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Atmospheric modelers and development engineers need accurate measures of NO2 emissions from motor vehicles. Due to the oxidative reaction of oxygen with NO, these measurements (typically taken from a bag sample) can be inaccurate if care is not taken to minimize the sample residence time in the bags. This reaction occurs slowly at low NO concentrations, however, at higher NO concentrations the reaction can rapidly speed up (for example, 50 ppm NO will experience a 10% concentration reduction in 6.5 minutes). This report explores the factors contributing to this artifact for emissions test cells. Estimates of the error in NO2 emission rate measurements for several scenarios are presented. Additionally, kinetic expressions of the reaction rate are shown to be fairly accurate for our test conditions, but should not be used in general without verification of the non-existence of competing, hindering or accelerating species within the sample bag.

The use of Selective Catalytic Reduction (SCR) for NOx emissions control has resulted in a new challenge for the emissions measurement community. Most SCR systems require injection of urea or ammonia into the exhaust stream. Residual ammonia present in vehicle exhaust can have deleterious effects on NOx analyzers using chemiluminescent detectors (CLD). Ammonia can poison converter catalysts in CLD NOx analyzers and may react with NO2 across the converter. Both of these issues lead to erroneous NOx measurements, as well as increased maintenance costs and downtime. This paper will describe the development and use of a low-cost, simple ammonia scrubber that can easily be integrated into sampling systems and requires little change in test cell maintenance procedures. Validation results show the scrubber to have capacity sufficient to last for a full day of testing of typical vehicles.

Particulate matter (PM) emissions from vehicles are measured by passing diluted exhaust through an efficient sampling filter and determining the filter's weight gain. For vehicles meeting the currently regulated levels, the PM mass change may be as little as a few tens of micrograms, and the weighing requirements to accurately detect the change are severe. The difficulty is compounded by the insulating nature of the sampling filters used. Proper neutralizing of electrostatic charge on filters before weighing is critical to achieving accurate, repeatable results. Surface potential is sometimes used to verify that filters have been sufficiently neutralized. Unfortunately, while the surface potential of a conductor is well defined, that of an insulator is not and cannot be measured uniquely. This paper provides background electrostatic calculations needed to interpret the measurements.

PM (Particulate Matter) emitted by vehicles and engines is most often measured quantitatively by collecting diluted exhaust samples on filters that are weighed pre-and post-test. Static charge that builds on filters from handling can dramatically influence the measurement results, especially at low PM levels such as those produced when testing typical gasoline-powered vehicles or diesel-powered vehicles employing DPF (Diesel Particulate Filter) technology. It was found that proper grounding of equipment, furniture, and floor was insufficient to mitigate the effects of static electricity when using the traditional method of weighing from a glass Petri dish in the presence of an ionizing bar. A stainless steel EDP (Electrostatic Discharge Platform), using commercially available ionizing bars, was developed and proven to successfully reduce filter measurement variability when weighing PTFE membrane filters on a 0.1 microgram balance.

The regulated level of particulate mass for 2007 heavy duty diesel on-road engines is 0.01 g/bkhp-hr. Measurement of this low level of particulate by weighing is costly and time consuming. The weighing method must measure 100 μg or less of particulate on a filter that weighs about 100 mg with a resolution of ± 2.5 μg or better. This means that the microbalance and sampling handling procedure must be accurate within ±25 ppm by mass or ±1/40,000. It requires a microbalance with 0.1 μg precision housed in a special environment. Moreover, the weighing method involves a lengthy process. The filter must be equilibrated, and then pre- and post-weighed, usually with repeat measurements. An alternative to gravimetric analysis is a thermal mass analyzer that measures the semi-volatile organic fraction (SOF), as well as soot and sulfate fractions of the particulate matter (PM) collected on a cleaned quartz filter. The calibration of the thermal mass measurement is discussed in detail.

A direct comparison is made of time-resolved measurements of diesel PM emissions obtained using laser-induced incandescence (LII), an electrical low pressure impactor (ELPI), and a tapered element oscillating microbalance (TEOM). The measurements were made on two diesel passenger vehicles, one of which was equipped with a diesel particulate filter. Both LII and the ELPI performed well for both vehicles, whereas the TEOM lacked the sensitivity required for the filtered vehicle. We estimate that the LII system used has a limit of detection better than 0.2 mg/mi.

PM (Particulate Matter) emitted by vehicles and engines is most often measured quantitatively by collecting diluted exhaust samples on filters that are weighed pre-and post-test. The filter media used have high efficiency for small particles found in vehicle exhaust, but they also collect organic matter from the vapor phase with a lower, but nonzero, efficiency. In the past, organic vapor adsorption was usually negligible compared with PM levels from untreated diesel engine exhaust. For vehicles employing a DPF (Diesel Particulate Filter) and emitting very low PM, that is no longer the case. This paper reports measurements of the organic vapor deposition artifact for different filter media, including the two types (TX40 and Teflo) called for by the 2007 regulations for heavy duty diesel engines. The vapor artifact represents a substantial fraction of the 2007 regulatory standard of 10 mg/mi for light duty vehicles.

Collection of diesel exhaust using the Tapered Element Oscillating Microbalance (TEOM) instrument was investigated as an alternative to the traditional method of filter weighing for particulate matter mass determination. Such an approach, if successful, would eliminate considerable manual labor involved in weighing, as well as the delay of hours or days before final results were known. To avoid known artifacts in the second-by-second mode of operation, the TEOM was used in a phase-by-phase mode and was equilibrated with air of constant temperature and humidity before each measurement. Electrically operated valves were used to automate the equilibration and measurement process. The study also included a comparison between two types of TEOM filter - an older type and a new one designed by the TEOM manufacturer for more uniform flow and less flexing. Best results were obtained with the TEOM using the new filter under no-flow conditions.

Numerical models for a variety of vehicle emission measurement systems have been developed using Mathematica® software. The sampling systems evaluated include the Constant Volume Sampler (CVS) and the Bag Mini-Diluter (BMD). The CVS system was evaluated as the conventional fixed flow rate system and in a number of configurations designed for improved performance. The enhanced CVS system employs flow rate switch between phases and heated dilution air. This system with various other enhancements was also evaluated. The additional enhancements included proportional ambient sampling, dilution air refinement, heating of system including bags, and heated system with dilution air refinement. Lastly, the Bag Mini-Diluter system was evaluated. The purpose of these models is to help determine which system will be the most effective strategy for Ford Motor Company to utilize for SULEV and below emission measurements.

Previous research into Particulate Matter (PM) emissions from a spark-ignition engine has shown that the main factor determining the how PM emissions respond to transient engine operating conditions is the effect of those conditions on intake port processes such as fuel evaporation. The current research extends the PM emissions data base by examining the effect of transient load and speed operating conditions, as well as engine start-up and shut-down. In addition, PM emissions are examined during “real-world” driving conditions - specifically, the Federal Test Procedure. Unlike the previous work, which was performed on an engine test stand with no exhaust gas recirculation and with a non-production engine controller, the current tests are performed on a fully-functional, production vehicle operated on a chassis dynamometer to better examine real world emissions.

This paper explores the extent to which standard dilution tunnel measurements of motor vehicle exhaust particulate matter modify particle number and size. Steady state size distributions made directly at the tailpipe, using an ejector pump, are compared to dilution tunnel measurements for three configurations of transfer hose used to transport exhaust from the vehicle tailpipe to the dilution tunnel. For gasoline vehicles run at a steady 50 - 70 mph, ejector pump and dilution tunnel measurements give consistent results of particle size and number when using an uninsulated stainless steel transfer hose. Both methods show particles in the 10 - 100 nm range at tailpipe concentrations of the order of 104 particles/cm3.

As motor vehicle emissions have been reduced to meet requirements of the clean air acts, they have become low enough to be difficult to measure accurately. This is especially the case for hydrocarbons, because after warm-up, there are fewer hydrocarbons emitted from a modern vehicle's tailpipe than in the surrounding air. It is therefore important to correctly compensate for the ambient hydrocarbon levels of the air used to dilute the collected exhaust. In estimating the accuracy of the federally required testing procedures, previously published error analyses have examined the effects of random errors. This study examines the systematic errors inherent in the CVS (Constant Volume Sampling) technique specified in federal regulations, estimates their sizes, and proposes a method using proportional ambient sampling whereby they can be avoided.

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.

As vehicle tailpipe emission levels decrease with improvements in emission control technology and reformulation of gasolines, exhaust hydrocarbon levels begin to approach the levels in ambient air. Hydrocarbon speciation at these low levels requires high sensitivity capillary gas chromatography methods. In this study, a mixture of “synthetic” exhaust was prepared at two concentration levels (approximately 5 ppm C and 10 ppm C), and was analyzed by the widely-used Auto/Oil Air Quality Improvement Research Program (AQIRP) Phase II (gas chromatography) speciation method with a sensitivity of 0.005 ppm C for individual species. The mixture at each concentration level, along with a sample of ambient air, was analyzed a total of 20 times on 10 separate days over a 2½ week period. Concentrations of total hydrocarbons (HCs) and individual species (using the AQIRP library) were measured; averages and standard deviations were calculated.