Development of the European ZDAKW Catalyst Bench Aging Cycle on SwRI's FOCAS® System, 03-R9712Printer Friendly Version
Inclusive Dates: 05/09/07 05/09/08
Background - The benchmark for European aging cycles is the ZDAKW cycle, developed by a collaboration of Porsche, Audi, BMW, VW, and Mercedes-Benz. It uses high engine-out temperatures and fuel cuts. Engine durability limits the catalyst inlet temperatures to about 950°C, with only 'moderate' catalyst bed temperatures that produce about 80,000 km (50,000 miles) of aging in 100 hours. Operation of the cycle is very expensive and hard on engines, and the number of hours required will increase as the European regulations move to 160,000 km for Euro 6 in about 2013. In contrast, the FOCAS system is capable of providing 950°C inlet temperatures with relative ease and minimal durability issues. Because the FOCAS system did not have the control needed to perform fuel-cut aging cycles, a fuel cut simulation capability was developed under this IR&D program to allow FOCAS to run a ZDAKW cycle.
SwRI was first asked to perform ZDAKW catalyst bench engine aging in 1995. At that time, the cost to run the cycle using the Porsche engine was considered prohibitive to the clients, and SwRI elected not to pursue aging work using this cycle. The primary cost was the engine (approximately $15,000) with expected durability of only 1,000 hours. Since that time, the specified catalyst inlet temperature has risen from 900 to 950 degrees C, so engine wear is more of an issue. When FOCAS was first developed, it was recognized that it would be able to generate the catalyst inlet temperatures with relative ease and durability. However, it was also recognized that other aspects of the cycle would be difficult to achieve with the early FOCAS system. Nevertheless, it was clear that operation of this cycle in the future would be pivotal to entering the large European market. To date, efforts have been concentrated on developing U.S. and Asian aging cycles. A promotional European visit in 2006 to OPEL (GM), Volvo, and PSA revealed that OPEL and Volvo were very interested in the FOCAS aging system. Opel requested a proposal to perform ZDAKW cycle aging at SwRI. However, because of uncertainty of costs associated with setting up and running the cycle, the proposal was rejected as too expensive. A similar proposal to Sud-Chemie in India was also rejected. From this related research, it is clear that SwRI could obtain new project work running the ZDAKW cycle on FOCAS after the cycle is developed. It is also clear and timely that Europe is ready for this technology. Development of the ZDAKW cycle on FOCAS will provide the opportunity to expand project activities at SwRI and create the market for FOCAS systems in Europe.
Approach - There were several elements to this cycle that required the development of new capabilities to enable the SwRI FOCAS system to run the cycle. The concept that was developed to simulate the fuel cut-off portion of the cycle was to temporarily divert the majority of the exhaust gas flow through a bypass leg in the system, while simultaneously adding air upstream of the catalyst to simulate the lean exhaust conditions seen during the fuel cut-offs. The low flow stepped portion of the cycle was achieved using the same bypass flow leg and variable burner air control to achieve the low catalyst flows.
Suitable matched catalysts for both engine burner aging were obtained from a commercial catalyst supplier. The catalysts were aged in pairs, with three pairs sequentially aged on the FOCAS system and three pairs sequentially aged on a bench engine. The aged performance of the catalysts was determined by European cycle emissions testing using a test vehicle.
Accomplishments - The vehicle emissions were grouped by cycle type on an aging bench, and the mean and standard deviation for each exhaust pollutant was calculated. Figure 1 shows a summary of the results of the analysis.
The data in Figure 1 show that the two aging methods produced equivalent aging effects for THC, CO and NOx in the cold-start (ECE cycle) and fully warm conditions (EUDC). Of the two correlations, aging typically impacts catalyst light-off more visibly than stabilized performance, so cold-start correlation is typically more heavily weighted. Although, all species show equivalent impact, it was noted from an engineering standpoint that the NOx aging effect on the burner appeared to be less severe than on the engine. It was felt that perhaps the level of the exotherm (indicative of unburned HC and CO in the exhaust) and the reduced level of oxygen produced during the fuel cut may have resulted in a less severe impact on NOx aging.
Overall, the fuel cut simulation worked well and the approach appears valid. Also, the variable flow control for the FOCAS system now allows the rig to run variable flow aging cycles as well. The work performed here has expanded the capabilities of the system and should provide material to allow discussion on the FOCAS system with European companies.