Francis H. Chen

Cavity resonances in engine combustion chambers and some applications

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 ...

Coupled response and noise of roller chain drive systems

A chain drive system consists of a closed loop roller chain wrapped around two or more sprockets. One of the most significant noise sources in an operating roller chain drive emanates from the repeated impacts between the chain links and sprocket teeth during their meshing. Previous studies on the local‐global meshing of the chain with the sprockets only considered the dynamic transverse motion of an axially moving chain while uncoupled from the sprockets. In this study, the analysis is extended to axial‐transverse motions of the moving roller chain coupled with the dynamic response of the rigid sprockets over which the chain is wrapped around. The analysis thus integrates the local impact meashing to the global response of the chain‐sprocket system. Numerical simulations of the analytical model showed that the coupling effects between the two sprockets, the two chain spans, and the chain‐sprocket meshing impulse intensity increase with decreasing sprocket inertia and chain longitudinal stiffness. Control...

Modeling of impact response in moving chains

A significant contributor to noise from chain drives can be traced to the impact of a roller chain on a sprocket. A model is developed to estimate the impact impulsive load generated by an axially moving roller chain on a sprocket during the meshing process. Due to the dependence of the impulsive impact force on the velocity of the chain before impact, the impulsive load at each impact varies from impact to impact. The meshing process then produces nonperiodic and nonuniform impulsive impact forces. The model is used to analyze the response of the roller chain after each impact. The chain response model is being developed to increase the understanding of the noise generated from engine drive chains. [Work supported by General Motors Corporation.]