| 1. |
- Andrae, Johan, 1973-, et al.
(författare)
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A Numerical Study of Sidewall Quenching with Propane/Air Flames
- 2002
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Ingår i: Proceedings of the Combustion Institute. - 0082-0784 .- 1878-027X. ; 29, s. 789-795
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Tidskriftsartikel (refereegranskat)abstract
- The head-on (i.e., stagnation) configuration has generally been used to numerically and experimentally characterize the flame-wall interaction with complex chemistry and multicomponent transport. Other studies have treated the transient case of a flame propagating toward a wall, and combustion in a boundary layer has also been dealt with. In this paper, a two-dimensional stationary model has been used to study the sidewall quenching,of laminar propane/air flames in a boundary-layer flow. This geometry may be described as a flame parallel to the wall that is swept away with a laminar boundary-layer flow while propagating toward and interacting with the wall. The main purpose has been to examine the extent to which the flame can propagate toward the cooled wall for lean flames compared to stoichiometric flames. A detailed kinetic model is used to examine the oxidation of both the fuel and the intermediate hydrocarbons (IHCs). For stoichiometric and near stoichiometric mixtures, the thermal coupling between the flame and the wall is small but significant. However, for very lean flames, the thermal coupling between the flame and the wall is found to be very significant. The intermediate hydrocarbons are the dominant emissions for stoichiometric and near-stoichiometric flames in contrast to the leaner flames in which the fuel becomes more significant. This implies that the IHCs are very important for the overall hydrocarbon emissions from flame quenching; as a result detailed kinetics of complex fuels should be used when determining the unburned hydrocarbon emissions.
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| 2. |
- Nygren, Jenny, et al.
(författare)
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Three-dimensional laser induced fluorescence of fuel distributions in an HCCI engine
- 2002
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Ingår i: Proceedings of the Combustion Institute. - 0082-0784 .- 1878-027X. ; 29, s. 679-685
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Konferensbidrag (refereegranskat)abstract
- Three-dimensional imaging of fuel tracer planar laser-induced fluorescence in a homogeneous charge compression ignition (HCCI) engine is presented. A high-speed multiple Nd:YAG laser and detection system, in combination, with a scanning mirror, are used to collect eight images, with an equidistant separation of 0.5 mm. Three-dimensional isoconcentration surfaces calculated from the data are visualized. Three-dimensional imaging offers new opportunities to study different combustion events, specifically the topology of flame structures. For example, it is possible to distinguish if separate islands in a fluorescence image really are separate or if it is an effect from wrinkling in and out of the laser sheet. The PLIF images were also analyzed by identifying five intensity ranges corresponding to increasing degrees of reaction progress. The gradual fuel consumption and thus combustion was then analyzed by calculating the volumetric fraction of these intensity ranges for different crank angle positions. The occurrence of multiple isolated ignition spots and the observed gradual decrease in fuel concentration indicates that HCCI combustion relies on distributed reactions and not flame propagation.
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| 3. |
- Lövås, Terese, et al.
(författare)
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Comparison of automatic reduction procedures for ignition chemistry
- 2002
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Ingår i: Proceedings of the Combustion Institute. - 0082-0784. ; 29, s. 1387-1393
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Konferensbidrag (refereegranskat)abstract
- In this paper, we present a comparison between the reduced mechanisms obtained through a computational singular perturbation method (CSP) and the reduced mechanisms obtained through a lifetime analysis based only on the diagonal elements of the Jacobian matrix and a species sensitivity The two methods are used for the analysis of autoignition, which is an interesting test situation because of the sensitivity of ignition to the radical pool and the smaller range of timescales expected. It is found that the steady-state species selected by the two methods are in good agreement. The mechanisms are reduced to a 10-step mechanism when CSP is applied and an 11-step mechanism in the case of the simpler lifetime analysis. Both mechanisms are compared with the detailed mechanism and experimental data and are found to reproduce the physical and chemical parameters very well. This shows that for a large part of the timescale range, the system is close to linear. The comparison shows the advantage of the CSP method as being somewhat more accurate. However, the simpler lifetime analysis is of sufficient accuracy and of more convenience when applied to a system requiring a considerable reduction in computational time, as is the case when applying online reduction.
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| 4. |
- Omrane, Alaa, et al.
(författare)
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Two-dimensional surface temperature measurements of burning materials
- 2002
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Ingår i: Proceedings of the Combustion Institute. - 0082-0784. ; 29, s. 2653-2659
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Konferensbidrag (refereegranskat)abstract
- A new technique for two-dimensional temperature measurements of burning surfaces is presented. Laser-induced phosphorescence from a thermographic phosphor material applied to a surface of investigation was measured with a fast framing camera. The phosphor was excited by the 4th harmomic from a pulsed Nd:YAG operating at 10 Hz. The phosphorescence images measured by eight consecutively gated CCD detectors enable pixel-by-pixel lifetime evaluation of the phosphorescence by interpolating an exponential decay curve to the counts of the corresponding pixel positions of the sequential CCD images. The temperature at each pixel position was evaluated using a calibration procedure of temperature against lifetime. These measurement procedures were used for surface temperature measurements of the evolution of flame spread on low-density fiber boards. The results from experiments showed the possibility of measuring surface temperature during all phases of the flame spread. The total time window used for each two-dimensional temperature measurement was 800 mus to obtain high accuracy and precision at high temperatures, 680-780 K, temperatures characteristic of burning surfaces. The best precision, better than +/-5 K, was obtained at these temperatures. In this region, evaluation by the lifetime method shows a higher sensitivity to temperature than what can be expected from methods based on spectral line intensities. The results of the experiments were in accordance with those reported from previous one-point measurements. In the low-temperature region close to room temperature, the accuracy deteriorated considerably. The results obtained from the two-dimensional imaging experiments are presented and discussed.
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