José M. García

Development of a zero-dimensional Diesel combustion model. Part 1: Analysis of the quasi-steady diffusion combustion phase

Abstract The aim of this work is to identify and quantify the influence of injection parameters and running conditions on Diesel combustion. This theoretical–experimental analysis is the basis for the development of a zero-dimensional Diesel combustion model. The objective of this first part is to analyze the physical variables and processes that control the central phase of the quasi-steady Diesel diffusion combustion. For that purpose, a parameter as the apparent combustion time (ACT) characteristic of a diffusion combustion process has been used. This parameter allows to obtain explicit relations between, on the one hand, the injection rate law and in-cylinder conditions (air density, oxygen concentration…), and on the other hand, the rate of heat release. Results show a good correlation between the ACT and the instantaneous values of in-cylinder gas density, injection velocity, oxygen concentration and the nozzle diameter.

Development of a zero-dimensional Diesel combustion model: Part 2: Analysis of the transient initial and final diffusion combustion phases

The objective of this work is the development of a zero-dimensional Diesel combustion model. After the development of a model based on the apparent combustion time for the central phase of the quasi-steady Diesel diffusion combustion [Appl. Therm. Eng. 23 (2003)], this second part describes the work of generalization of the model for the final and initial transient phases of the diffusion combustion. For this purpose, those transient phases are analyzed mainly on the basis of the results of CFD calculations for pulsed gas jets. The generalization for the final transient diffusion combustion phase is based on the analysis of the evolution of the turbulent effective viscosity dissipation at the end of the injection process. For the initial transient diffusion combustion phase the work is based on the analysis of the air/fuel mixture at the beginning of the injection process. The result is a zero-dimensional model capable of predicting the diffusion combustion in a Diesel engine. The validation of the proposed model has been performed on both a high speed Diesel engine and a heavy duty Diesel engine.

Segmentation of diesel spray images with log-likelihood ratio test algorithm for non-Gaussian distributions

A methodology for processing images of diesel sprays under different experimental situations is presented. The new approach has been developed for cases where the background does not follow a Gaussian distribution but a positive bias appears. In such cases, the lognormal and the gamma probability density functions have been considered for the background digital level distributions. Two different algorithms have been compared with the standard log-likelihood ratio test (LRT): a threshold defined from the cumulative probability density function of the background shows a sensitive improvement, but the best results are obtained with modified versions of the LRT algorithm adapted to non-Gaussian cases.

The effect of swirl on combustion and exhaust emissions in heavy-duty diesel engines

Abstract The effect of in-cylinder air swirl on diesel combustion and exhaust emissions has been studied in a heavy-duty diesel engine. A 1.8 L single-cylinder diesel engine fitted with a device to modify the swirl rate was used. This device allowed variation of the mean swirl ratio, a parameter related to the ratio of the angular velocity of the air within the combustion chamber and crankshaft angular rotation, from 0 to 5.33. Although no single optimum swirl level has been found, the results presented here give an insight into swirl effects on diesel engine combustion and exhaust emissions over a wide range of engine operating conditions.

Influence of Boost Pressure and Injection Pressure on Combustion Process and Exhaust Emissions in a HD Diesel Engine

The scope of this study is the analysis of the influence of boost pressure and injection pressure on combustion process and pollutant emissions. The influence of these parameters is investigated for different engine speeds. Fuel mass was kept constant for all the tests in order to avoid its influence on the analysis. A single cylinder research diesel engine, equipped with a common rail injection system capable of operating up to a maximum pressure of 150 MPa was used. Special attention was paid to NOx, smoke (which are the most important pollutants for legislation) and brake specific fuel consumption.