Modern diesel engines NOx particles emission

Exhaust gases recirculation systems (EGR), together with catalytic reactors, are commonly installed in modern piston combustion engines. Their purpose is to reduce the amount of nitrogen oxides (NOx) emitted in fumes. The need for this reduction takes its source from introducing more rigorous EURO standards, which are treating about maximum levels of NOx, HC and particulates produced, as a side effect of engine's operation. Applied exhausts recirculation circuits can be roughly characterized by a principle, that a part of exhaust gases is redirected (through a cooler) and reaches a special valve. This valve, respectively to engine's current load and speed, drives more or less exhaust to suction manifold. The position of the valve determines the system’s overall efficiency, but also differentiates the amount of toxic gases and smoke produced by each of the engines cylinders. Recent research have focused only on the overall efficiency of recirculation systems, representing it by measuring the total amount of NOx particles emission from exhaust pipe. However, the quantity of exhaust gases that is reaching each cylinder can be negatively dependant on EGR valve’s physical position in the circuit. This happens due to the fact that combusted loads have different proportions of charged air and fuel. For estimating the difference among each of the loads, and in the same time, indirectly, in equal emission of NOx from corresponding cylinders, a research was carried out on a model VW 2.0 TDI engine, equipped with standard, factory mounted, exhausts gases recirculation circuit. Measurements of toxic emissions were executed with regards to thirteen-point ESC (European Stationary Cycle) test.