A research team at the Munich, Germany-based Technische Universitaet Muenchen (TUM) has managed to reduce the pollutants in exhaust emissions to barely measurable levels, just three months after the Euro 5 Norm for exhaust emissions has gone into effect

. According to TUM, the researchers are close to meeting the more stringent Euro 6 standard, scheduled to take effect by 2014.

The aim of the research project, called NEMo (Niedrigst-Emissions-LKW-Dieselmotor), is to achieve the "lowest emission truck diesel engine," one that complies with the Euro 6 standard without resorting to a catalytic converter.

The Euro 6 Norm would require a diesel engine to emit a mere 5 milligrams of soot particles and 80 milligrams of nitrogen oxides per kilometer. That is a fifth of the soot and a quarter of the nitrogen oxides allowed by the Euro 4 Norm that was valid until August, and less than half of the nitrogen oxides permitted by the Euro 5 Norm.

The TUM researchers designed the LVK test engine in such a way that the air-exhaust mixture is injected into the combustion chamber under high pressure. The engine's turbo-charger compresses the mixture to 10 times atmospheric pressure (measured in bar) - more than double the pressure mass-production vehicle engines can handle. Compressed in this way, the air-exhaust mixture contains enough oxygen for the diesel fuel to burn completely.

They coupled this innovation with another improvement, at the nozzle that injects diesel fuel into the combustion chamber. It atomizes the fuel into microscopic droplets, allowing them to burn completely. In larger droplets produced by conventional injectors, only the outer layer of fuel molecules are burned. The resulting exhaust fumes envelop the fuel droplets, shielding them from the oxygen. Eventually it becomes practically impossible for oxygen to react with the fuel.

The NEMo injector nozzle atomizes diesel fuel at a pressure of over 3000 bar - standard is 1800 bar, at most - to generate a fuel mist that burns very quickly and practically soot-free.

But the researchers also wanted to find out how soot is formed in the split seconds during which the fuel droplets burn up. To do so, they constructed a tiny pipe that is shot into the center of the combustion chamber at lightning speed. The gas-sampling valve needs only one millisecond to take a sample before leaving the combustion chamber again. Using this method, 13 samples can be taken during a single ignition - an ideal situation for studying the growth of soot particles and developing engines with even lower emissions.