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In this project funded by the Bayerische Forschungsstiftung two fundamental investigations had been carried out: first a new N-rich liquid ammonia precursor solution based on guanidine salts had been completely characterized and secondly a new type of side-flow reactor for the controlled catalytic decomposition of aqueous NH₃ precursor to ammonia gas has been designed, applied and tested in a 3-liter passenger car diesel engine. Guanidine salts came into the focus due to the fact of a high nitrogen-content derivate of urea. Specially guanidinium formate has shown extraordinary solubility in water (more than 6 kg per 1 liter water at room temperature) and therefore a possible high ammonia potential per liter solution compared to the classical 32.5% aqueous urea solution (AUS32) standardized in ISO 22241 and known as DEF (diesel emission fluid), ARLA32 or AdBlue® .

Due to its molecular structure, methane provides several advantages as fuel for internal combustion engines. To cope with nitrogen oxide emissions high levels of excess air are beneficial, which on the other hand deteriorates the flammability and combustion duration of the mixture. One approach to meet these challenges and ensure a stable combustion process are fuelled prechambers. The flow and combustion processes within these prechambers are highly influenced by the position, orientation, number and overall cross-sectional area of the orifices connecting the prechamber and the main combustion chamber. In the present study, a water-cooled single cylinder test engine with a displacement volume of 0.5 l is equipped with a methane-fuelled prechamber. To evaluate influences of the aforementioned orifices several prechambers with variations of the orientation and number of nozzles are used under different operating conditions of engine speed and load.

Polyoxymethylene dimethyl ethers (OME) are promising alternative diesel fuels with a biogenic or electricity-based production, which offer carbon neutral mobility with internal combustion engines. Among other e-fuels, they stand out because of soot-free combustion, which resolves the trade-off between nitrogen oxide (NOx) and soot emissions. Additionally, long-chain OME have a high ignitability, indicated by a cetane number (CN) greater than 70. This opens up degrees of freedom in the injection strategy and enables simplifications compared to the operation with fossil diesel. This study investigates the hydraulic behavior of two solenoid injectors with different injector geometry for heavy-duty applications on an Injection Rate Analyzer (IRA) in diesel and OME operation. For OME, both injectors show longer injection delays in all injection pressure ranges investigated, increasing with rail pressure.

Oxygenated synthetic fuels such as oxymethylene ether (OME) are a promising approach to reduce the emissions of diesel engines and to improve sustainability of mobility. The soot-free combustion of OME allows an optimization of the combustion process to minimize remaining pollutants. Considering the injection system, one strategy is to decrease the rail pressure, which has a positive impact on the reduction of nitrogen oxides without increasing the particle formation. Furthermore, due to the reduced lower heating value of OME compared to diesel fuel, an adaptation of the injector nozzle is recommended. This work describes a method for analyzing the injection process for OME, using the Mie scattering effect in an optically accessible heavy-duty diesel engine. The design of the 1.75 l single cylinder engine allows operation up to 300 bar peak cylinder pressure, providing optical access through the piston bowl and through a second window lateral below the cylinder head.

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.

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.

The synthetic fuels dimethyl ether (DME) and polyoxymethylene dimethylether (POMDME or OME) are promising oxygenated fuels to meet the rising challenges of air pollution control, CO2-neutrality, and sustainability. The sootless combustion and high ignitability of DME and OME represent ideal properties for an application in diesel engines. However, recent investigations of oxygenates reported an increase of nanoparticles, which are known to have fatal effects on human’s health. Besides nanoparticles, ongoing discussions about future emission legislation focus on a drastic reduction of NOx. For this reason, the present work investigates different measures to reduce NOx emissions using DME/OME and a paraffinic diesel fuel (PDF) as reference. Different rail pressures, exhaust gas recirculation (EGR) rates, and injection timings are evaluated, considering the effectivity on NOx reduction and the impact on other emissions, especially on nanoparticles.

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.

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.