Study of Intake System Wave Dynamics and Acoustics by Simulation and Experiment 940206

This paper presents the results of an investigation into the comparison between measured and simulated intake system dynamics of the General Motors Quad 4 engine. Simulations of the engine were conducted at eleven wide-open-throttle operating conditions ranging in engine speed from 2500 rpm to 6000 rpm under both firing and motoring operation. Comparisons of basic engine performance (torque, volumetric efficiency, BSFC), as well as dynamic pressure at two locations within the intake manifold (runner and plenum) showed good correlation between measurements and simulation. The total sound pressure level radiated from the intake orifice was also calculated and compared to measured data. The results of this study show that the simulation program has the ability to accurately capture the major features of engine intake system wave dynamics, including amplitude, phasing, and excitation of system resonances throughout the engine operating range. Thus, it may be used early in the design stage to develop intake and exhaust systems optimized for maximum engine performance as well as minimum radiated noise levels and superior sound quality.

UNTIL VERY RECENTLY, the design of engine intake systems has been driven primarily by engine performance and packaging constraint considerations. The introduction of the concept of total vehicle refinement has caused all auto manufacturers to pay more attention to the smaller details that cumulatively allow for the production of a highly refined automobile. One of these details revolves around the reduction of intake orifice noise levels and the improvement of the perceived quality of these noise levels.

Traditionally, the solution to any intake noise level and/or quality problems would be searched for strictly via an experimental approach, in which various prototype intake systems would be built and tested on the engine. Engine and intake system acoustic performance for each build would be assessed from the evaluation of experimentally gathered data, with success being determined by the prototype system's ability to meet some engine and acoustic performance goal.

This “cut and try” approach to intake system development can be very costly and time consuming, and while it may lead to an acceptable (but not necessarily optimum) solution to the problem, rarely does it provide the insight as to why the problem actually existed in the first place.

Complete intake and exhaust system simulation, on the other hand, can often be an extremely rapid, cost effective, and insightful method of determining not only how to correct a problem, but also to identify the physical phenomena responsible for the problem. This is a relatively new technology which became available only recently. This paper presents the results of a combined simulation/experimental program of the GM Quad 4 engine in which an engine and manifold dynamics simulation code was used to accurately capture the manifold dynamics of the engine, as well as accurately predict the total level and frequency distribution of the noise levels emanating from the engine's throttle body orifice.