Overview
Despite the diesel engines' environmental impact, there has not been an application for any after-treatment technology for a long time. In the last few years, diesel emissions have had to face increasing worldwide public pressure, which has led to more and more severe emission regulations. Although catalyst-equipped Otto-engines are nowadays cleaner than diesels, as far as soot and NOx production are concerned, diesel engines are preferred in almost all heavy-duty applications.
Since the first diesel engine emission regulations were issued, several engine modifications have been developed to reduce pollutant species production. While CO and HC emissions are manageable through the use of an oxidation catalyst, NOx and particulates are a harder task to handle and abate. Optimisation of the engine's combustion towards low NOx emission and soot emission has to face a trade-off .
The necessary compromise between NOx and particulate emissions make advanced after-treatment technologies a must to meet the current and future regulations; Euro IV regulations, at present in force, have been met by all car manufacturers thanks to the extensive use of after-treatment devices, in close synergy with engine management strategy. Anyhow the future emission limits will force the use of innovative after-treatment components/systems capable to contemporary reduce both NOx and soot emissions.
The objective of the project was to develop, procure and test the needed components and integrated systems, in order to achieve the following targets:
- Euro V (and beyond) emission levels for passenger cars, particularly in terms of NOx emission;
- low fuel/energy penalty (< 2%);
- compatibility with the engine and vehicle systems;
- system operation and maintenance that is fully transparent to the vehicle user; and
- cost-competitive system with a complete state-of-the-art after-treatment system.
The first part of the project was focused on providing the guidelines for an effective development work. The systems specification requirements defined at the beginning of the project has been used for the entire project duration to properly compare the effectiveness of the innovative aftertreatment systems that were developed. In this task, a State-of-the-Art engine and vehicle have been selected and characterised as a study case for the systems application. The information collected from the study case characterisation was then provided in to the partnership, to start with the definition of the systems specifications for the two aftertreatment concepts: the chemical and electrical based approach.
The second task was focused on the fuel processor devices development, needed for the on board production of activated species for NOx reduction; the device to be developed in this task are:
- Catalytic fuel processor (CFP).
- Electrical fuel processor (EFP).
To achieve the requested emission reduction, the production of active species by means of the fuel elaboration devices must be exploited in a specific aftertreatment device capable of actively reducing the NOx levels. The catalyst definition has been carried out according to the specs and boundary conditions and in particular considering the actual working parameters (exhaust temperature, gas composition, conversion efficiency, etc.); the selected catalyst will be the same for both the fuel elaboration devices (CFP and EFP). A number of base experiments have been carried out to explore different catalyst solutions capable to exploit the active species produced by the fuel processors.
Once collected, all the information coming from the test campaigns carried out onto the developed systems, the most promising technology for the final implementation on vehicle was selected; the the CATD (Catalyst based aftertreatment device) in two different configurations:
- CC (Close-coupled) and
- UF (Under-floor) systems.
Funding
Results
The main objective of Top-Expert project was the development of a novel, fully integrated active aftertreatment system based on the use of activated chemical agents, used to abate the pollutant compounds with particular reference to NOx emissions from Diesel engines. During the project two approaches have been evaluated:
- catalyst based approach and
- energy based approach.
The two technological routes have been developed and tested up to the application on engine bench: after that, the catalyst based approach (CATD) has been selected as the most promising technological route for the final vehicle test campaign. The final test campaign demonstrated that the CATD systems are able to work over a wide range of engine conditions controlling and maintaining the on-board diesel fuel reforming reaction, are compatible with the engine and vehicle systems and fully transparent to the vehicle user and the systems operation. The UF system demonstrated better performances than the CC one either in stationary conditions or over the homologation cycle. The main drawback of both the systems is anyway the high level of the secondary emissions (CO, HC and soot) which should be solved in order to exploit as much as possible the system performances.
Finally, the preliminary cost benefit analysis showed that in comparison to a standard SCR system (HN3 based), the costs for the both the systems should be competitive and a further cost saving is expected with some improvements in the manufacturing process.
Technical Implications
The two CATD systems have been successfully implemented on the selected demo vehicle (new Lancia Delta 2.0Mjet Euro5) with some minor modifications; moreover, a specific control box and software have been developed and installed in the vehicle in order to properly control the CFP.
The CATDs have been tested over a wide range of working conditions: on the road in real driving conditions, stationary driving conditions over the roller test bench, European homologation cycle (NEDC). It has been demonstrated that the CFP is able of working in many varying driving conditions and the reforming reaction can be effectively controlled and maintained.
Finally,a specific simulation tool has been developed during the project. The full-scale CATD model has been successfully implemented as well as the injection and ignition models. Moreover, the reaction models for ignition and reforming processes have been set-up to simulate the fuel vaporizer and the reformer catalyst and evaluate the H2 production. Then, the simulation of the whole TOP-EXPERT geometry has been carried out and the calculated reaction products for the whole system match quite well with the experimental data from CRF. The developed model is in good agreement with experimental data obtained from the 3D TopExpert geometry achieved with the newly adapted filter solver are in good accordance with the experimental data delivered from EMCON and CRF.