Characterization of Diesel Particulate Emissions in Heavy-Duty DI-Diesel Engines with Common Rail Fuel Injection Influence of Injection Parameters and Fuel Composition 2001-01-3573

The findings presented in this paper result from a collaboration between two Federal Laboratories in Switzerland. In this research project the characteristics of the particulates from internal combustion engines were investigated in detail. Measurements were carried out on a single-cylinder research engine focusing on exhaust particulate matter emissions. The single-cylinder diesel engine is supercharged and features a common-rail direct injection system.

This work analyzes the influence of fuel properties and injection parameters on the particulate number size distribution. For the fuel composition, five different fuels including low sulfur diesel, zero-sulfur and zero-aromatics diesel, two blending portions of oxygenated diesel additive and rapeseedmethylester were used. For the injection parameters the injection pressure, the start of injection and the fuel amount in the pilot- and in the post-injection phases were varied. The engine tests were run at different operating points of the engine map and the exhaust gas recirculation rate was widely varied.

For Scanning Mobility Particle Sizer (SMPS), Photoelectric Aerosol Sensor (PAS) and Diffusion Charging Particle Sensor (DC) measurements, the sample taken from the exhaust gas line has been immediately diluted with a rotating diluter. The SMPS data of each experiment were collected twice: the exhaust gas being heated at a temperature of 350°C with a thermodesorber placed before the SMPS or bypassed without conditioning. Gravimetric and coulometric measurements were conducted using a partial flow diluter.

To our knowledge, this is the first study that yields such detailed results on both the influence of several injection parameters and fuel properties in the same heavy duty diesel engine on the basis of the same measurement techniques. The interpretation of the results is based on heat release rate and engine combustion process analysis, in order to identify important relationships between combustion modes and particulate formation.

The results indicate that:

• The injection parameter settings have the predominant role in the shape of the particulate matter size distribution (Fig. 2). The total particle number detected in the exhaust gas is very sensitive to the variation of the injection pressure.
• At very high injection pressures, a nucleation mode appears in the particle number size distribution (Fig. 5).
• Post-injection lowers the particle number concentration in a significant way (Fig 10).
• Exhaust gas recirculation (cooled EGR) shifts the maximum in the number size distribution to more and larger particles (Figs 5 and 7).
• During the engine operation with Rapeseedmethylester, an unexpected large amount of ultrafine particles were detected in the exhaust (the mode of the particulate matter size distribution is under 20nm diameter), Figs 14 and 18.
• In most cases there is a clear correlation between the integrated particle number concentration over the entire measurement range and the exhaust gas opacity (Fig. 24).

The plausibility of these trends is confirmed by the analysis of the combustion process.