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The introduction of real driving emissions cycles and increasingly restrictive emissions regulations force the automotive industry to develop new and more efficient solutions for emission reductions. In particular, the cold start and catalyst heating conditions are crucial for modern cars because is when most of the emissions are produced. One interesting strategy to reduce the time required for catalyst heating is post-oxidation. It consists in operating the engine with a rich in-cylinder mixture and completing the oxidation of fuel inside the exhaust manifold. The result is an increase in temperature and enthalpy of the gases in the exhaust, therefore heating the three-way-catalyst. The following investigation focuses on the implementation of post-oxidation by means of scavenging in a four-cylinder, turbocharged, direct injection spark ignition engine. The investigation is based on detailed measurements that are carried out at the test-bench.

Ignition delay times are major information needed to allow the simulation of auto-ignition and knocking combustion in internal combustion engines (ICEs). Due to their variance over changing boundary conditions (BC) and limitations of measurement processes, a common way to obtain them is via reaction kinetic simulations. To facilitate and accelerate the simulation process with varying operating conditions and gas composition definitions, an efficient tool that uses Cantera’s Python interface has been created. It allows the end-user to easily calculate the ignition delay data needed for engine simulation without the necessity for in-depth knowledge of the underlying processes. All calculations are based on the creation of a homogeneously mixed gaseous mixture corresponding to engine-based environmental conditions. Depending on the desired fuel, oxidizer, temperature, pressure, water, and exhaust gas recirculation (EGR) rate, the resulting reactant composition is computed.

Today, mechanical systems such as the piston groups of internal combustion engines are simulated using Multiple Body-System (MBS) - approaches. However, the use of these models is restricted to a few problems as their adaptability is limited. The simulation of mechanical systems only by means of finite elements shows great promise for the future. In order to consider lubrication effects between two touching bodies of a mechanical system, a hydrodynamic contact algorithm (HCA) for finite element (FE) applications was developed. This paper discusses the technical background and first results for the simulation of a piston group using this new approach.

The presented results are part of a research project to create a universal residual gas fraction model. It is supported by the „Forschungsvereinigung Verbrennungs-kraftmaschinen e.V. (FVV)”. In the research project an universal formula has been developed which allows the determination of the residual gas fraction in allkind of IC engines. The formula is valid for naturally aspirated engine, turbo and super charged, variable valve timing and fully variable valve trains, as well. The formula (constant approach) developed during the project is based on variables like time averaged intake and exhaust pressure, exhaust temperature and geometric engine data which were measured on the test bench. As a result, online and real time calculation is possible already while the engine is running. This implies that the formula can be used within the engine control unit for control purposes.

The emission of particulate matter from future GDI engines has to be optimized, to comply with more stringent emission standards such as EU6. Therefore, the mechanisms responsible for the formation of particles have to be analyzed in detail. The understanding of the in-cylinder processes, necessary for this purpose, can only be achieved by a complementary use of optically accessible single-cylinder engines as well as the numerical simulation. This however leads to great demands on the 3D flow simulation. In this paper the complete CFD approach, incorporating a detailed description of the entire underlying model chain is shown. Particularly the wall surface temperature and the temperature drop due to the interaction with liquid fuel spray were identified as important parameters influencing the spray-wall interaction and thus also the particulate emissions. Nevertheless, in conventional CFD models, the spray cooling cannot be captured because of an assumed constant wall temperature.

As a consequence of reduced fuel consumption, direct injection gasoline engines have already prevailed against port fuel injection. However, in-cylinder fuel homogenization strongly depends on charge motion and injection strategies and can be challenging due to the reduced available time for mixture formation. An insufficient homogenization has generally a negative impact on the combustion and therefore also on efficiency and emissions. In order to reach the targets of the intensified CO2 emission reduction, further increase in efficiency of SI engines is essential. In this connection, 0D/1D simulation is a fundamental tool due to its application area in an early stage of development and its relatively low computational costs. Certainly, inhomogeneities are still not considered in quasi dimensional combustion models because the prediction of mixture formation is not included in the state of the art 0D/1D simulation.

Intensified emission regulations as well as consumption demands lead to an increasing significance of unburned hydrocarbon (UHC) emissions for diesel engines. On the one hand, the quantity of hydrocarbon (HC) raw emissions is important for emission predictions as well as for the exhaust after treatment. On the other hand, HC emissions are also important for predicting combustion efficiency and thus fuel consumption, since a part of unreleased chemical energy of the fuel is still bound in the HC molecules. Due to these reasons, a simulation model for predicting HC raw emissions was developed for diesel engines based on a phenomenological two-zone model. The HC model takes three main sources of HC emissions of diesel engines into account: Firstly, it contains a sub-model that describes the fuel dribble out of the injector after the end of injection. Secondly, HC emissions from cold peripheral zones near cylinder walls are determined in another sub-model.

Prospective combustion engine applications require the highest possible energy conversion efficiencies for environmental and economic sustainability. For conventional Spark-Ignition (SI) engines, the quasi-hemispherical flame propagation combustion method can only be significantly optimized in combination with high excess air dilution or increased combustion speed. However, with increasing excess air dilution, this is difficult due to decreasing flame speeds and flammability limits. Pre-Chamber (PC) initiated jet ignition combustion systems significantly shift the flammability and flame stability limits towards higher dilution areas due to high levels of introduced turbulence and a significantly increased flame area in early combustion stages, leading to considerably increased combustion speeds and high efficiencies. By now, vehicle implementations of PC-initiated combustion systems remain niche applications, especially in combination with lean mixtures.

With the increasingly strict emission regulations and economic demands, variable valve trains are gaining in importance in Diesel engines. A valve control strategy has a great impact on the in-cylinder charge motions, turbulence level, thus also on the combustion and emission formation. In order to predict in-cylinder charge motions and turbulence properties for a working process calculation, a zero−/quasi-dimensional flow model is developed for the Diesel engines with a fully variable valve train. For the purpose of better understanding the in-cylinder flow phenomena, detailed 3D CFD simulations of intake and compression strokes are performed at different operating conditions with various piston configurations. In the course of model development, global in-cylinder charge motions are assigned to idealized flow fields. Among them, swirl flow is characterized by an engine swirl number that is determined by both developments of the swirl angular momentum and the moment of inertia.

As a promising solution to improve fuel efficiency of a long-haul heavy duty truck with diesel engine, organic Rankine cycle (ORC) based waste heat recovery system (WHR) by utilizing the exhaust gas from internal combustion engine has continuously drawn attention from automobile industry in recent years. The most attractive concept of ORC-based WHR system is the conversion of the thermal energy of exhaust gas recirculation (EGR) and exhaust gas from Tailpipe (EGT) to kinetic energy which is provided to the engine crankshaft. Due to a shift of the operating point of the engine by applying WHR system, the efficiency of the overall system increases and the fuel consumption reduces respectively. However, the integration of WHR system in truck is challenging by using engine cooling system as heat sink for Rankine cycle. The coolant mass flow rate influences strongly on the exhaust gas bypass which ensures a defined subcooling after condenser to avoid cavitation of pump.

Fulfilling exhaust emissions regulations and meet customer performance needs mainly drive the current engine development. Turbocharging system plays a key role for that. Currently turbocharging should provide highest engine power density at high engine speed by also allowing a very responsive performance at low end. This represents a trade-off in turbocharger development. A large scaled turbine allows having moderate exhaust gas back pressure for peak power region, but leading to loss of torque in low engine speed. In the last years of engine development scavenging helped to get away a bit from this trade-off as it increases the turbine mass flow and also reduces cylinder internal residual gas at low engine speed. The mostly in-use lean strategy runs air fuel ratios of closed to stoichiometric mixture in cylinder and global (pre catalyst) of λ = 1.05 to l = 1.3. This will be out of the narrow air fuel ratio band of λ = 1 to ensure NOx conversion in the 3-way-catalyst.

Due to the demands for today's passenger cars regarding fuel consumption and emissions, exhaust turbo charging has become a fundamental step in achieving these goals. Especially in upper and middle class vehicles it is also necessary to consider the noise comfort. Today, floating bushings are mainly used as radial bearings in turbochargers. In the conventional operating range of the turbocharger dynamic instability occurs in the lubrication films of the bearings. This instability is transferred by structure-borne noise into audible airborne sound and known as constant tone phenomenon. This phenomenon is not the major contributor of the engine noise but its tonal character is very unpleasant. In order to gain a more detailed understanding about the origin of this phenomenon, displacement sensors have been applied to the compressor- and the turbine-side of the rotor, to be able to determine the displacement path.

The German Aerospace Center (DLR) is developing a free-piston engine as an innovative internal combustion engine for the generation of electrical power. The arrangement of the Free Piston Linear Generator (FPLG) in opposed-piston design consists of two piston units oscillating freely, thereby alternately compressing the common combustion chamber in the center of the unit and gas springs on either side. Linear alternators convert the kinetic energy of the moving pistons into electric energy. Since the pistons are not mechanically coupled to a crank train, the bottom and top dead centers of the piston movement can be varied during operation e.g. to adjust the compression ratio. Utilizing these degrees of freedom, the present paper deals with the analysis of different combustion processes in a port scavenged opposed-piston combustion chamber prototype.

CO2 emission constraints taking effect from 2020 lead to further investigations of technologies to lower knock sensitivity of gasoline engines, main limiting factor to increase engine efficiency and thus reduce fuel consumption. Moreover the RDE cycle demands for higher power operation, where fuel enrichment is needed for component protection. To achieve high efficiency, the engine should be run at stoichiometric conditions in order to have better emission control and reduce fuel consumption. Among others, water injection is a promising technology to improve engine combustion efficiency, by mainly reducing knock sensitivity and to keep high conversion rates of the TWC over the whole engine map. The comprehension of multiple thermodynamic effects of water injection through 3D-CFD simulations and their exploitation to enhance the engine combustion efficiency is the main purpose of the analysis.

Predictive physical modeling is an established method used in the development process for automotive components and systems. While accurate predictions can be issued after tuning model parameters, long computation times are expected depending on the complexity of the model. As requirements for components and systems continuously increase, new optimization approaches are constantly being applied to solve multidimensional objectives and resulting conflicts optimally. Some of those approaches are deemed not feasible, as the computational times for required single predictions using conventional simulation models are too high. To address this issue it is proposed to use data-driven model such as neural networks. Previous efforts have failed due to sparse data sets and resulting poor predictive ability. This paper introduces an AI Toolchain used for data-driven modeling of combustion engine components. Two methods for generating scalable and fully variable datasets will be shown.

In this paper the development approach and the results of numerical and experimental investigations on homogeneous charge compression ignition in a free piston engine are presented. The Free Piston Linear Generator (FPLG) is a new type of internal combustion engine designed for the application in a hybrid electric vehicle. The highly integrated system consists of a two-stroke combustion unit, a linear generator, and a mass-variable gas spring. These three subsystems are arranged longitudinally in a double piston configuration. The system oscillates linearly between the combustion chamber and the gas spring, while electrical energy is extracted by the centrally arranged linear generator. The mass-variable gas spring is used as intermediate energy storage between the downstroke and upstroke. Due to this arrangement piston stroke and compression ratio are no longer determined by a mechanical system.

The proposed paper deals with the development process and initial measurement results of an opposed-piston combustion engine for application in a Free-Piston Linear Generator (FPLG). The FPLG, which is being developed at the German Aerospace Center (DLR), is an innovative internal combustion engine for a fuel based electrical power supply. With its arrangement, the pistons freely oscillate between the compression chamber of the combustion unit and a gas spring with no mechanical coupling like a crank shaft. Linear alternators convert the kinetic energy of the moving pistons into electric energy. The virtual development of the novel combustion system is divided into two stages: On the one hand, the combustion system including e.g. a cylinder liner, pistons, cooling and lubrication concepts has to be developed.

Operating gasoline engines at part load in a so-called Gasoline-HCCI (gHCCI) combustion mode has shown promising results in terms of improved efficiency and reduced emissions. So far, research has primarily been focused on experimental investigations on the test bench, whereas fast, predictive burn rate models for use in process calculation have not been available. Such a phenomenological model is henceforth presented. It describes the current burn rate as the sum of a sequential self-ignition process on the one hand and a laminar-turbulent flame propagation on the other hand. The first mechanism is essentially represented by ignition delay calculation, in which the reaction rate is computed separately for some hundred groups of different temperatures based on the Arrhenius equation. Thermal inhomogeneity is described by a contaminated normal distribution which accounts for the influence of wall temperature on mixture close to the cylinder wall.

Variation of the geometric compression ratio in gasoline combustion engines during engine operation enables potential for decreasing fuel consumption as well as emissions. One way to achieve a variable geometric compression ratio (VCR) is the application of a connecting rod with a variable effective length between its large end and its small end. Such a system consists of a connecting rod body with an eccentrically supported piston pin and a linkage which is supported hydraulically. Therefore, the connecting rod evolves from a solid part to a complex assembly of mechanical and hydraulic parts. In order to deploy this system in the most efficient way, an understanding of the physics and the dynamic behavior of the VCR connecting rod is necessary. This includes the mechanical subsystem as well as the hydraulic subsystem. This paper describes the experimental examination of a two stage variable connecting rod.

In the competition for the powertrain of the future the internal combustion engine faces tough challenges. Reduced environmental impact, higher mileage, lower cost and new technologies are required in order to maintain its global position both in public and private mobility. For a long time, researchers have been investigating the so called Homogeneous Charge Compression Ignition (HCCI) that promises a higher efficiency due to a rapid combustion - i.e. closer to the ideal thermodynamic Otto cycle - and therefore more work and lower exhaust gas temperatures. Consequently, a rich mixture to cool down the turbocharger under high load may no longer be needed. As the combustion does not have a distinguished flame front it is able to burn very lean mixtures, with the potential of reducing HC and CO emissions. However, until recently, HCCI was considered to be reasonably applicable only at part load operating conditions.