Flamelet Model for a Three-Feed Non-premixed Combustion System with a Diluent Stream: Analysis and Validation of Quasi-Two-Dimensional Flamelet (Q2DF) Models

Abstract

Three formulations of quasi-two-dimensional flamelet (Q2DF) models are derived from the two-dimensional flamelet formulation on the basis of assumptions regarding the third stream (diluent), and these models are validated by means of a two-dimensional direct numerical simulation (DNS) of a three-feed non-premixed combustion system into which the diluent is injected as the third stream. DNS combined with the Arrhenius formation (ARF) together with a detailed mechanism is also performed as a reference case and compared with the present models. The characteristics of the flamelets in three-feed non-premixed combustion are discussed in detail for ARF in terms of the three mixture fractions, temperature, and major and minor species. Some discrepancies appeared between the ARF and the Q2DF models. The difference in the cross-scalar dissipation rates between Q2DF and the two-dimensional flamelet model is considered the major reason for the deviations. The cross-scalar dissipation rates for the reactor streams and the diluent are expected to be either positive or negative values in the two-dimensional flamelet model, whereas only positive numbers resulted in the Q2DF cases. And the cross-scalar dissipation rate for the fuel and the oxidizer in the Q2DF models are always negative which is also varied from that in the two-dimensional flamelet model. As the results are not determined solely by a single mixture fraction, one scalar dissipation rate is insufficient for establishing a complete database, and it is considered that an additional scalar dissipation rate is needed to improve the model. Overall, it is confirmed that the three Q2DF models presented in this study capture the fundamental characteristics of flamelets in the three-feed non-premixed combustion system, although further improvement is required.

Essentially non-oscillatory and weighted essentially non-oscillatory schemes

“…A parallel chemistry acceleration algorithm applied to gaseous detonation was developed in Wu, Dong and Li (2019b). A flamelet model for a three-feed nonpremixed combustion system was studied in Yu et al (2019a). Oblique detonation waves attached to a cone were simulated in Han, Wang and Law (2019d).…”

Large-eddy simulation of a three-feed non-premixed flame for an oxy-fuel gas turbine burner

“…In the current work, one of the models in literature [12,13] is used in which the diluent is premixed with the oxidizer stream with Large-eddy simulation of a three-feed non-premixed flame for an oxy-fuel gas turbine burner varied ratios. It is considered that the diluent stream mixes homogeneously with the oxidizer stream if the ratio increment is infinitesimal.…”

“…Since only one mixture fraction is involved when solving the flamelet equations for an individual library, and the second mixture fraction was considered in the post process, we name the model quasi-two-dimensional flamelet model. To clarify the quantity of the third stream, a parameter named diluent fraction is defined as W [12,13]. In the one-dimensional flamelet library, the mixture fraction of the fuel side (only fuel stream in the current model) is defined by Z * .…”

“…With a diluted stream injected as the third stream, Yu et. al [12,13] have compared three multi-mixturefraction-based flamelet models and applied them by both DNS and LES, concluding that as the mixture fraction for the third stream is not too large the three models are equivalent, while as it is quite large (> 0.8) the scalar dissipation rates play important roles for each model.…”

“…Due to the nature of the multi-mixture-fraction-based models, more dimensions should be taken into accounts compared to that of the one-mixture-fraction-based models, especially for LES applications. In this paper, one of the models in the literature [12,13] has been chosen to investigate the effect of the heat loss and the diluent fraction PDF, and the resolution of the diluent fraction has also been considered.…”