Aftertreatment Modelling 2

DETAILED MODELLING OF AFTERTREATMENT DEVICES IN GT-POWER :

EXAMPLES > Engine+Aftertreatment :

1. Detailed CI engine aftertreatment

2. Detailed SI engine aftertreatment

3. Engine state vehicle aftertreatment NEDC model :

ENGINE + AFTERTREATMENT :

* The integration of the aftertreatment model with the engine model is certainly complex one .

* The solver circuit of engine model is "explicit", but the solver circuit for the aftertreatment model is "Quasisteady",so we can't simulate it combinely .

* Hence we need the shadow model to explain the chemistry of the catalyst bricks.

1. Detailed CI engine aftertreatment model :

As discussed before the diesel aftertreatment device consists of :

* DOC(Diesel oxidation catalyst)

* DPF(Diesel particulate filter)

* SCR(Selective Catalytic Reduction)

* DOC :

1.DOC is used for the oxidation of CO and HC , and also some NO to NO2 to maintain the NO/NO2 ratios and the efficiency of these aftertreatment devices based upon the four main factors such as ;

1.Catalyst material

2.Mass flow rate

3.Temperature

4.No/No2 ratios

And every catalyst bricks are efficient only when the temperature is high above certain critical temperature known as " Light of temperature ".

And as per the diagram of DOC , the model in the green background is the shadow model which connects the catalyst brick with the chemical kinetics and all chemical natures of the reactions.

So the engine out emissions are given to the shadow model by the " assembly 24 " in the diagram.

ASSEMBLY24 :

* The every outputs from the engine is sensed and the average value is found and signal is formed and sent to the actuators which is to the catalytic bricks.

The various outputs from the engine are as follows;

And various DOC catalyst brick reactions are as follows :

The convergence efficiency increases when the temperature increases .

* DPF

* DPF is used to retain the soot mass while the engine is running to reduce the particulate matters and also particulate numbers .

* Like the catalyst bricks , DPF is also coated with the substrate materials , whichh makes the soot to be retained .

* SCR

As discussed before in SCR urea is injected which is the ammonia gas , which undergoes certain reaction with the NO and NO2 to give out the N2 , H2O and CO2 as the output products .

* And this urea injection is based on the exhaust temperature and the composition which is sensed and controlled by the UREA inj controller.

2.Detailed SI engine Aftertreatment model :

* SI engine uses the three way catalytic converter as the aftertreatment device and the three way catalytic converter works only if the exhaust temperature is low,as the gasoline engines works in equivalence ratio of "1" , the engine almost runs in the lean condition but not most , it also should run in rich condition if the exhaust temperature becomes more , to make the combustion efficiency drops .

* In this the Aftertreatment circuit is connected with the engine circuit through the shadow circuit ,which gets the information from the engine out and collects the information about the composition of the exhaust gas and it is passed on to the circuit which remains calculates the chemical actions and reactions that are carried out in the TWC .

SIMULATION PART :

1.Simulation of detailed CI aftertreatment model :

The monitor shows the real DOC,DPF,SCR scenerio as follows while running the model as follows ;

DOC monitor :

In this graph it clearly shows that ,afer certain inlet temperature , the CO,HC Aand NO ,drops which clearly shows the convergence efficiency is higher for the higher inlet temperature.

DPF Monitor :

This shows that the Soot mass trapped is increasing when the substrate temperature is increasing .

* But the main factor in DPF is the pressure drop across DPF , which is due to the trapped mass ,hence this should be regenerated for the good efficiency and this can be done by increasing the temperature of the DPF to remove the trapped mass.

SCR monitor :

This graph shows that the Nox output is decreased(red) comparing to the NOX input(blue)

as the Urea is injected accordingly .

2.Simulation of detailed SI aftertreatment model :

Convergence efficiency monitor :

> In TWC the convergence of CO,HC,Nox are not constant always , Nox convergence will be dropping until certain inlet temperature and after certain temperature ,Nox emissions is on higher rate.

Various case setups :

* here the AFR are changing case to case , to check about the emission strategy as AFR are in close related with the emissions.

CONCLUSION:

As we are using the non-predictive models,the results are not real enough . To capture the real emissions from the model ,we should use the predictive combustion models to get the exact emissions from the engine at various states and conditions.