Detailed Report on SI and CI Engine After treatment

OBJECTIVE:

To explore Detailed SI and CI Engine After treatment examples files

Detailed CI Engine After treatment case

Model

Below is the complete integrated model with detailed engine and detailed after-treatment system. The exhaust system is duplicated such that one copy uses the explicit flow solver and the second copy uses the Quasi-steady flow solver with a larger time step of 0.1sec.

A closeup look of Diesel of Oxidation, Diesel Particulate Filter and Selective Catalytic Reduction system.

This is the End Environment template which describes the boundary condition of Pressure, Temperature, Composition. Absolute Pressure of 1bar and 300K initial temperature BC is been kept.

A 4 cylinder 2 valved diesel engine model with Turbocharged Waste Gate Controller model is integrated with firing order 1-3-4-2. The Bore and Stroke are 100 and 110 mm with 156mm connecting Rod length.

For Engine Cylinder, Combustion object used is 'EngCylComb*' and Initial Wall Temperature is defined by 'twal' model. For SOOT, emission map is used and for NOx, extended zeldovich mechanism is been used.

RUN SETUP

In the flow control, we see Time Step and Solution control are kept to ExplicitControl for the engine model which has default time control and QSControl for after-treatment devices which has a time-controlled flag as continuous.

With the assembly 24, the cycled averaged mass flow, temperature, and species concentrations (CO2, H2, NO, CO, soot, H2O, O2, vap fuel) are transferred from the explicit circuit to the QS circuit.

Diesel OF Oxidation

In DOC, oxidation of CO and HC takes place which releases exothermic reactions which releases heat beneficial for the catalyst to work. It's always recommended to operate DOC or after treatment above the Light of Temperaturewhich assures the conversion efficiency of more than 50%. DOC also helps to maintain the equal ratios of NO and NO2 which is a very difficult task.

Here, the frontal area is been defined along with the length, discretization length cell density, substrate wall thickness, wash coat Layer thickness.

The substrate thermal material is been defined as Cordierite and Washcoat layer as Alumina

Below are the various Surface reactions with associated site elements as PGM (Precious Group Material) and zeolite.

DOC Monitor

Here, the conversion is been tracked for the oxidation of CO, HC, NO and inlet temperature.

Diesel Particulate Filter

In Diesel Particulate Filter, we remove the solid carbon material from the exhaust. The problem starts when the solid particles accumulate and start choking and the pressure drop which is undesirable and hence, we need a Regenerative mechanism which cleans out the filter. Two different strategies are Active and Passive regeneration. Generally, DPF provides 99% conversion efficiencies.

Selective Catalytic Reduction QS

After DPF, we are left with NO and NO2 in the exhaust which is at high temperature. A large gap is left after DPF, where we inject liquid ammonia which vaporizes and mixes with the exhaust uniformly further moved to SCR. SCR is a honeycomb structure with Iron Zeolite or Copper Zeolite, Vanadium based on the application.

For SCR, minimum temperature preferred is 180deg, below which ammonia does not get absorbed and hence gets accumulate on the surface causing the Ammonia Slip at the tailpipe.

Urea Control strategy plays a very important role which decides the injections of ammonia with the help of sensors for NH3 slip, Inlet and Outlet temperatures, NOx etc. It make sure that Urea does not get injected when the temperature is below 200deg C.

Below are the catalytic surface kinetic reactions for SCR.

This is the case setup

Simulation Results

Herewith the help of DOC monitor we are able to keep track of CO, HC, NO, and Inlet temperature with 0.1sec time step size. As seen, the inlet temperature is 808k, Conversion efficiency of CO, NO and HC are 13.29%, 9.12% and 5.73% respectively. As soon as the Light of temperature reaches, we see the conversion.

In DPF, we see a SOOT Mass retained of 0.0073g where the Substrate temperature reaches about 628K at the time of Steady-state converged data.

In the very start, the Pressure drop across DPF reaches up to 3.2 because of deposits of solid soot, and then due to passive regeneration strategy it gets reduces significantly.

For SCR monitor, the total NOx in detected was 785ppm which was reduced to 616.5 ppm at the time of convergence.

Detailed SI Engine After treatment case

Model

Below example is an IC Engine combined with Three-Way Catalytic Converter in a secondary after treatment circuit. A secondary circuit was used by TWC to solve the kinetic surface reactions using Quasi Steady Flow Solver with large master time step so that it does not restrict the computational time. The backpressure from the explicit engine circuit is passed to QS circuit and actuated as the downstream pressure boundary, and the outlet gas temperature from the QS circuit is passed back to the explicit engine circuit and actuated as the TWC wall temperature so that the exothermic heat release is captured for acoustics.

This is the engine circuit with EGR controller. It's a 4 valve 4 cylinder engine. SiWiebe combustion model and Woschni for heat transfer is been used.

The information of exhaust mass flow, gas temp, O2, CO2, H2O, CO, H2, NO etc is transferred to the QS catalyst brick.

This is the close-up circuit look for Three-way catalytic converter. The above is in direct connection with the engine and is explicit solver whereas the below one is the Quasi Steady solver.

The frontal area of the catalyst brick is about 8775 mm^2, the length is 150mm, and the cell density is 600 per inch square. A Fixed Mesh ODE/DAE solver is used with site elements as cerium and PGM.

Below is the surface reactions, with reactants and products and other terms used in the Arrhenius equation to determine the rate of reaction and hence solve the chemical kinetics happening into TWC.

There are 3 cases for 3 air to fuel ratios for rich(14), stoichiometric (14.5)and lean conditions (15). The engine speed is 3000 rpm and the throttle angle is kept 45deg.

Simulation Results

As we go rich to lean mixture, BSFC decreases but the Brake Efficiency increases.

The common observation we see here is that as the Air to fuel ratio is increased, the CO and HC conversion efficiency has increased but the NO conversion efficiency has decreased.