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The European research co-operation Lotus is presented. The main objectives of the project were i) to show the potential for a urea-based SCR system to comply with the EU standard of years 2005 and 2008 for heavy-duty Diesel engines for different driving conditions with optimal fuel consumption, ii) to reach 95 % conversion of NOx at steady state at full load on a Euro III engine, iii) to reach 75 % NOx reduction for exhaust temperatures between 200-300°C, and 85 % average NOx reduction between 200-500°C. The energy content of the consumed urea should not exceed 1.0 %, calculated as specific fuel consumption. These targets were met in May 2003 and the Lotus SCR system fulfilled the Euro V NOx legislative objectives for year 2008.

This paper describes the development and tests of a combined CO/O2 zirconia sensor for on-board diagnosis of oxidation catalysts. To achieve accurate measurements, preliminary model scale experiments have been carried out. These tests consist in careful calibrations with synthetic gases, measurements in exhaust gas from a laboratory scale lean premixed methane-air burner, and comparisons with classical and FTIR gas analyzers. Accordingly, a new sensor has been designed and prototyped. Held in a spark plug type housing, it simultaneously monitors the CO, and O2 content of the exhaust gas. Over the wide O2 range of interest, model scale tests of the sensor with burnt gases have shown good agreement with laboratory analyzers. Closed loop experiments carried out with the same burner also demonstrate the CO/O2 probe potential for combustion control.

The NOx/O2 sensor has been developed based on a simple tubular design. It is a potentiometric sensor that gives out two sensor voltages: one for the O2 concentration, the other for the NOx concentration. The NOx sensor has been extensively tested in synthetic gases and in real exhaust gases. It gives a good response towards NOx and NO2 for O2 concentrations between 0.5 and 20.8%. The sensor can be used to detect NOx in the range from 10-1500 ppm. Typical gas lab measurements to check the sensitivity and cross-sensitivity are shown. Succesfull sensor testings before and after a lean NOx trap (LNT) on a GDI engine are performed. The sensors are also tested on an exhaust gas simulator to check their sensitivity towards NO in more realistic circumstances.

This article describes the development and tests of a combined NOx/oxygen Zirconia sensor. To achieve accurate NOx and oxygen measurements under lean-burn conditions, preliminary model scale experiments with a premixed methane-air burner are carried out with current production oxygen sensors as well as with our own oxygen probe. It is found from these tests that accurate oxygen sensing requires sensor operating temperatures much lower than usually set, about 600°C. Moreover, this temperature is a good compromise for NOx sensitivity and time response of the sensor. Accordingly, a new NOx/O2 sensor has been designed and prototyped. Held in a spark plug type housing, it simultaneously monitors the NOx and oxygen content of the exhaust gas. Over the wide 02 range of interest, model scale tests of the sensor with burnt gases have shown promising agreement with laboratory analysers.