Transformation of morphological and chemical properties by coating materials on soot
Michael PriestleyXiangyu PeiTakuji OhigashiHayato YuzawaJan B. C. PetterssonRavi Kant PathakMattias HallquistXiangrui Kong
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Structuring
Carbon fibers
Reactivity
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less advanced than for single-injection strategies. Engine efficiency is limited to some degree by tradeoffs that must be accepted to meet particulate matter (including soot) emissions limits. Recent work on this project has filled some knowledge gaps on soot oxidation with multiple injections, and the current work for Fiscal Year (FY) 2018 addresses knowledge gaps on soot formation for multiple injections. While total in-cylinder soot is readily measured, discerning formation from oxidation is difficult. The FY 2018 experiments are designed to create in-cylinder conditions at the threshold of soot formation, where processes that affect soot formation can be more readily discerned. Soot formation pathways under such conditions are fraught with uncertainties, and soot models significantly overpredict polyaromatic hydrocarbon (PAH) and soot, so experimental data at these conditions will provide much needed data for improvements to PAH and soot models.
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Volume fraction
Extinction (optical mineralogy)
Incandescence
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Soot released from fires not only causes danger to lives and property damage, but also effects fire spread by altering the radiation characteristics of fire effluents. In many situations, it is the soot concentration that controls the fire development. Therefore, soot modelling is of great importance in fire safety science. This necessitates the development of a global and general soot model within fire field models that can simulate the amount of soot generated and transported in large-scale fires in order to obtain an accurate soot concentration distribution within the building.
A soot transport model, called Multi-Particle-Size (MPS) model, has been developed in this study to improve the prediction of soot particle behaviour during transportation by considering the uneven soot mass size distributions and gravitational settling force on soot particles. The efficiency of the MPS model was investigated by simulating soot movements in three real experiments. The first two validation experiments were cable fires in a large-scale enclosed corridor and the third experiment analysed the soot produced from a soot generator in a warehouse with a high ceiling. The soot layers predicted by the MPS model matched the measurements/observation better than that from the Conventional Model in which the soot generation is modelled with a constant soot yield (CY) value and soot particles are treated as a gaseous combustion product.
A global soot generation model, called Beta soot generation (BSG) model has also been developed for non-premixed laminar flames. By making use of the characteristics of the beta function, the model has been extended to turbulent flames in the pre-scribed probability density function (PDF) approach with low cost in terms of computational resources. The model was validated by two turbulent methane and ethylene pool fires. The simulation results demonstrated that the soot volume fractions produced by the BSG model were in good agreement with the experimental data.
Further, the two new models have been integrated into a single soot model called BSG+MPS model. The performance of the model was examined by predicting the soot generation and transport in a large-scale enclosed corridor. The BSG+MPS model improved the prediction of soot concentration distribution in the corridor compared with the CY +MPS model.
Finally, the entire work is summarised and future work is suggested.
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Reactivity
Carbon fibers
Dimethyl carbonate
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Saturation (graph theory)
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Abstract : This paper discusses how heuristics can be incorporated in decision aids that are used for structuring decision problems. First, decision theory in terms of linked subsystems is described; this permits identification of the sites where it is necessary to employ heuristic rather than normative, algorithmic procedures. These sites lie on the interface between decision maker's semantic memory, because no adequate formal specification of the structure of semantic memory exists as yet, and consequently no normative procedures for accessing information from semantic memory can be specified. Next, production systems are used to describe heuristic devices handling transactions across the interface between the decision theoretic system and the decision maker's semantic memory; it is suggested that these heuristics can be incorporated into decision aids designed to improve the quality of access to the information contained within the decision maker's semantic memory. Candidate heuristics for use in development of such decision aids are identified, and criteria for locating the site of operation of heuristics are reported in the literature. Selection of those heuristics that operate on the interface with semantic memory is developed. These heuristics are identified within a comprehensive table of heuristics cited in the literature.
Structuring
Heuristics
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Three major soot reaction processes are needed to predict soot properties in flame environments: soot growth, or the formation of soot on soot nuclei and soot particles; soot oxidation, or the reaction of soot with oxidizing species to yield the combustion products of soot oxidation; and soot nucleation, or the formation of soot nuclei from soot precursors having large molecular weights (generally thought to be large and particularly stable PAH molecules in flame environments, called stabilomers). These processes are addressed in the following, considering soot growth, oxidation and nucleation, in turn, by exploiting the soot and flame structure results for premixed and diffusion flames already discussed in Section 2.
Oxidizing agent
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The formation of particulate matter (PM or soot) emissions in diesel engines is of great interest, and the development of a predictive mechanism is an important part of understanding the production of these pollutants. In this paper, a soot-oxidization model is presented on the basis of previous soot-mechanism research, referred to as average-reaction-rate (ARR) model. The ARR soot-oxidization model was combined with the Hiroyasu soot-formation model to compose the H-ARR soot model. With the H-ARR soot model, the process of soot formation and oxidization was numerically modeled according to different conditions of fuel postinjection. Meanwhile, the impact factors and effect mechanism of fuel postinjection on soot oxidization were analyzed in combination with experimental data. Finally, it was demonstrated that the resulting H-ARR soot model could describe the real process of soot formation and oxidization in diesel engine, as well as the influence rule of fuel postinjection on soot oxidization. Especially, it was observed that the brake specific soot emission can be reduced to 30% at the best experimental point of fuel postinjection.
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