Marshall Miller

Development of a Retrofit Fuel Cell Auxiliary Power Unit for Truck Idle Reduction

In the last five years, there have been multiple demonstrations of fuel cell auxiliary power units (APUs) which provide power in lieu of idling of the main vehicle engine. The Institute of Transportation Studies at the University of California Davis has designed and evaluated a retrofitted, proton exchange membrane (PEM) fuel cell APU for powering accessories in heavy-duty truck cabs. The performance objectives for the system were determined based on truck driver feedback and industry design guidelines. The final FC APU system was developed to run for 3 days between refueling at a power output of 1.8 kW. The primary goals were to utilize exclusively commercially available components and to minimize costs. This paper discusses the performance targets, design tradeoffs, and evaluation of the developed system.

Life cycle testing of lithium batteries for fast charging and second-use applications

Two aspects of the life cycle testing of lithium-ion batteries were studied-(1) the effect of fast charging (4C) on cycle life and (2) extended cycling of cells beyond first-use requirements for second-use applications. In the case of the fast charging studies, the test data indicate that the Ah capacity of the lithium titanate oxide (LTO) cells is essentially independent of charge rate up to 6C with no current taper at the end of charge. This means that the LTO cells can be fully charged at the fast charge rates. The life cycle tests of a 24V module (10 cells in series) at the 4C charge rate and C/2 discharge rate showed negligible degradation in Ah capacity or resistance (voltage response) in over 1000 cycles. The temperature response of the module without cooling showed a maximum interior temperature of 40C that remained unchanged over the 1000 cycles of the testing. The second-use studies involved the life cycle testing of new and used 20 Ah prismatic cells (Lithium Manganese Oxide) obtained from EIG, Korea. Testing was done at room temperature and 45 deg C. The new and used cells were cycled (4.15V to 3.0V) about 850 times at room temperature and about 350 times at 45 deg C. The way in which the new and used cells degraded in terms of the decrease in Ah capacity and increase in the resistance were compared with second-use of the cells in mind. As expected it was found that the resistance degraded (%/100 cycles) more rapidly with cycles than the Ah capacity and that for both new and used cells the degradation was much more rapid at 45 deg C than at room temperature. The test results indicate second-use batteries will be best suited for applications requiring relatively high energy density, but relatively low power capability. The degradation of the used cells was gradual (no sudden failures), but accelerated with increasing cycles especially at 45 deg C.

Ultracapacitors in micro-and mild hybrids with lead-acid batteries: Simulations and laboratory and in-vehicle testing

This paper describes work directed toward the demonstration of ultracapacitors in a 2001 Honda Insight. The general approach used in this project is to replace the NMH battery with ultracapacitor modules maintaining the 12V lead-acid battery to power the accessories. Both the ultracapacitors and the 12V battery will be recharged from the electric motor/generator driven by the engine. The Insight is being modified so that it can operate as a stop-start hybrid with and without power assist and as a mild hybrid using the full power capability of its 10 kW electric motor. In the case of the start-stop hybrid, the modified Insight will use 16V ultracapacitor modules; in the case of the mild hybrid, the vehicle will use 48V modules as part of a 176V electric driveline. The energy storage units have been tested in the laboratory using cycles appropriate for the vehicle tests. The energy storage and maximum power capability of each of the storage units was found to be sufficient to meet the project requirements at high efficiency for the vehicle test cycles. Careful laboratory testing of the vehicle systems is being performed in the laboratory using a Bitrode battery tester, which controls the discharge of the ultracapacitors and the lead-acid battery and provides for their appropriate charge as specified in the control strategy for the system. The Honda Insight has been equipped with a modified on-board diagnostics (OBD) readout unit which plugs into the standard OBD port in the vehicle. The readout displays conventional engine and electric driveline component data. A MIMA (Manual Integrated Motor Assist) kit, which has been installed in the Insight, permits the driver to modify and control manually the operation of the hybrid powertrain via a manual joy stick. A circuit board, which will replace the joystick with a programmed digital signal, is being developed. The operation of the Honda Insight has been simulated using the Advisor program, which has been modified at UC Davis to treat various hybrid drivelines including the micro-HEV and the mild hybrid cases. The simulation results indicate that the fuel economy of the micro-hybrid can be significantly higher than the conventional ICE vehicle, but significantly lower than that of a mild-hybrid using a higher power electric motor and a more extensive energy storage unit (battery or ultracapacitor). The simulations indicate that the fuel economies of the mild-hybrid using the NMH battery or the ultracapacitors are not expected to be much different.