Taking the combustor composite structure of a high-strength diesel engine as the main research object, dedicated tests have been conducted to verify the accuracy of three distinct cylinder gasket pressure simulation models. Using the measured cylinder gasket compression rebound curve, a gasket unit has been designed and manufactured. For this unit, the influence of the bolt pretension, cylinder body and cylinder head material on gasket sealing pressure has been investigated systematically in conditions of thermo-mechanical coupling. The results show that the bolt pretension force is one of the most important factors affecting the cylinder gasket sealing pressure. The change of the body material has little effect on this pressure. The cylinder gasket seal pressure decreases progressively with the reduction of the elastic module of the cylinder head material.

Diesel engine combustion occurs in a combustion chamber which is enclosed by the cylinder head bottom, the cylinder liner, the piston top and the cylinder gasket. The cylinder gasket, located between the cylinder block and the cylinder head, acts as a critical sealing part to avoid the burned gas from leaking. It not only bears the pretension exerted by the cylinder head bolt, but also suffers high temperature, high pressure and additional force between the joint surfaces [

With the recent development trends of high power output and simultaneously light weight of the diesel engine, the working conditions for the cylinder gasket become even more critical. The cylinder gasket of the diesel engine now needs not only to ensure high durability and reliability, but also to correspond to a narrow land between the cylinder bores, minimize cylinder bore distortion and decrease crevice volume. In order to meet the requirements, the use of metal cylinder gaskets is rapidly increasing in modern engines [

In this paper, finite element numerical simulation and pressure experiment of the metal cylinder gasket were as the research object. The tests were conducted to verify the accuracy of three distinct cylinder gasket pressure simulation models. According to the experimental results of cylinder gasket compression rebound curve, the gasket element model was constructed. The influence of bolt preload, cylinder block and cylinder head material on gasket sealing pressure was analyzed systematically under the thermal-mechanical coupling condition, and in the end the different factors were investigated.

For the requirement of 22 MPa combustion pressure, the cylinder gasket was designed as a metal single-ring in order to meet the high strength and high sealing effect of combustion composite structure.

The loading and unloading curves of metal gasket were studied. According to the test, the compression curve was different from the rebound curve. Therefore a mathematical equation reflecting the real stress-strain relationship of the gasket was proposed to distinguish the loading and unloading stages [

The compression curve equation

where _{l}, a_{2}, a_{3}, a_{4}, a_{5} and a_{6} are regression coefficient from experiment.

The rebound curve equation

where

For the same cylinder gasket, the regression coefficient of cylinder gasket was obtained from compression and rebound test data. The regression coefficient, stress and strain of cylinder gasket were further brought into the rebound equation, and the rebound curve of cylinder gasket was produced. The above curve equation was trained through the compression rebound test data of cylinder gasket.

As shown in

The FE model of diesel engine assembly was analyzed by ABAQUS software in

(1) Constraint and Contact Condition

According to the assembly of engine, the lower surface of engine block were fixed in x, y, z direction.

The contact model was divided into two parts including the contact between the engine block, cylinder head and the cylinder gasket and the contact between the engine block, cylinder head and the bolt.

(2) Mechanical and Thermal Load Condition

For the FE model, the preloads of bolts, the gas pressure and the thermal loads were applied. The temperature and heat transfer coefficient of gas and coolant calculated by CFD were taken as boundary conditions and assigned to FEA heat transfer calculation model by surface method in ABAQUS software.

In order to study influence of cylinder gasket on sealing performance, the cylinder gasket model was defined as elastic, nonlinear elastic-plastic and gasket element respectively. The calculation results mainly investigated the cylinder gasket contact stress, and the measuring points were shown in

Location | Experiment (MPa) | Elastic material (MPa) | Elastic-plastic material (MPa) | Gasket element material (MPa) | Difference (%) | ||
---|---|---|---|---|---|---|---|

Elastic material | Elastic-plastic material | Gasket element material | |||||

1 | 177 | 168.5 | 181.1 | 185.0 | 4.8 | 2.3 | 4.52 |

2 | 199 | 242.4 | 221.3 | 208.1 | 21.8 | 11.2 | 4.6 |

3 | 139.5 | 158.5 | 126.4 | 135.4 | 13.6 | 9.4 | 2.93 |

4 | 201 | 257.1 | 228.3 | 204.0 | 27.9 | 13.5 | 1.49 |

5 | 193.5 | 167.4 | 182.4 | 184.2 | 13.4 | 5.7 | 4.8 |

6 | 190.5 | 259.2 | 229.1 | 199.7 | 36 | 20.2 | 4.82 |

7 | 140.5 | 157.4 | 129.1 | 137.9 | 12 | 8.1 | 1.85 |

8 | 227 | 253.2 | 225.7 | 223.6 | 11.5 | 0.57 | 1.49 |

The results show that elastic, elastic-plastic and gasket element material simulation models were consistent with the test data, and the maximum difference was less than 5%. Therefore gasket element model could be used for subsequent study on the sealing performance of the cylinder gasket.

Because the cylinder gasket not only bear the bolt preload, but also bear the explosion pressure and high thermal load. Thus it is more favorable to use the thermal-mechanical coupling gasket element model to study the sealing performance of cylinder gasket in subsequent projects. The stress distribution results of thermal-mechanical coupling model were higher than mechanical model, and the stress distribution result for cylinder gasket was shown in

Material | Young’s modulus (GPa) | Poisson’s ratio | Density (kg.m^{−3}) |
---|---|---|---|

Cast aluminum | 71 | 0.3 | 2.7 × 10^{3} |

Gray iron | 105 | 0.27 | 7.1 × 10^{3} |

Titanium alloy | 110 | 0.3 | 4.5 × 10^{3} |

Vermicular iron | 130 | 0.28 | 7.1 × 10^{3} |

Steel | 206 | 0.28 | 7.8 × 10^{3} |

Based on the measured compression rebound curve of cylinder gasket, nonlinear mechanical properties of the cylinder gasket material were studied, and the gasket element was constructed. The pressure test of cylinder gasket verified the gasket model reliability, which provided theoretical support for further research on the sealing performance of thermal-mechanical coupling for cylinder gasket.

The change of bolt preload force contributed greatly to the sealing pressure of cylinder gasket, and it was further verified that the uniformity of cylinder gasket could be adjusted by changing the pre-tightening force. It had certain reference value for the design of cylinder gasket sealing structure.

The effect of changing the cylinder block material on the sealing pressure of cylinder gasket was not obvious. The sealing pressure of cylinder gasket decreased sequentially with the decrease of elastic modulus of the cylinder head material. It could be considered as the reference when selecting materials for the block and cylinder head in the engineering.