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Since the technology of direct injected engines has become more and more prevalent, combustion anomalies such as pre-ignition events have been occurring with increasing frequency. The interaction between the fuel-spray and the oil wetted cylinder liner is considered to be a partial cause for these phenomena. The incoming fuel jet can lead to a detachment of secondary droplets, which may affect pre-ignition events due to their changed flammability properties. To characterize these secondary droplets, spatially and temporally highly resolved optical investigations on the fuel-oil-film-interaction are carried out in this work. Using laser induced fluorescence and two high-speed cameras both fluids are optically separated. Thereby the secondary droplets can be detected and characterized in size, velocity vector, and composition.

The light-induced fluorescence (LIF) represents an important tool for the continuous improvement and further development of combustion engine systems regarding efficiency increase. In this work, the interactions between light-emitting diode (LED) and laser diode light radiation, engine oil/fuel and three fluorescence tracers are investigated on an application-related investigation system for the design of qualitative LIF experiments. Thereby two efficient light sources for engine combustion chamber lighting are presented. For different engine oil/fuel tracer combinations, the fluorescence is examined in its intensity and its spectrum depending on the temperature, concentration and temperature history. With oil temperature variations of up to 150 °C, changes in the fluorescence spectrum and fluorescence intensities that decrease by up to 80% are evident. For specific tracer oil/fuel mixtures, concentration-dependent maximum intensities and different temperature history behaviors can be revealed. The results shown support the design of spectral engine examination setups and give tracer dosage recommendations. Additionally, an engine LIF setup for in-cylinder tracking of engine operating media is presented.

In the future, synthetic fuels could replace fossil fuels to minimize the CO2 emissions of combustion engines. Dimethyl carbonate (DMC) and methyl formate (MeFo) represent not only possible synthetic fuels but, due to their oxygen content, also have properties to reduce the pollutant emissions. For a good combustion process, the spray targeting and evaporation properties are important. Due to the less known injection behavior of DMC and MeFo, the spray characteristics were examined in a pressure chamber. The penetration depth, projected spray area, and spray angle were investigated at injection pressures of 100 and 200 bar, chamber pressures of 1 and 2.5 bar, and a temperature variation of up to 90°C for two different injector spray angles and flow rates in comparison with gasoline E5. The spray was recorded with a high-speed camera in a constant-volume chamber with a N2 environment. Both fuels showed a faster evaporation than E5 even with a higher injection mass due to their lower LHV. MeFo showed extreme spray collapse and flash boiling effects, which lead to even faster evaporation rates and higher penetration velocities.

Direct injection in internal combustion engines is often realized with a multi hole injector which forms a spray pattern consisting of multiple jets with a small distance between their origin. This leads to an interaction of adjacent spray jets. The spray characteristic is significantly influenced by this interaction, and can considerably change the fuel evaporation and with it the emission behavior with varying number of holes or hole nozzle geometry [8]. Experimental investigations, especially if a good optical access to a single jet is necessary, often needs to use a comparable injector with a reduced number of holes. In addition to that, 3D-CFD simulation models can also use a reduction of spray jet number for a partial consideration of fuel mixture to reduce the computing time. For these cases a determination of the correlation between spray formation and reduced nozzle holes is important. In this work the spray patterns of an original 6-hole gasoline DI-injector and, after closing of 5 holes, the resulting 1-hole injector were compared. The fuel mass flow through one hole can change due to a change of hydrodynamic effects inside the nozzle and leads to a correcting factor for the injecting time, to get comparable fuel mass flows. The penetration depth, droplet speed, size and spatial distribution were measured. Additional investigations of the influence of the fuel pressure and fuel temperature were carried out.

As an important means of engine development and optimization, modelbuilding plays an increasingly important role in reducing carbon dioxide emissions of the internal combustion engines (ICEs). However, due to the non-linearity and high dimension of the engine system, a large amount of data is required to obtain high model accuracy. Therefore, a modelling approach combining the experimental data and prior knowledge was proposed in this study. With this method, an artificial neural network (ANN) model simulating the engine brake specific fuel consumption (BSFC) was established. With mean square error (MSE) and Kullback-Leibler divergence (KLD) serving as the fitness functions, the 86 experimental samples and constructed physical models were used to optimize the ANN weights through genetic algorithms. To improve the performance of the model, model-based feature selection method constructed by generalized regression neural network (GRNN) is introduced reducing the input dimension from 8 to 4. Subsequently, different fitness functions and features were applied to construct the models. Through the comparison of the models, the ANN model trained with MSE + KLD and selected features (ANNM+L,S) obtained the best comprehensive performance. ANNM+L,S can well reproduce the operating characteristics of the engine, such as the impact of air-fuel ration and ignition timing on the fuel consumption, while maintaining high accuracy. With the constraints of KLD, ANNM+L,S provides a higher predictive ability which is proved by the better performance in the test data set. With the embedding of prior knowledge, precise engine models with higher stability and predictive abilities can be established even under the conditions of small sample size.

Due to worldwide increasingly sharpened emission regulations, the development of Gasoline Direct Injection and Diesel Direct Injection engines not only aims at the reduction of the emission of nitrogen oxides but also at the reduction of particulate emissions. Regarding present regulations, both tasks can be achieved solely with the help of exhaust after treatment systems. For the reduction of the emission of particulates, Gasoline (GPF) and diesel Particulate Filters (DPF) offer a solution and their implementation is intensely promoted. Under optimal conditions particulates retained on particulate filters are continuously oxidized with the exhaust residual oxygen so that the particulate filter (PF) is regenerated possibly without any additional intervention into the engine operating parameters. The regeneration behavior of PF depends on the reaction rates of soot particles with oxidative reactants at exhaust gas temperatures. The reaction rates of soot particles from internal combustion engines (ICE) often are discussed in terms of order/disorder on the particle nanoscale, the concentration and kind of functional groups on the particle surfaces, and the content of (mostly polycyclic aromatic) hydrocarbons in the soot. In this work the reactivity of different kinds of soot (soot from flames, soot from ICE, carbon black) under oxidation conditions representative for PF regeneration is investigated. Soot reactivity is determined in dynamic Temperature Programmed Oxidation (TPO) experiments and the soot primary particle morphology and nanostructure is investigated by High-Resolution Transmission Electron Microscopy (HRTEM). An image analysis method based on known methods from the literature and improving some infirmities is used to evaluate morphology and nanostructural characteristics. From this, primary particle size distributions, length and separation distance distributions as well as tortuosities of fringes within the primary particle structures are obtained. Further, UV–visible spectroscopy and Raman scattering and other diagnostic techniques are used to study the properties connected to the reactivity of soot and to corroborate the experimental findings. It is found that nanostructural characteristics predominantly affect reactivity. Oxidation rates are derived from TPO and interpreted on a molecular basis from quantum chemistry calculations revealing a replication/activation oxidation mechanism.

The root cause of the initial low-speed pre-ignition (LSPI) is not yet clarified. The literature data suggest that a two-phase phenomenon is most likely triggering the unpredictable premature ignitions in highly boosted spark-ignition engines. However, there are different hypotheses regarding the actual initiator, whether it is a detached liquid oil-fuel droplet or a solid-like particle from deposits. Therefore, the present work investigates the possibility of oil droplet-induced pre-ignitions using a modern downsized engine with minimally invasive endoscopic optical accessibility incorporating in-cylinder lubrication oil detection via light-induced fluorescence. This setup enables the differentiation between liquid and solid particles. Furthermore, the potential of hot solid particles to initiate an ignition under engine-relevant conditions is analyzed numerically. To do so, the particle is generalized as a hot surface transferring heat to the reactive ambient gas phase. The gas-phase reactivity is represented as a TRF/air mixture based on RON/MON specifications of the investigated fuel. The chemical processes are predicted using a semi-detailed reaction mechanism, including 137 species and 633 reactions in a 2D CFD simulation framework. In the optical experiments, no evidence of a liquid oil droplet-induced pre-ignition could be found. Nevertheless, all observed pre-ignitions had a history of flying light-emitting objects. There are strong hints towards solid-like deposit LSPI initiation. The application of the numerical methodology to mean in-cylinder conditions of an LSPI prone engine operation point reveals that particles below 1000 K are not able to initiate a pre-ignition. A sensitivity analysis of the thermodynamic boundary conditions showed that the particle temperature is the most decisive parameter on the calculated ignition delay time.

In this work the surface structure of combustion chamber deposits (CCD) on the piston top and the cylinder head is described. By means of an optical profiler the roughness and maximum structure heights are measured. Scanning electron microscope images allow evaluating the structure of the deposits on the surface. The oil influence on CCD formation is assessed using energy-dispersive X-ray spectroscopy to quantify typical oil additives such as Mg, Ca or Zn in the deposits. By means of direct numerical simulation the influence of the CCD structure on near wall flow and hence on convective heat transfer is assessed. With fast surface thermocouples the temperature fluctuation on the cylinder head is measured. Applying two different model approaches—Hopwood and two-layer-model—the CCD layer thickness is calculated. By correlating the results with layer thickness measurements by the above mentioned optical profiler the values of the thermal conductivity for the CCD layers are calculated.

Direct Numerical Simulation (DNS) is carried out to investigate flow and heat transfer (passive scalar) over rough surfaces extracted from microscopy of combustion chamber deposits (CCD) in a direct injection test engine. The simulation set-up is a channel with one rough and one smooth wall. The roughness characteristic height, defined as maximum peak-to-valley height averaged over several subsets of the surface, in viscous units ( k + ) is varied from 11 to 46 in the simulations. Based on the simulation results, it is estimated that the equivalent sand roughness size of the CCD is approximately 300 µm , which is more than two times larger than the physical height of the roughness features. It is also demonstrated that the ratio of Stanton number to friction coefficient on a rough wall is smaller than that on a smooth wall at the same Reynolds number, and it decreases with an increase in k + .

The particle size distribution (PSD) of submicron exhaust engine-out soot, is typically determined using a method based on the electrical mobility is used. This measurement procedure is subjected to uncertainty mainly due to inaccurate dilution of the sampled aerosol, unknown flow conditions at the probe inlet and the limited measurement accuracy of the device itself. In order to determine the measurement uncertainty, two different aerosol spectrometers, a TSI EEPS 3090 and a Cambustion DMS500 were installed and operated simultaneously at a single-cylinder heavy-duty diesel engine at the Institute of Internal Combustion Engines of the Karlsruhe Institute of Technology (KIT).The engine was operated at various operating points to evaluate the ability of the spectrometers to correctly determine the PSD and the total particle number concentration (TPNC) at different boundary conditions. Variations of the position and geometry of the probe systems were performed, to evaluate the influence of the flow conditions at the probe inlet. The dilution systems of both measuring devices were verified by varying the dilution factor in three steps. Both particle sizers show good agreement in the TPNC. It could be confirmed that the probe geometry and its positioning had a negligible effect on the properties of the exhaust gas sample. A slight shift in PSD between the EEPS and the DMS was observed at the engine test bed. For a detailed evaluation, a device comparison with monodisperse polystyrene (PSL) particles with a SMPS as reference was performed at the Institute of Mechanical Process Engineering and Mechanics (KIT).

Mit der absehbaren Einfuhrung neuer gesetzlicher Zertifizierungszyklen (WLTP) und unter Berucksichtigung des realen Kundenfahrverhaltens (RDE – Real Driving Emissions), gewinnt die Untersuchung der transienten Betriebsphasen eines Verbrennungsmotors zunehmend an Bedeutung. Eine detaillierte Analyse dieser Ubergangszustande stellt dabei besondere Herausforderungen sowohl an die eingesetzte Messtechnik als auch an die angewandte Entwicklungsmethodik. Dies wird vor dem Hintergrund deutlich, dass meist nur einige wenige Arbeitsspiele wahrend dieser transienten Betriebsphasen fur die vergleichsweise hohen Emissionen verantwortlich sind.

Recent gas engines developments tend to use more excess air to reduce NOx emissions. Under these circumstances the ignition in a single cylinder research gas engine with micro pilot injection of highly ignitable fuels has been investigated. Three igniting fuels, Hydrogenated Vegetable Oil (HVO), 2-ethoxyethyl ether (2-EEE) and a Diesel/2-ethylhexyl nitrate blend have been selected by a systematical assessment and their properties have been analyzed. These fuels have been evaluated concerning their aptitude as igniting fuels and compared with diesel as reference fuel. A higher ignitability of igniting fuel reduced the ignition delay of the injected fuel and enabled the diminution of the igniting fuel fraction. A significant share of NOx emissions have been attributed to the ignition injection, therefore micro pilot injection is necessary to reach emission targets. The micro pilot injection of 2-EEE as a highly ignitable fuel with the highest Cetane Number showed favorably low ignition delay. Depending on the selected fuel and the igniting fuel fraction, the combustion phasing can be controlled directly by the injection timing. In the last section, the results for pilot injection with 2-EEE as an igniting fuel have been compared with the results using a conventional spark plug. Advantages and disadvantages for both ignition systems have been identified at constant Air Fuel Ratio (AFR). A thermodynamical comparison with each ignition system has been performed to explain the different effects on combustion.

The combination of gasoline direct injection and turbocharging is a promising method to reduce the fuel consumption of internal combustion engines through engine downsizing, which leads to increased engine efficiencies and a reduction of CO2 emissions at a comparable power output. Spray-guided direct injection allows overall lean and unthrottled operation, which is realized with a highly stratified mixture at part load. However, exhaust gas aftertreatment with conventional three-way catalysts is currently not possible. Furthermore, insufficient mixture preparation, especially at the upper load limit of stratified charge operation, causes increased particulate matter emissions. This paper discusses the advantages of engine downsizing, by gasoline direct injection in combination with turbocharging, to reduce fuel consumption and presents the results of experimental and numerical investigations of stratified exhaust gas recirculation in a single-cylinder gasoline engine to reduce nitrogen oxide emissions. The radial exhaust gas stratification was achieved by a spatial and temporal separated induction of exhaust gas and fresh air, performed by specially shaped baffles and impulse charge valves in the inlet port. The thermodynamic and optical investigations with injection pressures up to 1000 bar demonstrate the capability to reduce soot emissions in a spray-guided direct-injection engine.

The gasoline direct-injection engine with spray-guided combustion is one of the most promising strategies to reduce fuel consumption and CO2 emissions of spark-ignition engines. This benefit results primarily from lean and unthrottled operation, which is realized with a highly stratified mixture at part load. At the upper load limit of stratified charge operation, charge stratification is insufficient to realize substantial fuel economy benefits, especially when using multihole injectors. This can be attributed to a lower injector flowrate than is available from outward-opening piezo injectors. One measure to increase the flowrate is to increase the injection pressure. A higher stratification gradient thereby can be achieved, which leads to combustion at richer air–fuel ratios. As a result, combustion duration and hydrocarbon emissions decrease. The enhanced evaporation due to the increased injection pressure reduces soot emissions. This paper presents the results of thermodynamic and optical investigations at the upper load limit of stratified charge operation in a spray-guided direct-injection engine. To this end, variations of the injection pressure from 200 to 1000 bar are performed. The associated effects on mixture preparation and soot formation are investigated. The mixture preparation process and flame propagation information are recorded using a high-speed intensified complementary metal oxide semiconductor (CMOS) camera. In order to investigate soot formation and oxidation behaviour, soot concentrations are measured using the extended two-colour method.

Laser-induced ignition has shown huge advantages for the combustion of lean air-fuel mixtures in SI engines. A research project founded by the FVV under “DI Laserzundung” and No. 928 was set up at the Institute for Reciprocating Engines (IFKM) and the Institute for Technical Thermodynamics (ITT) at the Karlsruhe Institute of Technology (KIT) to investigate the potential of the laser-induced ignition. The emphasis was on improving combustion initiation and heat release during a direct injection with a spray-guided combustion.

Die laserinduzierte Zundung im Ottomotor hat in der Vergangenheit grose Vorteile bei der Entflammung magerer Luft-Kraftstoff-Gemische gezeigt. Im Rahmen des FVV-Vorhabens „DI-Laserzundung“, Nr. 928, wurden am Institut fur Kolbenmaschinen (IFKM) und am Institut fur Technische Thermodynamik (ITT) des Karlsruher Instituts fur Technologie (KIT) die Potenziale der Laserzundung untersucht. Die Optimierung von Entflammung und Brennverlauf bei der Direkteinspritzung mit strahlgefuhrtem Brennverfahren stand dabei im Vordergrund.

Der Schichtbetrieb mit strahlgefuhrter Benzin-Direkteinspritzung ist eine vielversprechende Technik, um die CO2-Emissionen von Ottomotoren zu senken. Die Hauptursachen fur die hohen Wirkungsgrade bei Teillast sind die niedrigen Ladungswechselverluste aufgrund des ungedrosselten Motorbetriebs und der hohe thermische Wirkungsgrad durch das global magere Gemisch. Ein weiterer oft genannter Grund fur die hohe Effizienz sind die geringen Wandwarmeverluste im Schichtbetrieb (1), (2), die meist durch isolierende Luftpolster zwischen verbranntem Gemisch und Brennraumwand (3), (4) erklart werden.

A high accuracy of full-vehicle thermal models are required to predict the vehicle heat-up behaviour at every conceivable combination of driving cycle and ambient air temperature down to −20 °C. Within this work a methodology for modelling the thermal behaviour of an IC-engine is presented. The focus lies on the heat-path beginning with the combustion process followed by heat conduction through the combustion chamber walls and convective heat transfer between engine structure and coolant. The thermal engine model is coupled with other models (HVAC-system, powertrain, etc.) by an independent co-simulation platform in order to describe the virtual vehicle as a whole. Finally, the model validation is performed with two different driving cycles at two different start temperatures. Using the described full-vehicle model the potential of a heat storage system is discussed for several heat-up strategies.

Spark ignition constitutes the most common way of mixture inflammation for gas engines of CHP units (combined heat and power). However, spark plug durability is limited due to spark erosion. High maintenance costs as a result of frequent spark plug replacements are the consequence. Beside the durability aspect, the inflammation of lean mixtures makes high demands on the inflammation process itself. Due to the small reactive mixture volume, the level of air-fuel ratio as well as the efficiency increase is limited. The ignition by means of a hot surface enables an increase of the reactive mixture volume and, as a result, an enhancement of the lean burn limit. A hot surface ignition (HSI) system was developed for stationary lean burn operation in due consideration of low manufacturing costs and electrical characteristics that allow a reliable control of the ignition timing. The main component of the inflammation element is a pin-shaped glow plug, whose temperature can be regulated by adjusting the electrical power. Due to external influences such as fluctuating ambient pressure and gas quality a control unit is essential for securing an optimal combustion phasing of the engine. Several designs of hot surface ignition, including passive prechamber and shielded versions, were tested on a single cylinder test bed engine operating with a homogeneous air-petrol mixture. The engine tests were accompanied by 3D flow simulations. The trials showed that the power consumption, and hence the temperature of the hot surface, as well as the flow conditions around the glow plug have a strong influence on the ignition timing. Furthermore, a strong correlation between the mean combustion chamber temperature and combustion phasing became evident. Based on this coherence, it was possible to develop a closed-loop control that adjusts the combustion phasing by controlling the combustion chamber temperature at a stationary operating point. The shielded inflammation element stood out to be the target-aiming version of hot surface ignition. It is characterised by an accelerated inflammation which allows reducing the cycle-to-cycle variations compared to prechamber spark ignition and, hence, to enhance the lean burn limit. As a result, a significant improvement of the efficiency-NOx trade-off is possible. The obtained results provide the basis for further trials on a gas engine CHP module operating with natural gas.

Contemporary diesel engines are high-tech power plants that provide high torques at very good levels of efficiency. By means of modern injecting-systems such as Common-Rail Injection, combustion noise and emissions could be influenced positively as well. Diesel engine are therefore used increasingly in top-range and sports cars.