Pierburg, 13.03.2018 (PresseBox) – For years now, secondary air systems have established themselves as robust and effective in reducing gasoline engine emissions. They accelerate catalytic converter heat-up while consuming little electric energy in the process. And, their effectiveness is not contingent on the quality of the gasoline.
Pierburg GmbH has now further developed the associated secondary air blower and provided it with a speed-controlled motor. The latter allows secondary air injection across a much wider engine map range and hence, at any given point in time, the precise air mass required for accelerating converter heat-up is injected into the exhaust system. The new speed-controlled secondary air blower rounds off Pierburg’s line-up of secondary air blowers and valves while extending the array of applications to cater for the requirements of RDE legislation, including for hybrid drive systems.
Through the secondary air pump, the new air blower not only accelerates catalytic converter heat-up, it lowers electric energy consumption and emissions. It thus helps many engines to comply with such standards as EU 6.2, RDE, SULEV 20 or Beijing 6. In a related application, the blower, which can run uninterrupted, permits controlled particle filter regeneration independent of ambient and driving conditions.
The way secondary air injection works
Secondary air injection accelerates converter heat-up during cold starts or repeated starts as on hybrid cars or during start/stop cycles. The technique consists in creating an oxidizable gas mixture through combustion under air shortage conditions in the combustion chamber. With the injection of air directly into the exhaust system, this gas mixture undergoes an exothermal reaction. The unburned exhaust constituents are oxidized and the temperature at the converter entrance point rises significantly. The consequences: accelerated converter heat-up, reduced carbon monoxide and hydrocarbon emissions during the heat-up phase.
The air blowers used nowadays are normally designed to cover a specific range of air mass flow rates. When this is low at low engine load/speed, a secondary air pump designed for a high air mass flow can lead to excessively lean and cool exhaust gases. This, in turn, would cause failure in the exothermal reaction. On the other hand, in the case of a high air mass flow rate, the air flow generated by the secondary air pump can be too low for even triggering an exothermal reaction. Hence, an unregulated secondary air pump restricts the functional range of secondary air injection to a limited engine map range.
Injecting just the right air mass flow
The new Pierburg secondary air pump comes with a brushless 12-V motor and all the relevant electronics. Its speed is variable, it can run continuously and allows any number of start/stops. It accelerates converter heat-up at any given point of time within a wide range of engine operating parameters and directs the necessary air mass air flow with absolute precision. This, in turn, avoids phases of too lean exhaust gases and excessive cooling as well as phases with insufficient oxygen content. This on-demand injection of air also cuts air pump energy consumption. The secondary air pump can be controlled by a LIN bus or PWM and, since the blower is smaller, less installation space is needed.
Controlled regeneration of gasoline particle filters
The properties of the new secondary air pump (speed adjustability, continuous operation, efficiency) facilitate other measures designed for emission reduction. The blower not only allows the air ratio in the exhaust system to be controlled, it also serves for controlled regeneration of a gasoline particle filter by assisting in the management of temperature and oxygen content. This is, for example, necessary in phases of low exhaust gas temperature occurring at low travel speeds and low ambient temperatures. Here it might be necessary for the particle filter to be heated and supplied with additional oxygen for controlled regeneration similarly as during catalytic converter heat-up.