Modeling scavenging process for large two-stroke diesel engines

By Sajjad Haider, PhD student at the Technical University of Denmark, Department for Mechanical Engineering.

Background
This Ph.D. project is focused on the improved performance of large two-stroke diesel engines for ship propulsion. With the increasing prices of fossil fuels and decreasing amount of fuel resources, the engine manufacturers are facing huge demands for more efficient engines. However, this task is getting more and more challenging with tougher environmental regulations for the marine sector. Now the situation has driven the engine manufacturers to develop engines which should be efficient not only in terms of fuel but also in terms of the amount and type of pollutants produced.

In order to achieve the aforementioned targets, it is very essential to have a detailed knowledge of the main in-cylinder processes like spray formation and evaporation, Diesel combustion, Heat Transfer in the gaseous phase and the Cylinder walls, and the scavenging process.

Methodology

The overall task of this study is to develop numerical models and perform experiments to study the scavenging process in a MAN B&W DIESEL large 2-stroke diesel engine. Commercial CFD code FLUENT 6.3 will be used to develop the models. The CFD model will be equipped with Moving and Dynamic Meshing so as to simulate a complete engine cycle including compression, fuel injection, Combustion, expansion and scavenging process.  The scavenging process is very important from the point of view of engine efficiency. An improvement in the scavenging process will reduce the load on the turbocharger by requiring less amount of air and provide a good ambient flow distribution for the fuel evaporation and ignition. This in turn will increase engine efficiency and reduce pollutant formation. To optimize the scavenging process, an improvement in the current knowledge of this process by both numerical and experimental means is required.

The model will involve a 3-dimensional, non-isothermal flow with time varying geometries as the piston and exhaust valve are moving during the scavenging process. Velocity distribution in the swirling flow, velocity profile at the inlet ports and exhaust valve are to be studies in detail. An important aspect is to develop a numerical model based on the computation fluid mixing as the scavenging process involves mixing of two fluids with different composition and other physical properties in a confined swirling flow.

The experimental work will be based on developing a scaled model of the engine cylinder. The scaled model will have the ability to mix two different species with different densities for a ‘fresh fluid’ and ‘exhaust fluid’. Optical measurement techniques will be used to investigate the required physical properties both at microscopic and macroscopic level.

Furthermore, numerical models will be developed for the spray formation and evaporative combustion. This will help in understanding and improving the engine efficiency in terms of heat transfer and pollutant formation. The model performance will be compared to the experimental results provided by MAN B&W DIESEL and other PhD colleagues in the department working on those aspects of the large two-stroke diesel engines for ship propulsion.

	PIV Study of In-Cylinder Confined Swirling Flow for Scavenging 2-Stroke Marine Diesel Engine
	PIV Study of the Effect of Piston Motion on the Confined Swirling Flow in the Scavenging Process in 2-Stroke Marine Diesel Engines