Explore emission reduction technology for SI & CI Engine by use of GT-POWER

Tilte: Understand Aftertreatment Device of SI & CI Engine

Objective: 

            To list down diffrence between Petrol Vs Diesel Engine for following points

                                   1.The pollutants 

                                   2.Aftertreatment devices with catalyst materials

                                   3.The example files

                                   4.Strategies used for reducing tail pipe emissions

Pollutants

 

After treatment device with catalyst material

1. Two-Way converter

A 2-way (or oxidation) catalytic converter has two simultaneous tasks:

1. Oxidation of carbon monoxide to carbon dioxide

         CO+O2→2⋅CO22⋅CO+O2→2⋅CO2
2. Oxidation of hydrocarbons (unburnt and partially burned fuel) to carbon dioxide and water

CxH2x+[3x+12]O2→x⋅CO2+(x+1)⋅H2OCxH2x+[3x+12]O2→x⋅CO2+(x+1)⋅H2O (a combustion reaction)
This type of catalytic converter is widely used on diesel engines to reduce hydrocarbon and carbon monoxide emissions. Because of their inability to control oxides of nitrogen, they were superseded by three-way converters. Material uses Platinum or Palladium.

2. Thee-Way converter

The use of TWCs, in conjunction with an oxygen sensor-based, closed-loop fuel delivery system, allows for simultaneous conversion of the three criteria pollutants, HC, CO, and NOx, produced during the combustion of fuel in a spark-ignited engine. The active catalytic materials are present as a thin coating of precious metal (e.g., Pt, Pd, Rh),

                                              

Reduction of nitrogen oxides to nitrogen and oxygen: 2NOx → xO2 + N2

Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2

Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water: CxH2x+2 + [(3x+1)/2]O2 → xCO2 + (x+1)H2O

The use of TWCs, in conjunction with an oxygen sensor-based, closed-loop fuel delivery system, allows for simultaneous conversion of the three criteria pollutants, HC, CO, and NOx, produced during the combustion of fuel in a spark-ignited engine. The active catalytic materials are present as a thin coating of precious metal (e.g., Pt, Pd, Rh), and oxide-based inorganic promoters and support materials on the internal walls of the honeycomb substrate. The substrate typically provides a large number of parallel flow channels to allow for sufficient contacting area between the exhaust gas and the active catalytic materials without creating excess pressure losses. Although the primary components and function of a TWC has remained relatively constant during its more than twenty years of use on light-duty gasoline vehicles, each of the primary converter components (catalytic coating, substrate, mounting materials) has gone through a continuous evolution and redesign process in order to improve the overall performance of the converter while maintaining a competitive cost effectiveness of the complete assembly.

3. Diesel oxidation catalyst

In most applications, a diesel oxidation catalyst consists of a stainless steel canister that contains a honeycomb structure called a substrate or catalyst support. There are no moving parts, just large amounts of interior surface area. The interior surfaces are coated with catalytic metals such as platinum or palladium. It is called an oxidation catalyst because the device converts exhaust gas pollutants into harmless gases by means of chemical oxidation.

                              

In most applications, a diesel oxidation catalyst consists of a stainless steel canister that contains a honeycomb structure called a substrate or catalyst support. There are no moving parts, just large amounts of interior surface area. The interior surfaces are coated with catalytic metals such as platinum or palladium. It is called an oxidation catalyst because the device converts exhaust gas pollutants into harmless gases by means of chemical oxidation. In the case of diesel exhaust, the catalyst oxidizes CO, HCs, and the liquid hydrocarbons adsorbed on carbon particles. In the field of mobile source emission control, liquid hydrocarbons adsorbed on the carbon particles in engine exhaust are referred to as the soluble organic fraction (SOF) -- the soluble part of the particulate matter in the exhaust. Diesel oxidation catalysts are efficient at converting the soluble organic fraction of diesel particulate matter into carbon dioxide and water

4.Selective Catalyst Reduction

A Selective Catalytic Reduction (SCR) system uses a metallic or ceramic wash-coated catalyzed substrate, or a homogeneously extruded catalyst and a chemical reductant to convert nitrogen oxides to molecular nitrogen and oxygen in oxygen-rich exhaust streams like those encountered with diesel engines. In mobile source applications, an aqueous urea solution is usually the preferred reductant. Upon thermal decomposition in the exhaust, urea decomposes to ammonia which serves as the reductant. In some cases ammonia has been used as the reductant in mobile source retrofit applications. As exhaust and reductant pass over the SCR catalyst, chemical reactions occur that reduce NOx emissions to nitrogen and water. SCR catalysts can be combined with a particulate filter for combined reductions of both PM and NOx.

5.Diesel particulate filter (DPF)

Diesel particulate filters operate by trapping soot particles from the engine exhaust, preventing them from reaching the environment.  Unlike a catalytic converter which is designed to reduce gas-phase emissions flowing through the catalyst, the particulate filter is designed to trap and retain the solid particles until the particles can be oxidized or burned in the DPF itself, through a process called regeneration.

Ceramic materials are widely used for particulate filters, given their good thermal durability, with the most common ceramic materials being: cordierite, silicon carbide, and aluminum titanate.

Example

Three way catalytic converter

Selective catalytic Reduction

Gasoline particulate filter

Diesel particulate filter

Diesel oxidation catalyst

Strategies used for reducing tail pipe emissions

Nox Emission Reduction for Diesel Engine

The combustion chamber temperature can be decreased by

1. Decreasing compression ratio               2. Retarding spark timing
2. Decreasing charge temperature            4. Decreasing engine speed
3. Decreasing inlet charge pressure          6. Exhaust gas recirculation
4. Increasing humidity                             8. Water injection
5. Operating the engine with very lean or very rich air fuel ratio
6. Decreasing the coolant temperature
7. Decreasing the deposits                      12. Increasing S/V ratio

CO can be decreased for Petrol Engine

1. Use of Lean air fuel ratio
2. Adding oxygen in the exhaust
3. Increasing coolant temperature

HC emission can be decreased for petrol & Diesel engine

1. Decreasing the compression ratio           2. Retarding the spark
2. Increasing charge temperature              4. Increasing coolant temperature
3. Insulating exhaust manifold                   6. Increasing engine speed  
4. Lean mixture                                        8. Adding oxygen in the exhaust
5. Decreasing S/V ratio                             10. Increasing turbulence
6. Decreasing the deposits                         12. Increasing exhaust manifold volume
7. Increasing exhaust back pressure

PM emission can be decreased for  Diesel engine

1. Increasing turbulence
2. Homogenous mixture

List down one set of chemical reactions for TWC and SCR from example files 

SCR

 

Three way catalytic Reaction

$CO+0.5\cdot O2\to CO2$

$C3H6+4.5\cdot O2\to 3\cdot CO2+3\cdot H2O$

$C3H8+5\cdot O2\to 3\cdot CO2+4\cdot H2O$

$H2+0.5\cdot O2\to H2O$$CO+NO\to CO2+0.5\cdot N2$

$C3H6+9\cdot NO\to 3\cdot CO2+3\cdot H2O+4.5\cdot N2$

$H2+NO\to H2O+0.5\cdot N2$

$C3H6+3\cdot H2O\to 3\cdot CO+6\cdot H2$

$2\cdot Ce2O3+O2\to 4\cdot CeO2$

$Ce2O3+NO\to 2\cdot CeO2+0.5\cdot N2$

$CO+2\cdot CeO2\to Ce2O3+CO2$

$C3H6+12\cdot CeO2\to 6\cdot Ce2O3+3\cdot CO+3\cdot H2O$

$C3H8+14CeO2\to 7\cdot Ce2O3+3\cdot CO+4\cdot H2O$

$H2+2\cdot CeO2\to Ce2O3+H2O$

SCR 

SCR Reaction

$Z+NH3\to ZNH3$

$ZNH3\to Z+NH3$

$4\cdot ZNH3+3\cdot O2\to 2\cdot N2+6\cdot H2O+4\cdot Z$

$4\cdot ZNH3+4\cdot NO+O2\to 4\cdot N2+6\cdot H2O+4\cdot Z$

$NO+0.5\cdot O2\to NO2$

$ZNH3+2\cdot NO+2\cdot NO2\to 4\cdot N2+6\cdot H2O+4\cdot Z$

$8\cdot ZNH3+6\cdot NO2\to 7\cdot N2+12\cdot H2O+8\cdot Z$

Explore -Example-aftertreatment-DOC-sampara & Bisset 

DOC Model 

                         

 

Inlet 

              

The above template uses fro define the inlet boundry condition

                         

1. Mass flow Rate: We can define mass flow rate in kg/s with respect to Time .for Case 1 define the 0.02kg/sec & for case 2 define mass flow rateFTP i.e input data per sec 

2. Gas Temprature: for case 1 define , for 0sec 300k & for 2000 sec 650k. for case 2 input data given for temprature per sec

3.Composition specification: Mole fraction defined

4. Inlet composition : for Case 1 ConcentrationSteady & case2 cocentration FTP

Inlet cone

                

This template define flow volume 160000mm3 of pipe & initial state name

Initial state name

                   

This object define initial pressure, temprature & fluid properties in flow components

Temprature: Initial catalyst wall temprature is 300k for both case 1 & 2

Pressure: Initial pressure is 1 bar for both case 1 &2 

Composition : air composition 

                                     

        

Imposed wall temprature of catlyst is 300 k for case 1 &2

Boundry data for inlet & outlet of cone 

Non-code orifice

non code orifice helps to find out mass flow rate of adajcent volume & avoid the heat conduction between two components

Catalyst

1. Frontal area: its cross-sectional of the substrate & its 20000mm^2

2.Length : its length of substrate 160mm

3. Discretization length is 4mm for casse1 &2

4. Channel type is square we can choose other type also like circle, triangle

5.cell density of susbstrate is 400m2

6.substrate wall thickness 1.5e-5m

7. Washcoat thickness for layer 1&2 we can provide 

1. Material used for substrate is corderite .so, its all properties defined like density, thermal conductivity 

2. Material used for washcoat is Alumina .so, its all properties defined density, thermal conductivity 

            

              

        

DOC Reaction Template 

1.above template explain the species & reactions

2. There are three basis fr reaction 1. Area 2. Reactor volume 3. site (turnover number)

3. Concentration is specifies in mol/m3

4. Diffusion : This flag indicates whether the system is reaction/kinetically controlled or dependent on the mass transfer diffusion rate: on indicates that the diffusion will be solved, and that the reaction rate is assumed to be equal to the diffusion rate. Only the gas phase concentrations are integrated and the surface concentrations are related to the gas phase concentration through an algebraic equation

 

above template indicates the diffrnet harmful & non-harmful species & its diffrent properties. 

 

Except for the ODE/DAE Solver Selection attribute, the remaining attributes in this folder should typically all be set to "def" and you should not need to change any of these values unless there is a specific numerical problem.

ODE/DAE Solver Selection
Advanced Adaptive is a flow-through reactor solution method that uses an adaptive mesh to adjust to the demands of the moving reaction fronts. It is generally faster than the other solvers. Since this solver is more advanced, special modeling considerations are required, and the user should consult the Advanced Adaptive Solver section in the Aftertreatment Application Manual for more information. This is the recommended chemistry solver for flow-through catalyst models for speed.

Fixed Mesh is a flow-through reactor solution method introduced in V2019 that uses a user-specified fixed axial mesh. It is the most robust solver available, although it is generally slower than the Advanced Adaptive solver. In addition to the asymptotic solution, it is also supports a full numerical 1+1D pore diffusion solution, where the washcoat is discretized into multiple slab elements. This is the recommended chemistry solver for flow-through catalyst models for robustness

 
BDF solver is the recommended solver for wall-flow particulate filter models. It is may also be used for flow-through models in certain situations where both Advanced Adaptive and Fixed Mesh solvers are not supported. For example, Advanced Adaptive and Fixed Mesh solvers are currently supported only with the QS flow solver whereas BDF solvers can be used with the QS, Implicit, and Explicit solvers. BDF is also recommended for 2D/3D modeling.

 
RADAU indicates a 3-stage, 5 th order RADAU DAE solver will be used to solve the kinetics. This solver has high numerical robustness; however, there is a computational penalty when using this solver. For most problems it is more robust than BDF, but is slower than BDF. RADAU may be used for flow-through and wall-flow filter models.

 
Adaptive RK indicates "Adaptive Runge-Kutta" ODE method, which is more efficient than the BDF method, but is only suitable for non-stiff ODE systems. It is not suitable for large reaction mechanisms, and if the number of reactions is greater than 40, the solver will automatically switch to BDF, and use the default error tolerances for BDF. This solver is NOT recommended, and it will be phased out in the next version.

 
RK-BDF indicates a combination of both methods above, in which the code always starts with RK method and then switches to BDF when RK integration requires excessive subdivisions of the time step. The recommended procedure is to make certain BDF gives the desired results, then switch to RK-BDF and make sure the results remain the same, but run time is faster. This solver is NOT recommended.

 

Loading of Site Element

The site element loading in the washcoat in units of mass per unit total volume of the catalyst. An ' XYTable' reference object may be used to define the loading Y vs. normalized length X.

If the attribute Active Site Density is defined then this attribute must be set to "ign".

Atomic Weight (g/mol)

Standard atomic weight of the site species in units g/mol. It will be used to calculate the Active Site Density in conjunction with the Loading of Site Element and Dispersion Factor when those attributes are defined. This attribute may be, but is not required to be, set to "ign" if Active Site Density is entered.

Dispersion Factor

The ratio of active sites to total sites. This tells the solver how much of the site element loading is actually available to react. This can be used to account for reduced activity due to aging, poisoning, or general deactivation

Array of names of the site coverage species. Set entire first row to "ign" if modeling a PGM catalyst with no storage/coverage.

Conversion efficiency monitor

                          

for monitor convergence efficiency we need to give four input of species

1. Carbon monoxide(Co)

2. Hydro carbon(HC)

3.Nitrogen oxide(Nox)

4. Inlet Temprature

 : This template is used in an internal subassembly model to define the linking interface from parts in the subassembly to the main subassembly. For example, if an internal subassembly (such as a muffler) has been created and is to be incorporated into the larger model (such as a whole engine), this connection must be placed at the end of each component that is to be attached to a connection in the main subassembly. 

his template provides a control sensor link between "physical" (i.e. non-control) parts such as flow, mechanical, electrical, thermal or chemical parts and control components parts. They pass "output signals" at each timestep. Typical examples include state variables such as pressure, temperature, voltage, and the like, but sensors in GT-SUITE are much more powerful and flexible than in the real world because almost anything that is calculated can be sensed, such as fluid properties, moments of inertia, etc. 'SensorConn' connections are unique in that they may connect to both components and connections (as opposed to a typical connection, which may only connect to components)

.This template performs mathematical calculations on an input signal(s) from a mathematical expression typed by the user to compute the output signal.

 

Signal Send to conversion monitor

                  

Output signal from outlet cone to Mathamatical calculator

                    

Output signal of CO to Conversion Monitor

Percentage conversion of CO formula

Hydrocarbon (HC)

From above template we can see that input given of C3H6(Proplyne), Diesel-Vapour ads, Diesel Vapour Nasa signal given to the Mathamatical converter from that  it send perecent convert HC.

 

    

For calculation of HC use of folowing formula

Nitrogen Oxide

Nox on mole fraction input signal given to mathamtical calculator & send signal to the conversion meter

          

Mathamatical formula for find out Nox

Inlet Gas-Tempraure 

                            

Monitor signal Template 

input we can co, HC, NO, & inlet temprature 

Conversion effiicency after Simulation 

Overall conclusion

1. Understand the pollutant  for petrol & diesel engine 

2. After treatment device for petrol & diesel engine

3. Stratergies used for reduce tail pipe emission

4. Explore DOC model of aftertreatment-DOC-sampara & Bisset