Performing a Port fuel Injection simulation to capture engine performance

Aim

Run PFI simulation with the Engine parameters mentioned above. Answer the question given below

1)The compression ratio of this engine

2)Do we need a wall heat transfer model to predict the wall temperature

3)Combustion efficiency of this engine

4)Determine the power and torque for this engine

5)Significance of ca10, ca50, and ca90

Performing Transient Simulation. Steps involved in running Simulation

1. Introduction
2. Geometry Creation
3. Boundary flagging
4. Diagnosing the geometry
5. Case Setup
6. Solve
7. Post-processing the results

Step 1

Introduction

Spray Modelling

For Gaseous sprays, converge uses the eulerian solver. Set the species mass fraction and mass flow rate at the inflow boundary

For liquid sprays, converge uses the lagrangian solvers to model discrete parcels and the eulerian solver to model the continuous fluid domain. Heat, momentum and mass transfer occur between the discrete and continuous phases via source terms in the transport equations

Parcels

Converge introduce parcels (collection of drops) into the domain at the injector. Each parcel represents a group of identical drops(i.e. same radius, velocity, temperature, etc). Converge solves for radius, velocity, etc on a per parcel basis rather than a per-drop basis(because the drops in a parcel are identical

The parcels statistically represent the entire spray field

• Parcels undergo several physical processes
• Primary breakup
• Secondary Break up
• Drop Drag
• Collision and Coalescence
• Turbulent dispersion
• Evaporation

Parcel Distribution

For solid cone sprays, converge assume the injection is conical.While setting up spray modeling we need to choose one of the parcel distribution mentioned below

SGM Sub-Grid Modeling

Converge Uses sub-grid models for the spray processes that occur on length scales that are too small to be resolved

Combustion Modeling

Combustion facilitates te energy transfer in the engine. Converge contains a detailed chemistry solver and simplified combustion chamber

SAGE detailed chemistry solver

• Most predicted an accurate way to model combustion
• Accurate model ignition and laminar flame propagation

Simplified Combustion Models

• Generally less computationally expensive and predictive than sage
• May provide acceptable results for specific applications

SAGE

The SAGE detailed chemistry solver uses local conditions to calculate reaction rates based on the principles of chemical kinetics. In our study, we have 42 species and 168 reactions involved in combustion chemistry.

Spark Ignition Engine

Step 2

Geomentry

Import the geometry file into Converge CFD

Step 3

Boundary flagging

Step 4

Diagnosing the geometry

We will just run the diagnosis for a set of important problems which are going to affect the solution

After running the diagnosis we see that no errors are present let us proceed to the case setup

Step 5

Case Setup

Applications

Imported Engine Design parameters need to be entered

Materials

In this section, we need to import a mech and thermo file so that the properties of all elements are available. So enter the as per mentioned in the below table

Simulation Parameters

we are running transient hydro simulation and simulation time parameters are entered as mentioned below and rest parameters are set to default

Boundary Conditions

Here we have total 16 boundary condition as specified below

The below table is Mass Fraction calculation for the gaseous present in cylinder and exhaust

Initial Conditions

4 regions got created and their data are mentioned below. Events are created ad shown below

Physical Models

Spray Modelling

Selection in Spray modeling is done based on the data mentioned below

Combustion Modelling

Here we choose the SAGE model to run combustion rest of the parameters are set as shown below

Model-SAGE

Turbulent Model-RANS RNG k-epsilon Model

Source/sink Modelling

In order to stimulate spark, there is a thing called the source and sink. Here energy is introduced and equations for continuity will be solving with external energy. The spark energy required for the best Maximum brake torque is achieved when the energy value of 50 mJ and around 0.5 degree of crank angle but this is a very generic thing it has depending on a lot of factors i.e. why in order to determine that lot of experiment to determine the time. For our case, we consider 40 MJ of energy over the period as shown below.

Grid Control

Base Grid

Adaptive mesh refinement

Fixed Embedding

Other Embeddings for Spark and Injection

output/Post-processing

The time interval for writing 3D output data file:- 1 deg.

The time interval for writing text output:- 0.0001 deg.

The time interval for writing restarting output:- 10 deg

Timing Map

We can have a clear understanding of the overview of the simulation by looking into timing Map

After Case step, the ICE domain looks like below

Step 6

Solve

Then we need to export the input files to a folder to start running a simulation.then by using Cygwin we are directing to the input file and simulation is stared by using an executable file and simulation ran by using two processors. After successfully running the simulation we can post-process the results and check the general outcomes whether simulation ran properly and are they making any sense.

Step 7

Results:-

Compression Ratio

In a combustion engine, the static compression ratio is calculated based on the relative volumes of the combustion chamber and the cylinder. It is a fundamental specification for combustion engines. The dynamic compression ratio is a more advanced calculation which also takes into account gasses entering and exiting the cylinder during the compression phase. Most engines used a fixed compression ratio, however, a variable compression ratio engine is able to adjust the compression ratio while the engine is in operation.

Gasoline (petrol) engines: Compression ratios are typically between 8∶1 and 12∶1

Diesel engines: Compression ratios are often between 14∶1 and 23∶1 for direct injection diesel engines, and between 18∶1 and 23∶1 for indirect injection diesel engines.

Other fuels: Kerosene engines typically use a compression ratio of 6.5 or lower for the fuels with octane rating between 55 and 70.

1)The compression ratio of this engine

As we took Iso octane as the fuel and the Compression ratio lies under 8:1 to 12:1 CR's

2)Do we need a wall heat transfer model to predict the wall temperature

• Heat transfer is one of a number of indispensable issues in studying of internal combustion engines, due to its influence on decisive parameters of operation such as temperature and pressure inside the cylinder. It is safe to say that analyzing and modeling of the engine heat transfer are among the most complex problems for engineers.
• There are three heat transfer mechanisms: conduction, convection, and radiation
• Thus, the magnitude of engine heat transfer is strongly dependent on engine efficiency. Heat flux results were predicted by solving an energy equation without using a heat transfer coefficient, while the core region was considered a global region with uniform properties without spatial distinction.
• However, in-cylinder core regions for the internal combustion engine cannot be considered globally since there are local changes in the core regions due to turbulence, swirling, and tumbling. Also, in order to obtain an accurate value of heat flux, the multi-dimensional model for core regions and one-dimensional heat transfer near walls are necessary.
• In these multi-dimensional models, conservation of mass, momentum, and energy was directly solved in the core region, whereas the wall models were generally used within the wall layers. Since the mechanism of wall layers is similar to the physics in the boundary layers, the predicted heat fluxes were solved by using thermal boundary layer assumptions.
• So unless we take wall heat transfer models we cannot able to predict wall temperature

3)Combustion efficiency of this engine

Coming to the graph the IHR curve rises after -5 deg because that is when combustion starts taking place and the curve becomes straight when the temperature no longer increases

The heat Rate value is extracted from thermo_region0

4)Determine the power and torque for this engine

Power

• engine power depends on both torque and speed
• power can be increased by increasing the torque or the engine speed
• high power is important for high vehicle speeds, the higher the maximum power the higher the maximum speed of the vehicle
• engine power distribution at full load, through the engine speed range, affects the acceleration capability of the vehicle at high speeds
• for best acceleration performance, a vehicle should be operated in the powerband, between maximum engine torque and power

Torque

• torque is a component of power
• torque can be increased by increasing the mean effective pressure of the engine or by lowering the torque losses (friction, pumping)
• having a lower maximum torque distributed on a range of engine speeds it's better from the traction point of view than having a higher maximum torque point
• low-end torque is very important for the launch capabilities of the vehicles
• high torque is beneficial in an off-road situation when the vehicle is operated at high road gradients but low speed

In order to know the performance of the engine, it is better to calculate power and torque

5)Significance of ca10, ca50, and ca90

• CA10 (deg)
  The crank angle at which the amount of burned fuel reaches 10 percent of its maximum value for the cycle. For ease of comparison, this value is relative to the start of the cycle (CA From) in the current row.
• CA50 (deg)
  The crank angle at which the amount of burned fuel reaches 50 percent of its maximum value for the cycle. For ease of comparison, this value is relative to the start of the cycle (CA From) in the current row.
• CA90 (deg)
  The crank angle at which the amount of burned fuel reaches 90 percent of its maximum value for the cycle. For ease of comparison, this value is relative to the start of the cycle (CA From) in the current row.

This helps us to know how fast the combustion taking place inside the engine let us take an example

CA10=6.48, CA50=18.5, CA90=31.7 from this data we can know at 6.48 degrees of crank 10% of combustion is completed, at 18.5 degrees 50% of combustion is completed and at 31.7 degrees almost all the combustion is completed. This helps us to compare two engines or and same engine while changing its design or their characteristics.

ICE Simulation Video Link

https://youtu.be/HklshFw4peE