JP2017089608A - Method for designing combustion chamber structure of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for designing a combustion chamber structure of an engine that can operate combustion reaction calculation in the computation fluid dynamics at higher speed than before.SOLUTION: In parallel calculation processing of the fluid combustion reaction calculation in multiple calculation lattices sectioned in a combustion chamber of the engine, multiple calculation lattices are appointed to any one of multiple calculators randomly.SELECTED DRAWING: Figure 9

Description

  The present invention relates to a method for designing a combustion chamber structure of an engine, and more particularly, to a method for designing a combustion chamber structure of an engine capable of performing a combustion reaction calculation using numerical fluid dynamics at a higher speed than before.

  In recent years, computational fluid dynamics (CFD) has been frequently used as a design tool for engine combustion chamber structures (see, for example, Patent Document 1). In this analysis and evaluation by CFD, the chemical reaction associated with the combustion of fuel spray in the multiple calculation grids partitioned in the combustion chamber, the reaction in the flame propagation zone and the chemical reaction related to unburned gas self-ignition (knock phenomenon) are analyzed. Combustion reaction calculation is performed. Since this combustion reaction calculation is complicated and diverse, in order to improve the calculation speed, parallel calculation processing is adopted in which each calculation grid is assigned to one of a plurality of computers (CPUs) and processed in parallel. Is done.

  However, in the combustion mode of the engine, the concentration state and temperature of chemical species generated by the chemical reaction, and the propagation flame and unburned gas auto-ignition are unevenly distributed in space and time. If they are simply assigned in order, there is a problem in that it is difficult to improve calculation performance because the calculation load among a plurality of CPUs is biased.

JP 2005-257517 A

  An object of the present invention is to provide a design method of a combustion chamber structure of an engine that can perform combustion reaction calculation in computational fluid dynamics at a higher speed than before.

  The engine combustion chamber structure design method of the present invention that achieves the above object is characterized in that a plurality of calculation reactions of fluid in a plurality of calculation grids partitioned in the combustion chamber of the engine are calculated for each of the plurality of calculation grids. In a design method of an engine combustion chamber structure using computational fluid dynamics including parallel calculation processing that is assigned to any one of the computers and processed in parallel, no assignment of the calculation grid to the computers in the parallel calculation processing is performed. It is characterized by the fact that it is done in a random manner.

  According to the engine combustion chamber structure design method of the present invention, since the combustion reaction calculation in the plurality of calculation grids is randomly assigned to any one of the plurality of computers, the calculation load on each computer is reduced. Since the efficiency of parallel calculation processing is improved by being uniformized, combustion reaction calculation using numerical fluid dynamics can be performed at a higher speed than in the past.

It is a structural diagram showing an example of a combustion chamber of a diesel engine. It is a structural diagram showing an example of a combustion chamber of a gasoline engine. It is a structural diagram which shows another example of the combustion chamber of a gasoline engine. It is a structural diagram showing an example of a combustion chamber of a diesel dual fuel engine. It is a structural diagram which shows another example of the combustion chamber of a diesel dual fuel engine. It is a flowchart explaining the design method of the combustion chamber structure of the engine which consists of embodiment of this invention. It is a schematic diagram which shows a part of division example of the calculation grid set to the combustion chamber of the type which has a cavity. It is a schematic diagram which shows a part of division example of the calculation grid set to the combustion chamber of the type which does not have a cavity. It is a schematic diagram explaining the example of the method of assigning a calculation grid to CPU at random.

  Embodiments of the present invention will be described below with reference to the drawings. 1 to 5 show examples of a combustion chamber to which a method for designing a combustion chamber structure of an engine according to an embodiment of the present invention is applied.

  A combustion chamber 1 </ b> A shown in FIG. 1 is a combustion chamber of a diesel engine, and includes a cavity 5 </ b> A that is recessed in the central portion of the top surface 4 of the piston 3 that reciprocates in the cylinder bore 2. Examples of the cross-sectional shape of the cavity 5A include a shallow dish type and a reentrant type.

  In the combustion chamber 1A, light oil as fuel is accumulated in a common rail (not shown), and is injected into the compressed air in the cavity 5A at an appropriate timing through the light oil injector 6 to become fuel spray, which is combusted and expanded by self-ignition. This pushes down the piston 3. The burned gas is discharged from the cylinder bore 2 through the exhaust pipe 8 when the exhaust valve 7 is opened. On the other hand, the intake air is introduced into the cylinder bore 2 through the intake pipe 10 when the intake valve 9 is opened.

  A combustion chamber 1B shown in FIG. 2 is a combustion chamber of a so-called port injection type gasoline engine, and includes an inner wall 11 of a cylinder bore 2 and a top surface 4 of a piston 3 that reciprocates in the cylinder bore 2.

  In the combustion chamber 1B, gasoline as fuel is supplied into the intake pipe 10 through a carburetor or a fuel injection device (not shown) to generate an air-fuel mixture, and is introduced into the combustion chamber 1B when the intake valve 9 is opened. After that, the piston 3 is pushed down by being ignited by the spark plug 12 while being compressed and burned / expanded. The burned gas is discharged from the cylinder bore 2 through the exhaust pipe 8 when the exhaust valve 7 is opened.

  A combustion chamber 1C shown in FIG. 3 is a combustion chamber of a so-called in-cylinder injection type or direct injection type gasoline engine. The combustion chamber 1C is formed on the inner wall 11 of the cylinder bore 2, the top surface 4 of the piston 3, and a part of the top surface 4. The cavity 5C is recessed.

  In the combustion chamber 1C, gasoline as fuel is directly injected into the compressed air in the cavity 5C through the gasoline injector 13 at an appropriate timing, and is ignited by the spark plug 12 to be burned and expanded.

  A combustion chamber 1D shown in FIG. 4 is a combustion chamber of a so-called port injection type diesel dual fuel engine, and is composed of a cavity 5D that is recessed at the center of the top surface 4 of the piston 3 that reciprocates in the cylinder bore 2. ing. Examples of the cross-sectional shape of the cavity 5D include a shallow dish type and a reentrant type.

  In the combustion chamber 1D, natural gas as one fuel is supplied to the cylinder bore 2 into the intake pipe 10 through the CNG injector 14 while the intake valve 9 is opened. The natural gas introduced into the combustion chamber 1D is combusted and expanded by self-ignition at the time of compression together with light oil that is the other fuel injected into the cavity 5D through the light oil injector 6 at an appropriate timing. Press down. The burned gas is discharged from the cylinder bore 2 through the exhaust pipe 8 when the exhaust valve 7 is opened.

  A combustion chamber 1 </ b> E shown in FIG. 5 is a combustion chamber of a so-called in-cylinder injection type or direct injection type diesel dual fuel engine, and is recessed at the center of the top surface 4 of the piston 3 that reciprocates in the cylinder bore 2. It consists of a cavity 5E.

  In the combustion chamber 1E, natural gas and light oil, which are fuels, are respectively injected into the cavity 5E through the CNG injector 14 and the light oil injector 6 at appropriate timing, and are combusted and expanded by self-ignition during compression.

  The analysis and evaluation during combustion by CFD in the design method of the combustion chambers 1A to 1E will be described below with reference to FIG.

  First, a plurality of calculation grids are set and set in the combustion chambers 1A to 1E having shapes designed in advance (S10). An example in which a calculation grid is set in a combustion chamber of a type having a cavity (for example, combustion chamber 1A) is shown in FIG. FIG. 8 shows an example in which a calculation grid is set in a combustion chamber of a type having no cavity (for example, the combustion chamber 1B). In these examples, each calculation grid is partitioned regularly, but may be partitioned irregularly.

  Next, the combustion reaction calculation in each calculation grid is performed (S20), and the increase / decrease amount of the chemical species due to the chemical reaction is obtained. In this combustion reaction calculation, parallel calculation is performed in which a CPU is assigned to each calculation grid and processed in parallel.

  Next, the movement between the calculation grids of the fuel spray is evaluated by fluid analysis (S30), and the spatial concentration of the chemical species in the combustion chamber is obtained (S40).

  Finally, the temperature change in each calculation grid is obtained (S50). These processes of Steps 20 to 50 are repeatedly performed.

  In such analysis and evaluation by CFD, assignment of calculation grids to CPUs in step 20 is performed randomly.

  An example of this random assignment method will be described in the case of assigning n consecutive calculation grids to m CPUs, respectively (see FIG. 9). Normally, the relationship is n> m.

  First, numbers 1 to n and 1 to m are assigned to n calculation grids and m CPUs, respectively (FIG. 9A). Next, n different random numbers are assigned to the 1st to nth calculation grids in the order of generation (FIG. 9B). This random number generation can be performed by a random number generation process or the like incorporated in advance in the CFD. Next, the order of the 1st to nth calculation grids is rearranged based on the magnitude relationship between the distributed random numbers (in this example, in ascending order) (FIG. 9C). Then, according to the rearranged order, each calculation grid is sequentially assigned to m CPUs one by one (FIG. 9D). At this time, the calculation grids whose order is over m are assigned again in order from the first CPU.

  As described above, by randomly assigning combustion reaction calculations in a plurality of calculation grids to any one of a plurality of CPUs, the calculation load in each CPU is equalized and the efficiency of parallel calculation processing is improved. Therefore, the combustion reaction calculation using CFD can be performed at a higher speed than before.

  The engine combustion chamber structure design method according to the present invention is not limited to the combustion chambers 1A to 1E of the diesel engine, gasoline engine, and diesel dual fuel engine described above, and an engine in which combustion occurs in which the combustion reaction varies in time and space. If so, it is applicable.

1A to 1E Combustion chamber 2 Cylinder bore 3 Piston 4 Top surface 5A, 5C, 5D, 5E Cavity 6 Light oil injector 7 Exhaust valve 8 Exhaust pipe 9 Intake valve 10 Intake pipe 11 Inner wall 12 Spark plug 13 Gasoline injector 14 CNG injector

Claims (3)

Numerical values including parallel calculation processing in which a combustion reaction calculation of a fluid in a plurality of calculation grids partitioned in a combustion chamber of an engine is assigned to one of a plurality of computers for each of the plurality of calculation grids and processed in parallel In the design method of the combustion chamber structure of the engine using hydrodynamics,
A design method of a combustion chamber structure of an engine, wherein the calculation grid is randomly assigned to the computer in the parallel calculation processing. Including random number generation processing,
Distributing a plurality of different random numbers generated in the random number generation process to the plurality of calculation grids in order, and setting the order of the plurality of calculation grids based on the magnitude relationship between the distributed random numbers, The engine combustion chamber structure design method according to claim 1, wherein the calculation grid is assigned to the computer according to a set order.   The engine combustion chamber structure design method according to claim 1, wherein the engine is a diesel engine, a gasoline engine, or a diesel dual fuel engine.

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