Cummins said it has demonstrated a tubular solid oxide fuel cell in a hybrid-configured auxiliary power unit (APU) configured to power a Class 7/8 truck's "hotel loads" while running on commercial ultra-low sulfur diesel fuel.
The Cummins APU incorporated hybrid power electronics, system controls, and balance-of-plant components combined with SOFC modules supplied by Protonex Technology Corporation.

The SOFC power unit was integrated with a modified power electronics section derived from Cummins Power Generation's Hybrid Quiet Diesel (HQD) recreational vehicle power system. The hybrid power electronics provide dynamic load sharing between the SOFC and a battery pack.

The testing replicated the 10-hour rest period that is part of the daily routine of a typical over-the-road truck. The test found that the unit could operate on ULSD and could power the truck's air conditioner and lighting solely from the SOFC sub-system power. Other results of the test included combined heat and power generation, recharging batteries from the SOFC sub-system, 1,260-watt net peak demonstrated DC power, and 940-watt net peak AC power. The demonstration was held at Cummins Power Generation facilities in Minneapolis.

The SOFC APU system form factor and mission capabilities are comparable to commercially available diesel engine-based APU generators, so it can be integrated into the same form factor as existing production hardware.

The hybrid-configured APU provides both AC power and DC power to the truck's hotel loads. It controls charging of the energy storage system by regulating the power output of the SOFC sub-system and dynamically distributing loads between the fuel cell and stored energy. The SOFC sub-system converts chemical energy in the ULSD fuel directly into useful electrical power.

"This demonstration marks a real milestone in Cummins' experience: an integrated SOFC power system-in a package consistent with conventional technology-operating on the main engine fuel without supplemental water that's capable of supporting a real-world mission of providing heating, cooling, and electrical convenience to a Class 7/8 truck sleeper," said Dan Norrick, manager, advanced development, Cummins Power Generation.