CAT3410 Engine Simulation
Objective:
To perform combustion simulation of CAT3410 engine chamber block with two bowl profile: 1. Open W Piston. 2. Omega Piston.
Introduction:
The diesel engine analysis performed is a closed cycle analysis, as the valves of the engine are not present. Such analysis are done for computational efficiency. The main area of interest in engine combustion is the combustion chamber, as a result, the closed cycle analysis focuses only on the chamber, asssuming the intake and exhaust valves to be shut.
Also, the injector of the diesel engine is mounted at the centre of the chamber with n number of nozzles. This allows us to analyze only a sector of the entire chamber and still get the same results as for the entire chamber analysis. It helps reduce computational time.
Following is the image of 360 combustion chamber.
Depending on the number of nozzles present, the chamber can be reduced to a sector size, which can be used for combustion analysis.
Now to create sector and the required bowl profile, we start with extracting the profile using the tool 'Make Engine Sector Surface'. Once we extract the head, bowl, forward and reverse profile, the 'Make Engine Sector Surface' tool is used again to input the engine dimensions and the required bowl profile.
Open W Piston
Omega Piston
Case Setup:
Ic Engine (Crank based) simultion is used for solving the closed cycle analysis of diesel engine. Following image shows the dimension and basic geometry requirements of the chamber.
With the help of mech.dat and therm.dat, all the species involved in the reaction along with their thermal properties are imported into the simulation.
Follwing figure provides the runtime for the simultion
Since this is a closed cycle analysis, there is only one region present i.e Cylinder. The initial pressure, temperature and the species to be present in the chamber are given in the following figure.
Following Models were used during the simulation:
1. Spray Model:
For Liquid spray Converge uses Lagrangian solver to model discrete parcels and the Eulerian solver to model continuous fluid domain.
Heat, momentum and mass transfer occur between the discrete and the continuous phases with the help of souce term in the transport equation.
Converge introduces parcels into the domain at the injector. Each parcel represents identical drops (radius, velocity, temperature) and as a result converge solves for per-parcel basis rather than per-drop basis. These parcels statiscally represent entire spray field.
Also, spray modeling uses subgrid models to model various physics of fuel spray after it interacts with the air in the chamber.
The interaction of fuel parcels with the air results in breakup of the parcels and leads to various physical interaction provided in the above diagram. Sub grid model takes care of these interactions so as to provide accurate results closely matching the experimental data.
- Injector:
2. Combustion Modeling:
Converge contains detailed chemistry solver and simplified combustion model to provide the result for combustion. The detailed chemistry solver provides accurate way to compute combustion which can be easily compared with experimental data. Due to this the computational time taken by detailed chemistry is more as compared to simplified combustion model.
- Sage Solver:
It uses the local condition to calculate reaction rates based on principles of chemical kinetics. Each mesh cell present inside the engine has a unique value for various thermo-physical properties, which the SAGE solver uses to calculate the reaction rates. The solver uses Arrhenius rate law equation to solve the rate of change of species concentration.
3. Turbulence Modeling:
RNG K-e model is used for turbulence modeling.
Grid Control:
The base grod size used for the solution is 0.0014m.
Adaptive mesh refinement, as the name suggests, adapts according to the current value of the prescribed variables. The mesh refines itself if the gradient of provided variable changes beyond the prescribed limit.
Fixed embedding grid control technique is used to modify the mesh size in critical areas so as to get an accurate result. All the critical areas inside the chamber are provided with fixed embedding (eg. Piston, Nozzle).
Plots:
1. Mean Temperature:
2. Integrated Heat Release Rate:
3. Nox:
Diesel engines use highly compressed hot air to ignite the fuel. Air, mainly composed of oxygen and nitrogen, is initially drawn into the combustion chamber. Then, it is compressed, and the fuel is injected directly into this compressed air at about the top of the compression stroke in the combustion chamber. The fuel is burned, and the heat is released. Normally in this process, the nitrogen in the air does not react with oxygen in the combustion chamber and it is emitted identically out of the engine. However, high temperatures above 1,600 °C in the cylinders cause the nitrogen to react with oxygen and generate NOx emissions. So, it will not be wrong to say that the major influences of the formation of NOx are the temperature and concentration of oxygen in the combustion.
4.Soot:
Diesel particulate matters are typically spheres about 15–40 nm in diameter, and approximately more than 90 % of PM is smaller than 1 μm in diameter. The formation process of PM emissions is dependant on many factors as the combustion and expansion process, fuel quality (sulfur and ash content), lubrication oil quality, and consumption, combustion temperature, exhaust gas cooling.
Particulate matter emissions from diesel engines are considerably higher (six to ten times) than from gasoline engines. Diesel particle emissions can be divided into three main components: soot, soluble organic fraction (SOF), and inorganic fraction (IF). More than 50 % of the total PM emissions are soot that is seen as black smoke. SOF consists of heavy hydrocarbons adsorbed or condensed on the soot.
5. UHC:
Hydrocarbon emissions are composed of unburned fuels as a result of insufficient temperature which occurs near the cylinder wall. At this point, the air–fuel mixture temperature is significantly less than the center of the cylinder.
Hydrocarbons consist of thousands of species, such as alkanes, alkenes, and aromatics. They are normally stated in terms of equivalent CH4 content. Diesel engines normally emit low levels of hydrocarbons. Diesel hydrocarbon emissions occur principally at light loads. The major source of light-load hydrocarbon emissions is lean air–fuel mixing. In lean mixtures, flame speeds may be too low for combustion to be completed during the power stroke, or combustion may not occur, and these conditions cause high hydrocarbon emissions.
Timing Map:
It provides an overview of the entire combustion process.
Calculation:
1. Open W Piston:
Power= Work done/ Time.
RPM= 1600
Time in sec for 270.215 deg= 0.02814 sec.
Therefore, Power= 3390.33/0.02814 = 120.480 KW.
IMEP= 1.38898e+06
2. Omega Piston:
Power= Work done/ Time.
RPM= 1600
Time in sec for 270.215 deg= 0.02814 sec.
Therefore, Power= 4381.05/0.02814 = 155.687 KW.
IMEP= 1.79487e+06