IC engine is the main power source in most of the automobiles. IC engine is a heat engine which converts the chemical energy of a fuel into thermal energy and this thermal energy is used to perform the useful work. Lenny (2011) in his work reported that within the cylinder, the combustion process produces rapid and periodic rises in temperature and pressure, shear loading, and impingement of hot gases. The temperature rise causes the material to undergo an expansion. This thermal expansion will lead to the thermal stress which is the main cause for failure of a component. Apart from the effects of the other loads experienced by the engine, thermal load is considered to be greater, as it initiates cracks and leads to the failure of the engine and its components. To have a long life, the engine block and its components should be capable to withstand this high temperature, pressure, and stress. Mon et al. (2011) in their research work have proposed the materials used to construct the engine and its parts strongly influenced the temperature distribution in the engine. Thus, the thermal analysis of an engine plays a vital role in gaining the knowledge on the heat distribution and stresses handled by the engine.

Automobile manufacturers these days are concentrating more on efficiency of the engine and the fuel economy of the vehicle. Leard et al. (2017) in their work depicted a graph which clearly portrayed that the manufacturers concentrated more on increasing the fuel economy. By reducing the weight of the vehicle, the fuel consumed by the vehicle decreases without compensating the power. This led the researchers to find an alternative material for the engine. Vinoth et al. (2014) in their article stated that the material for an engine application should have properties like greater strength, lightweight, controlled thermal expansion, high thermal conductivity, and good wear resistance. Grosselle et al. (2010) in their research work discussed that Aluminium has been found as a better alternative to replace cast iron. By replacing the cast iron with aluminium, the weight of the engine reduces nearly by 45%. Aluminium alloy with cast iron liner is being used widely these days. Aluminium alloy metal matrix composites with good wear resistance can be used to manufacture a fully aluminium engine which further reduces the weight of the engine.

Today, predictions are increasingly being done with numerical simulations at an ever earlier stage of engine development (Bovo, 2014). This enables the researchers to try different alternative materials for engine. Finite Element Analysis plays a very important role to have analytical solutions for the practical problems with various materials, shapes, and complicated boundary conditions.

In this paper, a single cylinder engine block has been modeled using Pro-E and the thermal analysis is done through ANSYS. Two materials Aluminium alloy 6061 and Metal Matrix Composites (MMC), i.e., Aluminium alloy 6061 reinforced with 20% SiC have been used and their thermal stress, thermal flux, and thermal gradient have been compared.

To reduce the weight of the engine, aluminium finds a best place for cast iron. Pure aluminium cannot be used to cast an engine. Aluminium is used as an alloy with the addition of other chemical compositions mainly to increase its strength. Navthar and Narwade (2012) designed the cylinder and cylinder head with Aluminum alloy of type LM-13 to shed weight. They used the cylinder bore coating using NIKASIL coating to improve strength of cylinder with minimum weight. Prabhala and Kumar (2012) designed and analyzed the engine piston, crankshaft, and connecting rod with Al alloy. They also observed that the weight of the engine reduces by replacing the engine components with Al alloy.

To obtain the low density and high mechanical properties, Aluminium metal matrix composites have been used increasingly. The major advantages of Aluminium matrix composites compared to unreinforced materials are greater strength, improved stiffness, reduced density, improved temperature properties, controlled thermal expansion, and improved wear resistance (Singh et al., 2014). SiC (Silicon Carbide) and Al₂O₃ (Aluminium oxide) are the most common reinforcing ceramics for Al-Si alloys (Ye, 2003). Vinoth et al. (2014) have investigated the mechanical characteristics of aluminium-silicon based hybrid metal matrix composites reinforced with Silicon Carbide (SiC) and cenosphere particulates for engine applications. They proved that the ultimate tensile strength, compressive strength, and hardness of the composite is increased, and density of the composite is decreased with increasing the weight percentage of reinforcements.

Kheder et al. (2011) concluded that increasing wt% of SiC, MgO and Al₂O₃ increased their strengthening effect, but SiC is the most effective strengthening particulates, for higher strength, hardness, and grain size reduction. Kumar et al. (2010) have presented the experimental results of the studies conducted regarding hardness, tensile strength, and wear resistance properties of Al 6061-SiC and Al7075- Al₂O₃ composites. They concluded that the Al 6061-SiC exhibits superior mechanical and tribological properties. In this paper, Aluminium alloy 6061 and Aluminium alloy 6061 with 20% SiC is used. Singh et al. (2014) evaluated the ultimate tensile strength, hardness, density, and the microstructure of SiC particulate reinforced Al matrix composites as a function of volume of SiC. They obtained the best results for 20% weight fraction of SiC particles. The chemical composition and properties of Aluminium alloy 6061 are given in Tables 1 and 2, respectively.

Table 1. Composition of Al 6061

Table 2. Properties of the Material

A single cylinder engine block is modeled using Pro-E and its specifications are shown in Table 3. This engine block is imported to ANSYS, meshed, and the necessary boundary conditions are applied and analyzed.

Table 3. Specification of Engine

Figure 1 shows the meshed model of the engine block considered for the analysis. This also shows the thermal load applied to the engine block.

Figure 1. Meshed Model of the Engine

3.1 Analysis Result of Al 6061 Alloy

Figures 2-4 show the thermal flux, thermal stress, and thermal gradient, respectively for Al 6061 alloy considered for the study and analysis. The thermal flux, a maximum of 0.616 W/mm² is obtained at the end of the analysis. It can be seen from Figure 2 that the thermal flux near the cylinder bore is maximum. The concentration of the thermal flux is high in the cylinder bore region as the combustion of the fuel takes place in that zone. Also it can be noted that the thermal flux decreases along the depth of the cylinder bore.

Figure 2. Thermal Flux of Al Alloy

Figure 3. Thermal Stress of Al Alloy

Figure 4. Thermal Gradient of Al Alloy

The thermal stress distribution for the engine block made of Al 6061 alloy is shown in Figure 3. The maximum thermal stress is found to be 91.051 N/mm². The thermal stress is higher at the bore of the engine block. The reason for the high thermal concentration on the top portion of the cylinder bore is due to the combustion of the fuel, which takes place at TDS part of the engine. The combustion of fuel results in high temperature and the pressure created during combustion is much more higher.

The thermal gradient of the Al alloy considered for the analysis is found to be a maximum of about 96.836 K/mm. The temperature gradient is high in the BDC part of the engine, the reason is that combustion takes place at the TDC portion of the engine, where the temperature is very high when compared to the BDC portion of the engine.

3.2 Analysis Result of MMC

Thermal conductivity of MMC is low compared to Al alloy which indicates that the thermal gradient will be lower. This is because thermal conductivity and thermal gradient are inversely proportional to each other. As known, thermal gradient is the main cause for thermal stress, which implies that if thermal gradient for a material is low then thermal stress will be low. Figures 5-7 show the analysis result of a SI engine block using MMC.

Figure 5. Thermal Flux of MMC

Figure 6. Thermal Stress of MMC

Figure 7. Thermal Gradient of MMC

From the results, MMC i.e., Al alloy+20% SiC has low thermal gradient and low thermal stress. Low thermal stress enables the engine to have a good life. Thermal flux of Al alloy is lower than the MMC. The maximum values of thermal stress, thermal flux, and thermal gradient obtained for Al alloy and MMC are listed in Table 4.

Table 4. Maximum Values of Analysis Result

Thus, the engine was designed and analyzed using Al 6061 and Al 6061 + 20% SiC (MMC).

• From the above results, it can be concluded that the engine block with MMC showed a reduction in thermal stress and thermal gradient when compared to Al 6061.
• Also the thermal flux of MMC increased by about 21.2% when compared to Al 6061.
• It can be concluded that the MMC which is having better mechanical property and wear resistance can be used as a material for engine, as it reduced the thermal stress by about 17.9% when compared to Al 6061 alloy. The thermal stress acts as the root cause for the failure of the engine.