuration improve the emissions levels and fuel consumption considerably.
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| 10. |
- Gjirja, Savo, 1945, et al.
(författare)
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Investigation on Methanol Engine with DME Fumigation
- 1999
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Ingår i: 32nd ISATA International Symposium on Automotive Technology and Automation, 14th-18th June 1999 - Vienna-Austria. ; 32:99CPE029, s. 83-91
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Tidskriftsartikel (refereegranskat)abstract
- Being a non-soot and low NOx emission level fuel, methanol (MeOH) might be considered as an attractive candidate for use in diesel engine. However, having low cetane number and high heat of vaporization, it is not possible to use in diesel engines without engine modifications. In order to take advantages of the alcohol fuels and to avoid engine complexities, which might come along with such modifications, the use of ignition improver additives dissolved in the base fuel is a normal practice. Another promising solution for qualitative combustion in methanol diesel engines is to design an onboard methanol dehydration reactor which can generate dimethyl ether (DME), for use as ignition improver. As a dissolved mixture MeOH-DME requires a special fuel system, the main emphasis was put on the fumigation technique, where a small quantity of DME has been injected into the inlet duct of the engine and the base fuel (MeOH) is conventionally injected through the common rail pump. A research program was set up for evaluating the effectiveness of DME as ignition improver and to compare results with the conventional additive poly-ethylene-glycol (PEG). The heat release analysis has shown that, the fumigated DME undergoes sufficient combustion during compression stroke. Consequently, the temperature and pressure of the gases in the cylinder increase to the point, where the ignition delay of the base fuel (MeOH) is very short. Such precombustion affects the engine performance and emission output, especially NOx and HC levels. It was generally observed that, the regulated emissions were lower and the engine efficiency slightly higher when compared with those obtained when ethanol (EtOH) mixed with PEG or EtOH with fumigated DEE were used. However, the fumigation tests have shown that running on MeOH fuel, the maximum torque and maximum power could not be reached, as it was expected, due to the limited delivery of flow from the fuel pump.Nevertheless, verified possibilities for using DME as ignition improver in a methanol diesel engine, leads to a proper version of the on-board DME reactor design, which would bring to another solution for methanol fuelled engines.
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