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In this work a detailed model to simulate the transient behavior of catalytic converters is presented. The model is able to predict the unsteady and reacting flows in the exhaust ducts, by solving the system of conservation equations of mass, momentum, energy and transport of reacting chemical species. The en-gine and the intake system have not been included in the simulation, imposing the measured values of mass flow, gas temperature and chemical composition as a boundary condition at the inlet of the exhaust system. A detailed analysis of the diffusion stage triggering is proposed along with simplifications of the physics, finalized to the reduction of the calculation time. Submodels for water condensation and its following evaporation on the monolith surface have been taken into account as well as oxygen storage promoted by ceria oxides.

When increasing EGR from low levels to a level that corresponds to low temperature combustion, soot emissions initially increase due to lower soot oxidation before decreasing to almost zero due to very low soot formation. At the EGR level where soot emissions start to increase, the NOx emissions are low, but not sufficiently low to comply with future emission standards and at the EGR level where low temperature combustion occurs CO and HC emissions are too high. The purpose of this study was to investigate the possibilities for shifting the so-called soot bump (where soot levels are increased) to higher EGR levels, or to reduce the magnitude of the soot bump using very high injection pressures (up to 240 MPa) while reducing the NOx emissions using EGR. The possibility of reducing the CO and HC emissions at high EGR levels due to the increased mixing caused by higher injection pressure was also investigated and the flame was visualized using an endoscope at chosen EGR values.

Modeling combustion of transportation fuels remains a difficult task due to the extremely large number of species constituting commercial gasoline and diesel. However, for this purpose, multi-component surrogate fuel models with a reduced number of key species and dedicated reaction subsets can be used to reproduce the physical and chemical traits of diesel and gasoline, also allowing to perform CFD calculations. Recently, a detailed surrogate fuel kinetic model, named C3 mechanism, was developed by merging high-fidelity sub-mechanisms from different research groups, i.e. C0-C4 chemistry (NUI Galway), linear C6-C7 and iso-octane chemistry (Lawrence Livermore National Laboratory), and monocyclic aromatic hydrocarbons (MAHs) and polycyclic aromatic hydrocarbons (PAHs) (ITV-RWTH Aachen and CRECK modelling Lab-Politecnico di Milano).

To characterize the effects of renewable fuels on particulate emissions from GDI engines, engine experiments were conducted using EN228-compliant gasoline fuel blends containing no oxygenates, 10% ethanol (EtOH), or 22% ethyl tert-butyl ether (ETBE). The experiments were conducted in a single cylinder GDI engine using a 6-hole fuel injector operated at 200 bar injection pressure. Both PN in raw exhaust and solid PN (SPN) were measured at two load points and various start of injection (SOI) timings. Raw PN and SPN results were classified into various size ranges, corresponding to current and future legislations. At early SOI timings, where particulate formation is dominated by diffusion flames on the piston due to liquid film, the oxygenated blends yielded dramatically higher PN and SPN emissions than reference gasoline because of fuel effects.

In recent years, the increase of gasoline fuel injection pressure is a way to improve thermal efficiency and lower engine-out emissions in GDI homogenous combustion concept. The challenge of controlling particulate formation as well in mass and number concentrations imposed by emissions regulations can be pursued improving the mixture preparation process and avoiding mixture inhomogeneity with ultra-high injection pressure values up to 100 MPa. The increase of the fuel injection pressure in GDI homogeneous systems meets the demand for increased injector static flow, while simultaneously improves the spray atomization and mixing characteristics with consequent better combustion performance. Few studies quantify the effects of high injection pressure on transient gasoline spray evolution. The aim of this work was to simulate with OpenFOAM the spray morphology of a commercial gasoline injected in a constant volume vessel by a prototypal GDI injector.

This investigation utilizes energy analysis and statistical methods to optimize step gear automatic transmissions gear selection for fuel consumption. A full factorial matrix of simulations using energy analysis was performed to determine the optimal number of gears and gear ratios that provide the best fuel consumption performance for a particular vehicle - engine application. The full factorial matrix setup as a design of experiment (DOE) was applied to five vehicle applications, each with two engines to examine the potential differences that variations in road load and engine characteristics might have on optimal transmission gearing selection. The transmission gearing options considered in the DOE were number of gears, launch gear ratio and top gear ratio. Final drive ratio was also included due to its global influence on vehicle performance and powertrain operating speeds and torque.

Adoption of high-pressure common-rail (HPCR) fuel systems, which subject diesel fuels to higher temperatures and pressures, has brought into question the veracity of ASTM International specifications for biodiesel and biodiesel blend oxidation stability, as well as the lack of any stability parameter for diesel fuel. A controlled experiment was developed to investigate the impact of a light-duty diesel HPCR fuel system on the stability of 20% biodiesel (B20) blends under conditions of intermittent use and long-term storage in a relatively hot and dry climate. B20 samples with Rancimat induction periods (IPs) near the current 6.0-hour minimum specification (6.5 hr) and roughly double the ASTM specification (13.5 hr) were prepared from a conventional diesel and a highly unsaturated biodiesel. Four 2011 model year Volkswagen Passats equipped with HPCR fuel injection systems were utilized: one on B0, two on B20-6.5 hr, and one on B20-13.5 hr.

Development of the next generation internal combustion engines and automatic transmissions for automotive applications is a mandatory powertrain engineering activity required now and in the coming years to meet forthcoming global emissions regulations. This paper details a preliminary investigation into possible synergies for fuel consumption reduction considering emerging automotive technologies integrated into the next generation combustion engine and automatic transmission architectures. A range of hypothetical gasoline engines were created and paired with a generalized set of step gear automatic transmissions designed to meet the performance requirements of high volume longitudinal full size truck application. These designs were then run through a design of experiments orthogonal array for prediction of fuel consumption on the WLTP test schedule and stand still acceleration to 100 kph.

The potential of 48V Mild Hybrid is promising in meeting the present and future CO2 legislations. There are various system layouts for 48V hybrid system including P0, P1, P2. In this paper, P2 architecture is used to investigate the effects of water injection benefits in a mild hybrid system. Electrification of the conventional powertrain uses the benefits of an electric drive in the low load-low speed region where the conventional SI engine is least efficient and as the load demand increases the IC Engine is used in its more efficient operating region. Engine downsizing and forced induction trend is popular in the hybrid system architecture. However, the engine efficiency is limited by combustion knocking at higher loads thus ignition retard is used to avoid knocking and fuel enrichment becomes must to operate the engine at MBT (Maximum Brake Torque) timing; in turn neutralizing the benefits of fuel savings by electrification.

Today, Direct-Injection systems are widely used on Spark-Ignition engines in combination with turbo-charging to reduce the fuel-consumption and the knock risks. In particular, the spread of Gasoline Direct Injection (GDI) systems is mainly related to the use of new generations of multi-hole, high-pressure injectors whose characteristics are quite different with respect to the hollow-cone, low-pressure injectors adopted in the last decade. This paper presents the results of an experimental campaign conducted on the spray produced by a GDI six-holes injector into a constant volume vessel with optical access. The vessel was filled with air at atmospheric pressure. Different operating conditions were considered for an injection pressure ranging from 3 to 20 MPa. For each operating condition, spray images were acquired by a CCD camera and then post processed to evaluate the spray penetration and cone angles.

In order to investigate the effects of split injection on emission formation and engine performance, experiments were carried out using a heavy duty single cylinder diesel engine. Split injections with varied dwell time and start of injection were investigated and compared with single injection cases. In order to isolate the effect of the selected parameters, other variables were kept constant. In this investigation no EGR was used. The engine was equipped with a common rail injection system with a piezo-electric injector. To interpret the observed phenomena, engine CFD simulations using the KIVA-3V code were also made. The results show that reductions in NOx emissions and brake specific fuel consumption were achieved for short dwell times whereas they both were increased when the dwell time was prolonged. No EGR was used so the soot levels were already very low in the cases of single injections.

Modeling plume interaction and collapse for direct-injection gasoline sprays is important because of its impact on fuel-air mixing and engine performance. Nevertheless, the aerodynamic interaction between plumes and the complicated two-phase coupling of the evaporating spray has shown to be notoriously difficult to predict. With the availability of high-speed (100 kHz) Particle Image Velocimetry (PIV) experimental data, we compare velocity field predictions between plumes to observe the full temporal evolution leading up to plume merging and complete spray collapse. The target “Spray G” operating conditions of the Engine Combustion Network (ECN) is the focus of the work, including parametric variations in ambient gas temperature. We apply both LES and RANS spray models in different CFD platforms, outlining features of the spray that are most critical to model in order to predict the correct aerodynamics and fuel-air mixing.

Eight different cylinder pressure trace based knock detection methods are compared using two reference cycles of different time-frequency content, reflecting single blast and developing blast, and a test population of 300 knocking cycles. It is shown that the choice of the pass window used for the pressure data has no significant effect on the results of the different methods, except for the KI20. In contrast to other authors, no sudden step in the knock characteristics is expected; first, because the data investigated contain only knocking cycles, and second, because a smooth transition between normal combustion and knock is expected, according to recent knock theory. It is not only the correlation coefficient, but also the Kendall coefficient of concordance, that is used to investigate the differences between the knock classification methods.

Combustion characteristics of dimethyl ether, DME, have been investigated experimentally, in a heavy duty single cylinder engine equipped with an adapted common rail fuel injection system, and the effects of varying injection timing, rail pressure and exhaust gas recirculation on the combustion and emission parameters. The results show that DME combustion does not produce soot and with the use of exhaust gas recirculation NOX emissions can also be reduced to very low levels. However, high injection pressure and/or a DME adopted combustion system is required to improve the mixing process and thus reduce the combustion duration and carbon monoxide emissions.

Cycle-resolved end-gas temperatures were measured using dual-broadband rotational CARS in a single-cylinder spark-ignition engine. Simultaneous cylinder pressure measurements were used as an indicator for knock and as input data to numerical calculations. The chemical processes in the end-gas have been analysed with a detailed kinetic mechanism for mixtures of iso-octane and n-heptane at different Research Octane Numbers (RON'S). The end-gas is modelled as a homogeneous reactor that is compressed or expanded by the piston movement and the flame propagation in the cylinder. The calculated temperatures are in agreement with the temperatures evaluated from CARS measurements. It is found that calculations with different RON'S of the fuel lead to different levels of radical concentrations in the end-gas. The apperance of the first stage of the autoignition process is marginally influenced by the RON, while the ignition delay of the second stage is increased with increasing RON.

The wavelet transform is used in the analysis of the cylinder pressure trace and the ionic current trace of a knocking, single-cylinder, spark ignition engine. Using the wavelet transform offers a significant reduction of mathematical operations when compared with traditional filtering techniques based on the Fourier transform. It is shown that conventional knock analysis in terms of average energy in the time domain (AETD), corresponding to the signal's energy content, and maximum amplitude in the time domain (MATD), corresponding to the maximum amplitude of the bandpass filtered signal, can be applied to both the reconstructed filtered cylinder pressure and the wavelet coefficients. The use of the filter coefficients makes possible a significant additional reduction in calculation effort in comparison with filters based on the windowed Fourier transform.

Experiments were performed using a Light-Duty, single-cylinder, research engine in which the emissions, fuel consumption and combustion characteristics of two Fischer-Tropsch (F-T) Diesel fuels derived from natural gas and two conventional Diesel fuels (Swedish low sulfur Diesel and European EN 590 Diesel) were compared. Due to their low aromatic contents combustion with the F-T Diesel fuels resulted in lower soot emissions than combustion with the conventional Diesel fuels. The hydrocarbon emissions were also significantly lower with F-T fuel combustion. Moreover the F-T fuels tended to yield lower CO emissions than the conventional Diesel fuels. The low emissions from the F-T Diesel fuels, and the potential for producing such fuels from biomass, are powerful reason for future interest and research in this field.

This work evaluates the effect of charge stratification on combustion phasing, rate of heat release and emissions for HCCI combustion. Engine experiments in both optical and traditional single cylinder engines were carried out with PRF50 as fuel. The amount of stratification as well as injection timing of the stratified charge was varied. It was found that a stratified charge can influence combustion phasing, increasing the stratification amount or late injection timing of the stratified charge leads to an advanced CA50 timing. The NOx emissions follows the CA50 advancement, advanced CA50 timing leads to higher NOx emissions. Correlation between CA50 can also be seen for HC and CO emissions when the injection timing was varied, late injection and thereby advanced CA50 timing leads to both lower HC and CO emissions.

The spray formation and consequent atomization of an outward opening piezo-electric gasoline DI injector have been experimentally investigated in a constant pressure spray chamber. The sizes and velocities of the droplets and the resulting spray shape were evaluated, under different boundary conditions, using Planar Mie scattering and Planar Laser-induced Fluorescence (PLIF) in combination with Phase Doppler Anemometry (PDA) analyses and high-speed video photography. The use of piezo-electric actuation for gasoline DI injectors provides an additional means to control the atomization and spray shape that is not available with solenoid-driven injectors such as swirling and multi-hole type injectors. For instance, with piezo injectors up to four injections per cycle are possible, and the fuel flow rate can be controlled by adjusting needle lift. The captured high-speed video images show that a hollow-cone spray forms as the fuel exits the outward-opening nozzle.

The expansion of current driving cycles for emission regulations to higher load operation in the near future (such as the US06 supplement to the FTP-75 driving cycle) requires attention to low emission combustion concepts in medium to high load regimes. One possibility to reduce NO emissions is to increase the EGR rate. The combustion-temperature reducing effects of high EGR rates can significantly reduce NO formation, to the point where engine-out NOx emissions approach zero levels. However, engine-out soot and CO emissions typically increase at high EGR levels, due to the reduced soot and CO oxidation rates at reduced combustion temperatures and oxygen concentrations. The work presented in this paper focuses on different strategies to reduce soot and CO emissions associated with EGR rates of up to 50%, at which NO formation is largely avoided, but combustion temperatures are not low enough to consider the process as Low-Temperature Combustion (LTC).