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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.

In this study different methods to reduce the soot emissions of Diesel engines were investigated and compared to obtain their soot reduction potential. Apart from investigations on the practically usable engine map area with so called homogeneous charge compression ignition (HCCI) combustion processes a new heterogeneous combustion processes was developed and investigated which offers significantly reduced soot emissions while still applicable in the entire engine map. For the HCCI experiments the emphasis was put on the achievable engine load range when using conventional injector nozzles which still allow a conventional heterogeneous engine operation.

A multi-optical fiber technique is presented, which enables one to detect the flame propagation during non-knocking and knocking conditions in real production engines. The measurement technique is appropriate to detect knock onset locations and to describe the propagation of knocking reaction fronts. With this knowledge, the combustion chamber shape can be optimized, leading to a better knock resistance and higher combustion efficiencies. Results of flame propagation under non-knocking and knocking engine operating conditions are presented. In addition, correlations between knock onset locations and areas in which knock damage occurs are shown for different engines. Presented are the effects of combustion chamber modifications on the combustion efficiency, based on the analysis of the optical fiber measurements.

Investigations of the fuel injection processes in a spark ignition direct injection engine have been performed for two different fuels. The goal of this research was to determine the differences between isooctane, which is often used as an alternative to gasoline for optical engine investigations, and a special, non-fluorescing, full boiling range multicomponent fuel. The apparent vaporization characteristics of isooctane and the multicomponent fuel were examined in homogeneous operating mode with direct injection during the intake stroke. To this end, simultaneous Mie scattering and planar laser induced fluorescence imaging experiments were performed in a transparent research engine. Both fuels were mixed with 3-Pentanone as a fluorescence tracer. A frequency-quadrupled Nd:YAG laser was used as both the fluorescent excitation source and the light scattering source.

The California LEV1 II program will be introduced in the year 2003 and requires a further reduction of the exhaust emissions of passenger cars. The cold start emissions represent the main part of the total emissions of the FTP2-Cycle. Cold start emissions can be efficiently reduced by injecting secondary air (SA) in the exhaust port making compliance with the most stringent standards possible. The thermochemical conditions (mixing rate and temperature of secondary air and exhaust gas, exhaust gas composition, etc) prevailing in the exhaust system are described in this paper. This provides knowledge of the conditions for auto ignition of the mixture within the exhaust manifold. The thus established exothermal reaction (exhaust gas post-combustion) results in a shorter time to light-off temperature of the catalyst. The mechanisms of this combustion are studied at different engine idle conditions.

The spray propagation and disintegration is investigated in a pressure chamber. With Particle Image Velocimetry the direction and velocity of both, fuel droplets and induced gas flow are detected. By means of shadow photographs the spray cone geometry is visualized. To verify the predictions made of the measurements mentioned above and to rate the quality of the tuning of the parameters in-cylinder gas flow, injection pressure, position of Injector and position of spark plug under real engine conditions, a fast gas sampling valve is used in three different engines. The in-cylinder gas temperature and the soot concentration are measured crank angle resolved by means of the Two-Colour-Method in a 1-cylinder GDI-engine. The soot concentration and temperature show the influence of the injection pressure on emissions like soot and nitric oxide.

The study presented in this two part paper was focused on the influence of primary mixture formation on engine running behavior covering the areas combustion and raw emissions. Two different concepts for primary fuel atomization were utilized and compared, the standard production injector and a flash boiling injector. The spray generated by the flash boiling injector was characterized by a significant reduction in droplet size and a partial direct vaporization during the injection process by preheating the fuel inside the injector. In this study special emphasis was put on the transient process of engine start between typical cooling water temperatures of -7°C and 85°C. Various measurements and visualization techniques were applied to investigate the mixture preparation, the deposition of liquid fuel on the walls, the start of combustion, and in-cylinder and engine-out UHC emissions.

The intention of the study presented in this two part paper is to investigate the influence oalf primary mixture formation on engine running behavior, covering the areas of combustion and raw emissions. Two different concepts for primary fuel atomization were utilized and compared, the standard production injector and a flash boiling injector. The flash boiling injector is characterized by a significant reduction in droplet size and a partial direct vaporization during the injection process by preheating the fuel inside the injector. In this study special emphasis was laid on the transient process of engine start between typical cooling water temperatures of -7°C and 85°C. Various measurements and visualization techniques had been applied to investigate mixture preparation, deposition of liquid fuel on the walls, start of combustion, and in-cylinder as well as engine-out UHC emissions.

High frequency ignition (HFI) and conventional transistor coil ignition (TCI) were investigated with an optically accessible single-cylinder research engine to gain fundamental understanding of the chemical reactions taking place prior to the onset of combustion. Instead of generating heat in the gap of a conventional spark plug, a high frequency / high voltage electric field is employed in HFI to form chemical radicals. It is generated using a resonant circuit and sharp metallic tips placed in the combustion chamber. The setup is optimized to cause a so-called corona discharge in which highly energized channels (streamers) are created while avoiding a spark discharge. At a certain energy the number of ionized hydrocarbon molecules becomes sufficient to initiate self-sustained combustion. HFI enables engine operation with highly diluted (by air or EGR) gasoline-air mixtures or at high boost levels due to the lower voltage required.

In this paper, results of experimental and numerical investigations of stratified exhaust gas recirculation in a single-cylinder gasoline engine are presented. The engine was operated in spray guided direct injection mode. The radial exhaust gas stratification was achieved by a spatial and temporal separated intake of exhaust gas and fresh air. The spatial separation of both fluids was realized by specially shaped baffles in the inlet ports, which prevent an early mixing up to the inlet valves. The temporally separation was performed by impulse charge valves, with one for the fresh air and one for the exhaust gas. From various possible strategies for time-dependent intake of fresh air and exhaust gas, four different strategies for the exhaust gas stratification were examined.

This paper presents a special optical fiber technique which allows to measure temperatures in SI engines using the emission bands or respectively emission lines of the temperature radiation of diatomic molecules. The measurement technique enables the detection of average temperature in a small volume element. These temperatures are used to determine the local NO concentrations using the extended Zeldovich-mechanism. First, theoretical background of both temperature and NO-determination and measurement technique including optical fiber sensors are described. Finally, the temperature and NO dependence versus crank angle are presented and discussed at different combustion chamber locations for different engine operating conditions.

Different particulate filter systems with an electrical heating for starting the filter regeneration were designed and tested to evaluate the parameters important for a successful filter and heating device layout. These results led to a new filter system with an improved electrical heating module. Particular emphasis was put on a modular design which allows a separate optimization of the different system parts with regard to function, durability and costs. In this paper the different development steps are presented. Experimental results show the performance and limitations for electrically heated particulate traps. The analysis of the experiments was done on the one hand by using data such as temperatures, pressures and exhaust gas composition during the regeneration. On the other hand the assessment of the regeneration rate was done by weighing the filter and optically with non-destructive and partly destructive methods.

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.

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.

In this work the influence of various engine load changes with different engine speeds on the soot particle concentrations and properties was investigated because these operating modes are well known for short but high soot emissions. To derive specific information on emission behavior of particle matters tests were carried out with the Two-Color-Method and the so called RAYLIX technique in a four-cylinder CR-Diesel engine. The Two-Color-Method (2CM) gives crank angle resolved information about soot formation and oxidation processes inside the combustion chamber of a single cylinder. The RAYLIX technique is a combination of Rayleigh-scattering, Laser-Induced-Incandescence (LII) and extinction measurements which enable simultaneous measurements of temporally and spatially resolved soot concentration, mean primary particle radii and number densities in the exhaust gas manifold of the same cylinder investigated by the Two-Color-Method.

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.

The focus of this work was to determine the influence of spray targeting on temperature distributions, combustion progress and unburned hydrocarbon (HC) emissions at cold operating conditions, and to show the capability of model and full engine tests adapted for different measurement techniques. A comprehensive study applying endoscopic visualization, infrared thermography, combustion and emission measurements was carried out in a 4-stroke 4-cylinder 16-valve production engine with intake port injection during different engine operating conditions including injection angle and timing. In addition 2D visualization and PIV measurements were performed in a back-to-back model test section with good optical access to the intake manifold and the combustion chamber. The measurements in both set ups were in good agreement and show that model tests could lead to useful findings for a real engine.

Optical investigations using optical fibres were carried out in the first available direct injection SI-engine, the Mitsubishi GDI, in the driving mode. The optical access to the combustion chamber was realized by 8 optical sensors evenly distributed in a ring on the ground electrode of the standard spark plug. All investigations, steady state (constant load and velocity) and unsteady state (engine starts), show, that there is preferred flame propagation to the intake valves, caused by a reverse tumble in-cylinder flow. As the inflammation depends on thermodynamic conditions, flow characteristics and the actual air/fuel-ratio at the spark plug, the optical sensors can be used to describe the quality of stratification.

The European Union (EU) has defined legally-binding targets for the fleet of new cars allowing 95 grams CO2 per kilometer in 2021. It is already under discussion to reduce average emissions of the EU car fleet by further 15% in 2025 and again by 30% in 2030 compared to 2021 goal. Therefore, improvement of fuel economy is becoming one of the most important issues for the car manufacturers. Today’s conventional car powertrain systems are reaching their technical limits and will not be able to meet future fuel economy targets without further development of additional measures. This paper presents the analysis of a Rankine cycle unit applied to improve the overall efficiency of a hybrid electric vehicle (HEV). The authors propose a new concept for recovering a considerable part of exhaust waste heat from an HEV with spark ignition internal combustion engine (ICE) by applying a bottoming Rankine cycle with a Ruths storage tank.

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.