In previous work, time-resolved laser-induced incandescence (TIRE-LII) has been introduced as a favorable and easy-to-use technique for accurate online measurements of soot within the exhaust gas of production engines without modifications and first experimental results have been presented.
The method relies on the detection of the thermal radiation of the particles after heating with a high power laser pulse. Additionally to soot concentration measurements, a simultaneous determination of soot primary particle sizes and, derived from these, also of the particle number concentrations is possible. Basic features of the technique are the high temporal resolution, which also makes transient tests feasible, and its high sensitivity and selectivity. These aspects suggest its application as a standard method for exhaust measurements with enhanced performance, which also leads to considerable new insight into internal combustion phenomena.
In this work, this approach is continued and a comparison to filter smoke number (FSN) measurements has been performed under realistic operating conditions for a medium-duty truck engine, showing significant deficiencies of current standard methods. However, a clear correlation was found for the whole range of practical concentrations and its shape is discussed in some detail. Further, an European Stationary Cycle test (ESC), being the current reference for emission regulations within the European Community (EU), has been analyzed by the LII method. Additionally, the primary particle size was determined under standard test conditions, and again a characteristic behavior was observed. Finally, the effect of boost pressure and injection pressure of a common-rail injector on the emission characteristics was investigated. It has been found that both mass concentration and particle size decrease with increasing rail pressure and with increasing boost pressure. As these measurements were performed simultaneously, an accurate evaluation of the number concentration within the raw exhaust gas was possible. No increase but a slight decrease of the particle number concentration has been obtained for higher injection pressures, which are preferably used for modern state-of-the-art diesel engines. These results are discussed in some detail.