Search Results

Coolant boiling detection is a key issue to ensure Exhaust Gas Recirculation (EGR) coolers performance and durability. Accurate boiling detection and prediction tools are thus increasingly demanded to support EGR coolers design in a context of raising requirements, mainly driven by the stringent regulations and the recent application of this technology to gasoline engines. In this scenario, a numerical tool for the detection and quantification of coolant boiling in EGR coolers has been developed. It is based on Computational Fluid Dynamic (CFD) simulations and its results have been successfully validated against experimental data obtained on a test bench fully instrumented for boiling analysis. As for the predictive tool, a mathematical model describing the EGR cooler performance, including conjugate heat transfer and sub-cooled boiling, has been developed. Then a numerical methodology to solve this model has been implemented using OpenFOAM® (open source CFD toolbox).

Degradation of anti-pollutant devices must be taken into account in design so durability of the function is guaranteed over the vehicle lifetime. As for NOx reduction of diesel engines, Exhaust Gas Recirculation (EGR) systems are a well-known and robust solution. However, exposure of the EGR cooler inside this system to the exhaust gas conditions leads to a degradation of its function, affecting to the EGR rate and therefore to potential for NOx reduction. So, sizing and technology of these heat exchangers must be selected to avoid malfunction during vehicle operation. Current scenario in Europe with new homologation cycles and focus on NOx emissions of diesel vehicles under real driving conditions is challenging for the design of EGR systems. This leads to the increase of the areas of the engine map using EGR. Moreover new homologation includes also the use of low ambient temperature.

Soot and NOx, may react in situ with each other and reduce, thus, their emissions. Therefore, this reaction can be considered as a strategy of elimination of both air pollutants at the same time. In general, it is well established that heterogeneous reactions between soot and the different gases, generally existent in combustion environments, are affected by soot properties. Detailed characterization of soot samples coupled to reactivity studies towards O2 and NO have been carried out in order to identify the differences and similarities among the kinds of soot studied for understanding in what extent the origin of soot samples is a key parameter on their structure and reactivity. The combined analysis and interpretation of the soot chemical-physical features are essential to correctly interpret and to predict its behavior in the combustion chamber when soot is in contact with the combustion gases at high temperature.

Spark ignition (SI) engines are increasing their popularity worldwide since compression ignition (CI) engines have been struggling to comply with new pollutant emission regulations. At the moment, downsizing is the main focus of research on SI engines, decreasing their displacement and using a turbocharging system to compensate this loss in engine size. Exhaust gas recirculation is becoming a popular strategy to address two main issues that arise in heavily downsized turbocharged engines at full load operation: knocking at low engines speeds and fuel enrichment at high engine speeds to protect the turbine. In this research work, a fuel consumption optimization for different operating conditions was performed to operate with a cooled EGR loop, with gasoline and E85. Thus, the benefits of exhaust gas recirculation are proven for a SI gasoline turbocharged direct injection engine.

Soot fouling on exhaust gas recirculation coolers (EGRc) decreases thermal efficiency, implying the unfulfillment of NOx standards, and increases the pressure drop producing the malfunctioning of this device. The characterization of soot is of great interest since soot physico-chemical properties may have a direct influence on the degree of malfunctioning of EGRc. Thus, the combined analysis and interpretation of all the soot physico-chemical features are essential to correctly interpret its behavior when soot is deposited on the EGRc walls. In this context, the aim of this study is the characterization of five different types of diesel soot which were collected from several high pressure EGRc, working at different conditions (engine bench and vehicle). Each soot sample was characterized by means of elemental analysis, specific surface area (BET method), FESEM, FTIR, TGA, GC-MS and UV-visible spectroscopy.

Fouling phenomenon is a key issue for EGR cooler operation. In spite of the fact that soot deposition is imposed by the characteristics of the exhaust gases flow, the design of the EGR cooler has a significant impact for effect on the engine. New combustion modes corresponding to new engine developments and combination of EGR system with other post-treatment devices make that fouling conditions for future generations of EGR coolers can be significantly different from previous applications from Euro 3 to Euro 5. An investigation has been performed in order to characterize the response of different EGR coolers designs for different conditions of the exhaust gases. As for the design, the technology selected has been tube-and-fin heat exchanger, which is a high performance technology that fits Euro 6 customer specifications. The variations in design have been made through modifications in fin characteristics, both in configuration and geometric dimensions.

An investigation was performed to characterize the effect of soot deposition on the performance of EGR coolers. The main objective was to determine the magnitude of the thermal resistance associated to the fouling on heat exchange surfaces. So far, values coming from literature have been used and generalized for all the heat exchanger technologies, sizes and operation conditions. What is more, normally the effect of fouling has been evaluated directly in the thermal efficiency or overall thermal resistance as a percentage factor. The study has enabled to establish a range of thermal resistance for each heat exchanger technology in a given operation condition. It has been proved that the proper way to consider fouling is to include this thermal resistance in the dimensioning tool for EGR coolers. Though the tests performed do not intend to be comparative with general durability, they help to understand the effect on different technologies and sizes.

An investigation was performed to characterize impact of soot deposition in the performance of exhaust gas recirculation (EGR) cooling devices used in the EGR systems for diesel engines. The objective was to find an experimental test able to represent durability of the function in a real vehicle application. In order to apply the test as a validation tool in the EGR cooler design chain, this experimental test must be feasible in terms of time and test facilities. Thus, the definition of a test facility and of a cycle containing representative operation points of the engine has been made. The number of cycles has been adjusted to reproduce effect of vehicle exposure. The comparison of experimental test characterization with parts recovered from field and engine bench tests shows a good agreement, proving therefore the representativeness of the experimental test.