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In Fall of 2001, a new emissions test cell was installed at Ford Motor Company that was specifically designed for precise low-level measurements (as described in Reference 6). The primary design focus for this cell was to ensure that optimal measurement capability was available to test vehicles that meet the stringent Partial Zero Emission Vehicle (PZEV) tailpipe requirements (NMOG = 10 mg/mile, NOx = 20 mg/mile). Over the past four years, there have been numerous improvements to the operational and Quality Assurance (QA) practices used in the PZEV Test Cell. Several investigations have also been performed to demonstrate the quality of its emissions measurements. Finally, a number of “lessons learned” have been documented from our experiences with PZEV measurements and with testing hybrid-electric vehicles. This paper summarizes these findings as a reference for others interested in low-level emissions measurements.

Variable Cam Timing (VCT) has been proven to be a very effective method in PFI (Port Fuel Injection) engines for improved fuel economy and combustion stability, and reduced emissions. In DISI (Direct Injection Spark Ignition) engines, VCT is applied in both stratified-charge and homogeneous charge operating modes. In stratified-charge mode, VCT is used to reduce NOx emission and improve combustion stability. In homogeneous charge mode, the function of VCT is similar to that in PFI engines. In DISI engine, however, the VCT also affects the available fuel-air mixing time. This paper focuses on VCT effects on the induction process and the fuel-air mixing homogeneity in a DISI engine. The detailed induction process with large exhaust-intake valve overlap has been investigated with CFD modeling. Seven characteristic sub-processes during the induction have been identified. The associated mechanism for each sub-process is also investigated.

Meeting EPA Tier 2 emission standards presents a great challenge to engine manufacturers. In addition to having an actively controlled aftertreatment system, engine-out NOx emission needs to be reduced significantly to achieve regulatory compliance. Using advanced combustion methods, such as low temperature combustion and/or HCCI, has been shown to reduce engine-out NOx emissions. However, all this new combustion technologies are yet to permeate down into any production system. In current practice, large amount of exhaust gas recirculation (EGR) into the cylinders is widely used to reduce emissions. However, NOx emission from transient engine operation still constitutes a very large percentage of the total NOx output during a Federal Test Procedure (FTP) cycle and has yet to be adequately addressed. Currently, the EGR flow is controlled using the intake mass airflow (MAF) measurement.

During the course of emissions and fuel economy (FE) testing, vehicles that are calibrated to meet Tier 3 emissions requirements currently must demonstrate compliance on Tier 3 E10 fuel while maintaining emissions capability with Tier 2 E0 fuel used for FE label determination. Tier 3 emissions regulations prescribe lower sulfur E10 gasoline blends for the U.S. market. Tier 3 emissions test fuels specified by EPA are required to contain 9.54 volume % ethanol and 8-11 ppm sulfur content. EPA Tier 2 E0 test fuel has no ethanol and has nominal 30 ppm sulfur content. Under Tier 3 rules, Tier 2 E0 test fuel is still used to determine FE. Tier 3 calibrations can have difficulty meeting low Tier 3 emissions targets while testing with Tier 2 E0 fuel. Research has revealed that the primary cause of the high emissions is deactivation of the aftertreatment system due to sulfur accumulation on the catalysts.

To meet stringent 2010 NOx emissions, many manufacturers are expected to deploy urea selective catalytic reduction systems. Indications from ARB are that a threshold monitor must be developed to monitor their performance. The most capable monitoring technology at this time relies on NOx sensors. This paper assesses the capability of the NOx sensor as an SCR monitoring device. To this end, the NOx sensor must be able to distinguish between a marginal and a threshold catalyst with enough separation to allow for variability. We present the noise factors associated with the NOx conversion of the SCR system, and analyze what NOx sensor accuracy we need to preserve separation in the face of those noise factors. It is shown that a 1.75 threshold monitor is not feasible with current NOx sensor technology. We analyze the benefit of a partial volume monitor, and show there is no advantage unless the slope error of the NOx sensor is drastically reduced from current levels.

The design of modern diesel-powered vehicles involves optimization and balancing of trade-offs for fuel efficiency, emissions, and noise. To meet increasingly stringent emission regulations, diesel powertrains employ aftertreatment devices to control nitrogen oxides, hydrocarbons, carbon monoxide, and particulate matter emissions and use active exhaust warm-up strategies to ensure those devices are active as quickly as possible. A typical strategy for exhaust warm-up is to operate with retarded combustion phasing, limited by combustion stability and HC emissions. The amount of exhaust enthalpy available for catalyst light-off is limited by the extent to which combustion phasing can be retarded. Diesel cetane number (CN), a measure of fuel ignition quality, has an influence on combustion stability at retarded combustion phasing. Diesel fuel in the United States tends to have a lower CN (both minimum required and average in market) than other countries.

It is likely that use of urea-based selective catalytic reduction (SCR) will be needed to meet U.S. Tier 2 diesel emission standards for oxides of nitrogen (NOx). The ideal ratio of ammonia (NH3) molecules to NOx molecules (known as alpha) is 1:1 based on urea consumption and having NH3 available for reaction of all of the exhaust NOx. However, SCR efficiency can be less than 100% at low temperatures in general, and at higher temperatures with high exhaust SCR catalyst space velocities. At the low temperatures where NOx conversion efficiency is low, it may be advantageous to reduce the alpha ratio to values less than one (less NH3 than is needed to convert 100% of the NOx emissions) to avoid NH3 slip. At higher space velocities and high temperatures, the NOx conversion efficiency may be higher with alpha ratios greater than 1. There is however concern that the additional NH3 will be slipped under these conditions.

The use of urea-based selective catalytic reduction (SCR) is a promising method for achieving U.S. Tier 2 diesel emission standards for NOx. To meet the Tier 2 standards for Particulate Matter (PM), a catalyzed diesel particulate filter (CDPF) will likely be present and any ammonia (NH3) that is not consumed over an SCR catalyst would pass over the CDPF to make nitrous oxide (N2O) emissions and/or oxides of nitrogen (NOx), or exit the exhaust system as NH3. N2O is undesirable due to its high greenhouse gas potential, while NOx production from the slipped NH3 would reduce overall system NOx conversion efficiency. This paper reviews certain conditions where NH3 slip past an SCR system may be a concern, looks at what would happen to this slipped NH3 over a CDPF, and evaluates the performance of various supplier NH3 slip catalysts under varied space velocities, temperatures and concentrations of NH3 and NOx.

Exhaust gas recirculation (EGR) coolers are used on diesel engines to reduce peak in-cylinder flame temperatures, leading to less NOx formation during the combustion process. There is an ongoing concern with soot and hydrocarbon fouling inside the cold surface of the cooler. The fouling layer reduces the heat transfer efficiency and causes pressure drop to increase across the cooler. A number of experimental studies have demonstrated that the fouling layer tends to asymptotically approach a critical height, after which the layer growth ceases. One potential explanation for this behavior is the removal mechanism derived by the shear force applied on the soot and hydrocarbon deposit surface. As the deposit layer thickens, shear force applied on the fouling surface increases due to the flow velocity growth. When a critical shear force is applied, deposit particles start to get removed.

Model low temperature NOx adsorbers (LTNA) consisting of Pd on a ceria/zirconia washcoat on monoliths were evaluated for low temperature NOx storage under lean conditions to assess their potential for adsorbing the cold-start NOx emissions on a diesel engine during the period before the urea/SCR system becomes operational. A reactor-based transient test was performed with and without C2H4, CO/H2, and H2O to assess the effects of these species on the NOx storage performance. In the absence of C2H4 or CO/H2, H2O severely suppressed the NOx storage of these model LTNAs at temperatures below 100°C, presumably by blocking the storage sites. When C2H4 was included in the feedgas, H2O still suppressed the NOx storage below 100°C. However, the C2H4 significantly increased the NOx storage efficiency above 100°C, attributable to the formation of alkyl nitrites or alkyl nitrates on the catalyst.

Selective Catalytic Reduction of NOx is a promising technology to enable diesel engines to meet certification under Tier 2 Bin 5 emissions requirements. SCR catalysts for vehicle use are typically zeolitic materials known to store both hydrocarbons and ammonia. Ammonia storage on the zeolite has a beneficial effect on NOx conversion; hydrocarbons however, compete with ammonia for storage sites and may also block access to the interior of the zeolites where the bulk of the catalytic processes take place. This paper presents the results of laboratory studies utilizing surrogate hydrocarbon species to simulate engine-out exhaust over catalysts formulated to operate in both low (≈175-500°C) and high temperature (≈250-600°C) regimes. The effects of hydrocarbon exposure of these individual species on the SCR reaction are examined and observations are made as to necessary conditions for the recovery of SCR activity.

FTP emissions tests on a passenger vehicle equipped with a 1.8 L IDI turbo-charged diesel engine show that the mass emissions of particles decrease by (36±8)% when 16.6% dimethoxymethane (DMM) by volume is added to a diesel fuel. Particle size measurements reveal log-normal accumulation mode distributions with number weighted geometric mean diameters in the 80 - 100 nm range. The number density is comparable for both base fuel and the DMM/diesel blend; however, the distributions shift to smaller particle diameter for the blend. This shift to smaller size is consistent with the observed reduction in particulate mass. No change is observed in NOx emissions. Formaldehyde emissions increase by (50±25)%, while emissions of other hydrocarbons are unchanged to within the estimated experimental error.

A study was performed on a lean NOx trap in which the loading of a ceria-containing mixed oxide in the washcoat was varied. After a mild stabilization of the traps, the time required to purge the NOx trap generally increased with increasing amount of mixed oxide. The purge NOx release also increased with increasing mixed oxide level but was greatly diminished after thermal aging. The sulfur tolerance of the NOx trap improved as the mixed oxide content was increased from 0% to 37%. The sample with 0% mixed oxide was more difficult to desulfate than the other samples due to poor water-gas-shift capability. After thermal aging, the NOx reduction efficiency on a 60 second lean/5 second rich cycle was highest for the samples with 0% to 37% mixed oxide at evaluation temperatures of 400°C to 500°C.

It is anticipated that future gasoline engines will have improved mechanical efficiency and consequently lower exhaust temperatures at low load conditions, although the exhaust temperatures at high load conditions are expected to remain the same or even increase due to the increasing use of downsized turbocharged engines. In 2014, a collaborative project was initiated at Ford Motor Company, Oak Ridge National Lab, and the University of Michigan to develop three-way catalysts with improved performance at low temperatures while maintaining the durability of current TWCs. This project is funded by the U.S. Department of Energy and is intended to show progress toward the USDRIVE target of 90% conversion of hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) at 150 °C after high mileage aging. The testing protocols specified by the USDRIVE ACEC team for stoichiometric S-GDI engines were utilized during the evaluation of experimental catalysts at all three facilities.

In anticipation that future gasoline engines will have improved fuel efficiency and therefore lower exhaust temperatures during low load operation, a project was initiated in 2014 to develop three-way catalysts (TWC) with improved activity at lower temperatures while maintaining the durability of current TWCs. This project is a collaboration between Ford Motor Company, Oak Ridge National Laboratory, and the University of Michigan and is funded by the U.S. Department of Energy. The ultimate goal is to show progress towards the USDRIVE goal of 90% conversion of hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) at 150°C after high mileage aging. A reactor was set up at Ford to follow the catalyst testing protocols established by the USDRIVE ACEC tech team for evaluating catalysts for stoichiometric gasoline direct-injection (S-GDI) engines; this protocol specifies a stoichiometric blend of CO/H2, NO, C3H6, C2H4, C3H8, O2, H2O, and CO2 for the evaluations.

Selective catalytic reduction (SCR) is a promising technology for diesel aftertreatment to meet NOx emissions targets in several countries. In established markets such as the US and Europe, zeolite SCR systems are expected to be used due to their ability to survive the exhaust gas temperatures seen in an active diesel particulate filter regeneration. In emerging markets where the fuel sulfur level may be as high as 2000 parts per million, zeolite SCR catalysts may have durability issues. In these markets, low sulfur fuel is needed overall to meet emissions standards and to avoid high sulfate emissions, but the aftertreatment system must be durable to high sulfur levels because there is a risk of exposure to high sulfur fuel. Also, emissions standards may be met without a DPF in some applications, so that the exhaust system would not see temperatures of 600°C or higher.

This work investigates the suitability of n-butanol for enabling PCCI, HCCI, and RCCI combustion modes to achieve clean and efficient combustion on a high compression ratio (18.2:1) diesel engine. Systematic engine tests are conducted at low and medium engine loads (6∼8 bar IMEP) and at a medium engine speed of 1500 rpm. Test results indicate that n-butanol is more suitable than diesel to enable PCCI and HCCI combustion with the same engine hardware. However, the combustion phasing control for n-butanol is demanding due to the high combustion sensitivity to variations in engine operating conditions where engine safety concerns (e.g. excessive pressure rise rates) potentially arise. While EGR is the primary measure to control the combustion phasing of n-butanol HCCI, the timing control of n-butanol direct injection in PCCI provides an additional leverage to properly phase the n-butanol combustion.

The goal of the present work was to investigate the ability of the SEMTECH®-D Portable Emissions Measurement System (PEMS) to provide simultaneous, accurate, real-time (1Hz) measurements of NO and NO2 in vehicle exhaust. Extensive chassis dynamometer laboratory evaluation studies of the SEMTECH® system were conducted. The instantaneous (1Hz) NOx emissions were measured using a conventional chemiluminescence analyzer (CLA) and were compared to the sum of the instantaneous NO and NO2 measurements from the SEMTECH®-D. The sum of the NO and NO2 emissions measured by the SEMTECH® were in excellent agreement (within 95% in most cases) with the total NOx measurements from the conventional CLA. During the laboratory evaluation studies, several Federal Test Procedure (FTP) drive cycles were conducted. Examples of the NO and NO2 concentration and mass emissions measured using the SEMTECH®-D are presented along with the corresponding SEMTECH®-D detection limits.

Selective catalytic reduction (SCR) with NH3 provides an attractive alternative to lean NOx traps for controlling the NOx emissions from lean-burn gasoline engines. This paper summarizes a laboratory study to assess the effects of temperature, space velocity, and the concentrations of NO, NH3, and O2 on the NOx conversion of an iron/zeolite SCR catalyst. A fresh sample was evaluated on slow temperature ramps with 5% O2 and 250, 500, or 1000 ppm of NO and NH3. The NOx conversion at low temperatures decreased with increasing NO and NH3 concentrations due to kinetic limitations. Conversely, the conversion at high temperatures increased with increasing NO and NH3 concentrations because the portion of NH3 oxidized by O2 decreased with increasing NO concentration.

A laboratory study was performed to assess the potential of using selective catalytic reduction (SCR) with NH3 to treat the NOx emissions from lean-burn gasoline engines. A primary concern was the potential for hot rich exhaust conditions on the vehicle, as such conditions could degrade the zeolite-based SCR catalysts being developed for automotive applications. Samples of an iron/zeolite formulation were aged for 34 hours behind samples of a three-way catalyst (TWC) on a pulse-flame combustion reactor using different A/F ratio schedules that exposed the catalysts to either continuously lean operation, mostly stoichiometric operation, or mostly rich operation. For each A/F ratio schedule, separate SCR samples were aged with inlet temperatures of 750°C, 800°C, or 850°C. The aged SCR samples were evaluated for NOx conversion at 25K hr-1 during lean temperature ramps with 500 ppm NO and NH3.