Capstone 30kW microturbine.
Capstone's 30kW microturbine engine (pictured at the right) recently received CARB certification. It's successor, a 60kW model is expected to meet 2007 heavy engine emissions rules.

Capstone Establishes Strong Presence In Heavy Hybrid Market

An interview with Mark Aramli, director of hybrid vehicle development, Capstone Microturbines

By Bill Moore

40 years ago carmakers like Chrysler experimented with powering some concept cars with small jet turbines. They geared the engine directly to the car's transmission and produced a vehicle with enormous power that was smooth as silk. The only trouble was, it had awful fuel economy and you could roast an ox in the vehicle's exhaust.

Now, jet turbines, like those built by Capstone Microturbines of Chatsworth, California -- are again seeing a resurgence. This time, however, they are small, compact units the size of a conventional beer keg. They offer all the advantages of the turbines of 40 years ago, and few of the disadvantages, according to Mark Aramli, Capstone's director of hybrid vehicle development.

Unlike the turbines of the past, Capstone's microturbine is not linked mechanically to the vehicle's drivetrain, but instead is used to generate electricity for a series hybrid-electric drive configuration. Also different from the past is the type of fuel used. Whereas 40 years ago, a turbine would have used some form of kerosene, typically a specially blended jet fuel like Jet 8 or JP4, today's turbines can run on a wider range of different fossil and even renewable fuels from kerosene to propane to natural gas to landfill-generated methane. Aramli even jested his microturbines could run on Johnny Walker Kentucky bourbon, though he admitted they hadn't really tried it.

Because Capstone's turbines can run on relatively cleaner fuels like propane and natural gas, California's Air Resource Board recently certified the engine as not only able to meet its current emissions standards for heavy vehicles. In addition, Capstone's soon-to-be-introduced 60kW unit is expected to meet the even tougher 2007 standards. This means in the near future a transit bus or garbage truck using a 60kW Capstone microturbine and a third-party developed hybrid electric drivetrain today meets both current and 2007 emissions requirements.

Aramli explained to EVWorld's editor that using a microturbine in a series hybrid configuration is significantly more efficient that the old direct mechanical linkage approach, "by an order of magnitude," he reported. This translates into improvements in fuel economy in real practical day-to-day operation of anywhere from 50-100% over a comparable ICE-powered vehicle with an automatic transmission, he added.

He went on to explain that Capstone's microturbine is a new design. "It is not a derivative product where we jammed a turbo-charger from a truck engine into a box. This is a blank sheet of paper design. Capstone was born as a transportation company. This engine has all the design characteristics built into that it needs for transportation."

"The number one characteristic of this microturbine is its emissions," he continued. "This is, without exception, the cleanest heavy-duty engine in the world that operates off standard fuels." Compared to the typical diesel bus engine, which usually produces between 210-250 hp, the 30kW Capstone turbine would seem under-powered. The company is about to introduce a 60kW version for use in larger city buses, because of this. At present, it takes two 30kW microturbines to power the larger 40 foot transit buses.

Contrary to what you might expect, this does not mean Capstone-powered, hybrid bus, of which there are some 30 in operation in Arizona, Atlanta, Washington, D.C and elsewhere, are under-powered. The vehicle's series hybrid configuration requires that the microturbine need only be sized to sustain the vehicle's battery pack, which provides the extra boost needed for hill climbing or acceleration. This, in turn, reduces emissions and improves fuel consumption. The added benefits are the once-noisy, smelly bus is now vibration-free and nearly odorless, resulting in dramatic improvements for both passengers and the environment.

Another important payoff, especially since a microturbine powered bus is about 30% more expensive than a conventional diesel bus, is its reduced maintenance expense. A microturbine has one moving part, the turbine rotor, which itself floats on frictionless "air bearings", can operate thousands of hours without significant maintenance. For example, there is no oil or engine coolant to change. Technicians need only replace the air filter once a year, Aramli said. This means operators will typically pay one-third what they would on conventional bus engine maintenance over a 12 year life cycle.

"Transit operators actually spend twice as much each year on service as they do buying new buses," he observed.

He said that over the normal operational lifecycle of the bus, there is virtually no difference in total costs, though the initial purchase price of a microturbine hybrid bus is higher than either a diesel hybrid or conventional diesel.

Lower service costs aren't the only payback for such an investment, Aramli stated. The transit operator now has a bus with that has "five or six times lower emissions" running off of the same fuel, as well as a bus that could see more service and much happier customers.

Software Fuel Change

Not only can the Capstone microturbine make use of a wide range of fuels, operates can each switch fuels based on pricing and availability. Aramli explained that to switch from propane to natural gas involves only a change in the engine's controlling software. To switch from heavy, liquid fuels like diesel to natural gas, for example takes about 3 hours labor and $1,500 in parts.

"This is true multi-fuel capability," he pointed out, adding that a natural gas-fuel ICE engine will always be a natural gas engine and a diesel will always be a diesel. While it is technically feasible to adapt these engines to different fuels, it's not really practical to do so. The costs will outweigh any potential savings.

Capstone has a number of hybrid-electric drive train partners it works with including ISE Research, Solectria, PEI and Enova Systems. Capstone provides the gas-turbine/electric generator component and the partners provide the electric drives and controls. In addition to buying buses that are specifically configured to be hybrid-electric, Aramli it is also possible to upgrade an existing transit bus, removing its diesel engine components and replacing them with a hybrid-drive. He also pointed out that the exhaust gas temperature of the microturbine is the same as a conventional diesel engine.

One of the first bus manufacturers to install a Capstone turbine is AVS in Chattanooga, TN whose largest order to date is for some 31 buses in Tempe, Arizona, with options for another 200 plus. AVS hybrid-electric buses are in service all around the US, Aramli said. AVS is currently developing 30 and 35-foot versions of their bus, which will use twin 30kW Capstone turbines.

In the Los Angeles area, the company is working with ISE Research and El Dorado Buses to convert existing El Dorado buses to hybrids. Three such buses are in operation in downtown LA, with a fourth in development.

Overseas, Capstone is working with a firm in New Zealand who has, what Aramli calls a very "futuristic" looking bus that is now being exported to Japan. He expects to see up to 100 of these buses on the streets of Tokyo in the next few years.

Beyond Buses

Capstone is working with Fuji Heavy Industries on a Capstone-powered hybrid-electric garbage truck. The company is also involved in a similar project in San Diego with a partner.

Aramli explained that there are also some light-rail applications in Japan they are looking at, as well as underground mining and construction.

Finally, Hyundai, the Korean carmaker and Enova Systems (the former US Electricar company) are jointly developing a hybrid-electric version of the new Santa Fe sport utility vehicle. Purely experimental, this SUV will be powered by a Capstone micro turbine. Aramli said that there are no plans today for commercial introduction of such a vehicle. It is simply a way for Hyundai to acquire experience with both hybrid drive and microturbines.

There is a second phase of this program, Aramli said, that will see a Capstone turbine installed in a Hyundai bus in Korea where Hyundai is a very large bus manufacturer. He added that he has high hopes that once Hyundai has completed its evaluation of the technology, it will lead to a long term commercial relationship.

Aramli concluded that given the fact that Capstone microturbines have only been in the marketplace for two years, the number of turbines the company has sold ­ including both mobile and stationary (distributed generation) applications ­ as a "fantastic market acceptance for the technology."

"Any technology that is fundamentally different from what people are used to, generally takes time to be absorbed, to be swallowed. People have a reluctance to go with things they haven't seen before and the concept of a jet engine powering a bus is foreign to many transit operators. To have the number of engines sold that we have sold in such a short time, and as the first market entry for this technology, has been very pleasing to us. We see this as an excellent start, and in the future, as emissions regulations change, the desire for transit operators to go to cleaner engine technology will be enhanced."

Times Article Viewed: 7690
Published: 17-Feb-2001


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