Importance of detailed chemical kinetics on combustion and soot modelling of ventilated and under-ventilated fires in compartment. (May 2016)

• Record Type: Journal Article
• Authors: Yuen, A.C.Y.; Yeoh, G.H.; Timchenko, V.; Cheung, S.C.P.; Barber, T.J.
• Is Part Of: International journal of heat and mass transfer. Volume 96(2016:May)
• Page Start: 171
• Page End: 188
• Publication Date: 2016-05
• Subjects: Large eddy simulation -- Compartment fire -- Detailed chemistry -- Combustion modelling -- Soot formation modelling -- Under-ventilated fire; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2016.01.026
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: Formations of hydrocarbons by-products and major asphyxiate gases were included. Acetylene plays an important role in the soot formation processes. The coupling between gas-phase model and soot kinetics is essential for soot predictions. Detailed kinetics is crucial for modelling ventilated and under-ventilated fires. Robust LES fire model with detailed chemistry for combustion was developed. Abstract: A novel in-house computation code based on large eddy simulations (LES) incorporating fully coupled subgrid-scale (SGS) turbulence, combustion, soot and radiation models for turbulent reacting flows in compartment fires has been developed. It uniquely embraces the detailed reaction mechanisms for the chemical processes involved during combustion, which provides a comprehensive description of the fuel oxidation processes. Furthermore, it gives a more complete representation of the generation of intermediate chemical by-products including toxic gases such as carbon monoxide and irritant gases such as soot. Since the modelling of hydrocarbons by-products are enabled when considering the full chemical profile, the formation of soot particles is correlated to the concentration of main soot incipient acetylene, which provides an appropriate representation of nucleation, surface growth processes. The LES code has been validated with experimental fire tests results for both ventilated and under-ventilated fires in compartment for confirmation of its robustness. The importance of incorporating the detailed reaction mechanisms in compartment fire simulations has been confirmed by comparing with experiments. For under-ventilated fires in compartment, the chemical kinetics become increasingly important since the combustion efficiency drops significantly involving generation of intermediate chemical species. It is discovered that species concentrations especially CO2 and CO are more accurately predicted by the detailed scheme comparing to the multi-step scheme, since the formation of hydrocarbons and nitrogen oxides are considered. In general, the simulation incorporating detailed kinetics showed an averaged improvement of 9.2% and 81.7% in the prediction of CO2 /CO ratio and volume fraction of soot respectively. This also improves the replication of the flame structure as the fire is chemically-driven within the combustion zone.