# CFD Analysis of a Large Marine Engine Scavenging Process

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Mathematical Model

#### 2.2. Engine Description

#### 2.3. The Computational Mesh and Simulation Details

#### 2.4. Validation

## 3. Simulation Results and Discussion

#### 3.1. Influence of Engine Load on the Scavenging Process

_{2}and O

_{2}are of great importance in the engine combustion process, the concentration of these species is calculated and tracked in the present work. The initial values of the concentrations in the cylinder after the previous combustion process and the values of the concentrations in the scavenging air are reported in Table 4.

_{2}and CO

_{2}, the main species responsible for the combustion process, is presented. This kind of analysis is possible with CFD simulations, since they can track single species. It can be seen that the concentration of O

_{2}has a faster rise for the low load cases. Consequently, also the concentration of CO

_{2}decreases faster for the lower load cases.

#### 3.2. Influence of the Pressure Difference on the Scavenging Process

#### 3.3. Influence of the Scavenging Port Angles on the Scavenging Process

_{2}and O

_{2}concentration during the scavenging process. The graph summarizes what can be seen in Figure 14: the replacement of combustion gases with fresh air is more efficient for scavenging ports with smaller angles to the normal direction. It can be seen that the concentration of O

_{2}rises fastest for the case with radial ports (0° inclination) and slowest for the 30° ports.

## 4. Conclusions

- -
- The open-source, free software package offers enough power and flexibility to allow the simulation of such a complex flow problem. The complexity consists of a large calculation domain with moving boundaries.
- -
- The problem of the size of the domain was attenuated by the use of cyclic boundaries and the simulation of just a 12-degree sector that embraces one of the 30 scavenging ports. The “pressure directed inlet velocity” type of inlet boundary condition is used instead of modeling the scavenging ports with sliding interfaces. Furthermore, a moderate mesh density proved to be adequate for the problem. It reduced the simulation domain and calculation time and allowed simulating many different cases.
- -
- The scavenging efficiency decreases with engine load but remains high enough for an efficient combustion. It is explained mostly by the shorter time available for the process because of the higher RPM. On the other hand, the driving forces responsible for the scavenging process, similarly to the pressure difference and the axial momentum, increase with load, but the effect is attenuated by the shorter time available.
- -
- The increased pressure difference between the inlet and exhaust improves all the scavenging parameters. Only the trapping efficiency is decreased, since more air is delivered. However, in practice, this method would require a more efficient turbocharger or more energy to power it.
- -
- The increase in the angle to the radial direction of the scavenging ports increases the angular momentum of the fluid in the cylinder at the expense of the axial momentum that drives the fluid exchange. As a consequence, the scavenging performances decrease. It can be concluded that the industry standard of 20° scavenging port inclination could be decreased as far as scavenging efficiency.
- -
- A pocket with remaining combustion gases is always found in the central region just under the exhaust valve. The region is bigger for higher loads, lower pressure difference, and greater scavenging port angle. In the worst cases, a pocket is found also in the cylinder center at the top of the piston.

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 3.**The computational mesh with schematic insertions of the components, the exhaust port, and piston bowl zones enlarged and the bottom view of the mesh.

**Figure 4.**Influence of mesh density (number of cells) on the total fresh air concentration (fresh air mass [kg]/total mass [kg]) in the cylinder.

**Figure 6.**Fresh air propagation for the moment CA = 200° for the loads of 25%, 50%, 75%, and 100%, from left to right. The depicted contours represent fresh air concentration (fresh air mass [kg]/total mass [kg]).

**Figure 7.**The variation of the concentration of O

_{2}and CO

_{2}over time for different engine loads.

**Figure 10.**Fresh air propagation for the moment CA = 200° for the cases with pressure difference 0.25, 0.3, and 0.35 bar respectively, from left to right. The depicted contours represent fresh air concentration (fresh air mass [kg]/total mass [kg]).

**Figure 11.**The variation of the concentration of O

_{2}and CO

_{2}over time for different pressure differences.

**Figure 15.**Fresh air propagation for the moment CA = 200° for the cases with scavenging port angles of 0°, 10°, 20°, and 30° respectively, from left to right. The depicted contours represent fresh air concentration (fresh air mass [kg]/total mass [kg]).

**Figure 16.**The variation of the concentration of O

_{2}and CO

_{2}over time for different scavenging port angles.

Engine | MAN 6S50MC |
---|---|

Bore | 500 mm |

Stroke | 1910 mm |

Number of cylinders | 6 |

Power | 8656 kW |

Rotational speed | 121 min^{−1} |

BMEP ^{1} | 18 bar |

BSFC ^{2} | 171 g/kWh |

Compression ratio | 17.2 |

^{1}Brake Mean Effective Pressure;

^{2}Brake-Specific Fuel Consumption.

Boundary | Type | T (K) |
---|---|---|

piston | movingWallVelocity | 575 |

liner | fixedValue | 475 |

cylinderHead | fixedValue | 550 |

exhaustPort | fixedValue | 475 |

presout | fixedValue | case dependent |

valveStem | fixedValue | 475 |

inlet | pressureDirectedInletVelocity | case dependent |

valve | fixedValue | 475 |

frontAndBack | cyclic | - |

axis | symmetryPlane | - |

Engine Load | 25% | 50% | 75% | 100% |
---|---|---|---|---|

RPM (min^{−1}) | 76 | 96 | 110 | 121 |

Scavenge air pressure (bar) | 1.39 | 2.03 | 2.76 | 3.55 |

Scavenging receiver temperature (°C) | 26 | 29 | 34 | 41 |

Exhaust receiver pressure (bar) | 1.3 | 1.86 | 2.51 | 3.26 |

Turbine inlet temperature (°C) | 308 | 327 | 346 | 404 |

Initial cylinder pressure (bar) | 8 | 8 | 8 | 8 |

Initial cylinder temperature (°C) | 400 | 400 | 400 | 400 |

Inlet Air (%) | Diesel Exhaust (%) | |
---|---|---|

N_{2} | 76.6 | 67 |

O_{2} | 23.4 | 10 |

CO_{2} | 0 | 12 |

H_{2}O | 0 | 11 |

Engine Load | 25% | 50% | 75% | 100% |
---|---|---|---|---|

m_{del} (kg) | 0.0309 | 0.0398 | 0.0504 | 0.05456 |

η_{scav} | 0.997 | 0.979 | 0.968 | 0.931 |

η_{scav,IPC} | 0.996853 | 0.977621 | 0.966 | 0.917707 |

η_{ch} | 0.883 | 0.924 | 0.901 | 0.840 |

DR | 2.031 | 1.679 | 1.563 | 1.315 |

η_{trap} | 0.544 | 0.688 | 0.721 | 0.798 |

**Table 6.**The pressure difference resulting from pressure in the scavenging and in the exhaust receiver.

Pressure Difference (bar) | 0.25 | 0.3 | 0.35 |

Inlet pressure (bar) | 3.5 | 3.55 | 3.6 |

Exhaust pressure (bar) | 3.25 | 3.25 | 3.25 |

Pressure Difference (bar) | 0.25 | 0.30 | 0.35 |
---|---|---|---|

m_{del} (kg) | 0.0506 | 0.0557 | 0.0604 |

η_{scav} | 0.928 | 0.931 | 0.942 |

η_{scav,IPC} | 0.9016 | 0.9218 | 0.9369 |

η_{ch} | 0.821 | 0.844 | 0.865 |

DR | 1.237 | 1.342 | 1.435 |

η_{trap} | 0.830 | 0.787 | 0.754 |

Port Angle | 0° | 10° | 20° | 30° |
---|---|---|---|---|

Inlet velocity components | −1, 0, 0 | −0.98, 0.17, 0 | −0.94, 0.34, 0 | −0.87, 0.5, 0 |

m_{del} (kg) | 0.05996 | 0.05813 | 0.05456 | 0.05051 |

η_{scav} | 0.971 | 0.972 | 0.931 | 0.912 |

η_{scav,IPC} | 0.967 | 0.953 | 0.918 | 0.879 |

η_{ch} | 0.9203 | 0.8965 | 0.8397 | 0.7842 |

DR | 1.4452 | 1.4013 | 1.31499 | 1.2176 |

η_{trap} | 0.7960 | 0.7997 | 0.7982 | 0.8051 |

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**MDPI and ACS Style**

Senčić, T.; Mrzljak, V.; Medica-Viola, V.; Wolf, I.
CFD Analysis of a Large Marine Engine Scavenging Process. *Processes* **2022**, *10*, 141.
https://doi.org/10.3390/pr10010141

**AMA Style**

Senčić T, Mrzljak V, Medica-Viola V, Wolf I.
CFD Analysis of a Large Marine Engine Scavenging Process. *Processes*. 2022; 10(1):141.
https://doi.org/10.3390/pr10010141

**Chicago/Turabian Style**

Senčić, Tomislav, Vedran Mrzljak, Vedran Medica-Viola, and Igor Wolf.
2022. "CFD Analysis of a Large Marine Engine Scavenging Process" *Processes* 10, no. 1: 141.
https://doi.org/10.3390/pr10010141