MSN Auto's own Chuck Tannert penned an excellent piece for Popular Mechanics on the innovations taking place in the world of the combustion engine. Let's take a look at the types of technologies that could keep the ICE -- albeit a far more efficient, cleaner version -- around for decades to come.

HCCI:
The acronym stands for "homogenous charge compression engine," and was in fact invented in Japan all the way back in 1978. The effort for a more efficient and cleaner-burning two-stroke engine, however, was hampered by the technological limitations of computers at the time. Obviously, computers have come a long way since then, which is why manufacturers are pushing hard to perfect the tech. An overview of HCCI from Tannert's article:
"HCCI employs exhaust trapped from one combustion cycle to achieve the desired ignition temperature for the next cycle, helping to vaporize the incoming fuel and raising the homogeneous charge to a higher-than-normal temperature. As the piston moves upward, the temperature of the fuel, air and exhaust cocktail rises to the point of spontaneous ignition, just before the piston reaches top dead center. The result is a more efficient burn at temperatures under 2000 degrees K (about 3140 F), too low to form harmful nitrogen oxides (NOx)."

There's still likely a decade left until this technology hits the streets, though, as it's still hampered by ignition timing issues and the fact that it's great for moderate speeds, but still not able to be utilized by cars putting the moves on.

Camless:
Imagine an engine that can run on gasoline, biofuels, or diesel, and at the same time can run two-, four-, six-, or eight-stroke cycles depending on which is ideal for the situation. Colorado-based physicist and inventor Eddie Sturman has created an engine that can do both. His idea of micromanaging airflow led him to construct an engine that replaces the camshaft with valves and hydraulic actuators that are digitally controlled and very precise. Since each valve can operate independently, airflow is always optimized, and different fuels can be used. Like HCCI, it also takes advantage of leftover exhaust to initiate a burn, and Sturman estimates his engine will be 55 to 60 percent more efficient than a standard engine.

Split-Cycle Combustion:
I'm going to let the PopMechanics piece handle the technical explanation of this new engine design from Massachusetts-based Scuderi Group (that's PM's forte, after all):
"This split-cycle air hybrid engine separates the four strokes of the Otto cycle (intake, compression, combustion and exhaust) across two cylinders (compression and power) that work in tandem. Air is pulled into the first chamber, compressed, then forced through a crossover passage into the second chamber, where it's mixed with fuel and ignited.

Combustion happens after the piston head has passed top dead center (i.e., has already started its downward motion). In a conventional setup, the piston would outrun the explosion, sapping power. But Scuderi claims that using highly pressurized air to create a turbulent environment inside the cylinder vaporizes the fuel more quickly, producing far more power than in a conventional engine."

What's more, there's a compressed air storage tank connected to the crossover passage to capture whatever excess compressed air is generated from the combustion process, then channel it back to the engine. This, in effect, supercharges the engine and, the group claims, boosts efficiency by 25 to 30 percent.

Ethanol Boost:
A group out of MIT are working on an ethanol-based solution to combat engine knock in vehicles running at high torque. When needed, a small amount of ethanol is injected into the combustion chamber. The ethanol vaporizes and cools the fuel-air mixture to 3140 F, which -- based on computer models -- boosts the engine to twice the power of spark-ignition and creates an increase in fuel efficiency of up to 30 percent. The major benefit of this system is that it mates easily with existing ICE topology, cutting the manufacturing costs to a fraction of that for hybrids. The drawback? Two fuel tanks -- one for gasoline, one for ethanol -- would be required.

Turbocompounding:
Essentially a waste heat-conversion technology that both increases efficiency and reduces emissions, turbocompounding is currently used in large trucks but has yet to make its way to passenger cars. Popular Mechanics, take it away:
"A conventional turbocharger uses exhaust from the engine to spin a turbine wheel, which in turn runs a compressor that crams more air into the engine for more power.

In a turbocompounding setup, there is a second turbine slightly downstream from the first. But instead of using the recovered energy to compress intake air, this supplemental turbine feeds it directly to the engine's crankshaft (via reduction gears) to increase fuel efficiency and torque."

As I've said before, new propulsion technology -- including ICE-based tech -- is not a zero-sum game. It's exciting to see technologies old and new get together for cleaner, more efficient solutions.