FULL HYDRO case set up PFI

Objective:-

To simulate the full hydro setup of a port fuel injected engine which uses isooctane as the fuel and based on the results from the simulation calculate the following parametrs

• Compression ratio
• Combustion efficiency
• power and Torque
• Significance of CA10, CA50 and CA90

Geometry and Boundry Flagging:- The geometry and boundry flagging aspects have been explained in details on the previous project i,e no hydro case

Case setup:- A crank angle based IC engine application was choosen to perform the simulation. The engine dimensions and rpm are choosen as given inputs.

The fuel choosen was Iso Octane(iC8H18) and the sprey parcel properties were taken from the data file of Iso Octane.

The trasport parameters were set as default values. Reaction mechanism was set based on the data file Iso Octane combustion.

A full hydrodynamic solver is used in this case and the simulation was run for-520 crank angle to 120 CAD with the initial time step being 1e-07s and final time step being 0.0001s.

The solver parameters were taken as default values.

Boundry condition:

The boundry were set as per given inputs.

Initial condition:-

The intial condition can be assigned to the setup based on four regions

• Cylinder
• Intake Port - 1
• Intake Port - 2
• Exhaust Port

Events:

The intake valve and exhaust valve opening and closing are controlled by an event. The valve lifts are provided as the input to control the opening and closing.

Spray modeling:

A Frossling spray model was used in this simulation to model the fuel spray. The parameters involved in the spray model was set to be the default values.A kelvin-Helmholtz injector model was used to model fuel injection. The total mass injected was set as 3e-5kg and the rate shape vaue as set as below

Combustion Model:-A SAGE model was used to model the combustion process in this simulation. The start time was specified as -17 CAD end time as 130 CAD. The SAGE model was assumed to be region independent for simplicity.

An RNG k-epsilon turbulence model with default paramters. The spark was modelled using a source model. The start of spark ignition is set as -15CAD and the duration is 10 degree. The spark radius is set as 0.0005m. The spark temp is set as 50000K.

Results and Discussion:

1. What is the compression ratio of this engine?

A compression ratio is the ratio where we are compressing the maximum cylinder volume into the minimum cylinder volume. Thats the volume of the cylinder when apiston is all the way down compared to all the way up to the top. Its written out and said as a ratio.

Copmression ratio = Maximum volume/Minimum volume

= 5.7418*10^(-4)/5.7*10(^-5)

= 9.97

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

The three dimensional transient heat conduction eqn is given by

The eqn is solved on the solid side and requires boundary condition provided in the solid fluid interface. Only this eqn is helpful for solving eqn near the wall boundry.

When we take our simulation in converge cfd we never setup stream IDs for the solid boundry and we only made use of Navier-Stokes eqn, turbulence and scalar transportation eqn which all govern fluid in general. Therefore , making use of energy eqn for solving the solid boundry i,e The wall was not required in the first place.

A spark is responsible for the ignition of fuel and air constitutes when compressed inside the cylinder which emits a flame that spreads throught the cylinder which emits a flame that spreads throught the cylinder. After a few time steps you can see the flame vanishing completely as soon as it makes contct with the liner which makes sense for heat to be transfered to the solid liner i,e wall . Also inside the cylinder because of turbulence some parameters are affected. These two reasons are sighted for making use of wall heat trasfer models to predict wall temperature.

3. Calculate the combustion efficiency of this engine

The heat released by our engine is given from the plot as shown in fig below

The total amount of energy from the combustion process alone is found out from the graph given below as 1241.16 J

Calorific value for gasoline = 45MJ/kg

Fuel mass per cycle = 3*10^(-5)kg

Total heat content effiency is given as ,

The combustion efficiency for engine is 92%

4. use the engine performance calculator, to determine the power and torque for this engine.

The engine performance calculator has obtained the values of all essential parametrs as shown in the image below

Power = work done/Time taken

= 468.646/0.01333

= 35.16 KW

The value for power is given by the relation

p = (2*`pi`*N*T)/60

T = P*60/2*`pi`*N

= 111.97 N-m

5. What is the significance of ca10, ca50 and ca90?

CA stands for crank angle and values 10 50 and 90 represents the various persentage for which combustion happens at various crank angles so,

1. 10 % combustion happens at 6.8 deg of CA
2. 50 % combustion happens at 18.4 deg of CA
3. 90 % combustion happens at 31.7 deg of CA

Conclusion:

The temperature and velocities of parcel in our simulation are obtained. Following videos described resulting in a full hydro simulatio