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Diesel Particulate Filters (DPF) made of cordierite are generally used for diesel engine aftertreatment systems in both on-road and commercial off-highway vehicles to meet today’s worldwide emission regulations. PM/PN and NOx emission regulations will become more stringent worldwide, as represented by CARB2027 and Euro7. Technologies that can meet these strict regulations are required. As a result, aftertreatment systems have become more complex with limited space. Recently, off-highway OEMs have been interested in downsizing the aftertreatment system using concepts such as DOConFilter in an effort to reduce the size of the exhaust system. DOConFilter can effectively replace DOC + CSF or DOC + bare DPF systems with a single zone coated particulate filter. DOConFilter systems have an increased amount of coating compared to CSF as higher-filtration filters will become the norm. An undesirable increase in pressure drop is expected by adopting this new technology.

Diesel Particulate Filters (DPF) are becoming mandatory for many Heavy Duty Vehicle (HDV) and Non Road Mobile Machinery (NRMM) applications as the requirement for particulate filtration performance has increased over this past decade. In a previous study, a new generation of cordierite DPF was developed to meet the latest major emission regulations; PN-PEMS requirement for EuroVI StepE, while maintaining a lower pressure drop and high ash capacity. Despite the improvements made in the latest generation DPF material, the introduction of tighter particulate regulations demands further improvement in DPF technology. More specifically, PN emission limits for Euro7 under wide operation conditions in conjunction with PN down to 10nm, as described in the proposal from Consortium for Ultra Low Vehicle Emission (CLOVE), requires further improvement in PN filtration performance. Pressure drop, which may negatively influence the CO2 emissions, remains a key performance criteria.

Heavy Duty Vehicle (HDV) Diesel emission regulations are set to be tightened in the future. The introduction of PN PEMS testing for Euro VI-e, and the expected tightening of PM/NOx targets set to be introduced by CARB in the US beyond 2024 are expected to create challenging tailpipe PN conditions for OEMs. Additionally, warranty and the useful life period will be extended from current levels. Improved fuel efficiency (reduction of CO2) also remains an important performance criteria. Furthermore, future non-road diesel emission regulations may follow tighten HDV diesel emission regulations contents, and non-road cycles evaluation needs to be considered as well for future. In response to the above tightened regulation, for Diesel Particulate Filter (DPF) technologies will require higher PN filtration performance, lower pressure drop, higher ash capacity and better pressure drop hysteresis for improved soot detectability.

Selective catalyst reduction (SCR) using cordierite honeycomb substrate is generally used as a DeNOx catalyst for diesel engines exhaust in both on-road and commercial off-highway vehicles to meet today’s worldwide emission regulations. Worldwide NOx emission regulations will become stricter, as represented by CARB2027 and EuroVII. Technologies which can achieve further lower NOx emissions are required. Recently, several technologies, like increased SCR catalyst loading amount on honeycomb substrates, and additional SCR catalyst volume in positions closer to the engine are being considered to achieve ultra-low NOx emissions. However, undesirable pressure drop increase and enlarging after treatment systems will be caused by adopting these technologies. Therefore, optimization of the material and honeycomb cell structure for SCR is inevitable to achieve ultra-low NOx emissions, while minimizing any system drawbacks.

With the push towards more stringent on-road US heavy duty diesel regulations (i.e. HD GHG Phase 2 and the proposed ARB 20 mg/bhp-hr NOx), emission system packaging has grown critical while improving fuel economy and NOx emissions. The ARB regulations are expected to be implemented post 2023 while regulation for EU off-road segment will begin from 2019. The regulation, called Stage V, will introduce particle number (PN) regulation requiring EU OEMs to introduce a diesel particulate filter (DPF) while customer demands will require the OEMs to maintain current emission system packaging. A viable market solution to meet these requirements, especially for EU Stage V being implemented first, is a DPF coated with a selective catalyst reduction (SCR) washcoat (i.e. SCRonDPF).

Particle Number (PN) regulation was firstly introduced for European light-duty diesel vehicles back in 2011[1]. Since then, PN regulation has been and is being expanded to heavy-duty diesel vehicles and non-road diesel machineries. PN regulation will also be expanded to China and India around 2020 or later. Diesel Particulate Filter (DPF) is significant factor for the above-mentioned PN regulation. This filter technology is to be continuously evolved for the near future tighter PN regulation. Generally, PN filtration performance test for filter technology development is carried out with chassis dynamometer, engine dynamometer or simulator [2]. This paper describes a simplified and relatively quicker alternative PN filtration performance test method for accelerating filter technology development compared to the current test method.

Diesel engines are widely used to reduce CO2 emission due to its higher thermal efficiency over gasoline engines. Considering long term CO2 targets, as well as tighter gas emission, especially NOx, diesel engines must become cleaner and more efficient. However, there is a tradeoff between CO2 and NOx and, naturally, engine developers choose lower CO2 because NOx can be reduced by a catalytic converter, such as a SCR catalyst. Lower CO2 engine calibration, unfortunately, leads to lower exhaust gas temperatures, which delays the activation of the catalytic converter. In order to overcome both problems, higher engine out NOx emission and lower exhaust gas temperatures, close-coupled a diesel particulate filter (DPF) system with integration of SCR catalyst technology is preferred. For SCR catalyst activity, it is known that the catalyst loading amount has an influence on NOx performance, so a high SCR catalyst loading will be required.

Since the implementation of Euro 6 in September 2014, diesel engines are facing another drastic reduction of NOx emission limits from 180 to only 80 mg/km during NEDC and real driving emissions (RDE) are going to be monitored until limit values are enforced from September 2017. Considering also long term CO2 targets of 95 g/km beyond 2020, diesel engines must become cleaner and more efficient. However, there is a tradeoff between NOx and CO2 and, naturally, engine developers choose lower CO2 because NOx can be reduced by additional devices such as EGR or a catalytic converter. Lower CO2 engine calibration, unfortunately, leads to lower exhaust gas temperatures, which delays the activation of the catalytic converter. In order to overcome both problems, higher NOx engine out emission and lower exhaust gas temperatures, new aftertreatment systems will incorporate close-coupled DeNOx systems.

Diesel engines are more fuel efficient due to their high thermal efficiency, compared to gasoline engines and therefore, have a higher potential to reduce CO2 emissions. Since diesel engines emit higher amounts of Particulate Matter (PM), DPF systems have been introduced. Today, DPF systems have become a standard technology. Nevertheless, with more stringent NOx emission limits and CO2 targets, additional NOx emission control is needed. For high NOx conversion efficiency, SCR catalysts technology shows high potential. Due to higher temperature at the close coupled position and space restrictions, an integrated SCR concept on the DPFs is preferred. A high SCR catalyst loading will be required to have high conversion efficiency over a wide range of engine operations which causes high pressure for conventional DPF materials.

Ammonia Selective Catalytic Reduction (SCR) and Lean NOx Trap (LNT) systems are key technologies to reduce NOx emission for diesel on-highway vehicles to meet worldwide tighter emission regulations. In addition DeNOx catalysts have already been applied to several commercial off-road applications. Adding the DeNOx catalyst to existing Diesel Oxidation Catalyst (DOC) and Diesel Particulate Filter (DPF) emission control system requires additional space and will result in an increase of emission system back pressure. Therefore it is necessary to address optimizing the DeNOx catalyst in regards to back pressure and downsizing. Recently, extruded zeolite for DeNOx application has been considered. This technology improves NOx conversion at low temperature due to the high catalyst amount. However, this technology has concerned about strength and robustness, because the honeycomb body is composed of catalyst.

The presentation describes technology developments and the integration of these technologies into new emission control systems. As in other years, the reader will find a wide range of topics from various parts of the world. This is reflective of the worldwide scope and effort to reduce diesel exhaust emissions. Topics include the integration of various diesel particulate matter (PM) and Nitrogen Oxide (NOx) technologies as well as sensors and other emissions related developments. Presenter Atsuo Kondo, NGK Insulators, Ltd.

The reduction of greenhouse gas is becoming increasingly important for humankind, and vehicles with low CO₂ emissions have a part to play in any reduction initiatives. Diesel engines emit 30% less CO₂ than gasoline engines, so diesel engines will make an important contribution to the overall decrease. Unfortunately diesel exhaust gas contains particulate matter (PM) which may cause health problems, and such PM emissions are regulated by law. In order to reduce PM, especially soot, diesel particulate filters (DPFs) are widely fitted to diesel vehicles. A DPF can remove more than 99% by weight of soot from exhaust gas under normal operating conditions, and they are one of the most important methods to achieve any regulation targets. But if the system malfunctions, the PM emissions may exceed the regulation limit. To detect such PM leakage, on-board diagnostics (OBD) are required.

As emissions regulations are becoming more stringent, various efforts to improve emission performance have been carried out in different areas including the honeycomb structure of catalytic converters. This report describes the development of a simulation tool to predict emission performance and simulation results for different cell structures. The simulation model was developed based on global kinetic chemical reaction model [1]. Having tuned the reaction parameters through a light-off test and estimated oxygen storage capacity through an oxygen storage test, we ultimately tuned the model in a vehicle test (with Bags 1 and 2, FTP 75). As a result, the simulated cumulative tailpipe emissions are within ±25 percent of the test results. Parameter analyses indicate that the amount of emissions decreased as the density of cells increased and that the amount of emissions also decreased the thinner the wall thicknesses were.

Developing ultra thin wall ceramic substrates is necessary to meet stricter emissions regulations, in part because substrate cell walls need to be thinner in order to improve warm-up and light-off characteristics and lower exhaust system backpressure. However, the thinner the cell wall becomes, the poorer the mechanical and thermal characteristics of the substrate. Furthermore, the conditions under which the ultra thin wall substrates are used are becoming more severe. Therefore both the mechanical and thermal characteristics are becoming important parameters in the design of advanced converter systems. Whereas square cells are used world-wide in conjunction with oxidation and/or three-way catalysts, hexagonal cells, with features promoting a homogeneous catalyst coating layer, have found limited use as a NOx absorber due to its enhanced sulfur desorption capability.

The future emission limits for gasoline fuelled passenger cars require more and more efficient exhaust gas aftertreatment devices - the catalytic converter being one essential part of the complex system design. The present paper summarizes the results of several basic research programs putting major emphasis on the application of highly sophisticated three-way catalyst technologies being taylored for the utilization on ultra thin-wall ceramic substrates. In the first part of the investigation the following effects were examined in detail: Different washcoat loadings at constant PGM-loadings Different volumes of catalysts for constant amounts of PGM and washcoat Similar washcoat technologies at different ratios of WC-loading to precious metal concentration in the washcoat.

NOx adsorber has already been used for the after-treatment system of series production vehicle installed with a lean burn or direct injection engine [1,2,3]. In order to improve NOx adsorbability at high temperatures, many researchers have recently been trying an addition of potassium (K) as well as other conventional NOx adsorbents. Potassium, however, reacts easily with the cordierite honeycomb substrate at high temperatures, and not only causes a loss in NOx adsorbability but also damages the substrate. Three new technologies have been proposed in consideration of the above circumstances. First, a new concept of K-capture is applied in washcoat design, mixed with zeolite, to improve thermal stability of K and to keep high NOx conversion efficiency, under high temperatures, of NOx adsorber catalyst. Second, another new technology, pre-coating silica over the boundary of a substrate and washcoat, is proposed to prevent the reaction between potassium and cordierite.

Regulatory compliance measurements for vehicle emissions are generally performed in well equipped test facilities using chassis dynamometers that simulate on-road conditions. There is also a requirement for obtaining accurate information from vehicles as they operate on the road. An on-board system has been developed to measure real-time mass emission of NOx, fuel consumption, road load, and engine output. The system consists of a dedicated data recorder and a variety of sensors that measure air-to-fuel ratios, NOx concentrations, intake air flow rates, and ambient temperature, pressure and humidity. The system can be placed on the passenger seat and operate without external power. This paper describes in detail the configuration and signal processing techniques used by the on-board measurement system. The authors explain the methods and algorithms used to obtain (1) real-time mass emission of NOx, (2) real-time fuel consumption, (3) road load, and (4) engine output.

This paper describes improvements achieved with regard to the long term stability and the system integrability of a previously described thick film NOx sensor for gasoline lean burn and diesel applications. (1, 2, 3) Durability test up to 1000 hours consisting of a temperature cycle have been carried out by a stoichiometric operating gasoline engine test bench. The NOx sensor demonstrates the NOx output shift in terms of the NOx sensitivity less than 5 % on a model gas apparatus and ± 7 % measuring accuracy in practical operating condition on a diesel engine after 1000 hours that is equivalent to approximately 60K miles driving. The integration of the control electronics for the sensor in its connector is achieved for the sensitive measuring current in the μA-range or less on vehicle applications. The developed electronics functions closed-loop controls for a tip temperature and oxygen pumps as well as a diagnosis of sensor malfunctions.

A practical ZrO2 NOx sensor using dual oxygen pumping cells has been introduced for the control of NOx emitted from a lean-burn gasoline engine and diesel engine.(1),(2). However, the measuring accuracy was not high enough to be useful for controlling or monitoring a low level of NOx concentration such as several tens ppm behind a three way catalyst or lean NOx catalyst which is NOx adsorption or De-NOx catalyst. This paper describes improvement of the interference effect of oxygen in the exhaust gas from the lean-burn gasoline engine and diesel engine. The cause of oxygen dependency is analyzed/revealed and a method of improvement is introduced. The improved NOx sensor has an approximately · · 2% measuring error in the wide range of oxygen concentration on a model gas system, compared to the · ·10% of the previous one.

This paper describes a thick film ZrO2 NOx sensor feasible for diesel and gasoline engine applications, and introduces modification items from the previous concept design.(1) The modification items comprise simplifying the sensing element design to reduce output terminals for package design and applying temperature control to the sensing element in order to minimize sensor performance dependency on gas temperature. The NOx sensor indicates a stable linear signal in proportion to NOx concentration in a wide range of temperature, A/F and NOx concentration as a practical condition on both gasoline and diesel engines. The NOx sensor shows a good response in hundred msec. and a sharp signal following NOx generation in a transient state as well. Besides, another type of a NOx sensor is proposed for low NOx measurement in a practical use, by an electromotive force(EMF) voltage instead of a pumping current.