Design optimization of exhaust manifold's length for Spark Ignition (SI) engine through CFD analysis on low-end rpm using Taguchi's Method

The exhaust system especially the exhaust manifold is an important factor that affects the performance of any SI engine. The most influential boundary condition in the exhaust manifold is backpressure where it is defined as the difference between maximum pressure in the exhaust system and the atmospheric pressure. Higher backpressure was documented to reduce the overall performance of an IC engine and increases its fuel consumption based on previous studies. Even though backpressure could not be removed entirely from the exhaust system, it could be reduced the maximize the engine's performance. This study aimed to reduce the backpressure in the exhaust manifold of the 115cc SI engine by optimizing its lengths (by taking consideration of the impact of bending angles) through Computational Fluid Dynamic (CFD) analysis and Taguchi's method. From the results, it was found that the bending angles are more dominant in reducing the backpressure even after the lengths are optimized. It was found that the optimal length configuration reduces the backpressure by 13.56%. Therefore, the outcome of this study shows that the optimal length configuration offers lower backpressure which significantly reduces the harmful impacts on the engine's performance.