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The acoustic attenuation performance of a single-pass, perforated concentric silencer filled with continuous strand fibers is investigated theoretically and experimentally. One-dimensional analytical and three-dimensional boundary element methods are employed to predict the acoustic attenuation in the absence of mean flow. Measured complex characteristic impedance and wave number are used to account for the wave propagation through absorbing fiber. The perforation impedance facing the fiber is also presented in terms of the complex characteristic impedance and wave number. The effects of perforate duct porosity and the fiber density are examined. Comparisons of predictions with the experiments illustrate the need for multidimensional analysis at higher frequencies, while the one-dimensional treatment provides a reasonable accuracy at lower frequencies, as expected. The study also shows a significant improvement in the acoustic attenuation of the silencer due to fiber absorption.

The acoustic characteristics of a hybrid silencer consisting of two dissipative chambers and a Helmholtz resonator are investigated first computationally and experimentally. Complex wave number and characteristic impedance are used for the dissipative chambers to account for the wave propagation through absorbing material. Three-dimensional boundary element method (BEM) is employed to predict the transmission loss in the absence of mean flow and the predictions are compared with the experimental results obtained from an impedance tube setup. Noting that the long connecting tube between acoustic elements may reduce the transmission loss near the resonance frequency, two alternative hybrid silencers with short connecting tubes are also investigated by BEM. The present study shows the effectiveness of hybrid silencers over a wide frequency range and demonstrates the importance of understanding each acoustic element, as well as their interaction in designing silencers.

Charge motion is known to accelerate and stabilize combustion through its influence on turbulence intensity and flame propagation. The present work investigates the effect of charge motion generated by intake runner blockages on combustion characteristics and emissions under part-load conditions in SI engines. Firing experiments have been conducted on a DaimlerChrysler (DC) 2.4L 4-valve I4 engine, with spark range extending around the Maximum Brake Torque (MBT) timing. Three blockages with 20% open area are compared to the fully open baseline case under two operating conditions: 2.41 bar brake mean effective pressure (bmep) at 1600 rpm, and 0.78 bar bmep at 1200 rpm. The blocked areas are shaped to create different levels of swirl, tumble, and cross-tumble. Crank-angle resolved pressures have been acquired, including cylinders 1 and 4, intake runners 1 and 4 upstream and downstream of the blockage, and exhaust runners 1 and 4.

This study investigates the autoignition of Primary Reference Fuels (PRFs) using a detailed kinetic model. The chemical kinetics software CHEMKIN is used to facilitate solutions in a constant volume reactor and a variable volume reactor, with the latter representing an IC engine. Experimental shock tube and HCCI engine data from literature is compared with the present predictions in these two reactors. The model is then used to conduct a parametric study in the constant volume reactor of the effect of inlet pressure, inlet temperature, octane number, fuel/air equivalence ratio, and exhaust gas recirculation (EGR) on the autoignition of PRF/air mixtures. A number of interesting characteristics are demonstrated in the parametric study. In particular, it is observed that PRFs can exhibit single or two stage ignition depending on the inlet temperature. The total ignition delay, whether single or two stage, is correlated withn-C7H16/O2 ratio.

The interface between a plenum and primary runner in log-style intake manifolds is one of the dominant sources of flow losses in the breathing system of Internal Combustion Engines (ICE). A right-angled T-junction is one such interface between the plenum (main duct) and the primary runner (sidebranch) normal to the plenum's axis. The present study investigates losses associated with the combining flow through these junctions, where fluid from both sides of the plenum enters the primary runner. Steady, incompressible-flow experiments for junctions with circular cross-sections were conducted to determine the effect of (1) runner interface radius of 0, 10, and 20% of the plenum diameter, (2) plenum-to-runner area ratio of 1, 2.124, and 3.117, and (3) runner taper area ratio of 2.124 and 3.117. Mass flow rate in each branch was varied to obtain a distribution of flow ratios, while keeping the total flow rate constant.

A prototype hybrid exhaust silencing system consisting of dissipative and reactive components is designed based on the boundary element method (BEM) with a specific emphasis on its acoustic performance as evaluated relative to a production system. The outer dimensions of the prototype system are comparable to its production counterpart, which has two silencers connected by a pipe. The predicted transmission loss by BEM for the prototype is compared with the experimental results in an impedance tube for both the prototype and production hardware, providing a design guidance for the former. The sound pressure levels measured at the tailpipe exit during the engine ramp-up experiments in a dynamometer laboratory are presented to compare the two systems, providing the final assessment.

A multi-chamber silencer is designed by a computational approach to suppress the turbocharger whoosh noise downstream of a compressor in an engine intake system. Due to the significant levels and the broadband nature of the source spanning over 1.5 – 3.5 kHz, three Helmholtz resonators are implemented in series. Each resonator consists of a chamber and a number of slots, which can be modeled as a cavity and neck, respectively. Their target resonance frequencies are tuned using Boundary Element Method to achieve an effective noise reduction over the entire frequency range of interest. The predicted transmission loss of the silencer is then compared with the experimental results from a prototype in an impedance tube setup. In view of the presence of rapid grazing flow, these silencers may be susceptible to whistle-noise generation. Hence, the prototype is also examined on a flow bench at varying flow rates to assess such flow-acoustic coupling.

In-cylinder charge motion is known to significantly increase turbulence intensity, accelerate combustion rate, and reduce cyclic variation. This, in turn, extends the tolerance to exhaust gas recirculation (EGR), while the introduction of EGR results in much lowered nitrogen oxide (NOx) emissions and reduced fuel consumption. The present study investigates the effect of charge motion in a spark ignition engine on fuel consumption, combustion, and engine-out emissions with stoichiometric and EGR-diluted mixtures under part-load operating conditions. Experiments have been performed with a Chrysler 2.4L 4-valve I4 engine under 2.41 bar brake mean effective pressure at 1600 rpm over a spark range around maximum brake torque timing. The primary intake runners are partially blocked to create different levels of tumble, swirl, and cross-tumble (swumble) motion in the cylinder before ignition.

The present experimental study investigates systematically the effects of primary intake runner configurations on a firing single cylinder research engine. Twelve different intake configurations were fabricated to investigate runners with tapers and bellmouths. For each configuration, the length from the base of the test configuration to the start of the inlet radius and pressure measurement locations were retained in an effort to isolate the effect of runner geometry only. Each configuration is presented against a baseline case with constant cross-sectional area and a ratio of inlet radius, Ri, to internal diameter, D, of 0.35. For the seven tapered runners, the length of the taper varied from 25% to 100% of the overall length of the test piece, and the taper area ratios (TAR) varied from 1.5 - 3; all tapers retained the inlet radius of the baseline. The four bellmouth runners had a constant cross-sectional area, and varying inlet radii from Ri/D = 0.05 to 1.0.

The introduction of tumble into the combustion chamber is an effective method of enhancing turbulence intensity prior to ignition, thereby accelerating the burn rates, stabilizing the combustion, and extending the dilution limit. In this study, the primary intake runners are partially blocked to produce different levels of tumble motion in the cylinder during the air induction process. Experiments have been performed with a Chrysler 2.4L 4-valve I4 engine at maximum brake torque timing under two operating conditions: 2.41 bar brake mean effective pressure (BMEP) at 1600 rpm, and 0.78 bar BMEP at 1200 rpm. A method has been developed to quantify the tumble characteristics of blockages under steady flow conditions in a flow laboratory, by using the same cylinder head, intake manifold, and tumble blockages from the engine experiments.

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.