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A Constant Volume Sampler (CVS) over dilutes the exhaust gas sample when testing Plug-In Hybrid Electric Vehicles (PHEV). This is because the CVS continues to fill the sample bag when the engine is shutdown. With a PHEV, it is possible to complete an FTP test with the engine running less than 20% of the time, resulting in a CVS bag dilution ratio in the range of 100 to 300. The CVS dilution ratio should be in the range of 5-25 for accurate results. At higher dilution ratios, the gas concentrations of CO, NOx and THC approach the ambient background level in the test cell. At a dilution of 100, the CO₂ concentration in the sample bag is about 0.13%, which is only 3 times the air background concentration. The measurement errors caused by over dilution create errors of 10% to 30% in the calculated mass of CO₂, CO, and NOx. Estimated errors for THC are in the range of 200%.

A test cell was developed for evaluating a 6-speed automatic transmission. The target vehicle had an internal combustion 5.4L gasoline V8 engine. An electric dynamometer was used to closely simulate the engine characteristics. This included generating mean torque from the ECU engine map, with a transient capability of 10,000 rpm/second. Engine inertia was simulated with a transient capability of 20,000 rpm/second, and torque pulsation was simulated individually for each piston, with a transient capability of 50,000 rpm/second. Quantitative results are presented for the correlation between the engine driven and the dynamometer driven transmission performance over more than 60 test cycles. Concerns about using the virtual engine in validation testing are discussed, and related to the high frequency transient performance required from the electric dynamometer. Qualitative differences between the fueled engine and electric driven testing are presented.

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.