Calculating intake noise in motorcycle engines

Abstract

This work considers issues related to noise generation at the motorcycle engine input, its propagation along the intake system with and without a silencer, and sound energy radiation into the environment. It is shown that the intake noise spectrum contains expressed harmonic components on frequencies that are multiples of the engine crankshaft rotation frequency mainly in the range up to 1000 Hz. Intake system air intake opening is a non-directional sound radiator. Dependences are provided to calculate the sound radiation impedance from this opening using the acoustic wave reflection coefficient from it and taking into account the air flow motion average speed. Original exact and approximate expressions were obtained for calculating the reflection coefficient modulus and phase. A method was developed to calculate the medium mass oscillation speed frequency spectrum in the engine intake device with its subsequent transformation during acoustic waves propagation along the intake system to the air intake opening and radiation thereof into the environment. Analytical dependence was obtained for calculating the intake channel transmission coefficient with the medium motion present and acoustic energy losses due to medium viscous friction, thermal conductivity and friction losses due to the flow turbulence. As an example, calculation of the octave spectrum for sound power levels of the intake noise of a single-cylinder two-stroke engine without a silencer for a 175 cm3 class motorcycle was carried out. Calculation results comparison with the experimental data demonstrated perfect agreement, while the error did not exceed 2 dB in the range of low and medium frequencies.