In Search of the Long-Distance Natural Gas Automobile

America is awash in clean-burning natural gas, with around 320 trillion cubic feet of the stuff, and we discovered more of it than we extracted in 2009 and 2010 (the latest years on the Department of Energy site). It produces more energy per carbon molecule than other fuels; it pollutes less than most other hydrocarbons; and it’s easier on engines. Win-win-win! So why is Honda’s Civic CNG the only factory-built natural gas car? Because storing the energy content of a single gallon of gasoline at atmospheric pressure would consume a Civic’s entire cabin and trunk—and stink to high heaven. Therefore, it has to be pressurized. A lot. At 3600 psi, it’s still 3.8 times as bulky as gasoline, and containing it at that pressure is expensive and requires outsized cylinders that don’t conform to underfloor space like cheap blow-molded plastic gasoline tanks do.

Science to the rescue! The DOE’s Advance Research Projects Agency recently doled out $30 million in grants to various organizations to figure out how to make natural gas storage more car-friendly, with a target onboard energy density of 12 MJ/kg at an installed price of $1500. (For reference, a Civic gasoline tank holds about 40 MJ/kg, for less than $100.) Here are three of my favorites:

Gas-tro Intestinal San Francisco’s Otherlab is working on a cylindrical high-pressure tank that loops back on itself like human intestines. Lead engineer Tucker Gilman explains that shrinking the diameter and increasing the length of a pressure vessel increases surface area, reducing stress so wall thickness can shrink and mass doesn’t increase much. Smaller diameter tubes can be bent (respecting a 1:8 ratio of tube radius to bend radius), and by stacking and nesting such bent tubes, the storage tank can better conform to underbody packaging. Tucker claims Otherlab can meet ARPA’s target with high-strength steel.

Metal Air Mattress Pacific Northwest National Laboratory’s approach layers sheets of metal and welds lines in them like an air mattress, then heats the metal and “inflates” it with air in a superplastic forming process. Senior research scientist Kevin Simmons explains that friction-stir welding produces a metal grain structure as formable as the unwelded metal, and that air pressure naturally forces the hot metal into an ideal shape for a pressure vessel, with hemispheres at the ends of each tube. So far, experimentation with a “high-strength lightweight alloy” is yielding 13-15 MJ/kg, with 80 percent better conformability.

Metal Sponge Ford is working on a low-pressure (500-1000 psi) alternative in which a tank is filled with powder or pellets of “metal organic” or “covalent organic” materials. These porous, high-surface-area materials grab natural gas at one temperature and release it at another. The most promising materials operate at near room temperature. The reaction creates heat while refilling, so it must be cooled during the recharge and heated slightly while releasing the gas. But fuel systems technology expert Mike Veenstra says this heating and cooling energy is far less than what would be required to compress gas to 3600 psi for standard tanks. (ARPA grants also were awarded to develop cheaper pumps.)

If one of these ARPA investments hits, T Boone Pickens’ CNG dreams may at last come true.

Illustration: Pep Montserrat

In Depth: Porsche’s new 911 GT3

As chief engineer Andreas Preuninger addressed a gathered throng at the New York International Auto Show, he described Porsche’s newest 911 GT3 as his group’s highest performing GT product, with “the most amazing gearbox on the planet.” Was this hyperbolic bluster, aimed at deflecting criticism of the new car for abandoning its motorsport-derived “Mezger” engine architecture and vaunted manual transmission? Immediately following the press conference I cornered “Mr. GT3” to find out.

Preuninger contends that this new engine does indeed provide a “replacement for displacement,” refuting the old muscle-car adage—it’s super-high-rev operation. Spinning an engine to 9000 rpm certainly isn’t trivial, and building in that capability drove a complete redesign of the current 911 engine that left only the raw engine block casting and the cylinder head bolts in common. The crankshaft, titanium connecting rods, and forged aluminum pistons are all newly optimized for high speed running, but it’s the valvetrain you really have to worry about at these speeds—especially in a road car with self-adjusting tappets (race engines frequently need their valve lash adjusted in between races).

To get mass out of the moving parts of the valvetrain, Preuninger’s team managed to relocate the hydraulic adjuster to the cylinder head itself. It now supports the pivot for an ultra-light cam follower that actuates the valve. Each of these little followers now weighs just over half-an ounce, slicing more than 3 pounds out of the valvetrain. He believes Porsche is the first to bring such a system to a production road car. Those race-bred cam profiles, by the way, reportedly produce a delightfully lumpy idle that gently rocks the car when standing still. The cylinder heads are configured to move mass quantities of air in and out of the cylinders at 9000 rpm, resulting in a rated output of “475-plus-plus [metric] horsepower.” This ultra-conservative rating might have been arbitrarily assigned to provide an emotional link with the outgoing GT3 RS 4.0—an identical power density of 125 PS/liter.

As for the choice to completely abandon the three-pedal stick-shift for a seven-speed PDK transmission, Preuninger claims that numerous modifications make this transmission feel like a proper racing sequential transmission (and in any case, the race-bred GT3 can no longer afford the competitive disadvantage of time-consuming manual shifts). The ratios are unique, with seventh a direct-drive gear—not an overdrive economy ratio. Top speed of 195 mph is achieved in seventh. Naturally, the powertrain executes throttle blips for ideal rev-matched downshifts. Shifting via the gear selector now happens according to racing convention—forward for downshifts, back for upshifts. The paddles themselves get stronger return springs and a more positive detent that feels sportier, and pulling both at the same time gives you neutral for as long as you hold them. This is useful for helping regain traction in a hard corner by relieving the tires of all acceleration or overrun forces, or for executing a hard launch with wheelspin. Switching off all the electronic aids activates what Preuninger calls “Hooligan mode,” for drifting and smoky burnouts. (He assures me that the system has been thoroughly tested, successfully withstanding 500 “Hooligan starts” in quick succession.) Finally, the GT3’s PDK provides no creep at idle in first gear (as the domesticated PDKs do).

Okay, Preuninger has convinced me of GT3’s fabulosity on paper, now let’s see how it fares in the crucible of Best Drivers Car competition.