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Diesel PM is understood to comprise elemental carbonaceous particles, an organic fraction of soluble or volatile hydrocarbons and sometimes a sulfate fraction. The need to measure such diesel PM at very low levels and to measure it outside of the usual engine test laboratory makes it helpful to sharpen our understanding of this detail composition and how it comes about. Real time instruments for measuring soot and particle number concentrations make it possible to discern emissions levels much lower than filter based laboratory measurements, but an understanding of the relationships between these measurements and the historical reference methods makes them more useful for development and certification of engines. Efforts to use soot measurements in-use in order to meet NTE requirements have shown good correlation to the laboratory reference and have also provided some new information on the shortcomings of the reference methods.

According to the ISO 16183 [1] protocol for heavy-duty diesel engines, particulate matter can be determined using a partial flow dilution system (PFDS). In order to control a PFDS, it is necessary to know the exact exhaust gas mass flow rate at the sample probe of the system at any given time. For the purpose of operating a PFDS with online control, a transformation time for the entire system (exhaust mass flow determination and partial flow adjustment) of equal or less than 300 ms is specified. In order to minimize the dynamic requirements for the PFDS a fast determination of the exhaust flow rate is necessary, which can be achieved most easily by using the intake flows (air + fuel flow) into the engine. This paper reports on the development and testing of an intake flow based model for calculating real time exhaust flow rate that accounts for the influence of the filling and emptying of the manifolds of a turbocharged diesel engine during dynamic operation.

The use of a partial flow sampling system (PFSS) to measure nonroad steady-state diesel engine particulate matter (PM) emissions is a technique for certification approved by a number of regulatory agencies around the world including the US EPA. Recently, there have been proposals to change future nonroad tests to include testing over a nonroad transient cycle. PFSS units that can quantify PM over the transient cycle have also been discussed. The full flow constant volume sampling (CVS) technique has been the standard method for collecting PM under transient engine operation. It is expensive and requires large facilities as compared to a typical PFSS. Despite the need for a cheaper alternative to the CVS, there has been a concern regarding how well the PM measured using a PFSS compared to that measured by the CVS. In this study, three PFSS units, including AVL SPC, Horiba MDLT, and Sierra BG-2 were investigated in parallel with a full flow CVS.

Partial flow sampling methods in emissions testing are interesting and preferred because of their lower cost, smaller size and applicability to engines of all sizes. However the agreement of the results obtained with instruments based on this method to those obtained with the traditional, large tunnel full flow sampling systems needs to be achieved, and the factors of construction that influence this agreement must be understood. These issues have received more attention lately in connection with ISO and WHDC standardization efforts underway to achieve a world-wide harmony in the sampling methods for heavy duty diesel engines, and with the introduction of similar Bag-minidiluter techniques into light duty SULEV gaseous pollutant measurement. This paper presents the theory and practice of a partial flow probe and tunnel design that addresses and minimizes the undesirable effects of the necessary differences between the two sampling methods.

The Bag Mini-diluter (BMD) is a proportional exhaust sampling system that is being studied as an improved measurement system for ultra-low level vehicle exhaust emissions. The traditional method for sampling vehicle exhaust has been the constant volume sampler (CVS) technique. This method dilutes the entire exhaust output from the vehicle, meters the mixture, and then takes a proportional sample for measurement. In contrast, the Mini-diluter sampling method meters a small sample of raw exhaust, and then dilutes this sample to a fixed dilution ratio. This approach offers new opportunities to improve the quality of the sample measurement at very low levels, which will be crucial for accurate vehicle exhaust emission measurements on vehicles that meet the ULEV and SULEV standards. A number of test programs have compared the performance of the Mini-diluter to the CVS on vehicles certified to Tier 1 and LEV standards, and the results demonstrated favorable correlation.

The traditional method for sampling vehicle exhaust has been the constant volume sampler (CVS) technique as described in the Code of Federal Regulations (CFR). This method dilutes the entire exhaust output from the vehicle, meters the mixture, and takes a proportional sample for measurement. The Mini-diluter sampling method reverses this process by first metering a small sample and then diluting to a fixed dilution ratio. This approach offers new opportunities to improve the quality of the sample measurement. This is especially interesting considering the lower emissions levels from ULEVs. The usefulness of this idea will depend on the development of stable and repeatable devices to implement it. This paper describes the operation of and presents results from a Mini-dilution system that uses critical flow venturis to provide a stable and repeatable dilution.

When a sampling system is attached to the exhaust tailpipe of a motor vehicle in order to measure pollutants, it should not alter its performance. The need to minimize any such influence has been translated into a specification on the maximum excursion of the static pressure observed at the connection of the vehicle's tailpipe to the sampling system while it is driven over a test cycle. This requirement is effectively a constraint on the design of the CVS ductwork that brings together the vehicle exhaust and the necessary dilution air. This paper describes the parameters of the ductwork design that affect the pressure observed at the vehicle's TP during emissions testing and outlines a fluid dynamics model that one can use to predict the performance of a sampling system. Finally, it describes an optimized design that minimizes the pressure effects on the vehicle while providing for other functions such as filtering, heating and measuring the dilution airflow.

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.

The elimination of water condensation is a familiar challenge to exhaust sampling system design and operation. The Constant Volume Sampler (CVS), commonly used to sample automotive exhaust, uses ambient air to dilute raw exhaust in order to keep water vapor, produced by the combustion process, in suspension. Without sufficient dilution, the water vapor will condense on the surfaces of the CVS and sample bags, absorbing water soluble compounds. These compounds are left unanalyzed resulting in nonrepresentative emissions and fuel economy measurements. Furthermore, condensation in the bag sampling system (pump, filter, lines, etc.) will increase all emissions measurements. Overdilution of the raw exhaust, on the other hand, produces low-level diluted concentrations which are more difficult to accurately measure.

A confusing number of equations have been developed and published for calculating the air/fuel ratio of an operating engine from the composition of its exhaust gasses. These methods make varying use of the information available from the gas concentration measurements, but they all are based on the same chemistry of combustion. The method described here is a single algorithm that duplicates the results of all the well known published equations and can adapt to different measurement circumstances, such as when an oxygen measurement is not available or if the gas sampling point is moved to after the catalyst. Data are presented to demonstrate the equivalence of the algorithm and equation evaluations.