# Computational Fluid Dynamics of Compartent Fires: A Review of Methods and Applications
## 3 CFD Simulation in Compartment Fires
### Physical Models
#### 3.3.3 Combustion and Kinetics  
As mentioned earlier in Section 3.3.1, compartment **fires** are predominantly **turbulent**. Therefore, combustion modeling can be challenging, especially when it comes to studying the turbulence effects, and pushes the researcher toward introducing different methods in combustion modeling [74]. Since combustion involves processes that include chemical reactions (i.e., fuel oxidation) and physical interaction (e.g., heat transfer, fluid dynamics, etc. ), both of these aspects must be considered. Combustion can be modeled using either single-step or multi-steps kinetics, depending on the level of detail required and the computational resources available. Moreover, the rate for these kinetics to be formed can be divided into two categories. * Infinite rate chemistry: it is assumed that fuel and oxygen can interact with each other instantly and the only limiting criteria is mixing [12], eliminating the influence of chemical kinetics. * Finite-rate chemistry: consider the actual chemical reaction rates and their dependency on temperature, pressure, and concentration of reactants. A variety of sub-models have been developed by researchers; the infinitely fast chemistry (IFC) combustion model [75] assumes that the combustion is mixing-controlled and combustion occurs instantly as soon as fuel and oxidizer mix (local equilibrium assumption). Eddy break-up (EBU) was first introduced by [PERSON] [76], assuming that chemical reaction rate is controlled by the turbulent eddy break-up rate and only considering fuel and oxidizer in determining the reaction rate; even though chemistry itself is infinitely fast in EBU, turbulence controls the reaction rate. Then, [PERSON] and [PERSON] [77] modified  
Figure 6: Comparison of measured and predicted mass loss rates for fuel with lower boiling temperature. Heptane (**left**)—higher boiling temperature. Diesel (**right**). Adopted from [PERSON] et al. [73]. the EBU and presented the Eddy Dissipation Model (EDM). Similarly to EBU, the EDM combustion model is mixing-controlled, with infinitely fast kinetics, but it also accounts for products in the reaction rate. In terms of kinetics reaction, EBU, EDM, and IFC are only compatible with one/two-step kinetics [53], resulting in them not considering all species. To overcome this barrier, implementing flamelet models helps to simulate all species using more detailed mechanisms. According to [PERSON] et al. [78] and cited by [PERSON] et al. [53], flamelet models simplify complex turbulent combustion by treating small-scale reaction zones as if they behaved like laminar flames, i.e., a flame which is viewed in multi dimensions can be modeled through a number of one dimensional flames [79]. Two different approaches for flamelet models have been presented, namely the laminar flamelet model with infinite rate and Flamelet-Generated Manifolds (FGM) [79; 80] with finite rate. In the development of finite rate models, [PERSON] [81] extended the EDM for finite rate chemistry and presented the eddy dissipation concept (EDC). Other models such as probability density function (PDF) by [PERSON] [82] and volumetric heat source (VHS) by [PERSON] and [PERSON] [83] handle turbulence-chemistry interactions differently. PDF focuses on direct solutions for the probability distributions of key variables such as species concentrations, temperature, and velocity instead of the mean values [84]. VHS is a simple combustion model which calculates the total heat release in each volume due to combustion. It simplifies the process by calculating the rate of energy release based on reaction rates without modeling the detailed turbulence-chemistry interactions [85]. Existing combustion models can predict the combustion products in a well-ventilated compartment [7]. For example, FDS proposes mixing controlled and finite-rate combustion approaches [12]. According to [PERSON] et al. [7], in a well-ventilated compartment fire, a single-step infinitely fast reaction with defined initial inputs for soot and CO yield is applicable.