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Diversity Key to Future Powertrain Development

A variety of drivetrains will be needed to meet more stringent fuel economy and emissions standards of the future, says expert panel.

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DETROIT – Automotive powertrains will continue to advance technologically and increase in diversity as the industry strains to adjust in the face of ever-mounting concerns for the Earth’s well-being, a panel of executive automotive engineers concludes at the SAE International World Congress here.

Tasked with envisioning the landscape of automotive powertrains in 2015, the panel foresees a culmination of existing and emerging technologies that will serve the individual needs of particular markets, segments and consumers worldwide.

Among the key players will be advanced gasoline and diesel internal combustion engines (ICEs), along with a growing number of hybrid-electric, hydrogen fuel-cell and flexible-fuel powertrains.

Each has its inherent advantages and disadvantages, the panel concludes, and each has a myriad of potential advancements that will improve efficiency, cost and performance over existing levels. But none will break out and offer a clear advantage over the other in the near future.

Although the Earth’s finite natural resources eventually will seal the fate of the ICE, continuous improvements will allow gas and diesel engines to remain relevant well past the time when emerging powerplants of today make up a significant portion of the market, panelists say.

However, the benefits of each technology will be lessened as gas engines improve in efficiency and diesels adopt better emissions controls and combustion technologies, says Guenter K. Fraidl, product line manager-gasoline, for engineering firm AVL LIST GmbH.

“The determining factor (between gas and diesel) will be fuel economy vs. the fun-to-drive factor related to cost,” he says.

Both technologies will feature improved combustion processes, with diesels also benefiting from developments such as advanced exhaust aftertreatments, low-temperature combustion and part-time homogeneous charge-compression ignition (HCCI).

HCCI, which operates in a lean-burn mode with minimal oxides of nitrogen emissions, may benefit the gas engine, as well, says Nigel F. Gale, vice president-engine, emissions and vehicle research, for the Southwest Research Institute.

The key is lower-octane gasoline, which reduces the tendency for the fuel to detonate prematurely under heavy loads.

Although this less-potent mix of fuel would require oil companies to reinvest in their refineries, they would benefit from a greater yield of gasoline from each barrel of crude, Gale says.

Other advancements for gas engines include the continued improvement of direct injection, turbocharging and variable-valve timing, along with the introduction of technologies such as plasma and laser injection and electromagnetic camless valvetrains.

Flexible-fuel engines capable of running on biofuels also will play an important role in improving ICE efficiency and performance, as well as reducing carbon-dioxide emissions and improving energy sustainability.

“Bioprocesses are key to carbon neutrality,” Toru Ogawa, managing officer, Honda R&D Co. Ltd., says, noting Honda recently partnered with the Research Institute of Innovative Technology for the Earth on developments for producing cellulosic ethanol from biomasses such as wood chips and switch grass.

However, “limited amounts of biofuel production capacity (compared with petroleum) mean that energy independence won’t come for a long time,” J. Gary Smyth, director-powertrain system research, General Motors Corp., says, adding GM currently is utilizing a “blending strategy” of energy carriers as emerging fuel sources move to supplant existing ones.

Hydrogen fuel cells and hybrids (conventional and plug-in types) will witness significant improvements in performance in the coming years but need more work in areas of energy storage and fuel infrastructure.

“Advancements in battery technology will guide the proliferation of advanced hybrids, but energy density, battery cost and the particular habits of certain drivers ultimately will determine the penetration of hybrids in various segments,” says Gerhard Schmidt, Ford Motor Co. vice president-research and advanced engineering.

Similar challenges face hydrogen fuel cells, Honda’s Ogawa says, noting Honda has improved the power-to-volume and power-to-weight densities of its fuel cells 50% and 67%, respectively, since it began development of the technology.

The issue of efficient electricity generation will come into play, as well, as hybrids and fuel cells become more commonplace in the market, Schmidt says.

Plug-in hybrids will draw electricity from various powerplants, while fuel cells must use hydrogen generated from some other power source. If excessive pollution results from the generation of electricity, the emissions benefits of each advanced powertrain will be reduced or cancelled out completely.

“(Protecting) the environment must be stressed,” says GM’s Smyth, “because the global usage of petroleum (currently) is unsustainable.”

Ultimately, continuous development is crucial for all future powertrain technologies, with fuel economy and emissions standing as the primary drivers for improvement in the future.

“Some trends seem to be clear,” says AVL’s Fraidl, “but the race has just started.”

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