Modular technology for Series 4000mtu
engineers have developed a modular concept involving an entire bundle of technologies that either avoid the generation of pollutants altogether, or prevent them from entering the atmosphere. The system includes the following elements:
> Increased injection pressure up to 2,500 bar: The higher the pressure at which fuel is injected into the combustion chamber, the more finely it is vaporized. As the vapour becomes finer, fuel combustion improves and fewer soot particles are formed. Multiple injection is also key here. This involves additional fuel injections both before and after ignition, and these cut down soot formation.
> Miller process: To reduce nitrogen oxide emissions, the inlet valves on each cylinder are closed just before the piston reaches bottom dead centre so that the air in the cylinder expands and cools. The process decreases nitrogen oxide emissions by up to 30%.
> Exhaust gas recirculation: Depending on the application in question, up to half the exhaust gas is first cooled and then returned to the engine. This lowers combustion temperature and reduces the generation of nitrogen oxides.
> Exhaust gas aftertreatment with SCR: To reduce nitrogen oxide emissions even further, mtu employs SCR technology on some engines. Here, an aqueous urea solution is introduced into the exhaust stream. The urea is converted into ammonia, which transforms the nitrogen oxides into harmless water and nitrogen in the catalytic converter. The chemical process is selective because only nitrogen oxides are reduced and unwanted side-reactions are largely suppressed.
> Exhaust gas aftertreatment with diesel particulate filters: Here, diesel particulate filters (DPFs) are used to prevent soot particles exiting the engine. Exhaust gases are routed through channels with porous walls that allow the exhaust to pass through, but filter out soot and other particles. This can reduce particle emissions by up to 99%.