The development of new generations of internal combustion engines requires appropriate measurement techniques for all relevant limited exhaust gas species and particulates. However, because of stricter future emission limits, there is a severe lack especially with respect to soot particles. Conventional methods, like gravimetric sampling, have substantial deficiencies in sensitivity and temporal resolution, which is strongly required for transient tests. Furthermore, artifacts arise from other exhaust components, like sulfuric acid, water vapor and volatile hydrocarbons.
In contrast to the state-of-the-art techniques, laser induced incandescence (LII) has been proved to be a favorable technique, which overcomes these deficiencies and offers additional information, which allows new insight into combustion phenomena. Besides soot mass concentration, also the soot primary particle size is accessible by this technique. In previous work, basic features of the technique have been introduced and some first applications have been shown for a passenger car and a truck engine. In these investigations a clear correlation was found between the soot mass concentration derived from LII and the filter smoke number measurements.
In this study, the application of an advanced soot sensor is demonstrated at a medium duty truck engine (MAN D08). This sensor prototype allows an easy adaptation to the exhaust pipe without the need of any further adjustment. A fully automatic on-line evaluation of the measurement data allows an easy use of the compact measurement system. The influence of a few different fuel types on particulate mass concentration and primary particle size was preliminarily investigated at different stationary operation points. Additionally, some first transient tests have been performed with particularly high temporal resolution. The results are discussed in some detail and an outlook on future work is given.