Emission control invariably consists of a particulate filter, and the particulate sensor developed by IMITEC is important for the closed-loop control of this filter. As the filter is clogged by the collected particulate it needs to be cleaned by oxidation of the accumulated soot. Cleaning—or regeneration—is done by increasing the exhaust temperature to oxidize the soot.

That regeneration process is launched when the Engine Control Unit senses the filter is full. Electronically-controlled engines can inject fuel during the last stage of the combustion cycle. This fuel enters the exhaust, where it oxidizes completely, producing temperatures in excess of 650º C, the soot’s oxidation point, cleaning or regenerating the filter.

The IMITEC sensor triggers regeneration in an adaptive and efficient fashion leading to fuel savings and increased reliability of the emission control system. In other words, sometimes filters need to regenerate after 500km, or 1000km, but to know exactly when, you need a sensor. The only way to know when is to know the history of the filter and the driving profile of the vehicle.

The project actually developed two types of sensors during its research. Hardware sensors measure directly the values of particulates, temperature and pressure in the exhaust. Software “virtual” sensors, on the other hand, measure other sensors in the car and then apply an algorithm to discover a given measurement.

As an example, a virtual sensor that computes the amount of soot load in a Diesel Particulate Filter from signals of filter pressure drop, exhaust flow and exhaust temperature. The output of these virtual sensors are used by the Engine Control Unit to manage the emission control system.

We spent about 70 per cent of our time on [particulate sensing and filter regeneration]. I think when we started the project it was considered highly ambitious, but we have met out targets and we now have several technologies that will be commercialized.

—Dr Athanasios G. Konstandopoulos, project coordinator and director of the Aerosol and Particle Technology Laboratory at CERTH/CPERI

IMITEC built more than the particulate filter sensors; it built an entire Emissions Control System for diesel engines, initially for light duty and passenger cars but the technology could be adapted for trucks.

The entire system consists of a Diesel Oxidation Catalyst (DOC), a soot sensor, a soot filter, another soot sensor downstream of the filter and then an optional NO_x trap and NO_x sensor.

The DOC oxidizes carbon monoxide, gaseous hydrocarbons and liquid hydrocarbon particles, or unburned fuel and oil. A sensor detects if particulates coming out of the exhaust are off-spec.

Next the first soot sensor detects how much soot is coming from the engine and hence when regeneration needs to launch. The second soot sensor downstream of the filter provides on-board diagnostics.

This detects if particulates coming out of the exhaust are off-spec, possibly caused by a hole in the filter or some other problem. In any case, it indicates to the driver that the systems needs to be repaired.

—A. Konstandopoulos

The team also offered an optional trap to remove NO_x exhaust gases. IMITEC also developed a NO_x sensor for diesels.

Before IMITEC there was no NOx sensor for diesel engines, though such sensors do exist for gasoline engines. We essentially adapted that technology for diesel, so we can offer another option to engine manufacturers.

—A. Konstandopoulos

The NOx trap and NOx sensor is an option in the system for automakers who chose not to implement EGR as a NO_x reduction technology.

The €3.8 million (US$4.6 million) project received around €1.75 million (US$2.1 million) from the EU under its Fifth Framework programme. The remainder came from industry partners including Fiat, UK catalyst specialist Johnson Matthey, AVL and Bosch.

The team developed a demonstrator of their Emissions Control System, fitted into a Fiat Ducato. The results from IMITEC will be disseminated at ICT 4 All exhibition to be held in Tunis in 16-18 November as part of the World Summit on the Information Society.

Resources:

• IMITEC