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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.

Engine testing in the United States has been updated with the new centralized testing procedure in 40 CFR 1065. This regulation introduces a variety of new checks and tests required for certification testing. Upgrading existing equipment to run these tests in some cases introduces error or does not follow the spirit of the regulation. The term “good engineering practice” is used within the regulation to insure users make decisions on differences or unclear implementation. This paper addresses some of the recommended modifications and evaluates the differences in the results with and without the modifications.

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.