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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.

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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.

ElsevierPayri González, F.; Payri, R.; Salvador Rubio, FJ.; Martínez López, J. (2012). A contribution to the understanding of cavitation effects in Diesel injector nozzles through a combined experimental and computational investigation. Computers and Fluids. 58:88-101. doi:10.1016/j.compfluid.2012 ABSTRACTIn this paper a combined experimental and computational study was carried out in order to assess the ability of a Homogeneous Equilibrium Model in predicting the experimental behaviour observed from the hydraulical characterization of a nozzle. The nozzle used was a six-orifice microsac nozzle, with cylindrical holes, and therefore inclined to cavitate. The experimental results available for the validation purpose comprised measurements of mass flow rate and spray momentum flux, which correctly combined provide also fundamental information such as discharge coefficient, nozzle exit effective velocity and area contraction. The model was proved to be able of 2 reproducing the experimental results with high degree of confidence and, through the exploration of the internal flow, allowed the explanation of widely reported experimental findings related to cavitation phenomena: the mass flow choking induced by cavitation and the increment of effective injection velocity.

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