Student-Run ITS Tests Hydrogen/CNG Bus in Davis, CA

Student-Run ITS Tests Hydrogen/CNG Bus in Davis, California
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By Jonathan Saks, Research Assistant, National Hydrogen Association

The Institute for Transportation Studies (ITS) at the University of California Davis is leading the way in the integration of hydrogen technologies into real-world transportation applications. This July, a 40-foot bus that has been modified to burn a mixture of hydrogen and natural gas will be delivered for evaluation and testing to the University’s transit agency, Unitrans.

The modified bus, known as a Hydrogen Enriched Natural Gas bus (HCNG), has the potential to reduce carbon-based and nitrous oxide emissions by over 90%. It can achieve this as a result of its fuel mixture of 70% natural gas and 30% hydrogen by volume. The hydrogen enriched natural gas allows the combustion process to be run “lean” (with excess air). Lean combustion reduces harmful exhaust emissions because the excess air lowers peak combustion temperatures. With most common fuels, natural gas and gasoline included, engine operation becomes excessively erratic with lean mixtures before exhaust emissions are reduced to the desired level. The addition of hydrogen to the fuel creates a mixture that allows for stable lean combustion, while achieving significantly reduced emissions.

The addition of the HCNG bus to the Unitrans fleet is part of the Phase I goals of the University’s Hydrogen Bus Technology Validation Program. This program was born in March 2000 as a multi-district partnership of the City of Davis, the Yolo County Transportation District (YCTD), and the University of California, Davis. It was created to keep the United States at the forefront of the international effort to develop hydrogen as a renewable energy source for transportation and beyond. Unitrans, which has been almost entirely student run since 1972, is the host and operator of the clean fleet and the refueling facility, and the Yolo County Transit District will operate project buses serving Sacramento, including the Sacramento International Airport.

Since the goal of the program is to demonstrate the feasibility of hydrogen, the creation of a fueling infrastructure is also part of the program’s Phase I plan. Air Products and Chemicals, Inc. is under contract to design and install hydrogen infrastructure at the Unitrans Compressed Natural Gas fueling facility to allow fueling with hydrogen enriched natural gas. The bus fueling station has allowed for a synergy with another UC Davis program, the Toyota light duty fuel cell demonstration program. Air Products has designed a skid that will draw hydrogen off the Unitrans buffer storage, compress the gas, and dispense it at 5000 psi to the Toyota vehicles. ITS plans to have the station and the skid installed by late August 2003.

The second phase of the program, slated to begin October 2003 will work to enlarge and improve the infrastructure already in place. This phase will include the following: delivery of a second HCNG bus with additional modifications for further emissions reductions, an upgrade of the fueling station by installing a large compressor capable of fueling the buses in real time, and comprehensive emissions testing of a HCNG bus and CNG bus for comparison.

Currently, the Hydrogen Bus Technology Validation Program is focused on phasing in its new HCNG bus, but its long-term goals include the addition of one state-of-the-art non-polluting Proton Exchange Membrane (PEM) fuel cell bus operating on compressed hydrogen. The program’s technical director, Marshall Miller, explains that, “HCNG bus projects hold the promise of being a financially feasible way for the U.S. to accelerate the development of hydrogen fueling infrastructure, and therefore, pave the way for fuel cell buses.” The eventual addition of these buses will validate the ITS goal of providing pollution-free transportation without compromising any of the conveniences of fossil-fuel powered transit.

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