Search Results

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.

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.

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?

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.

Regulatory standards on diesel engines emissions will decidedly become more restrictive in coming years. This has led to the development and implementation of alternative fuels. The objective of this paper is to evaluate the potential of Sasol Fischer-Tropsch (FT) diesel fuel to improve the reduction of emissions in a direct injection diesel engine with a high pressure common-rail injection system (HDI engine from PSA Peugeot-Citroën). In principle, FT diesel fuel shows significant advantages in reducing emissions over a standard diesel fuel due to its low aromaticity, high cetane rating and high H/C rating. Initial tests with two 406 HDI Euro 2 vehicles with standard calibration showed very favourable trends on exhaust emissions in comparaison with reference fuel (CEC RF73-A-93 type). Sasol FT diesel fuel gave significant improvement on specific fuel consumption, and decreased the HC, CO, CO2 and particulate emissions without degrading NOx emissions.

The purpose of this paper is to present the results of a study on the exhaust junctions geometry. Twelve three-branch junctions of different geometry have been tested on a single cylinder engine. The parameters studied have been exhaust junction outlet-to-inlet diameter ratio, length, angle between inlet branches and the existence of a reed separating inlet branches. An analysis of the pressure waves amplitude (incident, reflected and transmitted) obtained from instantaneous pressure measurements in some locations around the junction has been carried out. The analysis of results shows that junction length has a low influence on its behavior. The ratio between inlet and outlet branches diameters increases both reflection and directionality (avoiding pressure wave transmission to the adjacent branch). The existence of a reed separating the inlet flows may increase directionality with moderate pressure losses if the throat area is not reduced.

Perforated ducts are present in most designs of exhaust mufflers, due to their convenient sound attenuation properties. While suitable tools are available for the estimation of this attenuation, accounting for the influence on attenuation of the perforated ducts for different arrangements, a similar tool but related to the back-pressure generated by mufflers containing perforated ducts is not available. In this paper, the basis for such a tool are set by defining a suitable characterisation of perforated pipes that may allow for the consideration of the influence of a particular perforated duct on the back pressure generated by a given muffler. The results obtained have been validated in a particularly simple case, and the results confirm the feasibility of the proposed methodology, while suggesting possible future improvements.

In this paper, a numerical model is used to study the influence of several relevant parameters on the behaviour of a turbocharged Diesel engine as an exhaust noise source, with two main objectives: first, determine if it is possible to reduce exhaust noise at the source itself, thus simplifying the task of exhaust system design; and secondly, to asses up to which extent simple linear source models may be used to predict exhaust noise in these engines. The results obtained indicate that, on the one hand, exhaust noise is sensitive to the variation of certain engine design parameters and, on the other hand, that for certain running conditions simple source models may give an acceptable estimation of the actual engine behaviour as a noise source.

The aim of this paper is to present a new and simple approach to the one-dimensional modelling of the global fluidynamic behaviour of the catalytic converter placed in the automotive spark ignition engine exhaust system. Being that this component is the first singular element encountered by the flow, it imposes an influential boundary condition in the interaction with the cylinder exhaust process, thus affecting greatly the engine performance. A specific submodel has been developed, able to represent the main phenomena taking place in the exhaust flow: mean pressure drop, mean temperature variations and instantaneous pressure wave reflection and transmission. This submodel has been linked to a one-dimensional wave action model, which is, this way, able to predict the precise interaction and mutual influences between engine and catalytic converter. The results of the model have been experimentally validated with tests on engine in real running conditions.

In this paper, a parametric study on the combustion process of a 2 liter supercharged intercooled direct injection Diesel engine is presented, aiming to improve performance and pollutant emissions at a representative operational condition. Future and actual european emission standards have been taken as a reference for optimization. The study is based on the results of experimental tests carried out on a single cylinder research engine, where all the operating conditions are kept under severe control, and on the results of a phenomenological combustion model adjusted to the tested engine.