Optimization of a reactive muffler used in four-cylinder petrol engine into hybrid muffler by using CFD analysis

Abstract

Four-wheeler automotive vehicle is the basic need of people in today’s life all over the world. But the noise coming from the exhaust system is highly affecting the human health. Among all the noise produce in vehicle, exhaust system noise is maximum. Muffler is one such acoustic filter used for reducing this exhaust noise. Hybrid muffler is one type of muffler which combines the properties of both reactive muffler and dissipative muffler and it operates at wide frequency range. In this study an already existing muffler (Reactive type muffler) used in 91bhp, 6000 RPM four-cylinder petrol engine was optimized to hybrid muffler. Aerodynamic and acoustic performance parameters were the main performance parameter and were determined by CFD analysis and acoustic analysis. The existing reactive muffler of the four-cylinder petrol engine could be replaced by the hybrid muffler. Here the mufflers were designed in ANSYS design modular and analyses were performed in ANSYS Fluent and COMSOL software. CFD analysis was performed for the existing muffler and three other newly designed muffler by considering inlet velocity boundary condition at inlet velocity 40 m/s and 80 m/s. It was observed that increase in pressure drop (aerodynamic performance) in model 4, model 3 and model 2 is around 38%, 33.2% and 29% respectively. Again, from acoustic analysis the transmission loss (TL) in model 4 was observed to be 47 dB whereas in other models it was around 20 dB. Further it was observed that the sound pressure level from model 1 at the exit is around 75–78 dB whereas in model 4 it was observed to be around 45–50 dB at the exit. Hence from both the analysis it is concluded that model 4 which is hybrid type muffler is the most optimized muffler.