(582cb) Extinction Strain Rate Sensitivity and Calculation for Large Mechanisms

Keywords:

(1)  
Chemical Reaction
Engineering   

(2)  
Thermodynamics

(3)  
Transport
Phenomena

Abstract:

Our
interest in the flame parameter Extinction Strain Rate (ESR) is motivated by recent
work from the Ghoniem lab at MIT which has shown ESR to correlate strongly with
turbulent flame structure and stability [1]. This is in turn important for
predicting engine misfire, an important issue for natural gas engines.  While ESR is a valuable parameter for
describing flame behavior, it is unfortunately difficult to measure
experimentally under many conditions of interest. Therefore, accurate and
efficient computational methods become important to its use. However, current
software for computing ESR has two important weaknesses. First, the step wise
continuation solution method used to determine ESR doesn’t provide adequate
sensitivity analysis necessary for refinement of chemical kinetic mechanisms. Current
works reporting ESR sensitivity analysis have had to resort to brute force
techniques and other partial measures [2]. Second, the methods often fail or
take prohibitively long for larger detailed mechanisms, which are necessary for
predicting polycyclic aromatic hydrocarbon (PAH) and soot formation as well as
the oxidation of complex fuels like gasoline.   Characteristic
computation timings are shown in Figure 1, with these values neglecting
multicomponent transport formulation as well as thermal diffusion, both of
which increase accuracy at the cost of significant increases in computation
time.

               Our work seeks to address both of
these issues, focusing first on sensitivity analysis. We present further
analysis on how sensitivities might be obtained from current solver methods.  This is done through examination of the
underlying equations for the one dimensional, reacting, axisymmetric jet system
used for computing ESR, as well as investigation of the phenomena governing
extinction. With regard to the second problem, we’ve extensively investigated
initial value problem formulation (IVP) as opposed to the complete discretization
used by current ESR solvers. An IVP formulation would significantly improve
large mechanism computations since it avoids the issue of each additional
species in the chemical mechanism adding additional variables equal to the
number of discretization points. We are also actively examining how improved
sparsity solvers might be implemented to better handle the full discretization
method if it cannot be avoided entirely.

Research funded by ExxonMobil
as Founding Member of MIT Energy Initiative.

Figure
1: Correlation between run time for a single ESR data point in CHEMKINPro15151 and
mechanism number of species. Calculations for Methane-Air twin flames with an
equivalence ratio of 1 at ambient pressure, 1atm. Thermal diffusion and use of
multicomponent transport handling are neglected, both of which are necessary
for accurate results but require significant increases in computation time.

[1]  Shanbhogue, S. J., Sanusi, Y. S., Taamallah,
S., Habib, M. A., Mokheimer, E. M. A., & Ghoniem, A. F. (2016). Flame
macrostructures, combustion instability and extinction strain scaling in
swirl-stabilized premixed CH 4/H 2 combustion. Combustion and Flame, 163, 494-507.

[2]  Dong, Y., Holley, A.
T., Andac, M. G., Egolfopoulos, F. N., Davis, S. G., Middha, P., & Wang, H.
(2005). Extinction of premixed H 2/air flames: chemical kinetics and molecular
diffusion effects. Combustion and Flame,
142(4), 374-387.