Alternative power choices

Go ahead and drink the green Kool-Aid of your choice. Nice deep draughts of the flavor that best fits the power requirements of your fleet, that is. The big news is no longer that trucking is going green, but that there are now so many ways to green power a truck across virtually all commercial vehicle applications. To think that only 30 years ago, the only power choice some fleets (typically only

Go ahead and drink the green Kool-Aid of your choice. Nice deep draughts of the flavor that best fits the power requirements of your fleet, that is. The big news is no longer that trucking is going green, but that there are now so many ways to green power a truck across virtually all commercial vehicle applications.

To think that only 30 years ago, the only power choice some fleets (typically only those running trucks on the low to middle range of the GVW scales) could make was to pick either gasoline or diesel power. The '80s, of course, witnessed the emergence of “alternative fuels” — at first principally propane and natural gas-powered vehicles and initially within the light- to medium-heavy GVW range.

While natural gas vehicles (NGVs) made impressive headway (and for awhile were seen by many as “the” alternative fuel vehicle for many fleets contemplating running something other than diesel or gasoline), market forces and technological advances that have mounted over the past decade or so have delivered a dizzying array of alternative power choices for today's fleet owners to consider.

Along with early options like propane and natural gas, there are more recent offerings such as biodiesel (in place of “straight” diesel) in many applications and ethanol (in place of gasoline) in light-duty vehicles; hybrid electric and hybrid powertrains for light-, medium- and heavy-duty trucks; and full “plug-in” electric power for light- and medium-duty trucks. A bit further off still are production trucks fueled by DME as well as those powered by fuel cells.

And given the regulatory strictures put in place at the federal, state and local levels to clean the air, and general societal pressure to clean up our environment showing no sign of abating, the selection of “green juice” to pick from for fleet power will in time only expand further.

One sure measure of the potency of green juice is the bumper crop of alternatively powered vehicles introduced and/or displayed at last month's biggest yet “Green Truck Summit,” which was held in St. Louis alongside the National Truck Equipment Assn.'s (NTEA) Work Truck Show.

According to NTEA, the annual summit and wide variety of production-model green trucks displayed on the show floor helped drive up attendance to record levels.

When it comes to bellying up to the green juice bar and deciphering the growing menu of power choices, fleet owners should keep in mind that not every environmentally sound solution will fit every trucking operation, and some will be best served by implementing more than one power choice.

Pioneer Power

Propane is the earliest practical alternative fuel embraced by trucking. For example, at least as far back as the early 1980s, propane power was offered as a factory option on some medium-duty trucks. Today, it is available for powering everything from a pickup to a Class 8 truck.

Propane and trucking, in fact, have a long, intertwined history. The first bobtail truck to transport propane was built in 1928, states the Propane Education & Research Council (PERC), and in 1965, Chevrolet introduced four new truck engines designed to run on propane. Today, propane power conversions are often completed on production vehicles — including full-size pickups, vans and chassis cabs, step vans and both medium- and heavy-duty vocational trucks — by specialized outfitters.

Propane is a hydrocarbon and also referred to as liquefied petroleum gas (LPG) even though it is typically produced as a by-product of both natural gas processing and crude oil refining. It is nontoxic, colorless and virtually odorless and, as with natural gas, an identifying odor is added so the gas can be readily detected.

According to the Dept. of Energy (DOE), propane has a high octane rating and excellent properties for spark-ignited internal combustion engines. It is non-toxic and presents no threat to soil, surface water or groundwater, the agency adds. DOE ranks LPG as the third most commonly used engine fuel, after gasoline and diesel, in the U.S.

Propane is considered an alternative fuel under the Energy Policy Act of 1992. LPG sold as vehicle fuel can be a mixture of propane with smaller amounts of other gases, notes DOE. The Gas Processors Assn.'s HD-5 specification for propane vehicle fuel says it must consist of 90% propane, no more than 5% propylene, and 5% other gases, primarily butane and butylene.

Propane is a gas at normal temperatures and pressures. It is stored onboard a vehicle in a tank pressurized to around 300 lbs. per square inch, or about twice the pressure as in an inflated truck tire. Under this pressure, propane becomes a liquid with an energy density 270 times greater than in gaseous form, says DOE, which means a gallon of propane has about 25% less energy than a gallon of gasoline.

DOE adds that because propane is transformed into a gaseous state before it is burned in an internal combustion engine, the engine runs more efficiently in low-speed, light-throttle conditions.

The agency notes that the “introduction of liquid propane injection (LPI) engines promise higher fuel efficiency.” According to Cleanfuel USA, a converter of LPG trucks using such engines, LPI-equipped engines are “engineered to maximize the design benefits of the gasoline engine and utilize the OEM engine computer, specifically calibrated for propane. This allows for optimal fuel economy, performance and low emissions, while leaving the OEM-developed diagnostics intact.

Blue Flame

Arguably the alternative fuel choice with the most impressive track record thus far in trucking is natural gas, which is used either in compressed (CNG) or liquefied (LNG) form.

Despite the late arrival of biodiesel, not to mention diesel hybrids and electric trucks, NGVs are likely to remain a key alternative power choice for fleets that centrally fuel their vehicles at their own pumps or that have ready access to public NGV fueling facilities nearby.

According to the advocacy group Natural Gas Vehicles for America (NGVA), there are now more than 120,000 NGVs on U.S. roads today and over 1,100 NGV fueling stations in the country — with over half available for public use. The group also states that, on average, natural gas fuel costs one-third less than conventional gasoline at the pump, and truck operators can choose from over 50 different manufacturers that produce some 150 models of light-, medium- and heavy-duty vehicles and engines.

One of the benefits of NGVs is they are fairly straightforward. Natural gas can power the same vehicles currently powered by gasoline and diesel — be they light-, medium- or heavy-duty. They operate on the same basic principles as gasoline-powered vehicles. Fuel is mixed with air and fed into the cylinder, where it is then ignited by a spark plug to move a piston up and down. However, because a gas is being used rather than a liquid fuel at standard pressures and temperatures, some modifications are required for an NGV. These changes mainly involve the fuel storage tank, fueling receptacle/nozzle and the engine.

Most NGVs use CNG, which is stored onboard under high pressure in tube-shaped cylinders attached to the rear, top or undercarriage of the vehicle. These cylinders meet rigorous safety standards, points out NGVA, and are made of high-strength materials designed to withstand impact and puncture. In the case of fire, they are fitted with pressure relief devices (PRDs) to provide a controlled venting of the gas rather than letting the pressure build up in the tank.

Next Page: Grown Green

At CNG stations, explains NGVA, the gas is typically drawn from a local gas utility's line at low pressure, compressed and then stored in the vehicle's storage tanks at high pressure. Fueling equipment for CNG vehicles can be either “fast fill” or “time fill.” In fast fill, a large compressor coupled with a high-pressure storage tank (called a cascade) fills the tank in about the same amount of time it takes to fuel a gasoline or diesel vehicle. With time fill, there is no storage system and a much smaller compressor, and vehicles are typically refueled overnight at a rate of about a gallon an hour.

Natural gas can also be liquefied for use as a vehicle fuel. LNG requires only 30% of the space of CNG to store the same amount of energy onboard a truck and is typically only used with heavy-duty vehicles. To keep the natural gas cold and thus liquefied, LNG is stored onboard vehicles in double-walled, vacuum-insulated pressure vessels, which are essentially Thermos bottles.

NGVA points out that while LNG can be produced on-site from available natural gas, it is typically delivered to a fueling station via tanker truck. Regardless, LNG is then stored on-site in special cryogenic storage tanks. To fuel vehicles, LNG is pumped into the vehicles much like other liquid fuels, although the cryogenic fueling equipment is technically more sophisticated.

There are also LCNG fueling stations. These use LNG to fuel both LNG and CNG vehicles. LNG vehicles are fueled as described and for CNG vehicles, the LNG is compressed as a liquid and then gasified. From there, the high-pressure gas is stored on the vehicle as at a fast-fill CNG station. Since it takes less energy to compress a liquid than a gas, once the LNG is available, LCNG stations are less expensive to operate, according to NGVA.

Grown Green

Biodiesel (technically a blend with petroleum-based diesel) and ethanol (a gasoline blend) are derived from biomass energy gained from plants and plant-derived materials. Wood is the oldest and still the most widely tapped biomass energy resource. Other biofuel sources include food crops, grassy and woody plants, residues from agriculture or forestry, and the organic component of municipal and industrial wastes, including methane gas.

The essential fact about biofuels is they can be mixed with diesel or gasoline, to create biodiesel and ethanol respectively, to lower exhaust pollution without requiring changes in engine design or fuel-delivery infrastructure.


The U.S. Dept. of Energy's National Renewable Energy Laboratory (NREL) holds that tapping biomass energy can greatly reduce greenhouse gas emissions and their use can reduce dependence on foreign oil because they are the “only renewable liquid transportation fuels available.”

But the real kicker with this green juice — a function of agronomics and accompanying farm-belt politics — is that “biomass energy supports U.S. agricultural and forest-product industries.” The feedstocks that mainly make up biomass fuels in this country are corn (for ethanol) and soybeans (for biodiesel), which NREL calls “surplus crops.”

For fleets that have access to biofuels to fuel trucks and cars, the key benefit is these fuels can be used to power existing vehicles with virtually no extra investment because they require few if any modifications nor any new fuel-distribution infrastructure.

But potential biodiesel users must be aware of the different blends available so they can pick the right one for their trucks. As DOE points out, biodiesel can be legally blended with petroleum diesel in any percentage. The typical percentages are B20 for a blend containing 20% biodiesel and 80% petroleum diesel and B100 to indicate 100% biodiesel. B100 and blends of B20 or higher qualify for alternative fuel credits under the Energy Policy Act of 1992.

According to DOE, B20 — the most common biodiesel blend in the U.S. — “provides substantial benefits but avoids many of the cold-weather performance and material compatibility concerns associated with B100.” B20 can be used in nearly all diesel engines, and B20 and lower-level blends generally do not require engine modifications. The agency cautions, however, that not all diesel engine manufacturers cover biodiesel use in their warranties — and it is crucial to use biodiesel that meets the quality standards of the ASTM D6751-09 spec.

Biodiesel contains about 8% less energy per gallon than petroleum diesel. For B20, this can mean a 1 to 2% difference, but most B20 users report no noticeable difference in performance or fuel economy, says DOE. The greenhouse gas reduction and concurrent air-quality benefits of biodiesel are roughly commensurate with the blend — B20 provides about 20% of the benefit of B100 use and so forth.

There is also a place on the menu for lower-level biodiesel blends, points out DOE. Since today's “standard” highway diesel fuel — ultra-low sulfur diesel (ULSD) — may have reduced lubricating properties before additives are applied, adding as little as 0.25% biodiesel (which is very low in sulfur) can significantly increase fuel lubricity, the agency states, which is making B2 and B5 blends increasingly popular.



As for ethanol, an alternative light-duty fleets are likely to consider, the American Coalition for Ethanol (ACE) claims this biofuel substitute for straight gasoline is a “clean, renewable, high-performance fuel … up to a 10% blend of ethanol (E10) is covered under warranty by every auto manufacturer that sells vehicles in the U.S. for every make and every model of vehicle. E85 (85% ethanol/15% gasoline) is for use in flexible fuel vehicles (FFVs), which can operate on gasoline or any blend of ethanol up to 85%.”

ACE adds that since ethanol has a lower Btu value than gasoline, it “burns cooler and is gentler on the vehicle's engine — less wear and tear leads to longer engine life.”

Plus One

Few if any alternative choices have fueled the imagination of fleet owners like hybrid diesel-electric and diesel-hydraulic powertrains.

Hybrid electric and hydraulic drive-assist systems differ in where they draw their alternative power from, but both types are engineered to supplement — not replace — engines powered by diesel or gasoline or biofuel equivalents. These powertrains already power everything from cars to medium- and heavy-duty trucks (typically operated in urban areas) as well as reefer engines for refrigeration units.

One key to hybrid adoption is fleets can access the technology without switching from fuels they already use, or securing specialized vehicles or installing or accessing new fueling infrastructure. They save fuel and cut emissions literally on the fly, as the vehicles go about their workaday business.

While utility truck fleets were early adopters and continue to be dedicated proponents of this technology, OEMs and key drivetrain suppliers have been quick to drive into this green niche. Truck builders that now offer hybrid-drive power on at least some of their models or are running tests include Freightliner, Workhorse Custom Chassis, Hino, International, Peterbilt and Autocar. Hybrid drive suppliers to the trucking industry include such familiar industry names at Eaton, ArvinMeritor and Parker Hannifin.

All such systems use a hydraulic or an electric drive to supplement the existing powerplant. These can be built in series or parallel setups. Series hybrids have the electric motor turn the vehicle's wheels while the internal combustion engine provides power to charge the electric batteries. Parallel hybrids, on the other hand, derive power from an electric motor or engine or via some combination.

Also coming into play are so-called plug-in hybrids. A plug-in hybrid truck aimed at commercial applications is expected to return to a domicile after each work shift.

Power Jolt

All-electric trucks — both battery and plug-in variants — are also rolling onto the trucking scene. Due to the weight factor for those with onboard batteries as well as the limited range between full charge-ups for both types, all-electric trucks are currently seen as fitting best with light- to medium-duty local delivery applications.

An electric vehicle uses a battery or other energy storage device to store electricity to power the motor. These batteries must be replenished by plugging the vehicle into a power source. Some electric vehicles have onboard re-chargers, others are charged by plugging into an external outlet.

“Both types, however, use electricity that comes from the power grid,” points out DOE. “Although electricity production may contribute to air pollution, electric vehicles are considered zero-emission vehicles because their motors produce no exhaust or emissions.”

Arguably the most interesting development around all-electric trucks — besides their seemingly overnight arrival — is they are being rolled out here not only by established truck manufacturers, but also by brand-new truck builders and assemblers entering this market for the first time as well as through various partnership agreements between old-line OEMs and new-wave electric-drive suppliers.

For example, the new-to-the-U.S. Smith Newton electric truck was rolled out last year and in just the past two months, Ford announced an all-electric version of its Transit Connect van and Freightliner Custom Chassis an all-electric chassis.

And while Smith's independent U.S. arm is a vehicle assembler — essentially working off the original Newton truck's European blueprint — both Ford and FCCC partnered with North American-based suppliers to “electrify” their offerings.

The Transit Connect uses Azure Dynamic's Force Drive battery-electric powertrain and Johnson Controls-Saft's lithium-ion batteries while the FCCC walk-in was engineered with Enova Systems, a developer and producer of electric and hybrid-electric drive systems, and uses Tesla Motors' lithium ion batteries.

Down the Road

OEMs involved in fuel cell vehicle development include Daimler, Volvo and General Motors. UPS and FedEx have been involved in test programs for light delivery vehicles in the past several years.

The Port of Los Angeles is testing hybrid fuel cell-electric drayage tractors. The prototype vehicle, retrofitted for fuel-cell operation by Vision Industries, is undergoing testing. The zero-emission tractor's powertrain consists of a hydrogen fuel cell, electric motor and lithium batteries.

Dimethyl ether (DME) is another alternative fuel off on the horizon. It is relatively cheap to purchase, works with very low engine injection pressures, and produces little pollution from combustion.

Testing of DME as a diesel fuel alternative is being conducted by Sweden's AB Volvo and by Ford Europe. Chemical giant Chemrec AB is investing as well — beginning work on a DME plant in Sweden. The very idea of Green Juice may be tough to swallow at first. But there's no getting around the Blue Sky Café so it will pay to focus on how many choices are on the menu — and then work at figuring out which ones will best slake the energy thirst of your fleet.

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