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The European Commission has released strict emission regulations for passenger cars in the past decade in order to improve air quality in cities and limit harmful emission exposure to humans. In the near future, even stricter regulations containing more realistic/demanding driving scenarios and covering more exhaust gas components are expected to be released. Passenger cars fueled with gasoline are one contributor to unhealthy air conditions, due to the fact that gasoline engines emit harmful air pollutants. One option to minimize harmful emissions would be to utilize specifically tailored, low emission synthetic fuels or fuel blends in internal combustion engines. Methyl formate and dimethyl carbonate are two promising candidates to replace or substitute gasoline, which in previous studies have proven to significantly decrease harmful pollutants.

Synthetic fuels for internal combustion engines offer CO2-neutral mobility if produced in a closed carbon cycle using renewable energies. C1-based synthetic fuels can offer high knock resistance as well as soot free combustion due to their molecular structure containing oxygen and no direct C-C bonds. Such fuels as, for example, dimethyl carbonate (DMC) and methyl formate (MeFo) have great potential to replace gasoline in spark-ignition (SI) engines. In this study, a mixture of 65% DMC and 35% MeFo (C65F35) was used in a single-cylinder research engine to determine friction losses in the piston group using the floating-liner method. The results were benchmarked against gasoline (G100). Compared to gasoline, the density of C65F35 is almost 40% higher, but its mass-based lower heating value (LHV) is 2.8 times lower. Hence, more fuel must be injected to reach the same engine load as in a conventional gasoline engine, leading to an increased cooling effect.

To minimize the impact of global warming worldwide, net greenhouse-gas (GHG) emissions have to be reduced. The transportation sector is one main contributor to overall greenhouse gas emissions due to the fact that most of the current propulsion systems rely on fossil fuels. The gasoline engine powertrain is the most used system for passenger vehicles in the EU and worldwide. Besides emitting GHG, gasoline driven cars emit harmful pollutants, which can cause health issues for humans. Hybrid powertrains provide an available short-term solution to reduce fuel consumption and thus overall emissions. Therefore, an overview of the currently available technology and methodology of hybrid cars is provided in this paper as well as an overview of the performance of current HEV cars in real world testing. From the testing, it can be concluded that despite reducing harmful emissions, hybrid vehicles still emit pollutants and GHG when fueled with conventional gasoline.

On the way to a climate-neutral mobility, synthetic fuels with their potential of CO2-neutral production are currently in the focus of internal combustion research. In this study, the C1-fuels methanol (MeOH), dimethyl carbonate (DMC), and methyl formate (MeFo) are tested as pure fuel mixtures and as blend components for gasoline. The study was performed on a single-cylinder engine in two configurations, thermodynamic and optical. As pure C1-fuels, the previously investigated DMC/MeFo mixture is compared with a mixture of MeOH/MeFo. DMC is replaced by MeOH because of its benefits regarding laminar flame speed, ignition limits and production costs. MeOH/MeFo offers favorable particle number (PN) emissions at a cooling water temperature of 40 °C and in high load operating points. However, a slight increase of NOx emissions related to DMC/MeFo was observed. Both mixtures show no sensitivity in PN emissions for rich combustions. This was also verified with help of the optical engine.

In this study a mixture of dimethyl carbonate (DMC) and methyl formate (MeFo) was used as a synthetic gasoline replacement. These synthetic fuels offer CO2-neutral mobility if the fuels are produced in a closed CO2-cycle and they reduce harmful emissions like particulates and NOX. For base potential investigations, a single-cylinder research engine (SCE) was used. An in-depth analysis of real driving cycles in a series 4-cylinder engine (4CE) confirmed the high potential for emission reduction as well as efficiency benefits. Beside the benefit of lower exhaust emissions, especially NOX and particle number (PN) emissions, some additional potential was observed in the SCE. During a start of injection (SOI) variation it could be detected that a late SOI of DMC/MeFo has less influence on combustion stability and ignitability. With this widened range for the SOI the engine application can be improved for example by catalyst heating or stratified mode.

In this study, a fully optically accessible single-cylinder research engine is the basis for the visualization and generation of extensive knowledge about the in-cylinder processes of mixture formation, ignition and combustion of oxygenated synthetic fuels. Previous measurements in an all-metal engine showed promising results by using a mixture of dimethyl carbonate and methyl formate as a fuel substitute in a DISI-engine. Lower THC and NOx emissions were observed along with a low PN-value, implying low-soot combustion. The flame luminosity transmitted via an optical piston was split in the optical path to simultaneously record the natural flame luminosity with an RGB high-speed camera. The second channel consisted of OH*-chemiluminescence recording, isolated by a bandpass filter via an intensified monochrome high-speed camera.

Polyoxymethylene dimethyl ethers (OME) are synthetic fuels, which offer the property of sustainability because the reactants of production base on hydrogen and carbon dioxide on the one hand, and the air pollution control in consequence of a soot-free combustion in a diesel engine on the other hand. High exhaust gas recirculation (EGR) rates are a promising measure for nitrogen oxide (NOx) reduction without increasing particle emissions because of the resolved soot-NOx trade-off. However, EGR rates towards stoichiometric combustion in OME operation reveals other trade-offs such as methane and formaldehyde emissions. To avoid these, a lean mixture with a combination of EGR and exhaust after-treatment with selective catalytic reduction (SCR) is useful. The limitation of urea dosing due to the light-off temperature of SCR systems requires heating measures.

Hybridization is a promising way to further reduce the CO2 emissions of passenger vehicles. However, high engine efficiencies and the reduction of engine load, due to torque assists by an electric motor, cause a decrease of exhaust gas temperature levels. This leads to an increased time to catalyst light-off, resulting in an overall lower efficiency of the exhaust aftertreatment system (ATS). Especially in low load driving conditions, at cold ambient temperatures and on short distance drives, the tailpipe pollutant emissions are severely impacted by these low ATS efficiency levels. To ensure lowest emissions under all driving conditions, catalyst heating methods must be used. In conventional vehicles, internal combustion engine measures (e.g. usage of a dedicated combustion mode for late combustion) can be applied. A hybrid system with an electrically heated catalyst (EHC) enables further methods such as the increase of engine load by the electric motor or electric catalyst heating.

Beside the main trend technologies such as downsizing, down speeding, external exhaust gas recirculation, and turbocharging in combination with Miller cycles, the optimization of the mechanical efficiency of gasoline engines is an important task in meeting future CO2 emission targets. Friction in the piston assembly is responsible for up to 45% of the total mechanical loss in a gasoline engine. Therefore, optimizing piston assembly friction is a valuable approach in improving the total efficiency of an internal combustion engine. The form honing process enables new specific shapes of the cylinder liner surface. These shapes, such as a conus or bottle neck, help enlarge the operating clearance between the piston assembly and the cylinder liner, which is one of the main factors influencing piston assembly friction.

Pre-chamber ignition is a method to simultaneously increase the thermal efficiency and to meet ever more stringent emission regulations at the same time. In this study, a single cylinder research engine is equipped with a tailored pre-chamber ignition system and operated at two different compression ratios, namely 10.5 and 14.2. While most studies on gasoline pre-chamber ignition employ port fuel injection, in this work, the main fuel quantity is introduced by side direct injection into the combustion chamber to fully exploit the knock mitigation effect. Different pre-chamber design variants are evaluated considering both unfueled and gasoline-fueled operation. As for the latter, the influence of the fuel amount supplied to the pre-chamber is discussed. Due to its principle, the pre-chamber ignition system increases combustion speeds by generating enhanced in-cylinder turbulence and multiple ignition sites. This property proves to be an effective measure to mitigate knocking effects.

Diesel engines are arguably the superior device in the ground transportation sector in terms of efficiency and reliability, but suffer from inferior emission performance due to the diffusive nature of diesel combustion. Great research efforts gradually reduced nitrogen oxide (NOX) and particulate matter (PM) emissions, but the PM-NOX trade-off remained to be a problem of major concern and was believed to be inevitable for a long time. In the process of engine development, the modification of fuel properties has lately gained great attention. In particular, the oxygenate fuel oxymethylene ether (OME) has proven potential to not only drastically reduce emissions, but possibly resolve the formerly inevitable trade-off completely.

The reduction of both harmful emissions (CO, HC, NOx, etc.) and gases responsible for greenhouse effects (especially CO2) are mandatory aspects to be considered in the development process of any kind of propulsion concept. Focusing on ICEs, the main development topics are today not only the reduction of harmful emissions, increase of thermodynamic efficiency, etc. but also the decarbonization of fuels which offers the highest potential for the reduction of CO2 emissions. Accordingly, the development of future ICEs will be closely linked to the development of CO2 neutral fuels (e.g. biofuels and e-fuels) as they will be part of a common development process. This implies an increase in development complexity, which needs the support of engine simulations. In this work, the virtual modeling of real fuel behavior is addressed to improve current simulation capabilities in studying how a specific composition can affect the engine performance.

Given the increasing globalization and industrialization, the worldwide demand for energy continuously increases. In the context of modern Smart Grids, especially small and distributed power plants are a key factor. The present article essentially focuses on the investigation of different approaches for waste heat recovery (WHR) in small-scale CHP (combined heat and power) applications with an output range of approximately 20 kW. The engine integrated into the CHP system under investigation applies a lean-burn combustion process generally providing comparatively low exhaust gas temperatures, thus requiring a careful design that is crucial for efficient WHR. Therefore, this article presents the development and use of a simulation environment for the design and optimization of WHR in small-scale CHP applications.

Improving fuel efficiency while meeting relevant emission limits set by emissions legislation is among the main objectives of engine development. Simultaneously the development costs and development time have to be steadily reduced. For these reasons, the high demands in terms of quality and validity of measurements at the engine test bench are continuously rising. This paper will present a new methodology for efficient testing of an industrial combustion engine in order to improve the process of decision making for combustion-relevant component setups. The methodology includes various modules for increasing measurement quality and validity. Modules like stationary point detection to determine steady state engine behavior, signal quality checks to monitor the signal quality of chosen measurement signals and plausibility checks to evaluate physical relations between several measurement signals ensure a high measurement quality over all measurements.

In the present work the benefit of a 50 MPa gasoline direct injection system (GDI) in terms of particle number (PN) emissions as well as fuel consumption is shown on a 0.5 l single cylinder research engine in different engine operating conditions. The investigations show a strong effect of injection timing on combustion duration. As fast combustion can be helpful to reduce fuel consumption, this effect should be investigated more in detail. Subsequent analysis with the method of particle image velocimetry (PIV) at the optical configuration of this engine and three dimensional (3D) computational fluid dynamics (CFD) calculations reveal the influence of injection timing on large scale charge motion (tumble) and the level of turbulent kinetic energy. Especially with delayed injection timing, high combustion velocities can be achieved. At current series injection pressures, the particle number emissions increase at late injection timing.

Alongside with the severe restrictions according to technical regulations of the corresponding racing series (air and/or fuel mass flow), the optimization of the mixture formation in SI-race engines is one of the most demanding challenges with respect to engine performance. Bearing in mind its impact on the ignition behavior and the following combustion, the physical processes during mixture formation play a vital role not only in respect of the engine's efficiency, fuel consumption, and exhaust gas emissions but also on engine performance. Furthermore, abnormal combustion phenomena such as engine knock may be enhanced by insufficient mixture formation. This can presumably be explained by the strong influence of the spatial distribution of the air/fuel-ratio on the inflammability of the mixture as well as the local velocity of the turbulent flame front.

A new constant volume combustion chamber (CVCC) apparatus is presented that calculates the cetane number (CN) of fuels from their ignition delay by means of a primary reference fuel calibration. It offers the benefits of low fuel consumption, suitability for non-lubricating substances, accurate and fast measurements and a calibration by primary reference fuels (PRF). The injection system is derived from a modern common-rail passenger car engine. The apparatus is capable of fuel injection pressures up to 1200 bar and requires only 40 ml of the test fuel. The constant volume combustion chamber can be heated up to 1000 K and pressurized up to 50 bar. Sample selection is fully automated for independent operation and low levels of operator involvement. Capillary tubes employed in the sampling system can be heated to allow the measurement of highly viscous fuels.

At the Institute of Internal Combustion Engines of the Technische Universitaet Muenchen a drivetrain for urban and commuter traffic is under development. The concept is based on a lean-burn air-cooled two-cylinder natural gas engine which is combined with a hydraulic hybrid system. The engine is initially mechanically charged which results in an engine speed dependent torque. Turbocharging the natural gas fuelled engine derives increased engine torque especially at low engine speeds and exploits the potential of better knock resistance of natural gas compared to gasoline fuel. The paper presents a turbocharging concept for the two-cylinder engine at first. The firing order of 180/540°CA due to the crank shaft design and the lean-burn combustion are challenging restrictions to cope with. The consequences of the uneven firing order are investigated using 1D-simulation and the matching of the exhaust gas turbocharger is shown.

The development of today's drivetrains focusses on the reduction of vehicles' CO2-emissions. Therefore, a drivetrain for urban and commuter traffic is under development at the Institute of Internal Combustion Engines. The concept is based on a lean-burn air cooled two-cylinder natural gas engine, which is combined with a hydraulic hybrid system. On the one hand, lean-burn combustion leads to low nitrogen oxides emissions and high thermal efficiency. On the other hand, there are several challenges concerning inflammability, combustion stability and combustion duration. An approach to optimize the combustion process is the design of the piston bowl. The paper presents the engine concept at first. Afterwards, a description of design parameters for pistons of natural gas engines and a technical overview of piston bowls is given. Subsequent to the analysis of the different piston bowls, a new design approach is presented.

The development of today's powertrains focuses on the reduction of CO₂ emissions. Therefore several new technologies for internal combustion engines have been established. A further tendency is the successive electrification of powertrains in hybrid vehicles. However, these trends lead to increasing system costs which are a very important aspect at the market segment of compact cars. At the Institute of Internal Combustion Engines of the Technical University of Munich a drivetrain concept for urban and commuter traffic is under development. It is based on a lean-burn air-cooled two-cylinder natural gas engine which is combined with a hydraulic hybrid system. The paper contains detailed information about the engine as well as the hybrid vehicle powertrain in parallel structure. Particular characteristics and innovations of the hydraulic hybrid system compared to systems known so far are shown.