Investigations of the formation and oxidation of soot inside a direct injection spark ignition engine M. Rossbach 2 , A. Velji 1 , U. Wagner 1 , U. Spicher 1 , R. Suntz 2 , H. Bockhorn 2 1: Institute for Reciprocating Engines, Karlsruhe Institute of Technology, Germany 2: Institute for Chemical Technology and Polymer Chemistry, Karlsruhe Institute of Technology, Germany Abstract: In this work the formation and oxidation of soot inside a direct injection spark ignition engine at different injection and ignition timing was investigated. In order to get two-dimensional data during the expansion stroke, the RAYLIX-technique was applied in the combustion chamber of an optical accessible single cylinder engine. This technique is based on the quasi-simultaneous detection of Rayleigh-scattering, laser-induced incandescence (LII) and extinction which enables simultaneous measurements of temporally and spatially resolved soot concentrations, mean particle radii and number densities. These investigations show that in our test engine the most important source for soot formation during combustion are pool fires, i.e. liquid fuel burning on the top of the piston. These pool fires were observed under almost all experimental conditions. Keywords: soot, direct injection spark ignition engine, LII, Rayleigh scattering 1. Introduction Modern direct injection spark ignition engines, especially when they are operated in stratified mode, have to deal with the problem of soot emission in the exhaust gas, because fuel rich combustion takes place in the vicinity of the fuel injection jet, leading to soot formation. Later, a fraction of this soot is emitted by Diesel- as well as direct injection spark ignition engines in terms of fine and ultra-fine particles. Fine dust, having a particle diameter less than 10 micrometers (PM 10) can partly penetrate into the lung because the filtering function of the nasal-pharyngeal space is not adequate for these particles. Aggravated allergy symptoms, the increase in asthmatic attacks and even cardiovascular illnesses have been quoted as the possible consequences of the increasing concentrations of fine dust in the air we breathe [1-4]. Adverse health effects are apparently not caused by the mass, but rather primarily by the surface of the particles. Particles that are formed from combustion processes are apparently more relevant than, for example, ground particles or tire wear particles. The disadvantage of particle emission is well known from Diesel engines. As a consequence, a variety of technical solutions to reduce soot emissions are developed. Measures targeting fuel additives generally have the disadvantage that they simultaneously increase the nitrogen oxide emissions. External measures like exhaust gas treatment systems e.g. particle filters, considerably reduce particle emissions but are associated with difficulties in their application (e.g. regeneration of the particle filters) and generally also lead to an increase in fuel consumption [5]. Classical methods for the detection of soot, such as the determination of the blackening index (SZ according to Bosch or filter smoke number FSN) or gravimetric methods, to investigate e.g. the effects of load change, are very difficult to use or even fail because of the lack of temporal resolution. Furthermore, with these methods emission behaviour cannot be measured at the location where particle formation takes place, i.e. directly inside the combustion chamber. In contrast, optical techniques are capable to take measurements in the combustion chamber and in the exhaust system [6- 12]. Additionally, high temporal and spatial resolution of the phenomenon under investigation can be achieved. 2. Experimental Setup 2.1 Engine and test bed specifications The test engine was a single cylinder direct injection spark ignition research engine with spray guided combustion (Fig. 1), thus possible to operate in stratified mode. The spark ignition engine of the future – December 2 nd & 3 rd , 2009 – Strasbourg INSA Page 1/8