The New York City Transit (NYCT) agency, the largest in the Metropolitan Transportation Authority (MTA) network, is testing a diesel-fueled turbine series hybrid bus from DesignLine International Holdings in New Zealand.
The DesignLine hybrids, a few of which are in service in New Zealand and others of which are under evaluation in cities such as Hong Kong, use a 30kW Capstone MicroTurbine to power an auxiliary power unit (APU) to maintain the approximately 40 kWh battery pack at a medium state of charge. Under normal conditions, according to DesignLine, the buses will return to the depot with -60% SOC remaining within the battery pack.
|APU control for the DesignLine system. Click to enlarge.|
When the batteries are at a high charge level (>70%), the APU reduces the input to the batteries. At this level, the bus can operate in an electric mode with the APU turned off. At a medium state of charge (40% - 70%), the APU adjusts its output to maintain the average state of charge. Should the SOC drop below 40%, the APU will increase its output to return the battery level back to the required state of charge.
The company predicts that the bus will deliver about 7 mpg in New York. If that is the case, that would be approximately double the fuel economy of New York’s current series hybrid bus fleet, as measured by NREL during a comprehensive evaluation of New York’s Orion series hybrid buses. (Earlier post.)
(A hat-tip to Allen!)