CH_(4)/NO_(x) Reduced Mechanisms Used for Modeling Premixed Combustion

This study has identify useful reduced mechanisms that can be used in computational fluid dynamics (CFD) simulation of the flow field, combustion and emissions of gas turbine engine combustors. Reduced mechanisms lessen computational cost and possess the ability to accurately predict the overall flame structure, including gas temperature and species as CH4, CO and NOx. The S-STEP algorithm which based on computational singular perturbation method (CSP) is performed for reduced the detailed mechanism GRI-3.0. This algorithm required as input: the detailed mechanism, a numerical solution of the problem and the desired number of steps in the reduced mechanism. In this work, we present a 10-Step reduced mechanism obtained through S-STEP algorithm. The rate of each reaction in the reduced mechanism depends on all species, steady-state and non-steady state. The former are calculated from the solution of a system of steady-state algebraic relations with the point relaxation algorithm. Based on premixed code calculations, The numeric results which were obtained for 1 atm ≤ Pressure ≤ 30 atm and 1.4 ≤ ф ≤ 0.6 on the basis of the ten steps global mechanism, were compared with those computed on the basis of the detailed mechanism GRI-3.0. The 10-step reduced mechanism predicts with accuracy the similar results obtained by the full GRI-3.0 mechanism for both NOx and CH4 chemistry.

Interaction Dynamics Characteristics of Detonation Waves with Coolant Flow in a Hydrogen Fuelled Detonation Chamber

To analyze the dynamic interaction between detonation waves and coolant flow in a hydrogen fuelled detonation chamber,a hydrogen fuelled detonation chamber with a cooled liner was designed and a simulation model was established.An explicit high-resolution total variation diminishing(TVD)scheme was developed to solve the two-dimensional Euler equations implemented with an augmented reduced mechanism of the hydrogen/air mixture.A point-implicit method was used to solve the numerical stiffness of the chemical reaction source term.The interaction between detonative was and coolant flow were presented.The interaction dynamics between detonation waves and coolant flow in a detonation chamber were investigated.The results indicated that there were some negative interaction effects between detonation waves and coolant flow.

RANS simulations on combustion and emission characteristics of a premixed NH_(3)/H_(2) swirling flame with reduced chemical kinetic model

Ammonia(NH_(3))is considered as a potential alternative carbon free fuel to reduce greenhouse gas emission to meet the increasingly stringent emission requirements.Co-burning NH_(3) and H_(2) is an effective way to overcome ammonia’s relative low burning velocity.In this work,3D Reynolds Averaged Navier-Stokes(RANS)numerical simulations are conducted on a premixed NH_(3)/H_(2) swirling flame with reduced chemical kinetic mechanism.The effects of(A)overall equivalence ratio Φ and(B)hydrogen blended molar fraction XH2 on combustion and emission characteristics are examined.The present results show that when 100%NH_(3)-0%H_(2)-air are burnt,the NO emission and unburned NH3 of at the swirling combustor outlet has the opposite varying trends.With the increase of Φ,NO emission is found to be decreased,while the unburnt ammonia emission is increased.NH_(2)→HNO,NH→HNO and HNO→NO sub-paths are found to play a critical role in NO formation.Normalized reaction rate of all these three sub-paths is shown to be decreased with increased Φ.Hydrogen addition is shown to significantly increase the laminar burning velocity of the mixed fuel.However,adding H_(2) does not affect the critical equivalence ratio corresponding to the maximum burning velocity.The emission trend of NO and unburnt NH_(3) with increased Φ is unchanged by blending H_(2).NO emission with increased X_(H2) is increased slightly less at a larger Φ than that at a smaller Φ.In addition,reaction rates of NH_(2)→HNO and HNO→NO sub-paths are decreased with increased X_(H2),when Φ is larger.Under all tested cases,blending H_(2) with NH_(3) reduces the unburned NH_(3) emission,especially for rich combustion conditions.In summary,the present work provides research finding on supporting applying ammonia with hydrogen blended in low-emission gas turbine engines.

Analysis on First-stage Ignition of n-Heptane at Low Temperatures with a Lumped Skeletal Mechanism

Two-stage ignition exists in the low-temperature combustion process of n-heptane and the first-stage ignition also shows a negative temperature coefficient(NTC) phenomenon. To study key reactions and understand chemical principles affecting the first-stage ignition of n-heptane, a lumped skeletal mechanism with 62 species is obtained based on the detailed NUIGMech1.0 mechanism using the directed relation graph method assisted by sensitivity analysis and isomer lumping. The lumped mechanism shows good performance on ignition delay time under wide conditions. The study revealed that the temperature after the first-stage ignition is higher and a larger amount of fuel is consumed at lower initial temperatures. The temperature at the first-stage ignition is relatively insensitive to the initial temperature. Further sensitivity analysis and reaction path analysis carried out based on the lumped mechanism show that the decomposition of RO_(2) to produce alkene and HO_(2) is the most important reaction to inhibit the first-stage ignitions. The chain branching explosion closely related to the first-stage ignition will be terminated when the rate constant for the RO_(2) decomposition is larger than that of the isomerization of RO_(2) to produce QOOH. The NTC behavior as well as other characteristics of the first-stage ignition can be rationalized from the competition between these two reactions.

Numerical simulation of diesel combustion based on n-heptane and toluene

Considering the self-ignition characteristic and C/H ratio,n-heptane and toluene(6:4 by mass)are chosen to constitute diesel surrogate fuel,and a reduced oxidation mechanism was developed.This mechanism was firstly validated by the combustion of diesel fuel in different oxygen concentrations within a constant volume vessel by high-speed photography.The simulated flame temperature distribution reproduces the diesel combustion process quite well.For further validation,combustion in real diesel engine was also investigated numerically and experimentally using a light duty diesel and a marine diesel.The calculated pressure curves in different operation conditions fit the measured data reasonably well.The oxidation mechanism could reproduce the main characteristics including combustion phase and NOx emission of diesel combustion in different cases.