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Direct measurement of dilution air volume in a Constant Volume emission sampling system may be used to calculate tailpipe exhaust volume, and the total dilution ratio in the CVS. A Remote Mixing Tee (RMT) often includes a subsonic venturi (SSV) flowmeter in series with the dilution air duct. The venturi meter results in a flow restriction and significant pressure drop in the dilution air pipe. An ultrasonic flow meter for a similar dilution air volume offers little flow restriction and negligible pressure drop in the air duct. In this investigation, an ultrasonic flow meter (UFM) replaces the subsonic venturi in a Remote Mixing Tee. The measurement uncertainty and accuracy of the UFM is determined by comparing the real time flow rates and integrated total dilution air volume from the UFM and the dilution air SSV in the RMT. Vehicle tests include FTP and NEDC test cycles with a 3.8L V6 reference vehicle.

Diesel fuel may be blended with ethanol as a bio-fuel extender. However, ethanol is not miscible with diesel fuel, so an emulsifier must be added to a diesel-ethanol blend to prevent the ethanol fraction from separating in a fuel tank. This diesel-ethanol blending and storage problem can be avoided by installing a separate ethanol fuel tank, fuel pump, and ethanol fuel injector that operate in parallel with the standard diesel fuel injection system. A Medium Duty diesel truck has been modified for blending ethanol with the standard diesel fuel consumed by the engine. The ethanol is injected into the intake air so that diesel and ethanol aerosols are blended in the engine cylinder. The ethanol injection is synchronized with the diesel fuel injection, where the proportion of ethanol to diesel fuel is constant. Vehicle tests include EPA FTP procedures on a chassis test cell dynamometer.

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.

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.

The accuracy of low-level emission measurements has become increasingly important, due to the development and implementation of ULEV, SULEV, and PZEV vehicles. Measurement of these decreasing levels of automotive emissions requires new sampling and measuring techniques. Several alternative emission sampling techniques have been investigated to minimize measurement variability and maximize system repeatability. An alternative technique to obtain accurate low-level emissions measurement from SULEV vehicles is the Bag Mini-Diluter, which uses a proportional signal from an Exhaust Volume Measurement Device to sample vehicle exhaust. Crucial to successful proportional sampling of vehicle exhaust flow is the performance of the Exhaust Flow Measurement Device. This study evaluates an Exhaust Volume Measurement Device commonly used with a Bag Mini-Diluter.

A single vehicle (3.8L V6) underwent FTP75, HWFE, and US06 emission tests over a 6-month period. A bag mini-diluter and exhaust flowmeter sample system was installed in series with a CVS, so that mass emission results from an individual test could be directly compared between the bag mini-diluter and CVS. At one-month intervals, the bag mini-diluter and exhaust flowmeter sampling system was replaced with new units, while the vehicle and CVS remained unchanged. Assuming that the vehicle and CVS produce constant results, the variability of emissions over the test period are highly correlated with the variability of the bag mini-diluters and exhaust flowmeters. The average CO2 mass comparison between the bag mini-diluter and CVS shows the separate sample systems match within 0.5% for an individual test. The established baseline determined from the CVS has a standard deviation of about 2%, which we believe is predominantly due to vehicle variability.