Tim Brown

Comparison of constant-volume sampler and bag mini-diluter emissions measurements of a plug-in hybrid electric vehicle:

Abstract The impending introduction of dual-fuel plug-in hybrid vehicles (PHEVs) will impose significant challenges on current vehicle emissions testing equipment and protocols. One reason is the all-electric range and random start of the combustion engine. A second reason is the period of low or zero flow rate of exhaust volume. The present paper systematically evaluates these challenges by testing a Toyota prototype with an industry-standard, constant-volume sampler system in parallel with bag mini diluter equipment. Both systems exhibit technical difficulties when testing the PHEV. Discrepancies between the two methods can be corrected with software manipulations for a charge-sustaining operation. However, there are clear mechanisms of possible error in CO2 emissions collected during charge-depleting operation for both technologies. These findings indicate that alternative methods, including continuous sampling methods, may be required for accurate vehicle certification.

Evaluation of the constant volume sampler on plug-in hybrid electric vehicle cold start emission testing

Previous study shows that the constant volume sampler incorrectly measures some of the exhaust gas when testing a plug-in hybrid electric vehicle in the cold start condition when comparing the CO2 results from constant volume sampler and fuel flow meter. The main reason is likely associated with the exhaust left in the vehicle tailpipe and constant volume sampler sampling line. Other factors, such as fuel line expansion and water condensation in the exhaust system, are also considered to have contributions. This article evaluates these issues quantitatively by testing a Toyota Prius hybrid electric vehicle on the industry standard constant volume sampler system combined with both a fuel flow meter measurement and an electronic control unit record for fuel consumption. Cold start test cycles and test cycles with a system pre-purge event show that the constant volume sampler has a significant delay in measuring the exhaust, and the estimated exhaust losses for the test car are 15 g CO2. Tests with a purge event at the end of the driving cycle show that there are approximately 7 g of CO2 trapped in the exhaust system and the constant volume sampler sampling line, and the possible reasons for the discrepancy of the above two points (15 and 7 g) are evaluated. The expansion and air bubble influence the fuel flow meter, and the impact of water condensation on CO2 and CO appears to be negligible.

Unique Fuel Cell Test Fixture Allowing Independent Control of Gas Sealing and Electrical Contact Pressure

This paper describes the development of a unique single cell proton exchange membrane (PEM) test fixture to independently investigate the effects of gas sealing and assembly pressure. The test fixture is shown to provide useful insights into the effects of pressure on contact resistance. Two versions of gas diffusion layers (GDL) were tested to demonstrate that contact pressure significantly affects cell performance. In general, performance tends to increase with clamping force until a plateau is reached, after which performance drops rapidly. The rapid drop at high GDL pressure is due to puncture of the membrane or GDL mechanical failure. The performance improvements with pressure may be due to reductions in electrical or ionic resistance.

Two-Dimensional Dynamic Simulation of Hydrogen Storage in Metal Hydride Tanks

As proton exchange membrane fuel cell technology advances, the need for hydrogen storage intensifies. Metal hydride alloys offer one potential solution. However, for metal hydride tanks to become a viable hydrogen storage option, the dynamic performance of different tank geometries and configurations must be evaluated. In an effort to relate tank performance to geometry and operating conditions, a dynamic, two-dimensional, multi-nodal metal hydride tank model has been created in Matlab-Simulink®. Following the original work of Mayer, Groll, and Supper1 and the more recent paper from Aldas, Mat, and Kaplan2, this model employs first principle heat transfer and fluid flow mechanisms together with empirically derived reaction kinetics. Energy and mass balances are solved in cylindrical polar coordinates for a cylindrically shaped tank. The model tank temperature, heat release, and storage volume have been correlated to an actual metal hydride tank for static and transient adsorption and desorption processes. The dynamic model is found to accurately predict observed hardware performance characteristics portending a capability to well simulate the dynamic performance of more complex tank geometries and configurations. As an example, a cylindrical tank filled via an internal concentric axial tube is considered. Copyright