Risultati finali
The model has been validated comparing computational data with experimental ones provided to us by AVL. Initial comparison was conducted for modes C25, C100 and A50 for lean operation and lower Lambda values using throttling, EGR and advanced injection (mode C100). Since detailed test data for performance and emissions were provided to us by AVL, an analytical validation was made for modes A, B and C. Comparison was conducted for lean and rich operation, for engine loads 25%, 50%, 75% and 100% using the lowest achievable lambda value.
Concerning Performance Predictions for OM 906 CR Engine the following conclusions are derived for Cylinder Pressure Data, Brake Specific Fuel Consumption, Peak Pressure and Exhaust Temperature
The simulation predicts with reasonable accuracy the cylinder pressure trace and especially the effect of engine load and speed upon it. Furthermore the effect of rich combustion on the cylinder pressure trace is predicted adequately for all operating modes examined.
The coincidence between experimental and calculated values for bsfc for lean and rich operation was good revealing model¿s validity for engine performance prediction. This is important since a main issue of the investigation was the estimation of the fuel penalty resulting from rich combustion. During rich operation bsfc value is the same or only slightly higher compared to lean operation. Therefore a small fuel penalty was observed mainly at 25% load.
Concerning calculated and measured values of peak combustion pressure for lean and rich operation coincidence is good for both operating modes i.e. lean and rich, revealing model¿s validity to capture the in-cylinder combustion rate of fuel. In general lower peak combustion pressures are experienced during rich operation even though in most cases injection is advanced.
Concerning another major parameter for the investigation of rich combustion, the exhaust temperature before the turbine inlet, its variation is predicted quite well. For rich operation appears to be a small over prediction at part load in the order of 30-50C. This probably reveals the necessity for further improving the combustion model during rich operation.
Since exhaust temperature has to be maintained below 700C, rich operation becomes a problem at high load and engine speed. This results to an increase of the lowest possible lambda values.
Another important issue during rich operation is pollutant emissions, mainly NO and Soot at the engine exhaust. Rich combustion as observed from the previous investigation has a strong negative effect on soot emissions that may be a serious problem during the rich spike operation. For this reason it is necessary to verify model¿s ability to predict pollutant emissions.
NO Emissions:
Concerning calculated and measured NO emissions for both lean and rich operation for the modes considered, despite the small differences that are observed in absolute values it is clearly shown that the simulation model predicts trends accurately. Especially for lean operation the calculated NO values are almost the same with the experimental ones. For rich operation that is the major concern, final NO values that correspond to the lowest achievable lambda, are in all cases lower compared to lean operation. This effect is higher at low engine load (25%).
Soot Emissions:
The simulation predicts with reasonable accuracy soot variation with engine load and speed. Most important the simulation predicts the trends and the effect of rich operation upon it. Obviously soot emissions increase dramatically, compared to lean operation, especially for the case of low engine load. This is mainly attributed to the effect that lambda value for rich operation is lower and close to the one for the low load cases. As revealed from the simulation soot values are directly related to lambda for all operating conditions.
The outstanding concept of AHEDAT project, significantly different than other potential aftertreatment technologies, relies on intrinsic dynamic operation and synchronization of all units. It renders the unit integration and precise scheduling necessary to achieve desired performance. None of the models developed for other aftertreatment technologies required the degree of sophistication needed in this project.
Therefore, the main purpose of BGU was development of platform capable to simulate the dynamic behaviour of several connected units in the aftertreatment system. Several commercial simulation packages were considered: ACSL, HYSYS, Athena Visual Workbench and FEMLAB. FEMLAB software fits best the requirements for the simulation and optimization platform of the project due to its flexibility, user-friendly environment, robust numerical tools and a variety of graphical capabilities.
Therefore, a proprietary simulator based on FEMLAB was developed for analysis, optimization, design and control of the system. The proprietary programs, developed to overcome the numerical complexity and to facilitate the data analysis and presentation completed the simulation package. The package is general and flexible and may be used in simulations of other highly dynamic complex aftertreatment systems.
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