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Pre-chamber ignition systems enable the combustion of homogeneous lean mixtures in internal combustion engines with significantly increased thermal efficiency. Such ignition systems provide a much higher ignition energy compared to a common spark ignition by burning a small portion of the charge in a separate chamber, generating multiple ignition sites in the main combustion chamber and increasing the turbulent flame speed. Pre-chamber ignition systems are commonly used in large natural gas engines but the integration in automotive engines is not feasible so far due to the lack of suitable fuelling systems needed to keep the pre-chamber mixture stoichiometric at lean operation of the engine. Based on preliminary investigations we developed an ignition system with fuelled pre-chamber for automotive engines utilizing the available space for the conventional spark plug.

Homogeneous lean or diluted combustion can significantly increase the efficiency of spark ignition engines. Active fuelled pre-chamber ignition systems can overcome the problem that common spark ignitions systems are incapable to ignite strongly diluted mixtures. A small portion of the charge is burned in a separated chamber, which is connected to the main chamber by multiple small orifices. The combustion inside the pre-chamber generates hot gases, which penetrate into the main chamber and ignite the diluted charge on multiple sites. Active pre-chamber ignition systems feature a separate fuelling or scavenging system in addition to the one of the main combustion chambers. Preferably, gaseous fuel is used for the pre-chamber fuelling allowing better dosing accuracy and mixture preparation inside the pre-chamber.

The spray formation of two different gasoline port fuel injectors has been studied in three stages of the mixture formation process using measured liquid fuel distributions. The injector characteristics were determined in fundamental chamber experiments providing the time dependent spray penetration and the internal structure of the spray in quiescent air by a laser light sheet technique. For the sane injectors the interaction between port flow and spray was investigated inside the port of a production engine. A strong dependence of the fuel distribution inside the port on the engine operation point was found for both injectors. This fuel distribution provides information on wall film generation and the optimum orientation of the injector inside the suction pipe.

The fuel spray behavior in the near nozzle region of a gasoline injector is challenging to predict due to existing pressure gradients and turbulences of the internal flow and in-nozzle cavitation. Therefore, statistical parameters for spray characterization through experiments must be considered. The characterization of spray velocity fields in the near-nozzle region is of particular importance as the velocity information is crucial in understanding the hydrodynamic processes which take place further downstream during fuel atomization and mixture formation. This knowledge is needed in order to optimize injector nozzles for future requirements. In this study, the results of three experimental approaches for determination of spray velocity in the near-nozzle region are presented. Two different injector nozzle types were measured through high-speed shadowgraph imaging, Laser Doppler Anemometry (LDA) and X-ray imaging.

The nozzle geometry of fuel injectors has a strong influence on turbulences and pressure gradients within the nozzle flow. The flow situation at the nozzle outlet determines the spray propagation into the ambient atmosphere. This spray penetration is critical for gasoline direct injection (GDI) systems. When the spray penetration is too high, it can cause wall and cylinder impingement, which increases particle emissions drastically. However, prediction of fuel spray propagation in dependency of nozzle hole geometry is difficult due to the large difference in scale between the nozzle flow and the spray development. Because of this, spray measurements with varying nozzle geometry parameters and statistical evaluation of these datasets are useful for the future development of fuel injectors. In this study, shadowgraphy measurements of real-size single-hole glass nozzles are presented. The nozzles cover a wide range of geometry parameters relevant to a GDI system.

The influence of fuel composition on sprays was studied in an injection chamber at DISI conditions with late injection timing. Fuels with high, mid and low volatility (n-hexane, n-heptane, n-decane) and a 3-component mixture with similar fuel properties like gasoline were investigated. The injection conditions were chosen to model suppressed or rapid evaporation. Mie scattering imaging and phase Doppler anemometry were used to investigate the liquid spray structure. A spray model was set up applying the CFD-Code OpenFOAM. The atomization was found to be different for n-decane that showed a smaller average droplet size due to viscosity dependence of injected mass. And for evaporating conditions, a stratification of the vapor components in the 3-component fuel spray was observed.

The introduction of the so called Emission Controlled Areas within the IMO Tier III legislation forces manufacturers of maritime propulsion systems to adherence to stringent emission thresholds. Dual fuel combustion, which is characterized by the injection of a small amount of fuel oil to ignite a premixed natural gas air mixture, constitutes an option to meet this target. At high diesel substitution rates and very short pilot injection events, the injector is operated in the ballistic regime. This influences spray penetration, mixture formation and ignition behavior. In the present work, a seven-hole dual fuel injector was measured in a combustion chamber to provide data for the generation of a CFD model using the commercial code AVL FIRE®. The liquid and the vapor phase of the fuel spray were quantified by Mie-scattering and Schlieren-imaging technique for different chamber conditions.

Modern direct injection spark ignition (DISI) engine concepts have the drawback of higher particulate matter emission as compared to port fuel injection concepts. Especially, when driven with biofuels, the operation of DISI engines requires a deeper insight into particulate formation processes. In this study a modern optical accessible DISI engine is used. Pure isooctane, ethanol, E20 (20vol% of ethanol in isooctane) and E85 were investigated as fuels. Simultaneous OH*-chemiluminescence and soot radiation imaging was conducted by a high-speed camera system in order to separate premixed combustion with the sooting combustion. Furthermore, a laser-induced incandescence (LII) sensor was used to measure exhaust elementary carbon mass concentration. Systematically, operation points were chosen, which correspondent to the main sooting mechanisms, poolfire, mixture inhomogeneities and global low air-fuel ratio. Furthermore, they were compared to a homogenous charge combustion strategy.

A previous study by the authors has shown an efficiency benefit of up to Δηi = 10 % for stratified operation of a high pressure natural gas direct injection (DI) spark ignition (SI) engine compared to the homogeneous stoichiometric operation with port fuel injection (PFI). While best efficiencies appeared at extremely lean operation at λ = 3.2, minimum HC emissions were found at λ = 2. The increasing HC emissions and narrow ignition time frames in the extremely lean stratified operation have given the need for a detailed analysis. To further investigate the mixture formation and flame propagation und these conditions, an optically accessible single-cylinder engine was used. The mixture formation and the flame luminosity have been investigated in two perpendicular planes inside the combustion chamber.