The program of visualization of a mixture formation in a combustion
chamber of diesel engine
The "Fuel Jet Visualization" code is a program of visualization of a mixture formation in a diesel. This code is included in the DIESEL-2/4t kit. The code can be run both from the DIESEL-2/4t shell and in the DOS command line. The code is intended for visual mapping of calculation results obtained at simulation of the engine.
The code displays on the screen the moving image of
development of fuel jets and their wall surface flows and also the diagrams of allocation
of the sprayed fuel in characteristic zones. The program allows step by step to observe:
- the development of fuel jets and their wall surface flow in a combustion chamber in view of effect of a swirl;
- the deformation of jets by a swirl;
- the forming of wall surface flow depending on angle of meeting of jet with wall,
- the development of wall surface flow under effect of a swirl and interaction them among themselves;
- the curves of allocation of fuel in the characteristic zones;
- the curves of injection rate and heat release.
Example: Visualization of a mixture formation in a tractor diesel CMD
The animation of development of fuel jets
is carried out on the basis of calculation of their trajectories and deformation under the
influence of an air swirl. The forms of stains of wall surface flows are calculated
depending on the values of angles of collision of jets with walls and effect of swirl.
On the image "Longitudinal section of jet" the combustion chamber and chosen jet are represented. The secant surface passes through an axis of a jet before its collision with a wall, and further along the straight line which is tangent to the axis.
Notations of curves in diagrams
|Allocation of fuel in the zones
||Environ. is a curve of amount of fuel allocated in rare environment
of free jet, in front of free jet and in environment of wall surface flow. There are best
conditions of evaporation in this zone.
Jet Core is a curve of amount of fuel allocated in a core of free jet. There are very poor conditions of evaporation in this zone.
Pst.Wall is a curve
of amount of fuel allocated in a core of wall surface flow on a surface of piston
bowl. Conditions of evaporation in this zone a
depend on surface properties and temperature.
Cyl.Head is a curve of amount of fuel allocated on surface of cylinder head. Conditions of evaporation in this zone are not very good.
Cyl.Wall is a curve of amount of fuel allocated on surface of cylinder wall. There are very poor conditions of evaporation in this zone.
|Injection and heat release||dx/Fi
is a curve of heat release rate.
X is a curve of heat release.
Uo is a curve of injection velocity.
Observing the development of wall surface flow in the map of plan of combustion chamber it is possible to see an intersection of their spots among themselves. Creation of a large area of an intersection of wall surface flows causes a decrease of evaporation rate and heat release. The amount of fuel allocated in the intersection zone is registered in the common table of results. Allocation of fuel in these zones causes a reallocation of a summarized amount of fuel of all jets among the characteristic zones. Parts of fuel allocated in environment of all jets and in normal wall surface flow of all jets are diminished. It causes a deceleration of combustion of fuel, increase of a specific fuel consumption and emission of soot. (See. Simulation of interaction of jets with an air swirl and walls.)
At the end of calculation the data of allocation of
fuel in the zones are output for each jet and for all jets as a whole. Usage of these data, integral parameters of an engine and
the "Fuel Jet Visualization" code allows not only to compare different variants of constructions among themselves and to
estimate their advantages and disadvantages, but also to select optimum combinations
of a combustion chamber shape and fuel jets orientation which allow to achieve a small
level of harmful materials emission and specific fuel consumption.
The example of similar research is represented in site: Numerical research of possibility to decrease a level of NOx emission of diesel engine by means of optimization of the piston bowl shape, fuel jets orientation,... (The measures providing a lowering of NOx emission by 43 % and simultaneous reducing of fuel consumption are designed.)
To achieve a good mixture formation, fast combustion and low level of fuel consumption one should directed each jet so that the maximum amount of fuel was allocated in zones with good conditions of evaporation. It is first of all, zone of environment of a jet and, to a lesser degree, core of a wall surface flow. It is necessary to avoid allocation of fuel in zones of intersection of wall surface flows, and also the settlement of fuel on a wall of the cylinder and on the head of the cylinder, especially, if the head is made of aluminium alloy and has low temperature. For fast evaporation it is necessary to provide a small diameter of drops. To achieve a low level of NOx emission it is necessary to diminish self-ignition delay, to diminish amount of fuel burning down by volumetric mechanism at high local temperature. The software DIESEL - 2/4t and built-in "Fuel Jet Visualization" code allows to optimize the piston bowl shape, swirl intensity, fuel jets orientations, compression ratio, injection characteristic, etc. to coordinate these opposite tendencies and to find the favorable compromises.
You can observe on
your computer a moving image of development of fuel jets and their wall surface flows in
combustion chambers of different diesels. The "Fuel Jet Visualization"
code together with data kit can be sent free of charge to all
interested persons and
organizations. The "Fuel Jet Visualization" code is copyrighted
material and is protected by law. The distribution by you of this code in commercial
purposes is not admitted without a written permission of the developer.