Full Hydro case setup of Port fuel injection engine
Full hydro case setup and simulation of the PFI engine
OBJECTIVE: To Analyze the behaviour of the combustion and its effect on formation of some undesirable emissions inside the cylinder.
Simulation results of the no-hydro simulation is tested that the mesh generation is good. So it is enough to run the full-hydro simulation. In order to run the Full-hydro simulation we have select some more options.
NOTE: All pictures are the actual representations of the case setup windows.
Full Hydro simulation case setup
Application:
In this option, we have to select IC engine to input the details of the engine.
Materials
In no hydro simulation we have given all the inputs except the parcel simulation. In this option we have to give input liquid type as IC8H18 fuel type which is a representation of the gasoline fuel.
Since we have created the parcel file we have to define the parcel again in the species. This tells what are the liquids that are available in the cylinder and what is involving in the combustion process.
Simulation parameters
As we want full combustion process to take place, we are going for the Full hydro dynamic mode.
Physical models
In this section we will describe the phiyical properties of the flows that are involved in the combustion process.
Spray modelling:- it is required to specify the how the spray of the fuel has to propagates in the cylinder and what type of fuel is going to be sprayed. We use models for the simulation of the fuel to get near accurate results and computation time consumption will be less than direct numerical simulation. We spray fuel as lagrangian parcels. we use IC8H18 as the fuel.
This picture tells how the fuel drops behave after they are sprayed.
Once the fuel is sprayed they travel towards the walls around them and interact. this interaction will lead to different phenomenons. How ever to make things simple we can specify the way of interaction.
Injector define the spray. There design and placement can influence the performance of the engine. Here we are using one injector and 4 nozzles. We have to edit the injector to define the timings and other properties.
Rate and type of the fuel is defined here
Converge provides some models that tells injectors how the injection to be performed.
Timing of the injections are specified in this window.
Injector needs nozzels to spray the fuel. There location and shape can influence lot of parameters like efficiency and emissions. In this window we decribe the all about nozzles and configure them.
Combustion modeling
In this window we specify about the models that are involved for combustion and emissions. Turbulence model is set to default.
In spark ignition engines, we need a source to propagate the fire inside the cylinder. Source is configured in this window. we have two sources here.
Source location, shape and size can be determined here.
GRID CONTROL
grid control gives us the fisibilty to choose the size of the mesh and meshing will be done auomatically by the converge itself.
Adaptive mesh refinement is an advanced tool that is very efficient as well as less time consuming. we can give a corse mesh for entire domain and make mesh finer as the dependent parameters vary. Here we are using both velocity and temperature as the parameters that are going to influence the mesh refinement.
In the below picture we can see the fuel injectors spraying fuel in the inlet port.
Results and plots
Liquid spray drop graph tells number of drops that are created during the spray of the fuel into the combustion chamber. At the end of the graph we can see how many fuel drops are left over in in the port. By know the left over fuel we can tell how much fuel is used in the combustion process.
This graph tells us how much of fuel is injected into the combustion chamber with respect to crank angle. even though fuel injection started earlier, Fuel has entered the combustion chamber only after 100 degrees later the injection has started.
Pressure plots define how much pressure is generated during the entire combustion process. The min and max pressure can be used to derive the power output and efficiency of the engine. In the power stroke, pressure starts build up at 0 degree crank angle and started to build untill 50 degree angle and then the it slided down to the normal pressure, by this we can say that the combustion started taking place from 0 degree crank angle. We have taken only combustion chamber profiles in order get the accurate results.
Combustion process involves temperature that varies along with the crank angle. once the operational temperature reached, engine remains at a minimum temperature of 500 degrees however during the power stoke the temperature increases because of the reaction of the fuel, air and ignition.
This graph represents the volume of the cylinder. It can be used for calculation of volumetic efficiency.
This P-V graph represents the otto cycle. We can see the discontinuty at the begining and ending line which represents that no exchange takes place and system returns to the original position.
Integrated heat generation graph tells how much of heat energy is released in the combustion process and this data can be used to determine the combustion efficiency of the engine. difference between the energy released from the combustion process and the energy content of the fuel tells how effectively combustion has taken place.
Heat release rate tells how much heat energy is generated with respect to crank angle. we can see that the highest heat release at 20 degree angle where the combustion process has begun and highest amount of fuel is burned at that point.
Emissions play an important role in the efficiency of the engine. even if the performance is great some times emissions will also be great which will be against the purpose of better engines. Below we will be discussing about the graphs that tells us whether the engine good dealing with the emissions.
Soot is a black substance formed due to the combustion. this generally comes out from exhaust valves but some times stick to the walls of the cylinder, Head and piston. accumulation of the soot in the cylinder will effect the performance of the engine. As we have ran the simulation only for 1 cycle we don\'t have enough data to gather how much soot is formed.
Nox is the abbrevation of Nitrogen mono oxide which is a harmful gas. Nox formation is a result chemical processes that take place because of high temperatures that are generated during the combustion process. The less Nox generation the better the emissions are.
This graph tells the amount of the hydro carbons that are involved in the combustion process. We can any hydro carbons are left with out getting combusted which results in incomplete combustion.
Above two slides will help in understanding the formation of the carbon monoxide and dioxide. A fraction of the fuel is converted into the CO, which means this is a balanced combustion reaction. if the CO is high then that means it is fuel rich mixture.
1. What is the compression ratio of this engine?
it is the ratio of the maximum volume (when the piston is at the bottom dead center)to the minimum volume(when the piston is at the top dead cemter) of the cylinder.
Compression ratio = max volume/min volume =0.0005742/0.00005703 = 10.06:1
2. Why do we need a wall heat transfer model? Why can\'t we predict the wall temperature from the CFD simulation?
In order to reduce wall heat losses, it is important to understand the mechanism of heat transfer at the walls. This mainly comprises two parts – convective and radiative.This is being done by implementing wall models for flow and heat transfer into a URANS (unsteady Reynolds Averaged Navier Stokes) based solver. Models do some assumptions based on the experimental data and the DNS data and correct the constants accordingly.
Temperature in the combustion chamber alone can be predicted easily through the energy equations. However when the heat transfer takes places from cylinder chamber to the wall it becomes hard for us to predict as the flow of gases goes through swirling, rotating and high turbulent behaviour which results in high gradients of temperature.
Inorder to keep the engine in the operational conditions the walls of the engine is to be maintained at certain temperature. we pump coolent through the walls to maintain the temperature which complicates the things further.
3. Calculate the combustion efficiency of this engine
Combustion efficiency = total heat released/ total heat added
total heat added = the amount of the fuel sprayed per cycle times its calorific value. This tells how much energy is fed into the cyclinder.
Amoun of fuel added = 3*10^-5 kg/cycle
Calorific value of the fuel = 45 MJ/kg
Total heat added = (3*10^-5)*44.8 = 1344 J
From the integrated heat release graph we can know the total heat released per cycle = 1241 J
Combustion efficiency = (1241/1344) * 100 = 92.33%.
4. use the engine performance calculator, to determine the power and torque for this engine.
power is defined as the workdone for unit time.
time = (60*240.199)/360*3000 = 0.01334438888 sec/deg.
Work done=468.646 Nm
power=468.646 /0.01334438888
=35.119KW.
torque= (p*60)/2*pi*1600 = (35.119*10^3*60)/2*pi*3000
=111.78NM
5. What is the significance of ca10, ca50 and ca90?
ca10, ca50 and ca90 represents the crank angle at which the 10, 50 and 90% of the fuel is burnt. How much time is taken for the evoparation and combustion of fuel is understood by this. if the combustion process is very fast and takes very less crank angles it may results in the formation of high emissions. ca10 indicates ignition started, ca50 indicated Fuel-air mixture combustion ended and at the ca90 propagating flame burns unburnt fuel. Propagation of the flame wave can be seen in the above video links.