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The increasingly restrictive legislation on pollutant emissions is involving new homologation procedures driven to be representative of real driving emissions. This context demands an update of the modelling tools leading to an accurate assessment of the engine and aftertreatment systems performance at the same time as these complex systems are understood as a single element. In addition, virtual engine models must retain the accuracy while reducing the computational effort to get closer to real-time computation. It makes them useful for pre-design and calibration but also potentially applicable to on-board diagnostics purposes. This paper responds to these requirements presenting a lumped modelling approach for the simulation of aftertreatment systems.

In recent years, the spread use of after-treatment systems together with the growing awareness about the climate change is leading to an increase in the importance of the efficiency over other criteria during the design of internal combustion engines. In this sense, it has been demonstrated that performing an energy balance is a suitable methodology to assess the potential of different injection or air management strategies, to reduce consumption as well as determining the more relevant energy terms that could be improved. In this work, an experimental energy balance with the corresponding comprehensive analysis is presented. The main objective is the identification of how the energy is split, considering internal and external balances. For this purpose, some parametric studies varying the coolant temperature, the intake air temperature and the start of the injection timing have been performed. The results quantify the effect of each parametrical study on engine efficiency.

Direct injection compression ignited (CI) engines are today's most efficient engine technology, granting efficiencies exceeding 40% for their optimal operation point. In addition, a strong technological development has allowed the CI engine to overcome its traditional weak points: both its pollutant emissions and the gap in specific power regarding its competitor, i.e. the spark ignited (SI) engine, have been noticeably reduced. Particularly, the increase in specific power has led to the downsizing as an effective method to improve vehicle efficiency. Despite the reduction in total displacement, the cylinder displacement of current CI engines is still around 0.5 liters. For some applications (urban light duty vehicles, Range Extenders…) it may be interesting to reduce the engine displacement to address power targets around 20kW with high efficiencies.

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.

A fundamental study to experimentally analyze the effect of cavitation in common-rail diesel nozzles on the soot formation process was carried out. The soot content was characterized by measuring the soot radiation, and an original methodology was developed to suitably characterize the soot formation process from this soot content. After a significant effort to overcome the different difficulties when analyzing the experimental data, the results seem to show a promising conclusion: cavitation reduces the soot formation rate. This reduction is explained, on the one hand, because it leads to a reduction in the effective diameter, thus diminishing the equivalence fuel/air ratio at the lift-off length; and, on the other hand, because it provokes an increase in effective velocity, thus increasing the lift-off length and reducing the corresponding equivalence fuel/air ratio.

Observers can be used for combining different information sources, as fast models with slow but accurate sensors. For that, a Kalman filter can be used for identifying the bias and cancelling its variation during time. However, normal calibration procedure is iterative and ad-hoc and this does not get optimal results. Furthermore, the lack of enough accurate references make difficult to estimate the best tuning, and more if the calibration pretends to be an online procedure. For solving this, the paper presents a novel calibration method for Kalman filter based on a Monte Carlo analysis, simulating real conditions by means of statistical distributions. This makes possible to create actual references for estimating error metrics of the observer output. A previous sensitivity study is presented for understanding the performance of the algorithm under different conditions.

The relationship between ignition, lift-off length and soot formation was investigated for a collection of fuels in an optically-accessible modified 2-stroke engine under a set of typical quasi-steady state Diesel DI conditions. Five fuels including biodiesel blends and Fischer-Tropsch fuels have been selected for their potential to substitute conventional diesel with no major modifications on the engine hardware, and were previously characterized under ambient pressure following ASTM standards. Fuels were injected into a large volume through a single-hole nozzle at three levels of injection pressure, by sweeping ambient temperatures at constant density, and ambient densities at constant temperature. The 8 ms single-shot injections were long enough to reach the stabilization of a free diffusion flame. The OH-chemiluminescence was imaged and lift-off length was measured via image post-processing.

The use of particulate filters (DPF) has become in recent years the state of the art technology for the reduction of soot aerosol emissions for light, medium and heavy duty Diesel vehicles. However, the effect of the system location on engine performance is a key aspect that should be studied. In the present work a numerical study has been carried out with the objective to analyze the effect on the engine performance of an innovative DPF placement upstream of the turbine. This study has been performed by means of the gas dynamic simulation of a two-stage turbocharged heavy duty Diesel engine, which has been previously modeled from experimental data obtained under steady state conditions. The original DPF has been divided into two monoliths for the case of the pre-turbo DPF configuration. Three cylinders discharge in each of these monoliths and after the filtration the flow is driven towards the high-pressure turbine and the EGR system.

Acoustics of automotive intake and exhaust systems have been modelled very successfully for many years using 1D gas dynamic simulations. These use pseudo 3D models to allow complex components to be constructed from simple building blocks. In recent years, tools have appeared that automate the construction of network models from 3D geometries of intake and exhaust components. Using these tools, concurrent noise and performance predictions are a core part of most engine development programmes. However, there is still much interest in the more traditional field of linear acoustics: analysing the acoustic behaviour of isolated components or predicting radiated noise using a linear source. Existing approaches break the intake and exhaust system down into a set of components, each with known acoustic properties. They are then connected together to create a network that replicates the donor non-linear model.

Concepts of premixed diesel Low Temperature Combustion (LTC) have been shown to be advantageous in greatly reducing engine-out nitrogen oxide (NOx) and particulate matter (PM) emissions, even below the minimum detection limit of standard opacity-based PM mass instruments. Previous research has revealed that significant changes to the PM size and number emissions still occur for changes to the LTC engine operating conditions. This work investigates the influence of reductions in intake oxygen concentration on PM (mass, size, and number), NOx, hydrocarbon (HC), and carbon monoxide (CO) emissions from select LTC engine operating conditions. Exhaust particle size distributions were measured for multiple engine operating conditions of premixed diesel LTC within a range of five intake oxygen concentrations from 9% to 13% (by volume) at three intake pressures from 1.325 to 1.6 bar.

Despite the development in NOx aftertreatment for Diesel engines, EGR is a cost-effective solution to fulfill current and future emission regulations. There is a wide bibliography discussing the global effects of EGR on combustion and emissions. However, little has been published concerning the effects of the unsuitable EGR and air distribution among cylinders. Since current HSDI engines operate with EGR rates as high as 50% the effect of the unequal EGR distribution becomes important. In addition, cylinder-to-cylinder charge dispersion becomes a critical aspect on the control of low temperature combustion systems. In concordance with the aspects outlined before, the aim of this paper is to study the effects of the EGR cylinder to cylinder distribution on the engine performance and emissions. To cope with this objective, experiments have been conducted in a HSDI engine with two different EGR systems.

The onset and development of the inner cavitating flow in Diesel injectors is analyzed in relation with the needle movement, using Computational Fluid Dynamics studies realized with moving mesh. Two real six-hole injector geometries have been considered, one with cylindrical nozzles, the other with conical nozzles. A full analysis of the flow results is presented, including a dynamic picture of the developing pattern. Results show that depending on the needle lift, the cavitation pattern varies strongly throughout the nozzle, and affects the characteristics of the flow at the nozzle exit. A kind of hysteresis in the development of the flow has also been observed between needle opening and closing.

Traditionally the NOx prediction models use to take into account exclusively the NOx formation process. Nowadays diesel engines use to operate with high EGR rates and high fuel/air equivalence ratios, in opposition with what it was standard in the past years. In such conditions a considerable amount of NOx generated in the previous cycle (coming from the recirculated exhaust gases) or in the previous combustion is re-entrained by the flame, where a highly reducing region exists (due to a lack of oxygen and the presence of hydrocarbons and a high temperature level). Face to this fact a question arises: what happens with these re-entrained NOx?

Although in combustion diagnosis models the uncertainty in the trapped mass is not critical, different authors have reported non negligible effects on the rate of heat release. Usually, an emptying-and-filling model is used to estimate the residual mass, whence the trapped mass is obtained. Generally, the instantaneous pressure at the intake and exhaust ports are not measured for combustion diagnosis applications and hence, it is difficult to estimate accurate values of the residual mass. The objective of this work is to propose a simple physical model to estimate the residual mass in a DI Diesel engine for a combustion diagnosis model. The proposed model specially focuses on the exhaust port conditions, because they appear to be the most important factor affecting the residual mass estimation.

Diesel injector nozzles with different geometries have been investigated, firstly to study the effect of cavitation on the flow at the exit of the nozzle, and secondly to see its effect on the spray and the consequent flame formation. The flow at the exit of the nozzle was characterized by measuring both the injection rate and the momentum flux for a wide range of typical engine's rail and cylinder pressures. The injection rate is directly affected by cavitation and it will become choked when this phenomenon appears. The measurement of the momentum flux can be combined with the injection rate to derive the velocity at the nozzle exit. The momentum flux does not seem to be influenced by the appearance of cavitation. Apart from this hydraulic characterization, the different nozzles have also been mounted on an engine with optical access to the combustion chamber. During these tests, the spray, its vaporization and combustion were visualized and recorded with a high resolution camera.

Modern DI Diesel engines are widely used in automotive applications. Improvements in performance and emissions have been produced in the last ten years on these engines, so that they are now very competitive in comparison with petrol engines. However, cold startability is one of the main challenges of Diesel engines, since great differences with petrol engines still can be noticed. Today, in small engines glow plugs are universally used as an aid system for cold start. In large engines, where the cold start is less critical, intake air heating technology is employed. In this paper the application of this technology to small engines is evaluated in terms of its viability for cold starting and HC/CO emissions and combustion noise reduction during the warm-up phase of the engine.

In this paper the heat transfer of the hot gases to the cylinder walls of DI Diesel engines is analyzed using Computational Fluid Dynamics (CFD) and compared to the predictions obtained with a zero-dimensional thermodynamic model based on a variant of the Woschni equation. The final objective is to improve the simple model by modifying the original equations to better take into account the influence of important parameters, such as swirl, on the heat transfer. CFD calculations of the compression and expansion strokes have been made for two real DI Diesel engine geometries, a small one with a displacement of 0.4 l. and a heavy duty one of 2.0 l., and for different working points. The total heat transfer rate to the cylinder surfaces is highly dependent on the mean flow behavior and turbulence levels.

The purpose of the study reported in this paper was to exploit the possibility of adjusting some injection parameters in a diesel engine fitted with a common-rail injection system with the final goal of reducing pollutant emissions. Starting from the original settings, several injection parameters like nozzle hole diameter, injection pressure and injection duration, were adjusted following three different injection strategies, trying to produce some specific fuel spray patterns (spray penetration and cone angle, air entrainment, etc). Additionally, boost pressure was modified, in order to control spray-air interaction, and EGR was introduced to achieve the required NOx reduction. The adjusted injection setting allowed to generate starting values in pollutants emissions very tolerant to EGR, in such a way that the achieved reduction of NOx was not frustrated by an excessive increase in PM emissions.

The main objective of the study described in this paper is to explore the potential of different post-injection patterns, with a plain common rail system, for reduction of soot emissions in HD diesel engines. Test have been carried out in a single-cylinder engine at several critical engine operation points from the European Steady state test Cycle (ESC). At these operation points, EGR was introduced to reduce NOx emissions to a given value, and then different post-injection patterns were produced. A parametric study was performed, considering the time between injections and the post-injected fuel mass as the main variables. In every case the total injected fuel mass was kept constant. Aside from the experimental data obtained in the engine tests, a diagnosis model was applied to calculate heat release laws and other parameters depicting the combustion process.

The objective of this work is to make an analysis of the behaviour of the venturi in real working conditions. The modelling of the venturi, as well as the experimental and modelled results obtained, will be described. Modelled and measured techniques have been used to realize this work. A new model of the venturi was developed and using this, it is possible to find important instantaneous variables of the venturi. In order to adjust the calculated model, it was necessary to characterise the steady flow test rig of the venturi. In addition, the information obtained from the engine tests has been essential to correctly adjust the model. Therefore, a combination of the information obtained from both the venturi test and from modelled work was necessary in order to understand the behaviour of the venturi installed in an engine. Different tests have been performed on each venturi.