Cavity resonances in engine cylinders are caused by combustion events such as the rapid rate of pressure rise that occurs during compression ignition in diesels or from knock in gasoline engines. These resonances generally occur at frequencies greater than 4 to 5 kHz where the engine structure is not an efficient acoustical radiator. However, when they occur at lower frequencies such as in engines with a large bore or in indirect injection diesels, they can be important in the noise generation process. They are also important for knock detection in gasoline engines. Current knock detection systems are tuned to the frequency band of the lowest cavity resonance in the combustion chamber. It is shown in the paper that higher order resonances can also be detected by a knock vibration sensor on the surface of the engine. Another use for the cavity resonances is to determine the bulk temperature of the gas in the combustion chamber as a function of crank angle. This technique is demonstrated in the paper for a heavy-duty two-stroke diesel. Also, the results of several fundamental investigations of cavity resonances in engine combustion chambers are reported briefly. Good agreement is obtained between theoretical prediction of the resonant frequencies and experimental observation. The splitting of degenerate modes into two components is discussed.

No abstract

Similarity solutions to the incompressible axisymmetric Navier–Stokes equations have been obtained for the case of laminar flow in porous rotating annuli. The equations are reduced to a nonlinear ordinary differential system which is solved by a parametric differentiation method. The effect of radius ratio, radial Reynolds number, and the ratio of the radial flow rates at the two walls is investigated. For net injection the solutions are unique and tend to known asymptotic solutions. For net suction, regions of reversed flow are present and a multiplicity of solutions is encountered.

No abstract