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The use of portable emissions measurement systems (PEMS) for testing vehicle emissions while driving on the road has been demonstrated as early as the 1980s. Many users have taken the driving route and repeated the route in a chassis cell with the same vehicle expecting identical results. Emission results can be comparable but there are many factors that need to be considered. This study compares PEMS results for a driving route repeated across seasons and traffic conditions with a single vehicle. The ambient temperature variability and traffic is shown to cause variation in emissions for any individual run. Generating a test cycle to mimic the driving route can be done in a variety of ways. The simplest is to take an individual driving run and translate the time and speed trace directly. This does not address the statistical results from numerous driving runs on the same route.

A partial-flow sampling system, namely a Bag Mini-Diluter (BMD) is an accepted alternative to Constant Volume Sampling (CVS) for obtaining mass emissions in a chassis test cell. Our equipment delivers equivalent CVS and BMD emission results with gasoline engines of 2.0 to 5.6 liter displacement. However, while testing a vehicle with a 1.3 liter engine, CVS and BMD CO2 mass differences greater than 9% were observed during cold-start tests. This paper describes the modifications made to obtain BMD and CVS mass emissions that match within 2% during cold-start tests with a 1.3 liter vehicle.

A chassis dynamometer test cell is employed along with a CVS system to test for both vehicle mass emissions and for fuel economy. In addition to the standard test equipment for gasoline vehicles, a highly accurate fuel flow meter is installed that measures the mass of fuel consumed by the engine during chassis dynamometer tests. A 3.8 liter V6 vehicle was tested over standard United States E.P.A. FTP and Highway Fuel Economy protocols, where it is found that the fuel flow meter mass measurements correlate with the carbon-balance fuel consumption results measured with the CVS. However, there are significant differences between the fuel flow meter and the CVS measured fuel consumption during vehicle cold-start tests. This is a concern because a large fraction of gasoline engine emissions are generated only during a cold-start. It is important to be able to relate mass emissions to mass fuel consumption in order to understand and control cold-start gasoline engine performance.

This paper is a continuation [1] of the discussion of data collected during an effort in comparing on-board systems (Horiba OBS 1000 and MEMS built by West Virginia University) of Test Cell Equipment during Dynamometer runs (FTP) and on road routes (Sabraton-Bruceton Mills cycle). The OBS data in general, agreed within 6-11% of the lab equipment. In addition, data and installation experience on a heavy duty vehicle, a snow plow, will be presented.

For the past several years, manufacturers have been developing emission measurement systems for Super Ultra Low Emission (SULEV) measurements. The Bag Mini-Diluter (BMD) with an advanced exhaust flow measurement device is designed as an alternative to the traditional method for sampling vehicle exhaust, the constant volume sampler (CVS). Exhaust sampling instruments require system verification tests. The system verification test described and mandated for the CVS in the Code of Federal Regulations (CFR) §86.119-90(c) is a simulated test with propane. The very low concentration measurements required for SULEV regulations demand a more enhanced and accurate verification technique and procedure than the method described in the CFR. This investigation focuses on the technique and necessary equipment for verifying system integrity of the entire emission sampling system, including the Bag Mini-Diluter and the exhaust flow measurement device in the test cell.

As automakers begin to develop and certify vehicles that meet the California Air Resources Board LEV II and Environmental Protection Agency Tier II Regulations, emissions test cells must be designed and implemented that are capable of accurate low-level measurements. A new test cell has been installed at Ford Motor Company for use in testing vehicles that meet the stringent Partial Zero Emission Vehicle tailpipe requirements (NMOG = 10 mg/mile, NOx = 20 mg/mile). This test cell includes a redesigned Bag Mini-Diluter (BMD), improved analytical benches, an ultrasonic exhaust flow meter with an integrated tailpipe pressure control system, a conventional constant volume sampler (CVS), and a moveable electric dynamometer. The Bag Mini-Diluter will be used as the primary sampling system for the tailpipe measurements. The moveable electric dynamometer enables the test cell to be configured so that the vehicle is moved to the test equipment rather than moving the test equipment to the vehicle.