A.J. Torregrosa

Combustion chamber resonances in direct injection automotive diesel engines: A numerical approach

Abstract The resonant oscillation of burned gases in the combustion chamber of direct injection (DI) diesel engines appears to be the main excitation source of the engine block during combustion. This has led to the application of different techniques in order to study its generation mechanisms and to determine its relationship with combustion parameters such as bowl geometry, type of injector, injection parameters, etc. In this paper, a numerical methodology for the analysis of combustion chamber resonances is proposed. The numerical approach is validated by comparison with results from modal theory in a simple case. Then, this technique has been applied to the analysis of three different bowls, indicating their potential for the control of combustion chamber resonances.

Numerical Estimation of End Corrections in Extended-Duct and Perforated-Duct Mufflers

One-dimensional models for extended-duct and perforated-duct mufflers require the introduction of end corrections in order to account for multidimensional effects at the junctions. In this paper, a numerical two-dimensional finite element calculation has been used in order to obtain information on these end corrections. The results have been validated through comparison with experimental measurements performed with a modified version of the impulse method. Then, the influence of the different geometric characteristics of the mufflers on the end correction have been studied. A general correlation in terms of relevant nondimensional parameters is given for extended-duct mufflers, whereas for perforated mufflers a general correlation has not been obtained due to the eventual coupling with other attenuation mechanisms.

A Tool for Predicting the Thermal Performance of a Diesel Engine

This paper presents a thermal network model for the simulation of the transient response of diesel engines. The model was adjusted by using experimental data from a completely instrumented engine run under steady-state and transient conditions. Comparisons between measured and predicted material temperatures over a wide range of engine running conditions show a mean error of 7°C. The model was then used to predict the thermal behavior of a different engine. Model results were checked against oil and coolant temperatures measured during engine warm-up at constant speed and load, and on a New European Driving Cycle. Results show that the model predicts these temperatures with a maximum error of 3°C.

Evaluation through pressure and mass velocity distributions of the linear acoustical description of I. C. engine exhaust systems

Abstract Linear acoustic theory is still the most widely used tool for exhaust system design in I. C. engines. In this paper, the pressure and mass velocity distributions along the exhaust system are used to evaluate the results from linear acoustic theory. These results are compared with those obtained from a full non-linear calculation validated against engine test experiments. The analysis performed allows the influence of two relevant aspects to be separated: the linear representation of the source (engine and manifold) and the linear description of the exhaust system itself. The results indicate that good qualitative agreement may be attained in general, but some differences associated with non-linear effects can appear.

Development of non-reflecting boundary condition for application in 3D computational fluid dynamics codes

Abstract Numerical computations are commonly used for better understanding the unsteady processes in internal combustion engine components and their acoustic behavior. The acoustic characterization of a system requires that reflections from duct terminations are avoided, which is achieved either by using highly dissipative terminations or, when an impulsive excitation is used, by placing long ducts between the system under study and the duct ends. In the latter case, the simulation of such a procedure would require a large computational domain with the associated high computational cost, unless non-reflecting boundary conditions are used. In this paper, first the different non-reflecting boundary conditions available in ANSYS-FLUENT are evaluated. Then, the development and implementation of an anechoic termination in a 3D-CFD code is presented. The performance of the new implementation is first validated in the classic Sod’s shock tube problem, and then checked against numerical and experimental results of the flow and acoustic fields in automotive exhaust mufflers. The results obtained compare favorably with those from the conventional CFD approach and experiments, while the computational cost is significantly reduced.

Acoustic characterization of automotive turbocompressors

The performance of different experimental techniques proposed in the literature for acoustic characterization was assessed through the study of the noise generated by the compressor of an automotive turbocharger under different working conditions in an engine test cell. The most critical restrictions of in-duct intensimetry methods regarding frequency limitations are presented and experimentally demonstrated. The results provided by those methods were correlated against a reference intensity probe. A beamforming method based on three-sensor-phased arrays appears to be the most reliable approach in the plane wave range, presenting higher accuracy than the more common two-microphone method and simple pressure level measurements. Also, preliminary results from a novel radiated noise quantification technique based on acoustic particle velocity are presented and discussed. The results indicate that further research on this topic is required.

Identification of information sources and citation patterns in the field of reciprocating internal combustion engines

Processes and technology of reciprocating internal combustion engines (ICE) constitute a research field whose characteristics regarding information production and diffusion are determined by multidisciplinarity, the existence of pseudo-technical literature and the influence of confidentiality on the presentation of research outputs. The objective of this study is to provide a quantitative and objective basis for the evaluation of research in this field. This has been accomplished by identifying the most productive journals and the most cited sources, using the SCI and citation analysis. From this analysis, core journals have been identified, showing that their importance in this research area does not correlate with their impact factor. Moreover, conference proceedings (particularly those published by the Society of Automotive Engineers) are shown to be the most important information source in this field.

A study of the influence of mean flow on the acoustic performance of Herschel-Quincke tubes

In this paper, a simple flow model is used in order to assess the influence of mean flow and dissipation on the acoustic performance of the classical two-duct Herschel-Quincke tube. First, a transfer matrix is obtained for the system, which depends on the values of the Mach number in the two branches. These Mach numbers are then estimated separately by means of an incompressible flow calculation. Finally, both calculations are used to study the way in which mean flow affects the position and value of the characteristic attenuation and resonances of the system. The results indicate the nontrivial character of the influence observed.

A theoretical and experimental study of the behaviour of concentric perforated duct automotive mufflers

Concentric perforated duct mufflers are broadly used when designing automotive front mufflers because of their acceptable acoustic performance and their low backpressure. In the frame of the design methodologies presently used, suitable theoretical models are needed in order to estimate this performance without the need to build prototypes and perform experimental tests. A lot of work has been performed in this sense; nevertheless, there remains a reasonable doubt that the results obtained with purely linear models are representative of the muffler behavior under actual engine conditions. In the present paper, a two dimensional finite element model is used in order to compute the transmission loss of several concentric perforated duct mufflers, and the results are compared with experimental measurements performed with a modified version of the impulse method that allows for the use of high amplitude pressure pulses as excitation. The comparison reveals that the linear model gives qualitative guidelines about the muffler behavior but with important quantitative differences. Moreover, it is demonstrated by means of system identification techniques that the differences observed cannot be attributed to measurement problems.

Energy Balance During the Warm-Up of a Diesel Engine

In the present work, an automotive Diesel engine has been experimentally tested under a New European Driving Cycle (NEDC) with the aim of getting experimental plots of time dependent partitioning of energy injected during the warm-up process. An additional objective of this work is to assess the energy recovery capacity installed in the engine, i.e., to assess how much of the energy that leaves the engine with the exhaust gasses and the coolant is being employed. With this target, mean values of some parameters (intake and exhaust pressures and temperatures, coolant flow and coolant inlet and outlet temperatures, engine speed and torque) together with instantaneous variables (crankshaft angle, in-cylinder gas pressure, intake and exhaust mass flows) were continuously recorded during the warm-up of the engine. As a result of the work, the dynamics of the thermal balance of the Diesel engine under transient road conditions during the warm-up period was obtained. Gross equivalent and detailed cumulative energy flows were measured. The driving cycle averaged values of exhaust gases and coolant energy rates make up 3.75 and 4.31 kW respectively in the engine tested. Thermal losses account for more than 30 % of the input energy, while the larger part of the input energy goes to the heating of engine masses during approximately the first third part of the NEDC cycle. For the urban parts of the cycle the mean value of exhaust gases temperature does not exceed 200°C, and the corresponding averaged energy rates are 2.84 and 2.18 kW for the exhaust gases and the coolant. The coolant temperature takes approximately 720 seconds to reach 80°C. The mean value of the sum of the energy recovered by the exhaust gas recirculation (EGR) cooler and the passenger cabin heater core is of the order 1.5 kW. The data obtained can be used to establish nominal design parameters for efficient waste energy recovery systems.