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Technical Paper

Numerical Evaluation of Dual Oxygenated Fuel Setup for DI Diesel Application

Methanol, MeOH, is one of the most attractive alternative fuels for internal combustion engines. In diesel applications, methanol's poor ignition properties necessitate the use of expensive additives for ignition improvement [1]. Dimethyl ether, DME, as a combustion improver for methanol, was recently evaluated in [2]. This study is directed towards a better understanding of the auto-ignition and combustion of a blend fuel composition consisting of liquid methanol and gaseous dimethyl ether aspirated with the combustion air by using the results of numerical simulation. The numerical model was based on the computer code KIVA-3. The computational results show that the use of DME as an ignition improver is only reasonable for gas temperatures below 900 K. At typical diesel conditions, an amount of DME in a quantity less than 10-15 volumetric percent of oxygen content in the combustion volume is sufficient for ignition improvement.
Technical Paper

Neat Dimethyl Ether: Is It Really Diesel Fuel of Promise?

The CFD model, based on the LANL KIVA-3 computer code, modified to account for the multi-step dimethyl ether, DME/air, oxidation chemistry, was developed and used to study the neat DME combustion dynamics in a constant volume at Diesel-like conditions and in the Volvo AH10A245DI Diesel engine. Constant volume simulations confirm high ignition quality of neat DME in air. The results of engine modeling illustrate that the injection schedule used for Diesel fuel is not optimal for DME. Surprisingly, the positive gain and peak pressure levels comparable with those for Diesel fuel were obtained using an early (∼ -20 ATDC) injection through a nozzle of a larger diameter at reduced injection pressures and velocities (∼150m/s) preventing too rapid spray atomization. At these conditions, combustion heat release has a specific two-stage character with a peak value placed behind the TDC.
Technical Paper

3-D Diesel Spray Simulations Using a New Detailed Chemistry Turbulent Combustion Model

Until recently, the application of the detailed chemistry approach as a predictive tool for engine modeling has been sort of a “taboo” for different reasons, mainly because of an exaggerated rigor to the chemistry/turbulence interaction modeling. In terms of this ideology, if the interaction cannot be simulated properly, the detailed chemistry approach makes no sense. The novelty of the proposed methodology is the coupling of a generalized partially stirred reactor, PaSR, model with the high efficiency numerics to treat detailed oxidation kinetics of hydrocarbon fuels. In terms of this approach, chemical processes are assumed to proceed in two successive steps: the reaction follows after the micro-mixing is completed on a sub-grid scale.