To combat this effect, modern diesel engines recirculate part of their exhaust back into the combustion chamber after cooling it down, together with the fresh air. In this mixture, carbon dioxide and water from the exhaust gases moderate the combustion process, keeping the temperature in check. As a result, fewer nitrogen oxides are formed, albeit at the price of increased soot production since the proportion of oxygen in the air-exhaust mixture is lower.
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 ten 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, like an onion whose first layer has been peeled. The resulting exhaust fumes envelop the fuel droplets, shielding them from the oxygen. The shell of exhaust gases gets increasingly dense with each "onion layer" that goes up in flames. Eventually it becomes practically impossible for oxygen to react with the fuel. The result: soot formation.
The NEMo injector nozzle atomizes diesel fuel at a pressure of over 3000 bar standard is 1800 b
|Contact: Markus Bernards|
Technische Universitaet Muenchen