Search Results

In view of the large (and further increasing) range of fuels applied in marine diesel engines, there is a clear need for obtaining a better understanding of the effect of those fuels on the key in-cylinder processes governing the combustion characteristics of these engines. For this purpose, a constant volume chamber representative of the combustion system of large marine diesel engines has been complemented with a device allowing the investigation of small fuel quantities and the resulting setup has been used for studying the combustion behaviour of typical marine diesel fuels at conditions relevant for large marine two-stroke diesel engines. Specifically, two clearly distinct heavy fuel oils have been compared to a light fuel oil. Two optical measurement techniques were used to complement the findings made on the basis of rate of heat release analysis.

Computational investigations have been conducted to study the reduction of nitric oxide formation by means of water injection into the combustion chamber of large-bore diesel engines using a KIVA-based code. The main objective has been the development of an optimal fuel/water injection strategy which minimizes the nitric oxide formation for the same amount of injected water. The investigated water injection techniques include the injection of water via separate injectors, the injection of fuel/water mixtures and the stratified injection of fuel/water packages via specially designed nozzles. Both, the stratified and the emulsified injections yield best NOx reductions per injected water mass for the same power outputs and at identical cylinder peak pressures, depending on the particular injection configuration. The computational tool is a KIVA-based code where the nitric oxide formation is modeled with a variation of the extended Zeldovich mechanism.

A KIVA-based CFD tool has been utilized to simulate the effect of a Common-Rail injection system applied to a large, uniflow-scavenged, two-stroke diesel engine. In particular, predictions for variations of injection pressure and injection duration have been validated with experimental data. The computational models have been evaluated according to their predictive capabilities of the combustion behavior reflected by the pressure and heat release rate history and the effects on nitric oxide formation and wall temperature trends. In general, the predicted trends are in good agreement with the experimental observations, thus demonstrating the potential of CFD as a design tool for the development of large diesel engines equipped with Common-Rail injection. Existing deficiencies are identified and can be explained in terms of model limitations, specifically with respect to the description of turbulence and combustion chemistry.

A recently developed auto-ignition model based on a single transport equation in combination with a reduced kinetic scheme has been validated and tested in combination with a cascade jet and droplet breakup model. The validation has been performed by comparing ignition locations and delays for various thermodynamic conditions with experimental data from a high-pressure combustion cell. Also for medium-size diesel engine applications, predictions of ignition delay are in good agreement with experimental observations. In addition, a new approach to the modeling of the early flame development in diesel engine combustion is introduced. The reaction rate in the transition phase from the premixed to the mixing-controlled combustion mode is determined by means of a sub-grid scale model, which describes the evolution of a turbulent diffusion flame. The model has been tested during the early combustion phase of a medium-size, medium-speed DI diesel engine.

Emissions and performance parameters of a medium size, medium speed D.I. diesel engine with increased charge air pressure and reduced but fixed inlet valve opening period have been measured and compared to the standard engine. While power output and fuel consumption are slightly improved, nitric oxide emissions can be reduced by up to 20%. The measurements confirm the results of simulations for both performance and emissions, for which a quasidimensional model including detailed chemistry for nitric oxide prediction has been developed.