Search Results

New exhaust emission laws require significant reduction of tailpipe hydocarbon emissions. The cold start phase of engine operation is a critical period when HC emissions must be minimized. High driveability index (DI) or low volatility fuel causes the open loop air/fuel (A/F) ratio during an initial cold start of the engine to shift lean which in turn contributes to unstable combustion. To compensate for this lean shift, the open loop A/F ratio must be commanded richer than necessary to allow acceptable driveability with high DI fuels which consequently increases tailpipe HC emissions. With engine cold start conditions being equal, (coolant temperature, engine speed, engine load, ignition timing, and commanded A/F ratio), the difference in cold start engine-out A/F ratio can only be attributed to the volatility characteristics of the fuel. The A/F ratio in a combustion chamber and hence, the temperature of the exhaust gas, is a function of the volatility of the fuel.

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.