Under the Hood of a Fuel Cell

Earlier this year, Diesel News’ US Correspondent, Steve Sturgess, got to look under the hood of a fuel cell–powered truck, the Nikola One. Nikola Motor Co. had been showing artist renderings of its revolutionary cabover at Nikola.com. Finally, company founder and CEO Trevor Milton pulled the wraps off the real thing, an all independent–suspension electric-drive cabover using current generated by a hydrogen fuel cell. And the only emission from this high-performance prime mover is a little water.

Under the Hood of a Fuel Cell

So far, no real detail has been provided about the propulsion system other than that the fuel cell in the latest Nikola is a PEM (proton exchange membrane), which is a robust and fast-evolving technology. Interestingly, Toyota has recently announced it is looking at similar fuel-cell technology for heavy trucks.

The decision to go with the zero-emissions fuel-cell system was made only recently, switching away from the original concept of a high-speed natural-gas turbine to demand-charge the lithium-ion batteries. However, Milton says the primary electric powertrain is common and the fact that the chassis has been packaged for both turbine and fuel cell means that in markets where there is a less-robust hydrogen fuel infrastructure, the Nikola can be made available with turbine battery charging.

The fuel cell has significant advantages in where it can be used. Because there is far less heat rejection, some of the coolant radiators can be reduced in size or removed entirely, reducing complexity and weight. Other weight savings come from dispensing with the diesel engine, emissions after-treatment systems, transmission, prop shaft and differentials.

Spec for spec, a Nikola will be around 900kg lighter than a diesel truck, says Milton. The prototype at the reveal scaled 8.6 tonnes even with the first-generation motor gearboxes and apartment-sized appliances in the sleeper.

Whether with the fuel cell or turbine, approximately 300–400kW feed the Nikola-patented battery pack mounted between the frame rails beneath the sleeper compartment. This battery pack is unique in its cell cooling and maintains temperatures within two degrees, ensuring good charge density and longer battery life.

Using this powertrain in a truck is far easier than in a passenger car, says Milton, since a truck offers significantly greater flexibility and space to accommodate a heavy battery pack. The battery pack is sized to contain a maximum 320kW/h charge. Milton compared this to the biggest Tesla pack at 100kW/h. Having such a large capacity allows for reserve power for hill climbing.

The powertrain controller is fed with predictive cruise information to maintain the best charge for the upcoming terrain. If a grade is imminent, the charge increases: a downhill sees the state of charge at a minimum, so the batteries get recharged by regenerative braking going down the grade, incidentally taking all retarding effort away from the service brakes at the wheels.

The rated power for the battery/drive package is 1,000hp and 2,000 ft lb of torque, which is two or three times the horsepower of a diesel and means the Nikola should be able to climb a six-per cent grade at 65mph (105km/h). That torque rating is as much as the biggest 16-litre diesels produce but because the motor response is far faster than a diesel’s and peak torque is when the electric motor is stalled, the truck accelerates very quickly. Milton says drivers will enjoy the performance, and they’ll appreciate the shorter trip times that will put more money in their pockets.

Optimised Braking and Turns Swing Low

Author: Steve Sturgess

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