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Engines with gasoline direct injection promise an increase in efficiency mainly due to the overall lean mixture and reduced pumping losses at part load. But the near stoichiometric combustion of the stratified mixture with high combustion temperature leads to high NOx emissions. The need for expensive lean NOx catalysts in combination with complex operation strategies may reduce the advantages in efficiency significantly. The Bowl-Prechamber-Ignition (BPI) concept with flame jet ignition was developed to ignite premixed lean mixtures in DISI engines. The mainly homogeneous lean mixture leads to low combustion temperatures and subsequently to low NOx emissions. By additional EGR a further reduction of the combustion temperature is achievable. The BPI concept is realized by a prechamber spark plug and a piston bowl. The main feature of the concept is its dual injection strategy.

In this work, heat loss was investigated in two different HCCI single cylinder engines. Thermocouples were adapted to the surfaces of the cylinder heads and the temperature oscillations were detected in a wide range of the engine operation maps. The resultant heat transfer profiles were compared to the heat losses predicted by existing models. As major discrepancies were stated, a new phenomenological model was developed that is well-manageable and describes the heat loss in HCCI mode more precisely than existing models. To analyze the insulating effect of deposits, the heat transfer equation was solved analytically by an approach that allows consideration of multiple layers with different material properties and thickness. This approach was used for the first time in conjunction with engines to calculate the heat flux at the surface of deposits and the deposit thickness.

For spark ignition engines, the most effective way to reduce the overall fuel consumption and CO2 emissions respectively is the implementation of gasoline direct injection technology. In comparison to the current wall and air guided systems, the direct injection system of the second generation - the spray guided DI- is the most promising one with respect to fuel economy and emission. In order to exploit its full potential, a thorough combustion process development regarding injector and spark plug design and their positioning within the combustion chamber is essential. Especially multihole injectors offer many degrees of freedom with regard to the nozzle shape and spray pattern. To reduce the development work and costs necessary to identify the ideal nozzle characteristic and spray pattern, reliable CFD models are necessary.

A promising approach for reducing both NOx- and particulate matter emissions with low fuel consumption is the so called homogeneous charge compression ignition (HCCI) combustion process. Single-cylinder engine tests were carried out to assess the influence of several parameters on the HCCI combustion. The experiments were performed both with port fuel injection (PFI) and with direct injection (DI) under various compression ratios, intake air temperatures and EGR-rates. Special emphasis was put on the fuel composition by using different gasoline and diesel fuels as well as n-heptane. Besides engine out emissions (CO2, CO, NO, O2, HC, soot) and in-cylinder pressure indication for burning process analysis, the combustion itself was visualised using an optical probe.

The improvement of engine efficiency, without adversely affecting oil consumption, blowby-gas, wear, or costs are desirable objectives for today's engine manufacturers as they strive to improve engine performance while trying to meet increasingly stringent emissions regulations. In this context the development of piston ring designs as well as optimized surface texturing and lubricating oil formulation is of main interest. The combination of simulation programs and the application of dynamic online oil emission measurement techniques lead to a target oriented development and a deeper understanding of the mechanisms causing oil consumption. The paper presents the results of the experimental and theoretical investigations of oil consumption mechanisms. A mass spectrometric method developed by the author et al., was used to measure the online oil emission in the exhaust gas by means of direct analysis of the lubricating oil molecules.

When developing effective exhaust emission reduction measures, a better understanding of the complex working cycle in crankcase scavenged two-stroke gasoline engines. However, in a two-stroke gasoline engine detailed measurement and analysis of combustion data requires significantly more effort, when compared to a lower speed four-stroke engine. Particularly demanding are the requirements regarding the high speed (>10,000 rpm) which inevitably goes along with heavy vibrations and high temperatures of the air cooled cylinders. Another major challenge to the measuring equipment is the increased cleaning demand of the optical sensor surface due to the two-stroke gasoline mixture. In addition, the measuring equipment has to be adapted to the small size engines. Therefore, only a fiber optical approach can deliver insight into the cylinder for analyzing the combustion performance.

The hollow cone spray from a high pressure outward opening nozzle was investigated inside a pressure vessel by means of particle image velocimetry (PIV). The flow velocities of the air outside the spray were measured via PIV in combination with fluorescent seeding particles and optical filters. The high pressure piezo electric injector has an annular nozzle to provide a hollow cone spray with an angle of about 90°. During injection a very strong and stable vortex structure is induced by the fuel spray. Besides the general spray/air interaction, the investigation of double and triple fuel injections was the main focus of this study.

A multi-optical fiber measurement technique is presented which can determine spatial flame propagation with a high temporal resolution. With this measurement technique it is possible to investigate the combustion process in both Diesel and SI engines. The measurement technique can also be applied for the detection of flame propagation in research engines and in actual production engines for performing analysis of special problems such as knocking combustion, combustion chamber design studies which concern flame propagation, the influence of engine parameters on flame propagation, ignition and inflammability behavior. The new measurement technique is discussed in detail and the application of optical measuring points in the combustion chamber walls is demonstrated. A special non-contacting optical transmission system has been developed for the observation of flame propagation.

Reduction of fuel consumption and pollutant emissions are key factors in the current development of powertrains. Engine oil has proven to be an efficient lever for improving fuel economy. The full potential of a low viscosity lubricant could be achieved by a shift towards formulations with low viscosity, high volatility base oils. However, there is a concern that this might increase oil consumption and limit long oil drain intervals. This article deals with the engine lubricant contribution to oil and particle emissions. A series of 0W-12 oil prototypes have been evaluated both within laboratory measurements and on a modern turbocharged direct injection gasoline engine. Correlation between oil emission and engine oil properties will be presented. The impact of engine oil on particle emissions has also been investigated under different engine operating conditions.

Future demands for modern emission free drivetrains using hydrogen or liquid e-fuels also necessitate a fundamental reduction in oil emissions. Entry of lubrication oil into the combustion chamber can lead to pre-combustion phenomena (LSPI) in downsizing or hydrogen engines and is a cause of particle emissions, which play a significant role especially if fuel related particle emissions are already low. A fundamental understanding of the oil film behavior on the piston assembly and cylinder liner surface are crucial to avoid oil ingress into the combustion chamber. The processes involved take place mainly around the piston group. In particular, the area of the piston rings with the prevailing pressure and temperature conditions as well as the component geometries has a high influence on the exchange of media between the crankcase and combustion chamber. The objective of this paper is to increase the understanding of the processes leading to oil ingress into the combustion chamber.

Optical measurement technique became more and more common for the last few years. Especially optical fibre technique is often used to detect flame propagation. With optical sensors the ignition process can be investigated with high temporal and spatial resolution. An in-cylinder optical sensor has been developed and tested to analyze the ignition of mixture and luminous emission of burning gas. The sensor consists of eight optical probes fitted in a conventional spark plug. The results show good correlation between measured luminosity and combustion parameters such as load, engine speed, ignition timing and air-fuel mixture ratio. A correlation between development of light intensity and pressure was found. For evaluation of light signals different analysis methods are presented. Furthermore it is shown that the luminosity of the flame can be used to control the combustion process.

The emission behaviour of an internal combustion engine under test-bed conditions shows differences to the emission behaviour under real in-use conditions. Because of this fact, the developers of combustion engines and the legislator are focussing on the measurement and optimization of real in-use emissions. To this day, the research, the adjustment of the carburettor and the legislation of small handheld engines is performed under test bench conditions, especially conditioned fuel pressure and temperature, as well as air temperature. Also the engines are laid out for two operation points: rated speed with full open throttle and idle speed. This test-procedure is used for all kinds of handheld off-road applications and does not consider the load profile of the different power tools. Especially applications with transient load profiles, for example chainsaws, work in more than two operating points in real use.

An increasing environmental consciousness as well as the awareness for sustained preservation of natural resources causes new regulations for emissions and great efforts for fuel economy and increasing oil service intervals. For a better understanding of the process generating pollutants, the emissions of every phase of the combustion cycle have to be monitored online. Moreover, it is important to measure the raw exhaust gas during different driving cycles and investigate the influence of different parameters as for example changing engine operating conditions. The new mass spectrometer (MS) based measurement system allows the direct detection of unburned gaseous oil HC without tracers. The gas inlet system enables crank angle resolved monitoring of different raw exhaust gas compounds in the exhaust manifold or directly in the cylinder.

Rapeseed oil can be a possible substitute for fossil fuel in Diesel engines. Due to different physical properties of rapeseed oil like higher viscosity and higher compressibility compared to diesel fuel, rapeseed oil cannot be easily used in conventional Diesel engines without modifications. Especially incomplete combustion leads to deposits in the combustion chamber and higher exhaust gas emissions. These unfavorable characteristics are caused primarily by insufficient mixture preparation. The adjustment of the injection system will improve the mixture preparation and the combustion of a Diesel engine, operated with rapeseed oil. The nozzle geometry is the main parameter of the whole injection system chain to realize a better combustion process and so higher efficiency and lower exhaust gas emissions.

Advanced thermal management systems in passenger cars present a possibility to increase efficiency of current and future vehicles. However, a vehicle integrated thermal management of the combustion engine is essential to optimize the overall thermal system. This paper shows results of an experimental heat flux analysis of a state-of-the-art automotive diesel engine with common rail injection, map-controlled thermostat and split cooling system. Measurements on a climatic chamber engine test bench were performed to investigate heat fluxes and energy balance in steady-state operation and during engine warm-up from different engine start temperatures. The analysis includes the influence of the operating point and operating parameters like EGR rate, injection strategy and coolant temperature on the engine energy balance.

The investigation of transient engine operation plays a key role of the future challenges for individual mobility in terms of real driving emissions (RDE). A fundamental investigation of the transient engine operation requires the simultaneous application of measurement technologies for an integrated study of mixture formation, combustion process and emission formation. The major prerequisite is the combustion cycle and crank angle resolved analysis of the process for at least several individual consecutive combustion cycles during transient operation. The investigations are performed with a multi cylinder DISI engine at an Engine-in-the-Loop test bench, able to operate the engine in driving cycles as well as within target profiles (e.g. speed and torque profiles). The research project describes the methodology of analyzing elementary transient operational phases, (e.g. different variants of load steps).

In the present paper the results of a set of experimental investigations on LSPI are discussed. The ignition system of a test engine was modified to enable random spark advance in one of the four cylinders. LSPI sequences were successfully triggered and exhibited similar characteristics compared to regularly occurring pre-ignition. Optical investigations applying a high speed camera system enabling a visualization of the combustion process were performed. In a second engine the influence of the physical properties of the considered lubricant on the LSPI frequency was analyzed. In addition different piston ring assemblies have been tested. Moreover an online acquisition of the unburned hydrocarbon emissions in the exhaust gas was performed. The combination of these experimental techniques in the present study provided further insights on the development of LSPI sequences.

Increased quantities of fuel in the lubricating oil of CI engines pose a major challenge to the automotive industry in terms of controlling the oil aging and the wear caused by dilution. Due to a lack of methods to calculate the oil-fuel-composite transport across the ring pack, predicting the fuel ratio in the oil sump has been an extremely challenging task for engine manufacturers. An accurate and computationally efficient simulation model is critical to predict the quantity of fuel diluted in the oil in the preliminary development stage of automotive engines. In this work, the complex composite transport across the piston ring pack was reduced to a simple transport model, which was successfully implemented into a multi-body simulation of the ring pack. The calculation domain was partitioned into two parts, the ring grooves and the piston lands. Inside the grooves the oil flow caused by the pumping and squeezing action of the piston rings was calculated using the Reynolds equation.

The limitation of fuel entry into the oil sump of an internal combustion engine during operation is important to preserve the tribological properties of the lubricant and limit component wear. For observation and quantification of the effects leading to fuel entry, a highly sensitive and versatile measurement system is essential. While oil sampling from the sump followed by laboratory analysis is a common procedure, there is no system for automatic sampling of all the positions and fast online analysis of the samples. For the research project ‘Fuel in Oil’, a measurement system was developed especially for the described tasks. The system is placed next to the engine in the test cell. Sampling points are the target point of the fuel injector jet and the liner below, the oil sump and the crankcase ventilation system.

At part load and wide open throttle operation with stratified charge and lean mixture conditions the Direct Injection Spark Ignition (DISI) engine offers similar efficiency levels compared to compression ignition engines The present paper reports on results of recent studies on the impact of the in-cylinder processes in DISI engines e. g. the injection, the in-cylinder flow, the mixture preparation and the ignition on the combustion, the energy conversion and the exhaust emission behavior. The analyses of the spray behavior, of the in-cylinder flow during compression as well as of the flame propagation have been carried out applying advanced optical measurement techniques. The results enable a targeted optimization of the combustion process with respect to engine efficiency and exhaust emissions. The benefits of an increase in fuel injection pressures up to 100 MPa are discussed.