**1. Introduction**

The target of current diesel engines is low fuel consumption with near-zero emission levels for gaseous and particulate matter components at all operational conditions (engine speed and load). Thus, diesel engines require new concepts for the combustion process. The heterogeneous combustion in diesel engines causes nonuniform heat release in the combustion chamber and in the following: NOx, soot, CO, and UHC formation. Homogeneous combustion can solve this problem. Homogeneous combustion in diesel engines is described as a process of homogeneous mixture formation accompanied by volumetric heat release in the total combustion chamber space with a low-temperature gradient inside the chamber. A possible solution to achieving homogeneous combustion is applying PM inside the combustion chamber. One of the different combustion technologies is inside PM combustion. It is a flameless heat release inside an operating PM followed by homogeneous combustion

with near-zero emission [1–3]. This process is stable combustion with a high-power density in an extensive dynamic range. In a burner with an injection of liquid fuel, high-temperature PM acts like an effective evaporator. The large specific surface area with high heat transfer between fluid and solid phases of PM causes fast vaporization of fuel droplets. The large heat capacity of the PM leads to homogeneous combustion with approximately constant temperature.

Some remarkable features of the PM which attracts its application for combustion chamber of diesel engine, display in **Figure 1** [1].

Many experimental and numerical research has verified the combination of PM burners with flame stability and low emissions. Such exciting features of combustion inside PM make it plausible for application in diesel engines. However, mixture

### **Figure 1.**

*Remarkable features of PM for application in combustion chamber of diesel engine [1].*

**Figure 2.** *Diesel engine cylinder head of a with inserted PM [2].*

### *Mathematical Modeling of a Porous Medium in Diesel Engines DOI: http://dx.doi.org/10.5772/intechopen.108626*

formation and combustion in a diesel engine are complicated nonstationary high-pressure processes in with a direct spray inside the combustion chamber. So, PM can be applied to solve this problem. Ultra-lean burn combustion can be used in diesel engines with stable flame due to the high volumetric heat transfer coefficient between fluid and solid phases of PM. The large surface area of PM and the high heat capacity of PM can absorb some of the heat released during combustion and transfer it to fresh air during the end of the compression process. Hence, the temperature reduction decreases nitrogen oxides. Also, a reduction in the temperature gradient inside the cylinder leads to a decrease in carbon monoxide formation. **Figure 2** displays a view of the PM diesel engine. PM inserts in the cylinder head of a diesel engine, and permanent contact between the in-cylinder mixture and PM (open PM concept) exists [3–6].
