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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.

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.

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.

This SAE Technical Paper gives a summary of the essential findings in the development and operation of a test engine dedicated to the measuring of the friction between the piston group and the liner. Firstly the fundamental demands on the high-precision and close to real engine operation friction measuring are laid out. Subsequently the basic engine, the measuring system based on the floating liner method including a gas balance device, as well as the implemented measuring technique are specified. Major influencing variables on the friction of the piston assembly and its interference variables are also summarized. Extensive information about the systematic and strategies for the test engine's operation startup are given in acknowledgement of influencing and interference variables. This strategy reduces the developmental and startup process of an engine dedicated to the measuring of piston group friction.

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.

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.

Aging effects such as coking or erosive damage that occur in fuel injection nozzles are known to deteriorate the engine performance. This article proposes an optimization method to compensate for injector aging and to control the combustion behavior over engine lifetime by adapting the injection strategy. First, a control-oriented combustion model is presented, which takes the condition of the injection nozzle into account. In combination with a simulation model of the entire fuel injection system from a previous study, the model is capable of predicting the heat release rate (HRR) at different working conditions. Measurements with a single-cylinder diesel engine were performed, using injectors with modified and aged nozzles, to validate the proposed combustion model and particularly to analyze the influence of injector aging. Using the simulation model, optimal injection strategies were obtained by applying a line search optimization scheme to recover a reference HRR trajectory.

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.

Developing piston assemblies for internal combustion engines faces the conflicting priorities of blow-by, friction, oil consumption and wear. Solving this conflict consists in finding a minimum for all these parameters. This optimization can only be successful if all the effects involved are understood properly. In this paper only blow-by and its associated flow paths for a diesel engine in part load operating mode are part of a detailed numerical investigation. A comparison of the possibilities to do a CFD analysis of this problem should show why the way of modeling described here has been picked. Further, the determination of the complex geometry, which results in a challenging set of calculations, is described. Besides the constraints for temperature and pressure, a meshing method for the creation of a dynamic mesh that is capable of describing the movement of all three rings of the piston ring pack simultaneously is also explained.

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.

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.

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.

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.

The use of modern simulation tools in the engine product development process is explained using the layout of a piston and its piston ring-pack of AUDI V6 SI-engine as example. Based on the requirements for piston rings in a SI-engine the possible trade-offs are explained. A base layout for a ring-pack for the specific engine is presented. Further the validity of the simulation model is rated as the simulation output is compared to actual dynamometer measurements of the blow-by map of the engine. Additionally a test setup is presented, which measures piston ring movement and the pressures between the rings and in the ring grooves. Also these measurement results are compared to the simulation. Using DOE (design of experiments) on the base layout potentials for optimization are shown and applied. To identify the positive effects in the engine pistons with piston rings are fabricated in accordance with the DOE recommendations.

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.

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.

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.

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 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).

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.