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This review paper summarizes major developments in vehicular emissions regulations and technologies (light-duty, heavy-duty, gasoline, diesel) in 2012. First, the paper covers the key regulatory developments in the field, including finalized criteria pollutant tightening in California; and in Europe, the development of real-world driving emissions (RDE) standards. The US finalized LD (light-duty) greenhouse gas (GHG) regulation for 2017-25. The paper then gives a brief, high-level overview of key developments in LD and HD engine technology, covering both gasoline and diesel. Marked improvements in engine efficiency are summarized for gasoline and diesel engines to meet both the emerging NOx and GHG regulations. HD engines are just starting to demonstrate 50% brake thermal efficiency. NOx control technologies are then summarized, including SCR (selective catalytic reduction) with ammonia, and hydrocarbon-based approaches.

In this paper, we report the modeling of the selective catalytic reduction (SCR) of NOx using ammonia on a commercial vanadia-titania based catalyst. The model combines a steady-state two-dimensional channel model with a transient two- or three-dimensional monolith model of the whole catalytic monolith converter. The reaction mechanism includes the standard and fast SCR reactions and also the high-temperature oxidation of ammonia to model the decrease in conversion observed at higher temperatures. We used in-house experimental data spanning a wide range of inlet compositions and temperatures to validate the model. The model was found to be in excellent quantitative agreement with the experimental data.

Sub-23nm particles emission from the light-duty vehicle is widely discussed now and possible to be counted into the next stage emission legislation, such as Euro7. In this article, 16 China6 gasoline vehicles were tested over the WLTC and two surrogate RDE lab cycles for particulate number (PN) emission, the difference between PN23 (particle size >23nm) and PN10 (particle size>10nm) emission was analyzed. Testing results showed that the average PN10 emission increased 59% compared to PN23, which will bring great challenges for those vehicles to meet the future regulation requirement if sub-23nm particle is counted. The sub-23nm particles emission was proportional to the PN23 particles emission and generated mostly from the cold start or the transient engine conditions with rich combustion. Compared to the proposal of Euro 7, PN10 emission from some tested vehicles will need further two orders of magnitude reduction.

Recently, SiC has been investigated and pursued as an alternative material for diesel particulate filter (DPF) applications. SiC has acceptable physical properties such as good thermal conductivity, refractoriness, and chemical durability. Materials for DPF applications require a particular mean pore size, porosity, and permeability. In addition, these material attributes must be coupled to an appropriate thermal design so that the filter can survive the extreme temperature gradients generated during the regeneration process. In this report several approaches to making porous SiC will be discussed and performance data based on material properties and thermal design will be presented.

Diesel particulate filters are expected to be used on most passenger car applications designed to meet coming European emission standards, EU5 and EU6. Similar expectations hold for systems designed to meet US Tier 2 Bin 5 standards. Among the various products oxide filter materials, such as cordierite and aluminum titanate, are gaining growing interest due to their unique properties. Besides the intrinsic robustness of the filter products a well designed operating strategy is required for the successful use of filters. The operating strategy is comprised of two elements: the soot estimation and the regeneration strategy. In this paper the second element is discussed in detail by means of theoretical considerations as well as dedicated engine bench experiments. The impact the key operating variables, soot load, exhaust mass flow, oxygen content and temperature, have on the conditions inside the filter are discussed.

The diesel oxidation catalyst is required to remove hydrocarbons and carbon monoxide from the diesel engine exhaust stream while minimizing the impact of all other features such as cost, space, pressure drop, weight, fuel consumption, etc. The challenge of designing a catalytic converter for a particular application then becomes to: first, understand the emissions and other performance targets and requirements for the engine; second, understand the influence each of the converter parameters has on the overall system performance and; third, optimize the system using these relationships. This paper will explore some of the considerations with respect to the second of the above challenges.

Information on transport mechanisms in a Diesel Particulate Filter (DPF) provides crucial insight into the filter performance. Extensive experimental work has been pursued to modify, customize and validate a model yielding accurate predictions of a ceramic wall-flow DPF pressure drop. The model accounts, not only for the major pressure drop components due to flow through porous walls but also, for viscous losses due to channel plugs, flow contraction and expansion due to flow entering and exiting the trap and also for flow secondary inertial effects near the porous walls. Experimental data were collected on a matrix of filters covering change in filter diameter and length, cell density and wall thickness and for a wide range of flow rates. The model yields accurate predictions of DPF pressure drop with no particulate loading and, with adequate adjustment, it is also capable of making predictions of pressure drop for filters lightly-loaded with particulates.

Over the past decade, regulations for mobile source emissions have become more stringent thus, requiring advances in emissions systems to comply with the new standards. For the popular diesel powered passenger cars particularly in Europe, diesel particulate filters (DPFs) have been integrated to control particulate matter (PM) emissions. Corning Incorporated has developed a new proprietary aluminum titanate-based material for filter use in passenger car diesel applications. Aluminum titanate (hereafter referred to as AT) filters were launched commercially in the fall of 2005 and have been equipped on more than several hundred thousand European passenger vehicles. Due to their outstanding durability, filtration efficiency and pressure drop attributes, AT filters are an excellent fit for demanding applications in passenger cars. Extensive testing was conducted on engine to evaluate the survivability and long-term thermo-mechanical durability of AT filters.

Diesel particulate filters are becoming a standard for most light duty diesel applications designed for European EU5 and EU6 regulations. Oxide based filter materials are continuing to gain significant interest and have been in high volume serial application since 2005. Compared to carbide materials they show some unique properties. With respect to the design, the length of a filter is a key variable. Usually the prime design consideration is the desired filter volume. The diameter or frontal area is then usually defined by packaging constraints. Finally, the length is adapted. The paper provides experimental data on the impact this key design parameter has on the pressure drop and the thermal behavior under “worst case” regeneration conditions. A wide range of soot loads (from 4 g/dm3 to 9 g/dm3) as well as filter lengths from 6″ to 12″ is considered and evaluated under comparable experimental conditions.

With the introduction of a stringent particulate number (PN) limit and real driving emission (RDE) requirements, gasoline particulate filters (GPF) are widely adopted for gasoline engines in Europe and China. The filter collects soot and ash. Like in diesel applications, the collected soot will continuously burn under favorable exhaust conditions. However, at extreme conditions, there could be large amounts of soot build-up, which may induce a highly exothermal event, potentially damaging the filter. Thus, it is important to understand what drives the over-heating in application, and develop counter measures. In this study, an on-vehicle fuel cut (FC) testing procedure was developed. The testing was conducted on two vehicles, one gasoline direct injection (GDI) vehicle and one multiple port injection (MPI) vehicle, with different exhaust systems designs (a close coupled GPF and an under floor GPF) and catalyst coating levels (bare and heavily coated GPFs).

Diesel particulate filters (DPF) have become a standard aftertreatment component for a majority of current on-road/non-road diesel engines used in the US and Europe. The upcoming Stage V emissions regulations in Europe will make DPFs a standard component for emissions reductions for non-road engines. The tightening in NOx emissions standard has resulted in the use of selective catalytic reduction (SCR) technology for NOx reduction and as a result the general trend in engine technology as of today is towards a higher engine-out NOx/PM ratio enabling passive regeneration of the DPF. The novel filter concept discussed in this paper is optimized for low pressure drop, high filtration efficiency, and low thermal mass for optimized regeneration and fast heat-up, therefore reducing CO2 implications for the DPF operation.

A family of cordierite DPF filters were developed and studied for their efficacy for catalyzed soot filter applications. In addition to porosity and median pore size of DPF filters, breadth of pore size distribution, microstructure, and pore connectivity have a profound influence not only in filter performance (pressure drop, catalyst coatability, and filtration efficiency) but also on mechanical and physical properties. Through filter material composition development, optimum values for the %porosity, median pore diameter, and breadth of the pore size distribution for minimizing pressure drop have been identified, leading to the development of a new family of high-porosity cordierite diesel particulate filters that possess a unique combination of high filtration efficiency, high strength, and very low clean and soot-loaded pressure drop in both the catalyzed and non-catalyzed states. By controlling the microstructure, the impact of the catalyst on pressure drop has been minimized.

The present work intends to examine the selective NOx reduction efficiency of a current commercial Titanium-Vanadium washcoated catalyst and to develop a transient numerical model capable of describing the SCR process while using a wide range of inlet conditions such as space velocity, oxygen concentrations, water concentration and NO2/NO ratio. The concentrations of different components (NO, NO2, N2O, NH3, H2O and HNO3) were analyzed continuously by a FT-IR spectrometer. A temperature range from 150°C up to 650°C was examined and tests were carried out using a model exhaust gas comparable to the real diesel exhaust gas composition. There is a very good correlation between experimental and calculated results with the given chemical kinetics.

As demand for wall-flow Diesel particulate filters (DPF) increases, accurate predictions of DPF behavior, and in particular of the accumulated soot mass, under a wide range of operating conditions become important. This effort is currently hampered by a lack of a systematic knowledge of the accumulated particulate deposit microstructural properties. In this work, an experimental and theoretical study of the growth process of soot cakes in honeycomb ceramic filters is presented. Particular features of the present work are the application of first- principles measurement and simulation methodology for accurate determination of soot cake packing density and permeability, and their systematic dependence on the filter operating conditions represented by the Peclet number for mass transfer. The proposed measurement methodology has been also validated using various filters on different Diesel engines.

In this study quantitative techniques were established to assess the low temperature durability of commercially available mat systems. A new low temperature dynamic resistive thermal exposure (LT-RTE) test method was developed. The mats were evaluated in thermal cycling with maximum substrate skin temperatures from 280°C to 450°C. Results indicate that at low use temperatures the residual shear strength of the mat fell to ∼5-15KPa following 280°C cycling. Under the same LT-RTE exposure conditions an equivalent mat system, following thermal preconditioning to 500°C for 3 hours, possessed a residual shear strength of ∼30KPa. An alternative mat system with a lower shot content fiber was also evaluated, following the same thermal preconditioning previously described. This alternative mat was found to exhibit substantially higher residual shear strengths following LT-RTE aging. A residual shear strength of ∼95KPa was observed for this alternative mat following 280°C LT-RTE aging.

There is currently a need for a practical solution for NOx abatement in automotive diesel engines. Technologies developed thus far suffer from inherent technical limitations. The selective catalytic reduction (SCR) of NOx under lean conditions has been proven to be successful for stationary applications. A new approach is described to efficiently remove NOx from the exhaust of a diesel engine powered vehicle and convert it to nitrogen and oxygen. The key to the approach is the development of an on board (in-situ) ammonia generating catalyst. The ammonia is then used as a reagent to react with exhaust NO over a secondary SCR catalyst downstream. The system can remove over 85% of the exhaust NO under achievable diesel engine operating conditions, while eliminating the potential for ammonia slip with a minimal system of sensors and feedback controls.

Engine laboratory tests were conducted to assess the impact of B20 biodiesel on the performance of cordierite diesel particulate filters (DPFs). Test fuels included 20% soy based methyl ester blended into ultra low sulfur diesel fuel, and two ULSD on-road market fuels. B20 has a higher cetane number, boiling point and oxygen content than typical on-road diesel fuels. A comparative study was performed using a model year 2007 medium duty diesel truck engine. The aftertreatment system included a diesel oxidation catalyst (DOC) followed by a cordierite wall flow DPF. A laboratory-grade supplemental fuel doser was used in the exhaust stream for precise regeneration of the DPF. Tests revealed that the fuel dosing rate was higher and DOC fuel conversion efficiency was poorer for the B20 fuel during low exhaust temperature regenerations. The slip of B20 fuel past the DOC was shown to produce significantly higher exotherms in the DPF during regeneration.

India is the world’s largest two-wheeler (2Wh) market. With the proportion of its middle class rapidly rising, 2Wh sales and the resulting emissions, are expected to grow exponentially. The decision to leap-frog from BSIV to BSVI emission norms shows India’s commitment to clean up its atmosphere. As of now, the regulation mandates Gaseous Pollutant (CO, HC, NOx) emission limits for all 2Whs and a particulate limit (PM & PN) for 2Whs powered by Direct Injection (DI) engines. Most of the 2Whs manufactured in India are powered by gasoline engines using the Port Fuel Injection (PFI) technology, and hence by definition particulate emission limits do not apply to them. Particulates when inhaled - especially of the ultrafine sizes capable of entering the blood stream - pose a serious health risk. This was the primary motivation to investigate the particulate emission levels of the 2Whs, which as on date, do not come under the purview of BSVI regulation.

Current trends in automotive emissions control have tended towards reduced mass substrates for improved light-off performance coupled with a reduction in PGM levels. This trend has led to increasingly thinner walls in the substrates and increased open frontal areas, with a potential of reducing the overall mechanical strength of the substrate relative to the thicker walled lower cell density supports. This change in demand driven technology has also led to developments, at times costly, in the processing of the catalytic converter system. Changes in mat materials, handling technology and coating variables are only a few sources of overall increased system costs. Corning has introduced the Celcor® XS™ product to the market which significantly increases the strength of thin and ultra thin walled substrates.

The tightening of emissions regulations has required changes in many areas of vehicle systems, including calibration strategies, catalytic converter strategies and exhaust configurations. Engine calibration strategies can be engineered to complement the performance parameters of the converter. Knowledge of the precise window of converter performance for different substrates can therefore provide guidance in targeting engine calibration strategies as well as selecting compatible converter systems within calibration constraints. In a previous paper [5], we explored the effect of thermal mass on emissions performance in the context of the FTP. This paper expands on the previous work and explores the effect of the aging cycle and thermal mass differences on CO-NOx crossover and light-off profiles. This analysis provides a tool to assist in design by defining a window of performance in the converter to be used in matching to a window of operation in the calibration.