Optimization of flow directionality inside Diesel generator set by changing the Inlet and Outlet louver position, size and type to enhance the cooling inside the canopy of the DG set.

INTRODUCTION

A diesel generator is the combination of a diesel engine with an electrical generator (often an alternator) to generate electrical energy. Diesel generating sets are used in places without connection to the power grid, as emergency power-supply if the grid fails, as well as for more complex applications such as peak-lopping, grid support and export to the power grid. Sizing of diesel generators is critical to avoid low-load or a shortage of power and is complicated by modern electronics, specifically non-linear loads.

MODEL OF DG

Fig 1: Modelshowing interior subsystems of DG

Fig 2: Wire frame model of DG in Top view

Fig 3: Position of louvers

The Fig 3 shows the side view of canopy having louvers i.e., air inlets. The size of the louvers and canopy can be evidenced from the above diagram as follows.

Length of the canopy= 6.08m

Height of the canopy= 2.6m

Length of the inlet louvers= 1.04m

Height of the inlet louvers=1.82m

Angle of baffles=45⁰

Fig 4: Inlet and Outlet arrangements

The Fig 4 shows the inlet and outlet louvers position. The size and position of the outlet louver which is placed at the top surface side surface of the canopy can be evidenced from the above diagram. The details are mentioned below.

Length of the outlet louvers= 0.85m

Breadth of the outlet louvers= 1.2m

No of inlet louvers= 4

No of outlet louvers= 4

SPECIFICATIONS OF ENGINE AND ALTERNATOR

Engine	DEUTZ- TCD2014 L6 4V	Unit
Cooling air volume flow	16200	m³/h
Combustion air volume flow	909	m³/h
Sound power at full load	112.1	dB(A)
Engine heat dissipation	122.3	kW
CAC heat dissipation	48	kW
Heat dissipation(convection)	25	kW
Alternator	STAMFORD- UC127AH	Unit
Cooling air volume flow	1850.4	m³/h
Heat dissipation	11.2	kW
Total air volume flow- 1GENSET	18959.4	m³/h
Total air volume flow for 2GENSETS	37918.8	m³/h

Table 1: Specification of DG

PROBLEM DEFINITION:

• There is a marginal variation of flow rate at the various Inlets
• The Inlet Louvers which are closer to the Radiator Fan delivers less amount of volume of air comparing to the other one
• The heat generated from the engine are not effectively transferred to the radiator region

CALCULATION

MASS FLOW RATE

Heat generated on the engine =122kwthrough convection only 40% of heat generated on engine surface, therefore

Total heat generated on engine surface=48.8kw

Q= m*Cp*∆T

∆T= 9⁰ c

Cp=1.006 kJ/kg.k

Q= 48.8kw

48.8= m*1.006*9

m= 5.21 m³/s

HEAT FLUX

Heat generated on the engine is Q =122KW

Only 30% heat will be generated on the engine surface=122*30/100

Q =36.6KW

Total area of the one engine =2.998 m²

Heat flux =Q/A = 36.6/2.998

Heat flux on one engine surface is =12.208 KW/m²

STEPS FOLLOWED IN CFD

• Fluid Domain extraction
• Surface meshing
• Volume mesh
• Solving the CFD problem
• Post processing
• Report generating

SOLVING THE CFD PROBLEM

• Reading the file. The reading the file should clear as case file or data file or case and data file. In this we have to read case and data file.
• Scaling the grid.
• Checking the grid.
• Defining the models. Model should define whether it is steady or unsteady and whether it is viscous. The model is defined here is steady and viscous.
• Defining the materials.
• Defining the boundary condition.
• Controls
• Initialize
• Monitor
• Iterate

BOUNDARY CONDITIONS:

• Energy dissipation from Engine, CAC and through convection are modeled with 122.3 KW, 48 KW, and 25KW respectively
• In thermal boundary condition the internal emissivity is 0.65
• Inlets are assumed to be pressure inlet at total pressure =0.
• Outlets are assumed to be pressure outlet at static pressure=0.
• Fans are designed by fans boundary condition and it produces the mass flow rate of 5.21 m³/s.
• Engine walls are assumed to be heat generating source.
• Rest of the walls is assumed to be adiabatic walls.
• Fan boundary condition is setup as fan performance curve (Q vs. p).

CFD PROCESSING

BASE MODEL

Fig 5:Base model

The Fig 5 shows the DG set canopy with inlet and outlet louvers.

Fig 6:Wire frame model for base model

The Fig 6 shows the DG set wireframe model of canopy and integral subsystems.

Fig 7: Surface mesh for base model

The surface mesh is discretized by the triangular elements which is because of the complexity of the geometry.

Fig 8: Volume mesh for base model

The volume meshes are discretized by the tetrahedral elements which is shown in the Fig 8.

Model	Surface		Mesh	Quality	Volume	Mesh	Quality
	Mesh		Type		Mesh	Type
	Elements				Elements
Base	548051		Tetra	0.6	2253874	Tetrahedral	0.889

Table 2: Meshing Detail for Base Model

PATH LINES

Fig 9: Path lines from I inlets in base model

The Fig 9 shows the path lines of the air molecules which it traces from the I inlet louvers to outlet louvers in base model.

Fig 10: Path lines from II inlets in base model

The Fig 10 shows the path lines of the air molecules which it traces from the II inlet louvers to outlet louvers in base model.

VELOCITY PLOT

Fig 11: Velocity vector Top view -Base model

Fig 12: Velocity contour top view-Base model

The Fig 11 & Fig 12 shows the velocity vector plot and velocity contour plot in base model cut planes at different heights. Here we can evidence that the velocity is higher at the fan region and the recirculation region formation nearby the engine area which acts as a hindrance for air stream to concentrate over the engine area which is a highly heat evolving area. This area needs proper air flow concentration which is deficit here which is evident in contour plot showing some velocity regions near engine areas.

Fig 13: Temperature contour and output - Base model

The above Fig 13 shows the temperature contour over the engine surface, the maximum and minimum temperature over this surface is 1052.8233 K and 324.1468 K. Between this range only temperature distribution over this surface exists.

Fig 14: Pressure distribution on base model

The above Fig 14 shows the pressure distribution inside the DG canopy. From the figure we can say that majority space inside canopy experiences high fluid pressure due to the fluid accumulation and lot of flow recirculation regions. This causes flow hindrance and poor fluid transport inside canopy. The space inside canopy should have nominal minimum pressureto effectively transfer the heat generated inside canopy.

MODIFICATION-1

In the vision of increasing the mass flow rate in to system which can remove more heat and reduce the temperature levels we impart modification 1.It implies combining the two louvers in to one bigger louver and placing in a position which would concentrate the flow over the high heat evolving area on the engine, this modification is made on both the sides of canopy which would facilitate both the engines.

Fig 15: Wireframe and solid 3D view of Modification 1 model

Fig 16: Surface meshed Modification 1 model

Fig 17: Volume meshed Modification 1 model

The above Fig 15, 16 & 17 shows the model and meshing details of the modification 1 model.

Model	Surface	Mesh	Quality	Volume	Mesh	Quality
	Mesh	Type		Mesh	Type
	Elements			Elements
Modification 1	563890	Tetra	0.6	2544228	Tetrahedral	0.88

Table 3: mesh details for modification1

Fig 18: Path lines of air from modified inlet louver to outlet louver.

The above Fig 18 shows the path lines traced by the air molecules starting from the modified inlet louver to outlet louver. Due to combining two inlets of same side in to one inlet louver, the flow disturbance caused by two separate flow stream interaction is very much reduced in this model. We could notice that the flow is mainly directed towards the engine surface which makes improves the air-machine surface interaction to a greater extent.

Fig 19: Velocity vector profile of a cut plan in top view of Modification 1 model

Fig 20: Velocity contour profile of a cut plan in top view of Modification 1 model

The velocity profile shows an appreciable improvement by having increased average velocity and only few evidence of minimum velocity region inside canopy.

Fig 21: Temperature contour and output – Modification 1 model

The above Fig 21 shows the temperature contour over the engine surface, the maximum and minimum temperature over this surface is 1005.975 K and 319.914 K. Between this range only temperature distribution over this surface exists.This temperature range is very much lower than in the base model.

Fig 22: Pressure contour at inner space of canopy – Modification 1 model

The above Fig 22 shows the pressure distribution inside the DG canopy space at modification 1 model. From the figure we can say that fluid pressure inside the space is bit lower than the base model becausepresence of flow recirculation regions are low which improves the flow characteristics. Because of the reduced pressure inside canopy space mass flow rate is better than base model which transports the heat from the system to surrounding sooner than previous base model.

MODIFICATION-2

In order to get more mass flow rate on engine, louvers are arranged closer to engine. In this case only the positions of louvers are changed when compared to base model. In this modification also totally it has 4 louvers in total, 2 per engine-alternator set.

Fig 23: Wireframe and solid 3D view of Modification 2 model

Fig 24: Surface meshed Modification 2 model

Fig 25: Volume meshed Modification 2 model

The above Fig 23 shows the model of the modification 2 model in which you can notice the positions of the inlet louvers changed in a motive to target the flow directly towards engine area placing it in a position very much near the engine area. Fig 24 & 25 shows the surface and volume mesh of the modification 1 model.

Model	Surface MeshElements	Mesh Type	Quality	Volume Mesh Elements	Mesh Type	Quality
Modification 2	553842	Tetra	0.6	3040824	Tetrahedral	0.878

Table 4: mesh details for modification 2

Fig 26: Path lines of air from position changed inlet louver to outlet louver

From Fig 26 we can notice that the prime motive of concentrating the flow over the engine surface is achieved but the flow pattern very much disturbed and affects the flow over other subsystems when compared to the previous two models. This changed flow directionality makes another one disadvantage that after the flow hitting engine it directly directed towards the radiator fan area which makes the molecules to immediately move outside the canopy through outlet louver. So it doesn’t facilitate to interact with the hot surface for sufficient time.

Fig 27: Velocity vector profile of a cut plan in top view of Modification 2 model

Fig 28: Velocity contour profile of a cut plan in top view of Modification 2 model –Global range

From Fig 27 & 28 we can notice that the average velocity inside the canopy is very much low when compared to the previous two models. This is due to the immediate exit and disturbance the flow faces because of the flow directionality.

Fig 29: Temperature contour and output – Modification 2 model

The above Fig 29 shows the temperature contour over the engine surface, the maximum and minimum temperature over this surface is 1123.696 K and 326.8624 K. Between this range only temperature distribution over this surface exists.This temperature range is very much higher than in the base model and modification 1 models. This is because of the immediate exit of air molecules which reduces the fluid surface interaction. The overall heat content removed from the space is low due to less interaction time.

Fig 30: Pressure contour at inner space of canopy – Modification 2 model

The above Fig 30 shows the pressure distribution inside the DG canopy space at modification 2 model. From the figure we can say that fluid pressure inside the space doesn’t show any appreciable difference when compared to modification 1 model.

CONCLUSION

Thus the different models are analyzed computationally and the results are interpreted carefully. The flow rate is kept constant but the positions and configuration of louvers are varied. The temperature values on the engine surface for all the different models are tabulated below.

Table 5: Results

Thus the model is which both louvers are combined together called “modification 1” has better directionality which is very vivid from the surface temperature; on the engine. Thus modification is found to be optimal compare all other models.