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

Aim: To simulate the port fuel injection engine in converge CFD by using hydro simulation and calculate the important parameters like Compression ratio, Power, Combustion efficiency, and Torque.

Theory:

Fuel injection is the introduction of fuel in an IC engine, most commonly automotive engines, through an injector. Fuel injection replaced carburetors from the 1980s onward. The main difference between carburetion and fuel injection is that fuel injection atomizes the fuel through a small nozzle under high pressure, while a carburetor relies on suction created by intake air accelerated through a Venturi tube to draw the fuel into the airstream.

Historically, the most widely produced internal combustion engines were of the Port Fuel Injected (PFI) design, where the fuel is sprayed into the intake ports to mix with incoming air. In fact, many new vehicles are still manufactured with this engine design. The fuel injectors in PFI configurations are typically mounted in the intake manifold and the air/fuel mixture is pulled into the cylinder head as the intake valve opens.

Case setup:

• The geometry and case setup almost the same as the previous challenge(spark fuel engine with no hydro). Here hydro is using in the PFI engine. Select parcel simulation, and species in materials.

• Parcel simulation is required to simulate the fuel spray droplets as parcels which are required to simulate the combustion reaction. Click on predefined liquids and select IC8H18(IsoOctane) as fuel because its properties are similar to gasoline fuel. In species > click on parcels > and select IC8H18.
• In Run parameters select full hydrodynamic in simulation mode.

Physical models:

Select Spray, Combustion, and Source/Sink modeling.

Spray modeling is used to configure nozzles, injectors, boundary injections, injection rate-shapes, set various spray-related constants, and choose from several injection and drop models. Spray modeling is very important to obtain accurate solutions for predictive combustion simulations. Converge has a variety of spray modeling options. Here, we are using the O'rouke model for the turbulent dispersion of spray parcels

Under Injections add 1 injector and click on edit.

Select the Kelvin-Helmholtz and Rayleigh-Taylor models.

Add 4 nozzles in the nozzle as shown in the fig below.

Combustion modeling:

Source/Sink modeling:

Adaptive mesh refinement:

Fixed embedding:

Export all files and run the simulation.

Simulation results:

Animation link: https://youtu.be/VnFxxYtHayc

1. Compression ratio:

It is the ratio between the volume of the cylinder and combustion chamber in an internal combustion engine at their maximum and minimum values.

Maximum velocity = 0.000576; Minimum velocity = 0.0000576

Compression ratio:- Max vel/Min vel

= 57.6*10e-5/5.76*10e-5

= 10.061

2. Combustion efficiency:

The combustion efficiency ( η_c ) is defined as the ratio between the energy released by the burnt fuel and the theoretical energy content of the fuel mass during one complete engine cycle.

`eta_c` = Total heat released / Total heat added.

Total heat released = 1241.07J

Total heat added = amount of fuel added per cycle * calorific value of fuel

Amount of fuel = 3*10^-5 kg per cycle

Calorific value of fuel = 45.8 MJ/Kg

Total heat added = 3*10^-5*45.8*10^6 = 1374J

`eta_c = 1241.07/1374*100 = 90.325%`

3. Power and Torque of the engine:

Engine performance calculator tool automatically calculates engine work and other relevant engine design parameters for 360 degrees or 720-degree range from CONVERGE output and the engine parameters.

Power is work per unit time. From engine performance calculator

work = 468.645 Nm(i.e. 240.2 degrees)

RPM = 3000

Time per degree = `60/(360*RPM) = 60/(360*3000) = 5.5*10^-5 sec/(deg)`

Time per 240.2 degree = Time per degree*240.2

= 5.5*10^-5 * 240.2

= 0.013211 sec/cycle

So, Power(P) = work/time = 468.645/0.013211

P = 35.4738 KW

Torque(T) is a twisting force that speaks to the engine's rotational force and measures how much of that twisting force is available when an engine exerts itself.

As we know, power `p = (2piNT)/60`

Torque `T = (P*60)/(2*pi*N)`

T = `(60*35473.84)/(2*pi*3000) = 111.44 Nm`

4. Why do we need a wall heat transfer model:

In order to perform a good prediction of engine heat transfer and wall temperature, models are required to accomplish heat transfer from hot gases to engine parts, heat transfer inside each engine part, and also heat transfer to coolant and lubricating oil. We can't predict wall heat transfer because we are simulating only the fluid flow and heat transfer only inside the flow domain and we are not simulating the heat conduction inside the solid part.

5. Significance of ca10, ca50, and ca90:

The Crank angle(ca) CA10, CA50, and ca90 are defined as the crank angle (deg) position at which the cumulative heat release reaches 10%, 50%, and 90% respectively.

The calculated value of the PFI engine for CA10 is 6.837 degrees, for CA50 is 18.46 degrees, and for CA90 is 31.701 degrees.

Conclusion:

• Port fuel injection IC engine with hydro simulation was setup and successfully run in converge.
• Various plots and calculations were made and the results of the simulation were studied.