"Clean" and "Diesel" are 2 words that, in the past, were very rarely used in the same sentence. Thanks to new technology, diesels have become cleaner and more friendly to the environment. In fact, as more research is conducted, it is becoming clear that diesels may actually be more "Green" than Hybrids.New Diesel Technology: Cleaner and More Efficient
Before we get too far, let's look at the main difference in operation between Diesels and regular Gasoline engines. A gasoline engine takes in air and mixes it with vaporized fuel. The mixture in then compressed and a spark plug ignites it. The rapidly expanding gas forces the piston down and power is produced.
Diesels operate under the same general principals, with one exception. They do not require a spark to ignite the fuel. Air is taken in and compressed, to a higher pressure than gasoline engines. During compression, the air heats to over 800 degrees F. Fuel is then injected and upon contacting the air, it ignites.
The increased compression comes with some additional benefits. The most noticed is a longer lasting motor. All of the parts of the rotating assembly (Crankshaft, Connecting Rods,...) are build stronger to withstand the increased power. They also operate at a lower speed when compared to gasoline engines. This means less overall operating friction. Together they mean a longer lifespan for diesel powerplants.
Getting back to the Greenhouse Gases. Oil refineries are now producing a new kind of fuel, called Ultra-Low Sulfur Diesel (ULSD) that reduces the sulfur content to 15 parts per million. The rewards are 2-fold. The immediate result is less sulfur being dispersed into the atmosphere. The long term result is the ability to develop more effective emissions controls.
Sulfur clogs emissions controls measures, which is why development has been slow in the past. With ULSD, there is no sulfur to clog, so automakers are able to manufacture better filtering systems for diesles. After being filtered to remove soot and particulates, the systems rely on ammonia to break down the Nitrogen Oxides (NOx) and turn them into Nitrogen and water vapor. Mercedes-Benz reports of developing a system capable of reducing overall emissions by 80%-90% and disposing of the smell.
Another factor to take into account is the increase in fuel economy. The higher compression makes better use of the chemical energy in the fuel. It extracts more energy per combustion, hence, it takes less fuel to move the vehicle. Since it takes less to move, less will be used. If less is used, the amount of toxic fumes is reduced even farther.
Popular Mechanics featured a story where they put Europe's version of the Toyota Prius (Hybrid) against the Volkswagen Polo BlueMotion-1 (Diesel, Currently available overseas only). The results are pictured below. Popular Mechanics Comparison
As you can see, diesels have a very strong argument when it come to potential. They offer roughly the same when it comes to the environment and initial cost. Diesels do however have the advantage when it comes to performance and fuel mileage. Only time will tell who will win the battle for the vehicles of tomorrow.
Source: PopularMechanics , AutoBlogGreen , CARandDRIVER