Detailed or Complex Models
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RANS simulations are currently employed in a majority of the cases for the sake of simplicity and available computation time [8], whereas predominantly LES and DNS
simulations are used in fundamental research studies [33][61]. Owing to the limited understanding and the complexity of the reaction chemistry
at a fundamental level, there is considerable activity in this field of research, includ- ing studies on hydrocarbon reaction mechanisms [9] or turbulence-chemistry inter-
actions [107].
Applications Examples
Compared to empirical and phenomenological models, the generality of detailed complex models makes it possible to comply with almost any kind of problem.
Depending on the intention, and hence the level of sophistication, the models are commonly used to gain insight into the governing processes, provide information of
local in-cylinder phenomena or evaluate new combustion technologies.
• HEAT TRANSFER
Gosman and Watkins applied computational fluid dynamic simulations for turbulent in-cylinder flows including a one-dimensional gas-wall heat trans-
fer model [36]. Given the present LES and DNS turbulence models avail- able, the model accuracy is no longer restricted in terms of the turbulent flow
field resolution.
• RATE OF HEAT RELEASE COMBUSTION
Focusing on the combustion itself, numerous approaches, such as the char- acteristic time scale models by Magnussen et al. [65], the flamelet approach
by Peters et al. [76] or the Conditional Moment Closure CMC model by Bilger et al. [12] exist. Details about the advantages and disadvantages of
each of these models, as well as a general survey on multidimensional com- bustion modeling are given by [92].
• EMISSIONS
As the thermal nitric oxide formation based on the Zeldovich mechanism is included in most commercially available engine simulation codes, the main
emphasis in nitrogen oxide emission studies is on prompt NO, NO
2
and N
2
O formation, and catalytic removal processes e.g. Miller [68].
There is still only a limited understanding of the fundamental governing physical and chemical processes to be considered for the modeling of engine
out soot emissions [55]. Although it is derived for laminar premixed flames, the model by Frenklach and Wang [31], using detailed kinetics for acetylene
pyrolysis and the growth of polycyclic aromatic hydrocarbons PAHs, is being studied for engine applications [58].
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