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A multi-dimensional combustion code implementing the Conditional Moment Closure turbulent combustion model interfaced with a well-established RANS two-phase flow field solver has been employed to study a broad range of operating conditions for a heavy duty direct-injection common-rail Diesel engine. These conditions include different loads (25%, 50%, 75% and full load) and engine speeds (1250 and 1830 RPM) and, with respect to the fuel path, different injection timings and rail pressures. A total of nine cases have been simulated. Excellent agreement with experimental data has been found for the pressure traces and the heat release rates, without adjusting any model constants. The chemical mechanism used contains a detailed NOx sub-mechanism. The predicted emissions agree reasonably well with the experimental data considering the range of operating points and given no adjustments of any rate constants have been employed.

The presented concept in this study consists of a state of the art passenger car natural-gas engine fired by different hydrogen (H2) and compressed-natural-gas (CNG) fuel blends. The hydrogen content in the fuel was varied among 5 and 15vol% corresponding to 0.6-2.1 mass%, while comparisons include also engine operation on pure CNG. Increasing hydrogen content of the fuel accelerated combustion leading to modest efficiency improvements. Combustion analysis showed that the increasing burning rates mainly affected the initial combustion phase (duration for 5% mass fraction burned). With optimal combinations of spark timing and EGR rate the achievements are additional efficiency increase with substantially lower engine-out NOx while total unburned hydrocarbons or CO-engine-out emissions are not affected. Investigations using Design of Experiments (DoE) algorithms provided a comprehensive picture of the entire parameter space.

In this study, experimental results of homogeneous charge compression ignition HCCI of n-butane in a single shot machine are presented. N-butane measurements are compared with a multizone model. Individual zones are calculated using a perfectly stirred reactor and Chemkin chemistry. The influence of temperature before combustion on heat release rate and duration of combustion is shown in a sensitivity analysis. As a perfect homogeneous temperature and fuel distribution are difficult to establish under experimental conditions, deviations from perfect homogeneity are shown. The influence of a hot surface in the cylinder head in terms of heat release rate and ignitability is examined. Further, dual fuel injections of n-butane and diesel are studied to trigger the n-butane ignition with a defined start of combustion.

Numerical and experimental investigations are presented with regard to homogeneous-charge-compression-ignition for two different fuels. N-heptane and n-butane are considered for covering an appropriate range of ignition behaviour typical for higher hydrocarbons. One fuel is closer to diesel (n-heptane), the other closer to gasoline ignition properties (n-butane). Butane in particular, being gaseous under atmospheric conditions, is used to also guarantee perfectly homogenous mixture composition in the combustion chamber. Starting from detailed chemical mechanisms for both fuels, reaction path analysis is used to derive reduced mechanisms, which are validated in homogeneous reactors. After reduction, reaction kinetics is coupled with multi zone modeling and 3D-CFD through the Conditional Moment Closure (CMC) approach in order to predict autoignition and heat release rates in an I.C. engine. Multi zone modeling is used to simulate port injection HCCI technology with n-butane.

Diesel spray simulation with a Lagrangian approach for the dispersed phase and a Eulerian approach for the continuum phase is known to be sensitive to mesh resolution and its structure. Inaddition a dependency to turbulent length scale at nozzle exit has been reported in the computational literature. The aim of this work is to quantify these sensitivities and verify computational results for an extensive series of parameters on the basis of detailed shadowgraphy and PDA experiments in a constant volume bomb. The analysis consists of temporal and spatial resolution studies, initial turbulent length scale variation, investigation of the sensitivity to two different atomization models and the influence of the injection direction to the mesh orientation. This study has been done both for non-evaporating and evaporating diesel sprays. The calculations showed a high mesh sensitivity on spray penetration.

Coincident 3-d velocity measurements in the flat combustion chamber of a motored single cylinder engine have been performed using Laser-Doppler-Velocimetry. The 3-d LDV System consisted of three beampairs (514nm, 488nm and 476.5nm) and two fiberoptic probes operated in 90° cross-scatter mode obtaining high spatial and temporal resolution as well as high signal quality. Burst Spectrum Analyzers have been thereby used for signal processing. The time histories of the three velocity components have been acquired for moderate engine speeds (600, 1000 and 1500RPM). The swirling motion in the cylinder was also varied by choosing different fixed positions of a shrouded intake valve relative to the intake port. Several measuring locations in the combustion chamber have been studied in order to investigate homogeneity. Mean velocities and fluctuation intensities of the turbulent field were evaluated using ensemble averaging.

The underlying computations examine the spray mean flow and its influence on the fuel distribution under non-reacting conditions, with a particular focus on the application to intermittent, equally-pulsed DI-Diesel sprays. The fuel is injected from the top center of a cylinder in axial direction into quiescent air of 800 K and 120 bar. The fuel flow rates are controlled with the nozzle diameter, keeping the injection pressure constant. The computations have been performed with a KIVA-3 based code on a CRAY-YMP. The spray-induced gas flow interacts with the fuel droplets which leads to an increased collision activity at the tip of the spray and near the nozzle exit, and, via coalescences, results in the formation of larger lumps of fluid. The effect of this droplet clustering has been investigated for various fuel flow rates of continuous and intermittent DI-Diesel sprays.

Coincident 3-D velocity measurements have been made in a single-cylinder, motored research engine using a six-beam, three-wavelength LDV system. The engine had a pancake combustion chamber, a compression ratio of 8.0 and was operated with a fixed intake shroud valve position. Measurements have been performed at 600, 1000 and 1500 RPM and at three distinct locations within the combustion chamber. Software coincidence filtering and ensemble averaging have been thereby used for data processing.

The premixed flame growth period of about 1% of the cylinder mass burned has been theoretically investigated under typical homogeneous charge engine conditions. For this purpose various flame kernel development models have been tested against measured values of flame radius vs. time after ignition in a research engine. The flame kernel growth has been computed on the basis of a zero-dimensional model incorporating spark-induced energy, heat loss to the electrodes and flame curvature effects. Subsequently the transition phase from laminar to fully turbulent flame propagation is shown to depend strongly on the relationship between the turbulent kinetic energy spectrum and characteristic scales of the flame. We thereby make use of recently reported results of fundamental experiments on vortex-flamelet interaction, that yield typical vortex sizes for flame wrinkling and quenching.

Measurements of instantaneous in-cylinder heat transfer have been performed at a selected location of the cylinder head in a super long stroke, low speed, two-stroke experimental diesel engine operating under various conditions. The temperatures of both the wall and the process have been varied either by locally using titanium instead of steel as wall material or correspondingly by operating the engine with an unusually high equivalence ratio. A standard case with a steel wall and a typical full load point has been used as reference. For all conditions, measurements of the wall temperature very close to the surface of the apparent radiation temperature of the combustion chamber contents and of the gas temperature across the boundary layer (the latter by means of a for this purpose specifically developed fiber-optical sensor) have been carried out. As a result, the total heat flux as well as its two components, convection and radiation, have been determined.

The three components of the velocity were measured by laser Doppler velocimetry at 35 locations in each of the six intake ports of a single-cylinder I.C. engine motored at 600, 900, and 1200 rpm. The intake ports were designed to impart both swirl and roll to the air. Pressure was also measured at the intake and exhaust. The detailed information is valuable mostly for computations of engine flows and for the assessment of multidimensional models. However the following trends were observed. The intake velocity is affected by resonant pressure waves. The flows in the six ports tend to be similar. The three components of the ensemble-averaged velocity generally have uniform profiles across the port area, whereas the fluctuation intensities are higher at the top of the port. All velocities tend to be higher at the beginning and end of intake.