Week 10: Project 1 - FULL HYDRO case set up (PFI)

AIM: To simulate the Full-hydro case setup of PFI.

1. What is the compression ratio of the engine?
2. Calculate the Combustion efficiency of the Engine?
3. Determine Power and torque of engine by using an engine performance calculator?
4. What is the significance of CA10, CA50, and CA90?
5. Why do we need a wall heat transfer model? Why can't we predict wall temperature from CFD simulation?

The geometry was imported in Converge using the STL file given and the surface preparation and boundary flagging was done. Once the No-Hydro simulation ran smoothly the full hydro case setup was done.

CASE SETUP: A crank angle-based IC engine application was chosen to perform the simulation. The engine dimensions (bore, stroke and connecting rod length) was provided as inputs. The engine speed was chosen to be 3000 RPM

IC8H18 (Iso-Octane)- It has physical properties that are closer to the physical properties of GASOLINE fuel. That is the reason we chose Parcel species as "IC8H18".
Since we have selected IC8H18 as parcel species we will require it's thermodynamic data to involve more species in reaction mechanism contained in the file named "therm.dat"

SIMULATION PARAMETERS:

We are going to perform full hydrodynamic simulation and simulation time parameter is set as:

BOUNDARY CONDITION:

The following boundary conditions were applied as consolidated below

REGIONS AND INITIALIZATION:

Complete PFI geometry has been bifurcated into volumetric regions that contain all boundaries that we have flagged.

Initialisation of all regions are done with following boundary conditions:

EVENTS:

Events dialog box is used to create custom CLOSE (activate disconnect triangles), OPEN (deactivate disconnect triangles), or VALVE events between two or more regions at defined intervals.

Because CONVERGE cannot properly execute a simulation if surface triangles from two boundaries intersect, using the Events section is the only way to allow or block flow between two regions

PHYSICAL MODELS:

Following models, we have incorporated in this case setup in order to capture flow physics accurately inside the IC engine.

1. Spray Modelling- To define injectors, nozzles, and other spray-related parameters.

2. Combustion Modelling- To define how combustion takes place inside chamber.

3. Source/Sink Modelling- To define sources of energy (spark in case of PFI engine)

4. Turbulence Modelling- To define the parameters and constants associated with the selected turbulence model.

RNG k-epsilon turbulence model with default parameters was used for turbulence modelling

GRID CONTROL:

We will be working on 4mm base grid.

Fixed embedding is done at particular locations to capture accurate data.

AMR: Both velocity and temperature-based grid refinement are applied on a cylinder and intake port(near the combustion chamber) region

Velocity Based AMR:

Temperature Based AMR:

TIMING MAP OF ENGINE:

What is the compression ratio of the engine?

The compression ratio is the ratio of the volume of the cylinder and the combustion chamber when the piston is at the bottom, and the volume of the combustion chamber when the piston is at the top

Where:

Vt">Vmax= + ,Maximum cylinder Volume. Included both swept volume and clearance volume.

= displacement volume. This is volume swept by piston from BDC to TDC

= clearance volume. This is the volume of the space in the cylinder left at the end of the compression stroke.

CR = Vmax ÷ Vc

CR = 0.000574217/0.00005703

CR =10.069

Why do we need a wall heat transfer model? Why can't we predict wall temperature from CFD simulation?

Heat transfer in IC engines is a very vital phenomena and it has a direct effect on the engine performance. In an SI engine a spark ignites the compressed air fuel mixture and a flame kernel propagates throughout the system. This flame kernel gets quenched near the wall and thus heat transfer occurs between the flame and the wall. Inside the cylinder due to turbulence, swirling and tumbling, the accuracy of measurement of critical parameters get affected.

Hence due to the two reasons listed above a wall heat transfer model is used rather than CFD to predict wall temperature

What is the significance of CA10, CA50, and CA90?

CA10, CA50 and CA90 represent the crank angle during various stages of combustion. Ca10 represents the stage where 10% of the combustion is completed. Similarly, ca50 and ca90 represent the 50% and 90% stages. Generally, the duration/difference between the ca10 and ca90 stages of combustion is taken as the combustion duration where ca10 is assumed to be start of combustion and ca90 the end. Ca50 is assumed to be the stage where the energy release in combustion is maximum as it is nearly during the midway stage of the combustion process

Combustion efficiency of this engine

Combustion efficiency is defined as the ratio between the energy released by the burnt fuel and the theoretical energy content of the fuel mass during on complete engine cycle

The heat release rate is 1241.1646 J

The amount of fuel supplied 3×10−5kgcyl3×10-5kgcyl

Calorfic value of the fuel 45 MJ/k

combustion efficiency= Total heat released/ mass of fuel ××Calorific value of fuel

Combustion efficiency comes out to be 91.94%.

Determine Power and torque of engine by using an engine performance calculator?

Power = Work/Time

Work done = 1241.164 J

RPM = 3000, RPS = 3000/60 = 50, DPS = 50*360 =18000

Therefore, Time per degree = 1/DPS = 1/18000 = 5.55e-5 sec/degree

Time for moving 240.199 degree = 240.199 * 5.55e-5 = 0.013331 seconds

Power = 1241.15/0.013331 = 35.15 kW

Power = 2πNT/60

35.15 = (2*3.14*T*3000)/60

T = (35.15 * 60)/(2*3.14*3000)

T = 111.95 Nm

Therefore, Torque is 111.95 Nm

Following is link for full hydro animation: