Haitham Mezher

Transfer matrix measurements for studying intake wave dynamics applied to charge air coolers with experimental engine validation in the frequency domain and the time domain

The flows at the intake and the exhaust of an internal-combustion engine are most of the time simplified to a single space dimension, and the hyperbolic partial differential equations that govern the compressible and unsteady air flow are discretized and solved numerically. This method is the basis of today’s engine simulation codes. Models for complex parts such as the charge air coolers often need calibration with experimental engine data essentially for the pressure drop coefficients and the corrected lengths. Another technique for understanding wave action inside the pipes of an internal-combustion engine is to use the reciprocating nature of the engine itself and to gain access to the frequency spectrum of the pressure and the mass flow signals. This was achieved in this paper using a dedicated dynamic bench that identifies a transfer matrix which is defined in terms of the pressure and the mass flow rate. This new transfer matrix technique permits the dynamic pressure and the mass flow to be identified under similar conditions to those encountered in an engine. The transfer matrix is measured for two charge air cooler geometries and validated using experimental engine measurements. The results and methodology are explained in the frequency domain and the time domain, and the future objectives and perspectives discussed.

Wave dynamics measurement and characterization of a charge air cooler at the intake of an internal combustion engine with integration into a nonlinear code

There exist two fundamental tools for modeling and simulating wave action of internal combustion engines. The first is a nonlinear time domain solution of the Euler equations using a space–time meshing. The second is a frequency domain solution of the linear wave equations. These two methods exist with a wide range of complexity and sophistication. Hybrid coupled methods also exist; they attempt to bridge the gap between the two techniques while maintaining the overall goal of engine simulation in mind. This work deals with the frequency characterization of a complex intake element, the charge air cooler. First, a transfer matrix for a simple tube is defined and measured. Two identical versions of the previous tube serve for identifying the transfer matrix of the charge air cooler directly on an operating four-cylinder turbocharged engine. Once the transfer matrix is measured, it is coupled to GT-Power as four transfer functions coded into Simulink. The final validation comprises two tubes in GT-Power with measured boundary conditions of pressure and mass flow with the Simulink model in between. Results are presented in the time and frequency domains with future objectives and perspectives as well.

Transfer Matrix Computation for Wave Action Simulation in an Internal Combustion Engine

A new technique for simulating engine pressure waves consisting of linking pressure response and mass flow rate excitation in the frequency domain has been presented. This is achieved on the so-called “dynamic flow bench”. With this new approach, precise, fast and robust results can be obtained while taking into account all the phenomena inherent to compressible unsteady flows. The method exhibited promising results when it was incorporated in a GT-Power/Simulink coupled simulation of a naturally aspirated engine.However, today’s downsized turbocharged engines come with more stringent simulation necessities, where discontinuities such as the charge air cooler (CAC) must be correctly modeled. Simulating such engines with the transfer function methodology is quite difficult because it requires mounting the entire intake line on the bench. Modeling wave action for these engines requires an understanding in the frequency domain of the flow’s characteristics through the different elements that make up the intake line. This leads us to study the acoustic transfer matrices.In order to split the intake line into separate elements, a straight duct of 185mm length is chosen as a first reference. It is mounted on the dynamic flow bench and pressure response is measured after an impulse mass flow excitation. Transfer functions of relative pressure and mass flow rate are then identified at given points upstream and downstream of this reference tube. These functions produce the desired transfer matrix poles.The resulting matrix is validated by inserting the tube in the intake lines of two four-cylinder engines which are modeled in GT-Power. Pressure and mass flow are registered at the measurement points of the tube from the simulation. The time series data upstream of the tube is treated in the frequency domain and the transfer matrix is used to calculate the corresponding downstream values. Measured values from the native simulation and those calculated using the transfer matrix propagation are then compared.Finally, the experimental technique for identifying transfer matrices of more complex elements using two versions of the previous tube is presented.Copyright

Engine temperature management and control: Improvements and benefits linked to the replacement of map-controlled thermostat with a mechatronic part

In order to cope with new regulations and find a better compromise between fuel consumption, pollutant emissions and comfort, thermal management technologies are getting more complex. This is especially true when it requires replacing a basic passive solution or an open-loop control one with a mechatronic system. The latter enables the optimal setups to improve performance in cold/hot, transient/stable, partial/full load operation. A new Active Cooling Thermal-management valve concept has been developed to specifically replace map-controlled thermostat whilst keeping the same packaging and cost range. The system delivers a quick and precise close-loop control of the temperature to solve the main drawbacks of classic solutions such as a temperature-sensitive response time or hysteresis and temperature overshoots.

Coupling a Linear Pressure and Mass Flow Frequency Model Obtained From Measurements at the Intake of an IC Engine With a Non-Linear Time Domain Code

Engine simulation software has become synonymous with automotive design and component development. An integral part of any engine simulation is the correct modeling of the air flow at the intake. This air flow, which is highly compressible and unsteady, has a first order influence on the trapped air mass inside the cylinder and therefore on the behavior of the engine (torque response and emissions). The non-linear modeling of the air paths at the intake is done using a space-time meshing and by solving the 1D equations with a proper time scheme. Such methods are the bases of today’s engine simulation codes [1]. The main constraint with these methods is the time needed to model complex geometries, whether being the simulation time or the time spent on calibrating the said models with experimental measurements. These complicated geometries become problematic to accurately predict, particularly the charge air cooler (CAC) which is responsible for cooling the air flow on a turbocharged engine.Another approach is to use frequency domain models to describe the fluctuating pressure and mass flow [2]. Although this approach is simpler, faster in terms of computing time and offers many experimental techniques to characterize complicated geometries; important limitations can appear when it is confronted to the effects of high pressure levels and pulsating mass flow. Furthermore, the models behind such methods are designed to be used in the frequency domain, contrary to an engine simulation that works solely with time domain variables.In this article, a linear frequency domain model known as a transfer matrix is used. This concept is nothing new in acoustics; however here it was developed by experimentally measuring the transfer matrix [3] for a simple tube on a dedicated bench under conditions similar to those encountered on an engine [4]. The approach is then extended to measure the transfer matrix of a charge air cooler (CAC) on a real engine test bench. The measured discrete transfer matrix, defined in terms of fluctuating pressure and mass flow, is then transformed to a continuous frequency model and coded in Simulink®. The latter is coupled to the non-linear engine simulation software GT-Power®.The objective is to accurately model the pressure and mass flow of a complicated geometry using experimental measurements and a linear frequency model then to couple the transfer matrix to an engine simulation code, thus replacing the need for a meshed model.Copyright

Wave dynamics analysis at the intake of a turbocharged engine: concept proposal of a new active inlet charge air duct for low-speed tuning and high-speed permeability:

The unsteady-state gas dynamics at the intake of a turbocharged engine were analysed. The objective is to tune the intake line to low operating speeds where the exhaust gases lack the enthalpy needed to operate the turbocharger at rated speeds and to provide the boost pressure needed. The proposed methodology compensates for the lack of boost pressure by benefiting from the existing wave action at the intake. Zero-dimensional acoustic modelling is first used to investigate the geometrical parameters which have the most influnce on low-end acoustic tuning. Impedance bench and electrically driven engine tests complete the study and compare different intake configurations and two geometries of charge air coolers: an air-to-air charge air cooler and a water-cooled charge air cooler. Optimal intake configurations were found for low-end torque considerations as well as high-speed operation where a reduction in the pressure losses is most important. The findings were validated and established on an engine test bench with torque gain at different rotational speeds of the engine. The study led to the proposal of an active charge air duct which enables a solution to be found for the low-end torque where acoustic tuning is favoured and for high-speed operation where the boost pressure is readily available. The acoustic response of this part was compared with the reference solution, and conclusions and possible topics for future work were obtained from the analysis.

A model based system approach to innovative smart intake products: CO2 savings and specific performance

On modern combustion engines, air induction systems are evermore evolving into more complicated elements with an objective to find the best trade-off between fuel consumption, pollutant emissions and engine performance. This pursuit has led to the emergence of the downsized turbocharged engine. For such an engine, it’s necessary to reinforce the low end torque. This is because, at low operating speeds and loads, the lack of enthalpy at the exhaust side causes a poor behavior of the turbocharger which leads to a poor boost pressure and consequently a deficit of engine performance. The proposed idea in this case would be to benefit from an optimized ‘smart’ air intake system to solve this issue while assuring other interesting functions as well. First, cylinder filling can be enhanced by assuring acoustic resonance conditions at the intake. The result is an increase of air flow leading to a better torque response and vehicle responsiveness. Pressure waves induced boosting can also help to reduce the thermal stress on the turbocharger as well as the size of the charge air cooler. Secondly, pressure waves can help to save energy by ‘de-throttling’ at part load operation on an SI engine. This has the effect of reducing the pumping loop and thus enhancing specific fuel consumption. Mechatronic integration into smart systems at the intake is necessary to achieve such goals. The Active Charge Air Duct (ACAD) and the active air intake manifold presented in this paper are innovative plastic products that aim to reduce fuel consumption. This is achieved through geometries with a high flexibility of thermoplastic processes.