Transient Thermal Analysis of Engine Cylinder Head Using ANSYS

Abstract

In an internal combustion engine, the thermal analysis of cylinder block, cylinder head, piston, and other parts is of much importance. The proper analysis of these parts results in getting a closer result with that taken actually. So, if the material and design of the engine’s parts are chosen effectively cause to increases the efficiency of the engine. Which also causes the life of automobiles to increases. In this paper, an attempt has been made to carry out the thermal analysis using ANSYS software on the engine cylinder head. The results of the analysis will help to find out the temperature distribution and the total heat flux through the head at room temperature.

Introduction of Engine Cylinder Head

An engine is a mechanical device that transforms the chemical power of the fuel into mechanical power. Almost all vehicles have an engine. The engine plays an important role to empower the vehicle. According to the combustion process, there are two major types of engines.

1) Internal Combustion (IC) Engine

2) External Combustion (EC) Engine

IC engines are very common all over the world as compared to EC engines. Nowadays, the efficiency of the IC engine is of more concern than before. The IC engine cylinder head is of much importance because it is the part that has to bear high temperature.

In IC engines, the cylinder head (often informally referred to as the head for short) is located over the cylinder on the top of the cylinder block. It shuts at the cylinder top and forms a combustion chamber. The gasket is closed with a cylinder head joint. The Mostly engine cylinder head supplies the cylinder with air and fuel and also provides space for passageways to permit exhaust gases to discharge. This head can also be the place where the nozzle, spark plug, and fuel injector are installed. Inside the cylinder of the engine, the piston moves up and down for compressing the air-fuel mixture. The cylinder contains the following components.

  1. Camshaft
  2. Piston
  3. Inlet and Exhaust Valves
  4. Fuel injectors
  5. Spark plugs

engine

Thermal analysis of cylinder head is fundamental, so that idea will be taken that how much engine cylinder head can bear the temperature without fatigue. While considering the performance of vehicles, the selection of the efficient design of engine and manufacturing mostly depends on the material that has been selected, and the reason is that performance of internal combustion engine relates directly with thermal stresses. In Thermal analysis, the properties of materials studied by changing the temperature. Different thermal analysis types are used nowadays like DTA, DSC, DMA, etc., and many others, but these are of much importance. Thermal analysis is defined as a dependency of material on temperature that can be programmed.

Thermal analysis has a wide range of applications. It can be done on a substance where a temperature difference means where the mode of heat transfer occurs. Conduction occurs when there is heat transfer in the same medium like solid etc. Convection occurs when there is a change of medium like solid to gas, and radiation requires no medium. The design of the engine cylinder head, which is the most critical part of the internal combustion engine, can be described by the following matters.

  • Thermal Load
  • High Pressure of Combustion
  • Cooling Design

In most cases, the fatigue occurs in the engine cylinder head at elevated temperature, causing accidents. The phenomena that occur in the cylinder head and in-cylinder are very complicated, like the shape of the cylinder block, very high thermal resistance between cylinder head and cylinder block, and many others. Hence, the rational methods are not sufficient for further analysis of the cylinder head. The cylinder head in the IC engine bears a huge temperature than any other part. The thermal analysis requires before the design of the cylinder head.

Thermal stresses on the cylinder head occur when the maximum tensile thermal stress exceeds the fracture stress in the stress-strain diagram. Thermal stress is of much importance as the thermals stress increases the strength of the part decrease, and also it causes fatigue and causes wear and tear. So, it is essential to keep the thermal stress within limits that will not cause fatigue.

There is a greater chance for the accident to occur as the safety factor for thermal stress reduce. So, software like Ansys and many others are useful for simulation and to calculate the parameters like temperature, heat flux, thermal stress, and many more. The result taken from the software is not identical to the actual results but is very close. But an idea has been taken about the behavior of materials.

The thermal properties of engines have always been the most important area for the improvement of engine performances. There are many methods and tools to analyze the performance of the engines, such as CFD and ANSYS soft wares. Still, here we use ANSYS workbench to analyze the thermal properties such as the temperature and heat flow of the IC engine cylinder head.

The cylinder head of the engine is used to seal the working ends of the cylinder and limited combustion chamber in its cavity, spark plug, and valves. The studies show that the thermal analysis is performed on a conventional cylinder head of internal combustion engines made of structural steel using the analysis tool ANSYS 15.0.7. In this analysis, the temperature distributions and heat transfer models are developed for the IC engine cylinder head with thermal insulation integrated into the ANSYS. The results show that the peak temperature of the surface of the cylinder head with less thermal conductivity of steel material is increased by 20 to 30 percent.

The heat generated in the combustion chamber allows a very minute time to transfer the heat due to overheating. These effective waste heat distributions play a vital role in the smooth function of IC engines. This heat transfer consists of conduction through walls and convection due to surrounding airflow. The results have expressed the estimation of high-temperature damage in crucial areas. The results show very high stresses in the valve head. The temperature of the cylinder head of the engine and output power with high stresses calculation, mostly higher than the elastic limit, is found at Valve Bridge.

In IC engines, the combustion of fuel takes place, and heat energy will be generated. In this practice, heat will not totally be converted into work; only generated heat energy is transformed into useful work at the crankshaft. The remaining heat will be rejected as radiation through engine boundaries, exhaust heat, and heat rejected to the coolant.

The cylinder head is a very complicated part of the engine, and it bears high thermal stresses and mechanical loadings during working cycles. The valve bridge is the weakest part of the engine cylinder head due to the hot air through the exhaust valve and cooling air through the inlet valve. The fatigue in this part of the cylinder head is a very common issue that reduces the life of the cylinder head. It is very important to find a method to reduce restrictions of the heat distortion in this zone.

The object of this study shows that the ultimate temperature of burning gases inner the cylinder of the engine is very high. To overcome the overheating, the peak temperature of the metal surface surrounding the combustion chamber is restricted to significantly lower values. For this purpose, cooling must be provided to the cylinder head, cylinder, valves, and piston.

The temperature and heat flux no consistencies rising from the conditions that proceed to thermal pressures, which promote the substantial mechanical loadings from combustion pressures. The strategy of the engine cylinder head must be taken into account all these concerns to verify the effortless operation of engines. In this study, we required a piece of complete information to analyze all the processes included. Investigations show that the model is made on 3D solid work design software in which fins are fixed; they adjust the engine cylinder fins and reduces the thickness. It is concluded that material selection is a very important part.

The maximum temperature of burnt gases in the cylinder of IC engine is very high. To prevent heating, mostly the temperature of the surfaces, the combustion chambers are restricted to an exceeding number of lesser values. For this purpose, a cooling source is provided to the cylinder head, plate, and pistons of the engine. The heat fluxes and temperatures, no consistencies raising from these settings cause thermal stresses, and this added increase the otherwise significant mechanical loading from the combustion chamber.

The cylinder head of the engine is one of the main components of the IC engine that is straightly touched to the very high combustion pressure and temperatures. Further, the house suction and valves, the combustion fuel, and the intricate cooling ways. The consequences of all of these cylinder heads lead to failure to operate, such as fatigue cracking and distortions because of extreme heating in areas of limited cooling. During these, the stresses on the dangerous areas everywhere on the valve seats and small links between the valves. These areas are extremely thermal loadings, as they obtain heat from not only from burnt gases of the cylinder inside through the combustion amount.

The temperature of all these gases, which is extracted from the cylinder and valves, is extensively very and it is very harmful to the engine performance. The movement of these fast-flowing gases extremely promotes heat transfer to the walls. Mostly heat that is collected in the valves is rejected throughout the corresponding areas of the valve seat. These effects considerably increase the thermal stresses and loadings on the valves and cause damage to the engine parts. The temperature and mechanical stresses on the valves should be analyzed temperature field and pressure.

There is many software for thermal analysis of cylinder head, but one of the best is ANSYS. It is a complete CAE software with many capabilities like the structural, thermal, and transient analysis. Hyper Mesh is also good software, but it only provides meshing but not complete analysis. In ANSYS, there are also two Workbench and APDL products for analysis. Mechanical APDL has a good range of results and is suitable only for simple geometry; on the other hand, Workbench is suitable for complex geometry, but results are not so accurate. In this project, we use Ansys Workbench for the analysis of the engine cylinder head.

Methodology

The IC engine cylinder head model is being made in SOLIDWORKS 2018, and it is being imported in ANSYS for Thermal Analysis. The simple meshing has been generated using ANSYS 15.0.7, and further on, the boundary condition has been applied to get the results of temperature distribution and heat flux, and other parameters. The solid model is render using Photo View 360.

Cylinder Head Modeled in SOLIDWORKS
    Fig: Cylinder Head Modeled in SOLIDWORKS 2018

Results

The analysis of the model is done in ANSYS 15. In this simulation, the material being used is structural steel, and the boundary condition applied is given below

The temperature of the internal part is 900℃, and the analysis is done at room temperature, which is 25℃. The convection value is 1.25W/m2. ℃.

engine cylinder head
                                               Fig 1: Meshed Geometry

The above diagram (Fig 1) represents the meshing geometry of the engine head.

IC engine cylinder
                         Fig 2: ANSYS Imported Model 

The above diagram (Fig 2) demonstrates the imported model into the Ansys.

Temperature being applied
                                   Fig 3: Temperature being applied

The above diagram (Fig 3) represents the shape of the engine head when we applied temperature to it.

engine head
                            Fig 4: Convection being applied

The above diagram (Fig 4) represents the convection process in the Ansys software.

engine head
Fig 5
Transient temperature graph
                    Fig 6: Transient temperature graph

The above graph (Fig 6) represents the transient temperature during the Ansys analysis of the engine head.

cylinder head
                       Fig 7: Steady-State Thermal Analysis 

The above diagram (Fig 7) represents the steady-state thermal analysis of the engine head.

Ansys project, Ansys analysis
                                  Fig 8: Total Heat Flux

The above figure (Fig 8) represents the total heat flux.

cylinder
                              Fig 9: Steady-State Thermal Analysis

The above diagram (Fig 9) also represents the steady-state thermal analysis in the Ansys software.

Thermal graph of engine cylinder head
                  Fig 10: Thermal graph of the engine cylinder head

The above graph (fig 10) demonstrates the thermal analysis valve after the analysis. 

Temperature Global Maximum Temperature
                Fig 11: Temperature Global Maximum Temperature

The above diagram (Fig 11) represents the global maximum temperature after the analysis in the Ansys software.

Total Heat Flux of engine cylinder head
                Fig: Total Heat Flux of engine cylinder head

From the above solution results, it is to be observed that the temperature with the time increment increases gradually, and then it became constant. The maximum temperature bear by cylinder head of the engine is 1286.6℃. With the time interval, the minimum temperature noted is -34.35℃. The total heat flux decreases with the time increase.

Time [s]  Minimum [°C] Maximum [°C]
1.e-002 -559.95 1286.6
2.e-002 -446.78 918.01
3.2205e-002  -358. 900.
5.2319e-002 -265.31 901.01
8.329e-002 -202.25 931.4
0.13051 -144.82  941.55
0.20363 -119.74 939.22
0.30363 -96.347 933.18
0.40363 -75.712  928.19
0.50363 -56.607 924.36
0.60363 -48.412  921.4
0.70363 -45.735 919.06
0.80363 -42.319 917.17
0.90363 -38.417 915.63
1. -34.359 914.37

Conclusion

In this work, the thermal analysis of the engine cylinder head is performed with structural steel to determine the behavior of temperature in the cylinder head and the total heat flux that gives the best results throughout the Head. For the present work, the engine cylinder head is modeled in SOLIDWORKS 2016, and the thermal analysis of the cylinder head is performed in ANSYS 15.0.7. From the above results, it has been seen that structural steel is the best material for a cylinder head as it behaves normally at high temperatures. As far as the practical application concern, almost all cylinder heads are made from structural steel. From the above results, it has been seen that the thermal stresses are in control able range even at a high temperature of 900℃ applied at the internal part of the head.

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