Search Results

Helmholtz resonators are widely used for the noise reduction in vehicle induction and exhaust systems. This study investigates the effect of specific cavity dimensions of these resonators theoretically, computationally and experimentally. By considering one-dimensional wave propagation through distributed masses in the connector and cavity, a closed-form expression for the transmission loss of axisymmetric configurations is presented, thereby partially eliminating the limitations of a lumped-parameter analysis. Eight resonators of fixed neck geometry and cavity volume with length-to-diameter ratios of the volume varying from 0.32 to 23.92 are studied both computationally and experimentally. The first of the two computational approaches employed in the study implements a finite difference time domain technique to solve the nonlinear governing equations of one-dimensional compressible flow.

A time-domain computational approach is applied to analyze the acoustic performance of multiple-pass silencers containing perforated tube sections. The nonlinear, one-dimensional method may readily include temporal and spatial variations in sound pressure level, orifice flow velocities, and mean duct flow, all of which affect the behavior of perforated tube elements. The transmission loss characteristics of two anechoically-terminated multiple pass muffler configurations are determined computationally and experimentally for the limiting case of low sound pressure levels and zero mean flow. Comparisons between the numerical results and experimental data are shown to correlate well for frequencies where the one-dimensional assumption is justified.

The present study investigates the wave propagation and attenuation in catalytic converters. The relationships for wave propagation in a catalytic monolith are derived first and then coupled to the wave propagation in tapered ducts. Analytical predictions are compared with experimental results to validate the theory.

A fundamental thermodynamic model of the complete spark-ignited, homogeneous charge engine cycle has been used in several parametric analyses to predict the effects of engine design and operating alternatives on fuel consumption and emissions of NOx and unburned hydrocarbons (HC). The simulation includes sub-models for wall heat transfer, NOx and HC emissions, and the engine breathing processes. This work demonstrates the power and utility of a comprehensive engine simulation by presenting several independent parametric studies that were carried out in response to genuine engine design and/or operating strategy questions. Included in this compilation are the effects of cycle heat loss, exhaust port heat loss, combustion duration, and charge dilution (EGR and/or lean air-fuel ratio). In addition, the influence of the design variables associated with bore-stroke ratio, intake and exhaust valve lift, and cam timing are considered.

This work describes a thermodynamic model of the exhaust and intake processes in small prechamber, three-valve, stratified charge engines. The main objective is to study the coupled effects of the prechamber orifice diameter, auxiliary-to-main chamber intake manifold pressure ratio, auxiliary valve timing, and engine speed on the air-fuel stratification between chambers at the time of ignition. The analysis highlights the important dimensionless parameters that control the engine breathing processes. In addition, the unique numerical problems of solving the governing differential equations are analyzed and discussed. Results of a parametric study indicate that the charging processes are very complex, in general. The degree of stratification at the time of ignition strongly depends on the ratio of intake manifold pressures and on the auxiliary intake valve timing, particularly for lower engine speeds (<͂2000 RPM) and/or larger orifice diameters (>͂0.3 inches).

The coupling of shear layer instabilities with the acoustic resonances at the interface of two ducts, a main duct and a connecting sidebranch, leads to whistle noise. The present study investigates experimentally the mechanism of such pure tone noise. A generic sidebranch adapter is fabricated to allow for: (1) the ability to mount downstream of the throttle body in the induction system of a production engine; (2) the adjustment of sidebranch length; and (3) the changes in the diameter of the branch duct. Experiments are conducted both in a flow facility and an engine dynamometer facility for the same set of flow rates. The correlation of the whistle noise between these two facilities is examined in terms of frequency and the dimensionless numbers, including Strouhal and Mach.

Correlations for the ignition delay and combustion energy release intervals in a homogeneous charge, spark-ignited engine are developed. After incorporation within a simplified engine cycle simulation, predicted values of these two combustion parameters are compared to experimental engine data. The correlations are based on four fundamental quantities-the turbulent integral scale, the turbulent micro-scale, the turbulent intensity, and the laminar flame speed. The major assumptions include: (1) The turbulent integral scale is proportional to the instantaneous chamber height prior to flame initiation. (2) Angular momentum is conserved in the individual turbulent eddies ahead of the flame front (i.e., a “rapid distortion” turbulence model). (3) The turbulent intensity scales with the mean piston speed. Two empirical constants scale the correlations to a given engine.