Measurement of combustion-chamber volume using an acoustic resonance technique

This paper describes a method to measure the combustion-chamber volume of automotive engines by using an acoustic resonance technique. In this method, two resonance frequencies are used as follows; one is produced by the Helmholtz resonator formed by a combustion-chamber and acoustic tube, the other is one of the parasitic resonance frequencies arising in the resonator. And the speed of sound can be canceled by the ratio of them to eliminate temperature sensitivity. Furthermore a PLL (Phase-Locked Loop) can help to measure them precisely and quickly. Measuring systems using this method can be applied to measure the volume of combustion-chamber of assembled engine and of combustion-chamber in the cylinder head in isolation