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Investigating the oil transport mechanisms of a combustion engine is essential to decrease engine losses and optimize overall performance. As explained in [1] the amount of oil at predefined positions can be investigated by mixing the engine oil with a specific dye. Therefore, the technology of laser-induced fluorescence (LIF) is used. Fiber optics are assembled flush to the cylinder wall and give the possibility of inducing the dye locally by means of a laser. The emitted light intensity correlates with the amount of oil between the cylinder wall and piston ring. The oil film thickness of the piston ring running surface can therefore be determined for each crank angle (CA). However, the emission signal measured does not always correlate to the complete barrel shape of the piston ring.

Reliably calibrated simulation and combustion models not only enable the prediction of non-validated operating points, but also compensate for the time that would be required for costly test bench measurements. Under the premise of investigating various turbocharging concepts for a combustion engine without the need for recalibration, the present work will discuss the influence of two different exhaust gas turbocharger systems on model calibration. Replacing turbochargers is a practical way to test the predictive performance of simulations, since they can drastically affect and change the thermodynamic boundary conditions for comparable operating points. On the one hand, the choice of the appropriate calibration strategy and, on the other hand, the interchangeability of the respective calibration will be discussed.

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.

In the near future, pollutant and GHG emission regulations in the transport sector will become increasingly stringent. For this reason, there are many studies in the field of internal combustion research that investigate alternative fuels, one example being oxygenated fuels. Additionally, the design of engine components needs to be optimized to improve the thresholds of clean combustion and thus reduce particulates. Simulations based on PRiME 3D® for dynamic behaviors inside the piston ring group provide a guideline for experimental investigation. Gas flows into the combustion chamber are controlled by adjusting the piston ring design. A direct comparison of regular and synthetic fuels enables to separate the emissions caused by oil and fuel. This study employed a mixture of dimethyl carbonate (DMC) and methyl formate (MeFo).

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.

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.

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.

Laser induced fluorescence (LIF) is used to investigate oil transport mechanisms under real engine conditions. The engine oil is mixed with a dye that can be induced by a laser. The emitted light intensity from the dye correlates with the residual oil at the sensor position and the resulting oil film thicknesses can be precisely determined for each crank angle. However, the general expectation is not always achieved, e.g. an exact representation of piston ring barrel shapes. In order to investigate the responsible lubrication effects of this behavior, a new cavitation algorithm for the Reynolds equation has been developed. The solution retains the mass conservation and does not use any switch function in its mathematical approach. In contrast to common approaches, no vapor-liquid ratio is used, but one or several bigger bubbles are approximated, as have been observed in other experiments already.

Development processes for modern combustion engines already make substantial use of more or less sophisticated simulation approaches. The enhancement of computational resources additionally allows the increasing use of simulation tools in terms of time-consuming three-dimensional CFD approaches. In particular, the preliminary estimation of feasible operating ranges and strategies requires a vast multitude of single simulations. Here, multi-zone simulation approaches incorporate the advantages of comparably short simulation durations. Nevertheless, the combination with more detailed sub-models allows these rather simple modeling approaches to offer considerable insight into relevant engine operation phenomena. In the context of combustion process development, this paper describes a phenomenological model approach for the prediction of operating point characteristics of a dual-fuel pilot injection combustion process.

Over the past years, the question as to what may be the powertrain of the future has become ever more apparent. Aiming to improve upon a given technology, the internal combustion engine still offers a number of development paths in order to maintain its position in public and private mobility. In this study, an innovative combustion process is investigated with the goal to further approximate the ideal Otto cycle. Thus far, similar approaches such as Homogeneous Charge Compression Ignition (HCCI) shared the same objective yet were unable to be operated under high load conditions. Highly increased control efforts and excessive mechanical stress on the components are but a few examples of the drawbacks associated with HCCI. The approach employed in this work is the so-called Spark Assisted Compression Ignition (SACI) in combination with a pre-chamber spark plug, enabling short combustion durations even at high dilution levels.

Measurement techniques for piston ring rotation, engine oil emission and blow by have been implemented on a single-cylinder petrol engine. A novel method of analysis allows continuous and fast real-time identification of the piston ring rotation of the two compression rings, while the mass-spectrometric analysis of the exhaust gas delivers the cylinder oil emission instantly and with a high temporal resolution. Only minor modifications to the piston rings were made for the insertion of the γ-emitters, the rings rotate freely around the circumference of the piston. The idea of this setup is that through online observation at the test bench, instant feedback of the measured variables is available, making it possible to purposefully select and compare measurement points. The high time resolution of the measurement methods enables the analysis of dynamic effects. In this article, the measurement setup and evaluation method is described.

In order to fulfill future exhaust emission regulations, the variety of subsystems of internal combustion engines is progressively investigated and optimized in detail. The present article mainly focuses on studies of the flow field and the resulting discharge coefficients of the intake and exhaust valves and ports. In particular, the valves and ports influence the required work for the gas exchange process, as well as the cylinder charge and consequently highly impact the engine’s performance. For the evaluation of discharge coefficients of a modern combustion engine, a stationary flow test bench has been set up at the Chair of Internal Combustion Engines (LVK) of the Technical University of Munich (TUM). The setup is connected to the test bench’s charge air system, allowing the adjustment and control of the system pressure, as well as the pressure difference across the particular gas exchange valve.

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.

Improving efficiency and reducing emissions are the principal challenges in developing new generations of internal combustion engines. Different strategies such as downsizing or sophisticated after-treatment of exhaust gases are pursued. Another approach aims at optimizing the parameterization of the engine. Correct adjustments of ignition timings, waste gate position and other factors have significant influence on the combustion process. A multitude of application data is generated during the development process to predefine appropriate settings for most situations. Improvements in regards to the application effort and the quality of the settings can be achieved by measuring the combustion process and optimizing the parametrization in a closed loop. However, cylinder pressure sensors that are used during the development process are too expensive for series applications.

Aging effects such as coking or cavitation in the nozzle of common rail (CR) diesel injectors deteriorate combustion performance. This is of particular relevance when it comes to complying with emission legislation and demonstrates the need for detecting and compensating aging effects during operation. The first objective of this paper is to analyze the influence of worn nozzles on the injection rate. Therefore, measurements of commercial solenoid common rail diesel injectors with different nozzles are carried out using an injection rate analyzer of the Bosch type. Furthermore, a fault model for typical aging effects in the nozzle of the injector is presented together with two methods to detect and identify these effects. Both methods are based on a multi-domain simulation model of the injector. The needle lift, the control piston lift and the pressure in the lower feed line are used for the fault diagnosis.

Measuring and simulating the contact between piston pin and connecting rod (conrod) is very complex. The pin can rotate freely in the conrod as well as in the piston. Further, there is no defined oil supply with a constant pressure as it is for example in main bearings. A tribometer test bench was adapted to measure friction between pin and conrod. The system is loaded with a constant force and oil supply is realized as defined deficient lubrication. During one part of the schedule, the rotational speed is defined as ramp to measure friction coefficient over speed, in another part the speed was pivoted from positive to negative speed within less than 500 milliseconds. With this measurement method, the different friction coefficients between radial slider and pivot bearings could be quantified. The measurements were conducted for four different pin-coatings.

Scarce resources of fossil fuels and increasingly stringent exhaust emission legislation push towards a stronger focus to alternative fuels. Natural gas is considered a promising solution for small engines and passenger cars due to its high availability and low carbon dioxide emissions. Furthermore, natural gas indicates great potential of increased engine efficiency at lean-burn operation. However, the ignition of these lean air/fuel mixtures leads to new challenges, which can be met by fuel scavenged prechambers. At the Institute of Internal Combustion Engines of the Technische Universitaet Muenchen an air cooled natural gas engine with a single cylinder displacement volume of 0.5 L is equipped with a methane scavenged prechamber for investigations of the combustion process under real engine conditions. The main combustion chamber is supplied with a lean premixed air/fuel mixture.

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.

Modern methods of engine development use complex mathematical models. Adding advanced components such as variable valve trains or direct injection systems to the model increases the degrees of freedom resulting in a high number of measurements for validation. Steadily rising costs for development, time and staff make it crucial for industry to improve the quality of measurements with advanced analysis techniques. Often, such models consider the simulated system as stationary, implying that system variables no longer change with time. This paper presents an internal combustion engine measurement system utilizing algorithms for the real-time evaluation of the state of the engine or its components. Several approaches have been reviewed and tested regarding their applicability. The most straightforward algorithms compare the gradient of a sensor signal to a pre-defined threshold.