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Over the next decades to come, fossil fuel powered Internal Combustion Engines (ICE) will still constitute the major powertrains for land transport. Therefore, their impact on the global and local pollution and on the use of natural resources should be minimized. To this end, an extensive fundamental and practical study was performed to evaluate the potential benefits of simultaneously co-optimizing the system fuel-and-engine using diesel as an example. It will be clearly shown that the still unused co-optimizing of the system fuel-and-engine (including advanced exhaust after-treatment) as a single entity is a must for enabling cleaner future road transport by cleaner fuels since there are large, still unexploited potentials for improvements in road fuels which will provide major reductions in pollutant emissions both in vehicles already in the field and even more so in future dedicated vehicles.

The likely transition from today's conventional to future alternative fuels will be discussed. It will be shown that in the very long term renewable fuels might be the most promising road fuels with respect to low CO2 emissions. In the short and medium term, however, liquid alternative fuels will prevail being produced initially from natural gas and later increasingly from biomass. Methanol, Ethanol, GTL Hydrocarbons and other fuels are still under study since lowest WTW CO2 emissions and overall system costs are not yet clarified. The availability of alternative fuels in large quantities will depend on the costs for production and infra-structure, and not least of all, on the market benefits of the resulting fuel / power train systems in a holistic assessment. Cost trends for conventional and alternative fuels will be discussed.

Droplet formation and subsequent evaporation in Diesel sprays occur so fast that conventional diagnostic tools are generally too slow to resolve time dependent features. To overcome this drawback a very fast optical diagnostic system has been developed, providing a time resolution of 4 μs per sampling point over the full duration of automotive type Diesel sprays. In order to accomplish this high speed the simultaneously measurable quantities had to be reduced to the two most essential values: mean droplet size and number of droplets in the test section. A combined extinction-diffraction technique is used to determine the two free parameters in a generalized droplet distribution function which has been derived from a detailed analysis of spray characteristics using photo-graphic recordings of droplet distributions. It is shown that these two parameters are sufficient to characterize with good accuracy the full width of variations occuring in practical droplet distributions.

Engine knock causes severe damage to the surfaces of the combustion chamber in I.C. engines. Since the detailed damaging mechanisms are still unknown, we performed a theoretical and experimental study in order to identify potential erosion processes. To circumvent the considerable cyclic variations of combustion in I.C. engines the experiments use an optically accessible bomb. It is shaped to resemble a typical geometry which is known to be particularly susceptible for knock damage. In this way we establish well defined conditions for knock simulations. By means of very high speed Schlieren diagnostics we measure the propagation speeds of detonation waves in the duct and use the data to estimate the wall loading due to instantaneous pressure peaks and sudden large temperature increases. Qualitative agreement between numerical simulations and experimental observations is achieved in the calculations.