F. Payri

New methodology for in-cylinder pressure analysis in direct injection diesel engines: application to combustion noise

The objective of this paper is to present a new methodology for the analysis of in-cylinder pressure in direct injection (DI) diesel engines. Indeed, for some applications, the traditional study of total pressure is shown to be insufficient and the proposed technique is intended to be an alternative and more efficient tool, since it may provide a better understanding of the physical mechanisms. The main idea is to decompose the in-cylinder pressure evolution according to three phenomena taking place during diesel engine operation: pseudo-motored, combustion and resonance excitation. In order to validate this new method, it is applied to combustion noise analysis. Actually, the combustion process in DI diesel engines may be considered as an important source of noise, and the traditional approach is mainly based on the interpretation of objective overall spectral levels of both in-cylinder pressure and radiated noise, obtained from Fourier analysis. However, this approach has been shown unable to describe all the relevant aspects of the problem, whereas the results obtained from the proposed decomposition technique exhibit a fair qualitative correlation between in-cylinder pressure and combustion noise issues. Further development of this approach could provide a useful tool for the development of optimal injection strategies fulfilling not only performance considerations but also sound quality requirements for combustion noise in DI diesel engines.

Modelling of supercharger turbines in internal-combustion engines

Abstract A new physical model to calculate the fluid-dynamic behaviour and energy conversion in turbocharger turbines for internal-combustion (I.C.) engines is presented. The model has been developed to be used as a boundary condition in wave action models. The model uses data from the turbine characteristic curves and it is based on the idealization of the turbine by simple elements: ideal nozzles and an intermediate volume. Two typical turbine types are discussed here: a single entry turbine and a twin entry turbine. In order to validate the model, a comparison between calculated and measured engine running variables related to the turbine behaviour is presented.

Modelling of turbocharged diesel engines in transient operation. Part 2: Wave action models for calculating the transient operation in a high speed direct injection engine

Abstract Part 1 of this paper analysed the physical phenomena involved in the transient operation of turbocharged diesel engines, together with the principles of diesel combustion characterization during the transient process. This second part describes a calculation model developed to predict engine transient performance based on an existing wave action code. Relevant improvements introduced are combustion process simulation and modelling of heat transfer, variable geometry turbine behaviour and mechanical losses. Experimental load transient tests with a high speed direct injection engine have been performed, with the aim of assessing the model accuracy. The main evaluation parameters were instantaneous variation during turbocharger rotating speed transient, boost pressure, air mass flow, injected fuel and exhaust pressures.

Contribution to the application of two-colour imaging to diesel combustion

The two-colour method (2C) is a well-known methodology for the estimation of flame temperature and the soot-related KL factor. A 2C imaging system has been built with a single charge-coupled device (CCD) camera for visualization of the diesel flame in a single-cylinder 2-stroke engine with optical accesses. The work presented here focuses on methodological aspects. In that sense, the influence of calibration uncertainties on the measured temperature and KL factor has been analysed. Besides, a theoretical study is presented that tries to link the true flame temperature and soot distributions with those derived from the 2C images. Finally, an experimental study has been carried out in order to show the influence of injection pressure, air density and temperature on the 2C-derived parameters. Comparison with the expected results has shown the limitations of this methodology for diesel flame analysis.

Modified impulse method for the measurement of the frequency response of acoustic filters to weakly nonlinear transient excitations

In this paper, a modified impulse method is proposed which allows the determination of the influence of the excitation characteristics on acoustic filter performance. Issues related to nonlinear propagation, namely wave steepening and wave interactions, have been addressed in an approximate way, validated against one-dimensional unsteady nonlinear flow calculations. The results obtained for expansion chambers and extended duct resonators indicate that the amplitude threshold for the onset of nonlinear phenomena is related to the geometry considered.

A New Tool to Perform Global Energy Balances in DI Diesel Engines

The support of the Universitat Politecnica de Valencia (PAID06-09) and Generalitat Valenciana (GV/2010/045) is greatly acknowledged.

Sound quality assessment of Diesel combustion noise using in-cylinder pressure components

The combustion process in direct injection (DI) Diesel engines is an important source of noise, and it is thus the main reason why end-users could be reluctant to drive vehicles powered with this type of engine. This means that the great potential of Diesel engines for environment preservation—due to their lower consumption and the subsequent reduction of CO2 emissions—may be lost. Moreover, the advanced combustion concepts—e.g. the HCCI (homogeneous charge compression ignition)—developed to comply with forthcoming emissions legislation, while maintaining the efficiency of current engines, are expected to be noisier because they are characterized by a higher amount of premixed combustion. For this reason many efforts have been dedicated by car manufacturers in recent years to reduce the overall level and improve the sound quality of engine noise. Evaluation procedures are required, both for noise levels and sound quality, that may be integrated in the global engine development process in a timely and cost-effective manner. In previous published work, the authors proposed a novel method for the assessment of engine noise level. A similar procedure is applied in this paper to demonstrate the suitability of combustion indicators for the evaluation of engine noise quality. These indicators, which are representative of the peak velocity of fuel burning and the resonance in the combustion chamber, are well correlated with the combustion noise mark obtained from jury testing. Quite good accuracy in the prediction of the engine noise quality has been obtained with the definition of a two-component regression, which also permits the identification of the combustion process features related to the resulting noise quality, so that corrective actions may be proposed.

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.

Modifications to the Method of Characteristics for the Analysis of the Gas Exchange Process in Internal Combustion Engines

Some modifications to the method of characteristics for the analysis of the gas exchange process in internal combustion engines are presented in this paper. The modifications are related to the calculation of the path lines and the Riemann characteristic lines at the grid points. Regarding the path lines, the algorithm for the generation and elimination of path lines has been improved, mainly for the cases in which the fluid motion passes from being null or going out of the pipe to going into the pipe. In those cases the algorithm proposed by Benson can cause some mistakes in the entropy level field of the duct. An alternative method is proposed: the duplication ofpath lines. The other modifcation proposed is related to assuming a linear interpolation for the pressure and the volume flowrate between the nearest grid points, rather than assuming a linear interpolation of the value of the Riemann characteristics. These modijcations substantially improve the results obtained in the calculation of the fluid flow in manifolds of reciprocating internal combustion engines.

A phenomenological combustion model for direct-injection, compression-ignition engines

This paper describes the development and use of a phenomenological model for combustion in direct-injection diesel engines. The model is based on the analysis of the fuel evolution from the injection start till the combustion end. The fuel evolution is modelled by studying the spray atomization, penetration, air entrainment, and evaporation; the air motion; the ignition delay; and the combustion. The model consists of analytical and semiempirical submodels for each of the above-mentioned phenomena, with a special emphasis on the spray behaviour during the atomization process and after the impingement against the walls. The model gives the amounts of fuel atomized, vaporized, and burned, and the amounts of air entrained and burned. The heat released by fuel combustion is used to compute the pressure evolution in the combustion chamber. An application of the model is made for a real engine, and a comparison between experimental and calculated pressure diagrams is presented, showing a good agreement.