Aftertreatment Devices using GT-Power

OBJECTIVE:

• List down for Gasoline vs Diesel engine
• the pollutants
• after treatment devices with catalyst materials
• the example files
• Strategies used for reducing tailpipe emissions
• List down one set of chemical reactions for TWC and SCR from example files
• Explore - Example - after-treatment - DOC - Sampara & Bisset and write a detailed report

The Pollutants

After treatment devices with material

3 Way Catalytic Converter

Allows reduction of NOx (nitrogen oxides) to N2 (nitrogen) and O2 (oxygen)

Allows oxidation of CO (carbon monoxide) to less-harmful CO2 (carbon dioxide)

Allows oxidation of HC (unburned hydrocarbons) to CO2 (carbon dioxide) and H2O (water)

The three-way converter without air uses advanced catalyst chemistry to store and release O2, in conjunction with an O2 monitoring and control system. 

This system utilizes one or more O2 sensors to oscillate the fuel mixture between lean and rich conditions. This oscillation, combined with the O2 storage and release on the catalyst surface, allows for optimum reduction of all three emissions.

Diesel Oxidation Catalyst (DOC)

Diesel Oxidation Catalysts (DOC) are catalytic converters designed specifically for diesel engines and equipment to reduce Carbon Monoxide (CO), Hydrocarbons (HC) and Particulate Matter (PM) emissions. DOC's are simple, inexpensive, maintenance-free and suitable for all types and applications of diesel engines.

Modern catalytic converters consist of a monolith honeycomb substrate coated with platinum group metal catalyst, packaged in a stainless steel container. The honeycomb structure with many small parallel channels presents a high catalytic contact area to exhaust gasses. As the hot gases contact the catalyst, several exhaust pollutants are converted into harmless substances: carbon dioxide and water.

The diesel oxidation catalyst is designed to oxidize carbon monoxide, gas-phase hydrocarbons, and the SOF fraction of diesel particulate matter to CO₂ and H₂O:

CO + 1/2O2 ----------> CO2

Hydrocarbon + O2 ----------> CO2 + H2O

SOF + O2 ----------> CO2 + H2O

Diesel Particulate Filter (DPF)

Diesel particulate filters capture particle emissions through a combination of filtration mechanisms, such as diffusional deposition, inertial deposition, or flow-line interception. Collected particulates are removed from the filter, continuously or periodically, through thermal regeneration. Diesel filters are highly effective in controlling solid particulate emissions—including solid particle numbers—but may be ineffective in controlling liquid fractions of PM emission.

Ceramic materials are widely used for particulate filter, because of good thermal durability, with most common material used are: Cordierite, silicon carbide, aluminium titanate.

Selective Catalytic Reduction (SCR)

In the selective catalytic reduction (SCR) process, NOx reacts with ammonia, which is injected into the flue gas stream before the catalyst. Different SCR catalysts such as vanadium oxide or metal substituted zeolites have different operating temperature windows and must be carefully selected for a particular SCR process. Ammonia-SCR has been used in industrial processes, in stationary diesel engines, as well as in some marine engines. Urea-SCR technology—using urea as the ammonia precursor—has been adapted for mobile diesel engines in both heavy- and light-duty applications.

The example files

Strategies used for reducing tailpipe emissions

NOx (for Diesel and Gasoline)

• Exhaust Gas Recirculation
• Port Water Injection
• Decrease in load
• Decrease the incoming charge temperature

SOOT (for Diesel and Gasoline)

• Increase A/F ratio to avoid insufficiency of oxygen
• Increase homogeneity of the air-fuel mixture
• Increase swirl ratio for CI Engine and tumble ratio for SI Engine

CO & HC (for Diesel and Gasoline)

• Increase A/F ratio to avoid incomplete combustion
• A turbocharger can be implemented

Chemical Reactions for TWC and SCR from example files

TWC

CO + 0.5O2 ----------> CO2

C3H6 + 4.5O2 ----------> 3CO2 + 3H2O

C3H8 + 5O2 ----------> 3CO2 + 4H2O

H2 + 0.5O2 ----------> H2O

CO + NO ----------> CO2 + 0.5N2

C3H6 + 9NO ----------> 3CO2 + 3H2O + 4.5N2

H2 + NO ----------> H2O +0.5N2

CO + H2O ----------> CO2 + H2

C3H6 + 3H2O ----------> 3CO + 6H2

2Ce2O3 + O2 ---------->4CeO2

Ce2O3 + NO ----------> 2CeO2 + 0.5N2

CO + 2CeO2 ----------> Ce2O3 + CO2

C3H6 + 12CeO2 ----------> 6Ce2O3 + 3CO + 3H2O

C3H8 + 14CeO2 ----------> 7Ce2O3 + 3CO + 4H2O

H2 + 2CeO2 ---------> Ce2O3 + H2O

SCR

Z + NH3 ----------> Z.NH3 (adsorption)

Z.NH3 ----------> Z + NH3 (desorption)

4Z.NH3 + 3O2 ----------> 2N2 + 6H2O + 4Z (oxidation reaction)

4Z.NH3 + 4NO + O2 ----------> 4N2 + 6H2O + 4Z (standard NO surface conversion reaction)

NO + 0.5O2 <----------> NO2 (reversible NO oxidation reaction)

8Z. NH3 + 6NO2 ----------> 7N2 + 12H2O + 8Z (slower NO2 reaction)

4Z. NH3 + 2NO + 2NO2 ----------> 4N2 + 6H2O + 4Z (fast SCR reaction)

Explore - Example - after-treatment - DOC - Sampara & Bisset and write a detailed report

Model

Below is the simple Diesel Oxidation Catalyst model with EndFlowInletSpecies, Catalyst Brick, Outlet, Surface Reactions.

EndFlowInletSpecies

With EndFlowInletSpecies we have attributes like Mass Flow Rate, Gas Temperature, Gas Composition, and composition specification. The Composition Specification is been defined as MoleFraction and the other are defined as Variables.

CATALYSTBRICK

In Catalyst Brick Template, we define various aspects regarding the catalyst. The main attributes defined here are the length and the frontal area of the comb, channel shape, cell density, substrate wall thickness along with Washcoat Layer 1 Thickness and Washcoat Layer 2 Thickness. These attributes can be clearly seen and understood with the help of the following diagrams.

Catalytic Brick (Thermal)

Here the Substrate material selected is Cordierite with thermal properties objects like conductivity, Density, Specific Heat, Opacity. The material for Washcoat layer 1is selected to be Aluminium. Initial Temperature to be kept is 300k.

Surface Reaction

This template specifies the surface catalytic reaction kinetics that require the modeling of storage or coverage.

Main

Here, the diffusion option is enabled, species concentration is defined as mole/m^3.

Species Setting Object

Here all the species which would be taking part with the catalytic substrate and wall layers are listed out as seen in the below table.

ODE/DAE Solver used here is Fixed Mesh. Other solvers provided here are Advance Adaptive, BDF, RADAU, Adaptive RK, RK-BDF.

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 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

Arrhenius Equation is used to determine the rate of reactions.

K = A * Exp(-Ta/T)

List of Reactions

CO + 0.5O2 ----------> CO2

C3H6 + 4.5O2 ----------> 3CO2 + 3H2O

DF + 19.4O2 ----------> 13.5CO2 + 11.8 H2O

DF2 + 19.4O2 ----------> 13.5CO2 + 11.8H2O

H2 + 0.5O2 ----------> H2O

NO + 0.5O2 ----------> NO2

Z+DF1 ----------ZDF1

ZDF ----------> Z + DF1

CASE SETUP

These are the 2 cases set up in this case set up with Initial Temperature, dx value, mass flow rate, gas temperature, inlet composition been defined as variables and simulation duration, master time step, 1D plot frequency with absolute value.

Below is the mass flow rate for case2 defined with respect to time.

Gas Temperature for Case1

Temperature is been defined with respect to the time.

Gas Temperature for Case2

Temperature is been defined with respect to the time.

Conversion Efficiency Monitor

The input signals are CO, HC, NO and inlet temperature as 1, 2, 3 and 4 signals respectively.

Mathematical expression to compute the output signal for CO

Mathematical expression to compute the output signal for HC

Mathematical expression to compute the output signal for NO

Monitor Signal

This template is used to monitor instantaneous signals or RLT's (only wirelessly) during the simulation.

Monitor Signal part Conversion