Exhaust gas recirculation (EGR): one more method of reducing emissions
In order to be able to comply with future emission limits, stiff requirements are applied to engine systems. The tight tolerances call for a closed-circuit EGR system. Depending on the type of internal combustion engine, position or airflow control is employed. The effect of exhaust gas recirculation is based on a lowering of combustion temperature on diesel and gas engines. The lower temperature leads to a reduction in nitrogen oxides. On gas engines, this also brings about a dethrottling of the engine under part-load conditions and hence fuel consumption reduction. Available is a wide variety of EGR valves: rugged pneumatic valves with modulation of the open control pressure to electric motor-controlled valves which combine high actuating forces, very precise control and favorable dynamic properties. In combination with Pierburg aluminum coolers and exhaust gas flaps, EGR valves control the pressure difference for a further significant abatement in nitrogen oxides. An intelligent integration of all the EGR components such as valves, flaps, bypass devices, coolers and lines results in a cost-effective solution with extended service life.
The future of the automobile hinges largely on efficient techniques for reducing emissions. This is a function that the catalytic converter cannot perform all by itself. With its acknowledged competence in every aspect of the engine and over 30 years of experience in series production, Pierburg manufactures secondary air systems, exhaust gas recirculation systems as well as exhaust flaps all designed to satisfy present and future emission requirements.
Back at the start of the 90s, Pierburg had developed a secondary air system for effective after-treatment of the exhaust gases. This was necessary in view of the growing gap between untreated emissions and stipulated limits.
The secondary air assists the catalytic converter during the engine's warm-up phase since immediately after cold start, the converter fails to achieve any purifying effect. Only at a light-off temperature in the range of 300 to 350 °C does the converter come into operation.
Injecting secondary air into the exhaust gas manifold gives rise to exothermal oxidation of the unburned carbons and carbon monoxides. The heat released in the process allows the converter to reach its operating temperature more readily.
The secondary blower has a radial design and is driven by a DC motor. The engine compartment is sealed off with respect to the pump unit in order to protect the motor from the aggressive exhaust gas condensate while assuring, at the same time, low-noise operation.
With its variety of secondary air valves, pneumatically or electrically operated, with and without pressure sensor, Pierburg provides optimum systems for future applications, too.