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To enable better matching of Diesel Oxidation Catalyst (DOC) properties to aftertreatment system and application requirements, a systematic evaluation of the effects of sulfur poisoning and desulfation was undertaken on a number of Heavy Duty DOC formulations at representative Platinum Group Metal (PGM) loadings. Uniformly coated DOCs having PGM ratios from 1/0 Pt/Pd to 0/1 Pt/Pd with commercial HDD DOC washcoats were evaluated on a Tier 3 Non-Road engine. In addition, a new DOC formulation intended for reduced sulfur sensitivity, a DOC containing zeolite for hydrocarbon (HC) adsorption, and a layered DOC containing both high and low Pt/Pd ratio layers were compared. Two levels of PGM loading were included for three of the uniform sample formulations.

Control of N2O emissions is a significant challenge for manufacturers of HDD On-Road engines and vehicles due to requirements for NOx control and Green House Gas (GHG) Phases I & II requirements. OEMs continually strive to improve BSFE which often results in increased engine out NOx (EO NOx) emissions. Consequently, the necessity for higher NOx conversions results in increased N2O emissions over traditional SCR and SCR+ASC catalysts systems [1]. This study explores methods to improve NOx conversion while reducing the SCR contribution of N2O across the exhaust after treatment systems. For example, combinations of two traditional SCR catalysts, one Iron based and another Copper based, can be utilized at various proportions by volume to optimize their SCR efficiency while minimizing the N2O emissions. Results show that a proper combination of catalysts volume can significantly reduce N2O levels while simultaneously reaching the highest levels of NOx performance achieved in the study.

Significant reduction in Nitrogen Oxide (NOx) emissions will be required to meet LEV III Emissions Standards for Light Duty Diesel passenger vehicles (LDD). As such, Original Equipment Manufacturers (OEMs) are exploring all possible aftertreatment options to find the best balance between performance, robustness and cost. The primary technology adopted by OEMs in North America to achieve low NOx levels is Selective Catalytic Reduction (SCR) catalyst. The critical parameters needed for SCR to work properly are: an appropriate reductant such as ammonia (NH3) typically provided as urea, adequate operating temperatures, and optimum Nitrogen Dioxide (NO2) to NOx ratios (NO2/NOx). The NO2/NOx ratio is mostly influenced by Precious Group Metals (PGM) containing catalysts located upstream of the SCR catalyst. Different versions of zeolite based SCR technologies are available on the market today and these vary in their active metal type (iron, copper, vanadium), and/or zeolite type.

There is growing interest in application of SCR on DPF (SDPF) for light and heavy duty applications, particularly to provide improvements in cold start emissions, as well as improvements in system cost and packaging [1, 2, 3]. The first of systems containing SDPF are just coming to market, with additional introductions expected, particularly for light duty and non-road applications [4]. To provide real world testing for a new SDPF product design prior to availability of OEM SDPF applications, an SDPF and one SCR catalyst were substituted in place of the original two SCR catalysts and a catalyzed diesel particulate filter (CDPF) on a Ford F250 HD pickup. To ensure that the on-road emissions would be comparable to the production system replaced, and to make sure that the control system would be able to operate without detecting some difference in behavior and seeing this as a fault, initial chassis dynamometer work was done before putting the vehicle on the road.

Investigations of on-road emissions performance of vehicles have been made using various methods and instrumentation, some of which are very complex and costly. For the particular case of NOx emissions on Diesel road vehicles equipped with SCR catalysts (Selective Catalytic Reduction), many of these vehicles are equipped with NOx sensor(s) for the purpose of OBD (On-Board Diagnostics), and the ECU (Engine Control Unit) makes this data available via the diagnostic connector under the SAEJ1979 protocol for light duty vehicles. Data for mass air flow and fuel flow are also available per J1979, so the ongoing NOx mass flow can be estimated when the NOx sensors are active with no additional instrumentation. Heavy duty pickup trucks with SCR systems from 3 major US manufacturers, each certified to the optional chassis certification of 0.2 g/mi NOx on the FTP75, were obtained to be evaluated for SCR system behavior under normal driving conditions.