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Journal Article

Importance of Heat Transfer Phenomena in Small Turbochargers for Passenger Car Applications

Nowadays turbocharging the internal combustion engine has become a key point in both the reduction of pollutant emissions and the improvement of engine performance. The matching between turbocharger and engine is difficult; some of the reasons are the highly unsteady flow and the variety of diabatic and off-design conditions the turbocharger works with. In present paper the importance of the heat transfer phenomena inside small automotive turbochargers will be analyzed. These phenomena will be studied from the point of view of internal heat transfer between turbine and compressor and with a one-dimensional approach. A series of tests in a gas stand, with steady and pulsating hot flow in the turbine side, will be modeled to show the good agreement in turbocharger enthalpies prediction. The goodness of the model will be also shown predicting turbine and compressor outlet temperatures.
Journal Article

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

The generalization of exhaust aftertreatment systems along with the growing awareness about climate change is leading to an increasing importance of the efficiency over other criteria during the design of reciprocating engines. Using experimental and theoretical tools to perform detailed global energy balance (GEB) of the engine is a key issue for assessing the potential of different strategies to reduce consumption. With the objective of improving the analysis of GEB, this paper describes a tool that allows calculating the detailed internal repartition of the fuel energy in DI Diesel engines. Starting from the instantaneous in-cylinder pressure, the tool is able to describe the different energy paths thanks to specific submodels for all the relevant subsystems.
Journal Article

General Procedure for the Determination of Heat Transfer Properties in Small Automotive Turbochargers

These days many research efforts on internal combustion engines are centred on optimising turbocharger matching and performance on the engine. In the last years a number of studies have pointed out the strong effect on turbocharger behaviour of heat transfer phenomena. The main difficulty for taking into account these phenomena comes from the little information provided by turbocharger manufacturers. In this background, Original Engine Manufacturers (OEM) need general engineering tools able to provide reasonably precise results in predicting the mentioned heat transfer phenomena. Therefore, the purpose of this work is to provide a procedure, applicable to small automotive turbochargers, able to predict the heat transfer characteristics that can be used in a lumped 1D turbocharger heat transfer model. This model must be suitable to work coupled to whole-engine simulation codes (such as GT-Power or Ricardo WAVE) for being used in global engine models by the OEM.
Technical Paper

Evaluation of EGR Effect on the Global Energy Balance of a High Speed DI Diesel Engine

Regulated emissions and fuel consumption are the main constraints affecting internal combustion engine (ICE) design. Over the years, many techniques have been used with the aim of meeting these limitations. In particular, exhaust gas recirculation (EGR) has proved to be an invaluable solution to reduce NOx emissions in Diesel engines, becoming a widely used technique in production engines. However, its application has a direct effect on fuel consumption due to both the changes in the in-cylinder processes, affecting indicated efficiency, and also on the air management. An analysis, based on the engine Global Energy Balance, is presented to thoroughly assess the behavior of a HSDI Diesel engine under variable EGR conditions at different operating points. The tests have been carried out keeping constant the conditions at the IVC and the combustion centering.
Journal Article

Study of Air Flow Interaction with Pilot Injections in a Diesel Engine by Means of PIV Measurements

With ever-demanding emission legislations in Compression Ignition (CI) engines, new premixed combustion strategies have been developed in recent years seeking both, emissions and performance improvements. Since it has been shown that in-cylinder air flow affects the combustion process, and hence the overall engine performance, the study of swirling structures and its interaction with fuel injection are of great interest. In this regard, possible Turbulent Kinetic Energy (TKE) distribution changes after fuel injection may be a key parameter for achieving performance improvements by reducing in-cylinder heat transfer. Consequently, this paper aims to gain an insight into spray-swirl interaction through the analysis of in-cylinder velocity fields measured by Particle Image Velocimetry (PIV) when PCCI conditions are proposed. Experiments are carried out in a single cylinder optical Diesel engine with bowl-in-piston geometry.
Journal Article

An Investigation of Radiation Heat Transfer in a Light-Duty Diesel Engine

In the last two decades engine research has been mainly focused on reducing pollutant emissions. This fact together with growing awareness about the impacts of climate change are leading to an increase in the importance of thermal efficiency over other criteria in the design of internal combustion engines (ICE). In this framework, the heat transfer to the combustion chamber walls can be considered as one of the main sources of indicated efficiency diminution. In particular, in modern direct-injection diesel engines, the radiation emission from soot particles can constitute a significant component of the efficiency losses. Thus, the main of objective of the current research was to evaluate the amount of energy lost to soot radiation relative to the input fuel chemical energy during the combustion event under several representative engine loads and speeds. Moreover, the current research characterized the impact of different engine operating conditions on radiation heat transfer.
Journal Article

A Combination of Swirl Ratio and Injection Strategy to Increase Engine Efficiency

Growing awareness about CO2 emissions and their environmental implications are leading to an increase in the importance of thermal efficiency as criteria to design internal combustion engines (ICE). Heat transfer to the combustion chamber walls contributes to a decrease in the indicated efficiency. A strategy explored in this study to mitigate this efficiency loss is to promote low swirl conditions in the combustion chamber by using low swirl ratios. A decrease in swirl ratio leads to a reduction in heat transfer, but unfortunately, it can also lead to worsening of combustion development and a decrease in the gross indicated efficiency. Moreover, pumping work plays also an important role due to the effect of reduced intake restriction to generate the swirl motion. Current research evaluates the effect of a dedicated injection strategy to enhance combustion process when low swirl is used.
Technical Paper

Evaluation of Vortex Center Location Algorithms for Particle Image Velocimetry Data in an Optical Light-Duty Compression Ignition Engine

Ever decreasing permitted emission levels and the necessity of more efficient engines demand a better understanding of in-cylinder phenomena. In swirl-supported compression ignition (CI) engines, mean in-cylinder flow structures formed during the intake stroke deeply influence mixture preparation prior to combustion, heat transfer and pollutant oxidation all of which could potentially improve engine performance. Therefore, the ability to characterize these mean flow structures is relevant for achieving performance improvements. CI mean flow structure is mainly described by a precessing vortex. The location of the vortex center is key for the characterization of the flow structure. Consequently, this work aims at evaluating algorithms that allow for the location of the vortex center both, in ensemble-averaged velocity fields and in instantaneous velocity fields.
Technical Paper

An Investigation of the Engine Combustion Network ‘Spray B’ in a Light Duty Single Cylinder Optical Engine

Engine Combustion Network promotes fundamental investigations on a number of different spray configurations with the goal of providing experimental results under highly controlled conditions for CFD validation. Most of the available experiments up to now have been obtained in spray vessels, which miss some of the interactions governing spray evolution in the combustion chamber of an engine, such as the jet wall interaction and the transient conditions in the combustion chamber. The main aim of the present research is to compare the results obtained with a three-hole, 90 μm injector, known as ECN’s Spray B, in these constant-volume vessels and more recent Heavy-Duty engines with those obtained in a Light Duty Single Cylinder Optical Engine, under inert and reactive conditions, using n-dodecane. In-cylinder conditions during the injection were estimated by means of a 1-D and 0-D model simulation, accounting for heat transfer and in-cylinder mass evolution.
Technical Paper

Development and Validation of a Submodel for Thermal Exchanges in the Hydraulic Circuits of a Global Engine Model

To face the current challenges of the automotive industry, there is a need for computational models capable to simulate the engine behavior under low-temperature and low-pressure conditions. Internal combustion engines are complex and have interconnected systems where many processes take place and influence each other. Thus, a global approach to engine simulation is suitable to study the entire engine performance. The circuits that distribute the hydraulic fluids -liquid fuels, coolants and lubricants- are critical subsystems of the engine. This work presents a 0D model which was developed and set up to make possible the simulation of hydraulic circuits in a global engine model. The model is capable of simulating flow and pressure distributions as well as heat transfer processes in a circuit.
Technical Paper

Experimental and Numerical Assessment of Active Pre-chamber Ignition in Heavy Duty Natural Gas Stationary Engine

Gas engines (fuelled with CNG, LNG or Biogas) for generation of power and heat are, to this date, taking up larger shares of the market with respect to diesel engines. In order to meet the limit imposed by the TA-Luft regulations on stationary engines, lean combustion represents a viable solution for achieving lower emissions as well as efficiency levels comparable with diesel engines. Leaner mixtures however affect the combustion stability as the flame propagation velocity and consequently heat release rate are slowed down. As a strategy to deliver higher ignition energy, an active pre-chamber may be used. This work focuses on assessing the performance of a pre-chamber combustion configuration in a stationary heavy-duty engine for power generation, operating at different loads, air-to-fuel ratios and spark timings.