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The effects of in-cylinder water injection on a direct injection (DI) Diesel engine were studied using a computational fluid dynamics (CFD) program based on the Kiva-3v code. The spray model is validated against experimental bomb data with good agreement for vapor penetration as a function of time. It was found that liquid penetration increased approximately 35% with 23% of the fuel volume replaced by water, due mostly to the increase in latent heat of vaporization. Engine calculations were compared to experimental results and showed very good agreement with pressure, ignition delay and fuel consumption. Trends for emissions were accurately predicted for both 44% and 86% load conditions. Engine simulations showed that the vaporization of liquid water as well as a local increase in specific heat of the gas around the flame resulted in lower Nitrogen Oxide emissions (NOx) and soot formation rates.

For the development of new HD Diesel engines which meet the demands of future international emission regulations and, at the same time, ensure economic operation modern development tools need to be used, especially for an optimisation of the combustion principle. To find the optimal engine set up, the variation of a large number of engine and injection system parameters, i.e. injection system, number of nozzle holes and sizes, injection rate profiles, etc. is required. To speed up the design process, modern optical engine diagnostics and 3D-numerical simulation can help to analyse the highly transient in-cylinder processes in detail. These methods provide essential insight to understand the complicated physical and chemical interactions and acting mechanisms during mixture formation, combustion and pollutant formation as well as the function of components of the system.

The combustion process of a heavy-duty DI-Diesel truck engine has been investigated using numerical simulation. The numerical modeling was based on an improved version of the KIVA-2 engine simulation code, employing a modified characteristic time-scale combustion model and a modified Kelvin-Helmholtz spray atomization model. The NO-formation process was modeled using the extended thermal Zeldovich mechanism. The simulation efforts included the effects of different injection characteristics such as varying the injection rate profile or number of injection holes and sizes. The physical sub-models used to improve the simulation of the mixture-formation and the combustion process were validated through comparison with single-cylinder engine experiments. Special attention was given to accurately model the in-cylinder flame propagation of the individual sprays and their effect on thermal NO-formation. All simulations were based on full load cases at medium speed.