DETROIT – Marketplace uncertainties and concerns regarding pending U.S. regulations cast doubt on the diesel powertrain and several technical highlights of Mitsubishi Motors Corp.’s striking Concept-RA coupe.

The Concept-RA, which stands for “Road Alive,” bowed to much fanfare this week at the North American International Auto Show here.

Hinting at a bold future for some of the auto maker’s core models, the concept sports a sleek body of lightweight thermoplastic stretched over an aluminum spaceframe, 2.2L clean-diesel engine mated to a dual-clutch gearbox and part of the advanced all-wheel-drive system from the new Lancer Evolution.

Officials repeatedly deny the Concept-RA hints at the next-generation Eclipse coupe, claiming it is a design exercise and technology showcase. But the green, yet high-performance attitude of the concept likely would go over well in the energy-conscious U.S., as well as in Europe where diesels are more popular.

The auto maker also is reviewing the potential for electric vehicles and biofuels such as E85, as well as a renewed interest in direct gasoline-injection technology.

“But it’s really about what customers want to drive,” says David N. Patterson, senior manager-mobile emissions, regulatory affairs and certificates, adding auto makers cannot force people to drive what they don’t want to.

However, he says Mitsubishi’s “state of flux” on powertrain solutions is complicated by the uncertainty surrounding ongoing U.S. litigation regarding future emissions and corporate average fuel economy standards.

The 2.2L DOHC 4-cyl. turbodiesel in the Concept-RA, for instance, is tagged for introduction in Europe next year, with the possible rollout in the U.S. targeted for 2010.

As part of an all-new architecture that also includes a 1.8L variant, the engine does not rely on urea injection to reduce emissions, meeting Tier 2 Bin 5 standards through conventional aftertreatment technologies.

But more demanding testing procedures for emissions certification, currently being proposed in California and several other states, put a crimp on the potential success of diesel engines in the U.S.

If the new standards were enacted, Patterson says, limits for oxides of nitrogen emissions would be even lower than Tier 2 Bin 5 levels by 2012, effectively banning diesel engines from such markets all together.

The resulting quandary of satisfying varying requirements in the North American market makes the introduction of diesels a questionable action, he adds, as the vehicles could only be sold in some of the most lucrative markets for a couple of years.

Despite these issues, Mitsubishi affirms its environmental sensitivity with the Concept-RA and promises more new models and technologies are coming.

The Concept-RA’s active suspension, for example, is similar to Delphi Corp.’s electromagnetic MagneRide system and stands a good chance of being integrated into the Super-All Wheel Control (S-AWC) network of the next-generation Evolution, a spokesman for the auto maker says.

However, the vehicle’s active-steering technology, which can vary the steering ratio based on vehicle speed, does not appear as promising due to the complexity of integrating it within the S-AWC system’s net of electronic controls.

A diesel-powered Evolution also is a possibility, the spokesman says, particularly with the Twin-Clutch Sportronic Shift Transmission (TC-SST) reducing torque interruption during shifts and lag time from the diesel’s variable-turbine turbocharger.

But the overall performance requirements of the auto maker’s halo car make a new sport-coupe model, possibly along the lines of the Concept-RA, a more likely alternative for diesel power.

The most recent addition to Mitsubishi’s lineup is the 235-hp Lancer Ralliart, the middle child of the Lancer family designed to take on the Subaru WRX.

Unveiled this week at the show and set for a summer launch in the U.S., the Ralliart features a de-tuned version of the Evolution’s 2.0L turbocharged 4-cyl., TC-SST gearbox and most of its big brother’s styling cues and AWD functions. Pricing is expected to be in the mid-$20,000 range.

Meanwhile, the auto maker also displays two new vehicles powered by a 168-hp 2.4L variant of the 4-cyl. “World Engine,” the front-wheel-drive ’08 Lancer GTS and Outlander ES.

The Lancer GTS bridges the gap between the base Lancer and new Ralliart. The Outlander ES brings 4-cyl. fuel economy to the CUV, replacing the 3.0L DOHC V-6 still offered in LS and XLS models.

An Outlander ES Special Edition also is new, blending the new 2.4L engine with the upscale amenities and options of the range-topping XLS.

msutton@wardsauto.com