Plug-In Hybrid Bus at Denali NP Uses Up to 70% Less Fuel

Written by Nick Chambers

Enova Systems and IC Corporation have delivered a plug-in hybrid diesel electric bus to Denali National Park for use in carting visitors around the pristine wilderness.

The bus (similar to the one pictured above) has a GVWR of 27,500 pounds, carries up to 38 passengers and uses up to 70% less fuel than a similarly equipped conventional bus — so if the bus got 10 mpg with a conventional engine, it could get 30 mpg using Enova’s hybrid system.

The IC Bus uses Enova’s post-transmission parallel hybrid drive technology which couples a diesel engine with an 80-kilowatt power-train including a control unit, batteries and an electric motor. Enova is the exclusive supplier of hybrid electric drive systems to IC Bus (PDF).

Enova says that independent third party dynamometer testing confirms the vehicle uses up to 70% less fuel than a similarly sized internal combustion engine vehicle. In addition, the tests apparently show that carbon dioxide emissions are reduced by as much as 40%, nitrogen oxide by up to 20% and particulate matter by as much as 30%.

If the bus delivered to Denali is, in fact, the same HC Series hybrid bus listed on the IC Corporation website, then I find that Enova’s above claims are a bit overly rosy in some cases and downright contradictory to IC’s claims in others. After reading through both IC Corporation’s website and Enova’s website, I’m more than a bit confused.

For instance, the IC Corporation brochure about the HC Series hybrid bus (PDF) states that the vehicle has a 25-50% fuel economy improvement when the batteries are constantly charging (charge sustaining), and up to an 80% improvement when the bus is draining the batteries (charge depleting).

Also, another IC Corporation brochure about the HC Series states that the diesel-electric hybrid technology can result in up to a 90% reduction in particulate matter and up to a 60% reduction in NOx emissions. Compare these numbers to Enova’s claims of 30% and 40% reductions, respectively.

An article from Green Car Congress about the Enova/IC hybrid bus clarifies the issue a bit: the fuel economy of these buses is completely dependent on route, driving conditions and engine/power-train configuration.

A route with frequent stops and starts using a bus configured exactly like the one used in the dynamometer test will produce results similar to those claimed by Enova. A bus driven under highway conditions without frequent stops and starts will get much worse fuel economy.

So on a national park tour with many stops and starts, the hybrid bus will probably produce the claimed fuel economy and emissions results. This is excellent news in a place like Denali National Park where diesel prices are incredibly high and the preservation of its pristine beauty is key to its future value.

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