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Given the fact that, in an endeavor to achieve the goals of engineering for a trade-off between cleaning up exhaust emissions and maximizing fuel economy, two main paths are being followed in advancing and optimizing SI-engine operating strategy in the upper part-load range. On the one hand, homogenization and operation in the compression ignition mode seem to offer a promising means of minimizing NOx emission by keeping the combustion temperature below the formation borderline and accepting a high cylinder-pressure gradient to obtain benefits in fuel economy. On the other hand, there are ambitions to widen the range of stratified operation using a supercharger or turbocharger. This way, efficiency of the engine cycle can be improved by operating at a higher global air-fuel ratio and, with this, a higher polytropic exponent, thereby taking the efficiency chain to a higher level.

To this day, Diesel engines with direct injection are the most efficient internal combustion engines for passenger cars. The major challenge of these engines with a conventional Diesel combustion process is the high level of particulate matter and nitrogen oxide emissions. Diesel engines in passenger cars normally use a pilot injection strategy for NVH reasons, which influences the engine-out soot emissions negatively. The Diesel fuel of the pilot injection is still burning when the main injection takes place, so, liquid components of the main injection interact with the flame of the pilot injection. The time for mixture formation decreases and the combustion takes place under locally very rich conditions which results in high levels of soot formation. For this reason new emission level restrictions cannot be reached without modern exhaust gas aftertreatment systems, which are quite expensive and can have an impact on the gas exchange.

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.

The objective of this research work was to assess the potential of an electrostatic fluid atomization method for application in direct injection systems for combustion engines. The most important finding of this study was that it is possible to detect the influence of electrostatic atomization at injection pressures up to 300 bar using diesel fuel. The electrostatic force affects the liquid core of the fuel spray from typical diesel nozzles in such a way that additional surface waves are produced which in turn cause the spray to breakup earlier, i.e. the spray breakup length is reduced significantly. This early breakup leads to smaller mean droplet diameters, larger spray angles and as a result air entrainment of the fuel spray is enhanced. Theoretical models were derived to explain the effects of electrostatic charge on fluid atomization.