Stéphane Guilain

Transient response of a Turbocharged SI Engine with an electrical boost pressure supply

This paper deals with the transient response of a highly turbocharged gasoline engine. This downsized engine should behave as a naturally aspirated engine when the throttle is suddenly opened. However, a turbo lag occursand this phenomenon is of large importance for the vehicle acceleration and driver sensations. To reduce turbo lag effects, an electrical compressor (E-booster) was used to improve the main compressor and engine responses. The study was led on a three cylinder 1L turbo-charged engine. 1-D simulations (WAVE code) with a MATLAB-SIMULINK coupling were used to calculate the engine and vehicle transient responses. The vehicle, turbocharger and E-booster characteristics were simulated by the model. Second to third gear wide open throttle accelerations, varying engine loads at constant speed were also simulated. The calculations give important results like E-booster electrical consumption, and focus on the most significant parameters. By increasing the mass flow in the main compressor, the electrical booster largely improves the engine response. Large gains were obtained during the acceleration: the electrical booster reduces the response time from 3s to 1s.

The three-measurement two-calibration method for measuring the transfer matrix

Extensive use of transfer matrices (TMs) is made in determining the acoustic properties of a duct and in in-duct acoustic propagation models in the automotive industry and for musical acoustics purposes. The experimental apparatuses of classical TM measurement methods feature two measurement heads. Two microphones are flush with the walls of each head. The pressure signals are processed following the transfer function method constructed on an analytical model of acoustic propagation in measurement heads. The present paper aims at presenting a measurement method based on a three-microphone experimental apparatus and on its acoustic calibration through two reference measurements: the three-measurement two-calibration method for measuring the TM (3M2C-TM). Two microphones are flush with the measurement head walls and one is in the cap closing one side of the measured duct. 3M2C-TM proved essential for an accurate measurement of the four TM elements of two different ducts: a cylindrical duct and an expansion chamber.

Input impedance in flow ducts: Theory and measurement

This paper presents both a theoretical and an experimental investigation of the influence of the mean flow on the input impedance of a duct. The input impedance of an axisymetrical flow duct is calculated, taking into account the convective effect of a uniform flow, the dissipative effect of a turbulent flow and the radiation in an open jet. Each of these effects is separately studied. An experimental apparatus has been specifically designed to lower flow noise on the transducers, taking advantage of the Two-Microphone-Three-Calibration (TMTC) method [V. Gibiat and F. Laloë, J. Acoust. Soc. Am. 88, 2533-2545 (1990)], whose full calibration process allows any geometry for the measurement head. Theory and experiments are compared for a 1 m long cylindrical duct carrying a flow whose Mach number equals up to 0.15. The resonant frequencies are in close agreement, within 3%. The relative evolution of the magnitude maxima with increasing flow are in good agreement, within 10%. Despite similar tendencies when modifying the mean flow velocity, the amplitude of variation of the magnitude is 2 to 5 times smaller in the experiments.

A zonal approach for estimating pressure ratio at compressor extreme off-design conditions

Zero-dimensional/one-dimensional computational fluid dynamics codes are used to simulate the performance of complete internal combustion engines. In such codes, the operation of a turbocharger compressor is usually addressed employing its performance map. However, simulation of engine transients may drive the compressor to work at operating conditions outside the region provided by the manufacturer map. Therefore, a method is required to extrapolate the performance map to extended off-design conditions. This work examines several extrapolating methods at the different off-design regions, namely, low-pressure ratio zone, low-speed zone and high-speed zone. The accuracy of the methods is assessed with the aid of compressor extreme off-design measurements. In this way, the best method is selected for each region and the manufacturer map is used in design conditions, resulting in a zonal extrapolating approach aiming to preserve accuracy. The transitions between extrapolated zones are corrected, avoiding discontinuities and instabilities.

Determination of the transfer matrix of an automotive compressor under realistic flow conditions

Determination of the transfer matrix of an automotive compressor under realistic flow conditions Waves propagating into air intake pipes of automotive engines have been widely studied and are commonly used to obtain high volumetric efficiency. Nowadays, most of modern engines have a centrifugal compressor in their intake line. If the acoustic of intakes lines for naturally aspirated engines is well known, it is not the case for lines comprising a compressor, where both the geometry and the flow effects are of primary interest. As it is quite difficult to experimentally determine the acoustical behavior of a complete line comprising a compressor, a new system has been developed for determining acoustical transfer matrixes of each separated element of the line with flow. This new method is based on the two loads method; where a derivative of the Two Measurements Three Calibrations calibration method has been introduced. The basics of the determination of transfer matrixes with flow with our method are prese...

From frequency to time domain: Signal features and physical characteristics for resonant acoustical systems

The determination of the impulse response or the reflection function of an acoustical system from data expressed in the frequency domain is not immediate. Signal processing from frequency domain to time domain should involve phenomena of large amplitude as oscillations known as ”ripple” that does not correspond to any physical phenomenon. The ”ripple phenomenon” will be analyzed from both a signal processing and a physical point of view with the help of simple duct acoustic examples. A map designed as a new time-frequency tool helps us to show that it cannot be removed in most cases without the use of processing techniques involving modifications in the computed signal. This work has been developed for the automotive research, but can be applied to musical acoustics or to any field connected with time domain exploration of acoustic cues.