Exhaust-Stream and In-Cylinder Measurements and Analysis of the Soot Emissions From a Common Rail Diesel Engine Using Two Fuels

Abstract

The operation and emissions of a four cylinder, passenger car common-rail diesel engine operating with two different fuels was investigated on the basis of exhaust-stream and in-cylinder soot measurements, as well as a thermodynamic analysis of the combustion process. The two fuels considered were a standard diesel fuel and a synthetic diesel (fuel two) with a lower aromatic content, evaporation temperature, and cetane number than the standard diesel. The exhaust-stream soot emissions, measured using a filter smoke number system, as well as a photo-acoustic soot sensor (AVL Micro Soot Sensor), were lower with the second fuel throughout the entire engine operating map. To elucidate the cause of the reduced exhaust-stream soot emissions, the in-cylinder soot temperature and the KL factor (proportional to concentration) were measured using miniature, three-color pyrometers mounted in the glow plug bores. Using the maximum KL factor value to quantify the soot formation process, it was seen that for all operating points, less soot was formed in the combustion chamber using the second fuel. The oxidation of the soot, however, was not strongly influenced by the fuel, as the relative oxidized soot fraction was not significantly different for the two fuels. The reduced soot formation of fuel two was attributed to the lower aromatic content of the fuel. The soot cloud temperatures for operation with the two fuels were not seen differ significantly. Similar correlations between the cylinder-out soot emissions, characterized using the pyrometers, and the exhaust-stream soot emissions were seen for both fuels. The combustion process itself was only seen to differ between the two fuels to a much lesser degree than the soot formation process. The predominant differences were seen as higher maximum fuel conversion rates during premixed combustion at several operating points, when fuel two was used. This was attributed to the lower evaporation temperatures and longer ignition delays (characterized by the lower cetane number) leading to larger premixed combustion fractions.

Refinement of the two-color pyrometry method for application in a direct injection diesel and natural gas compression-ignition engine

“…after 20 CAD aTDC) where the refinements can increase robustness of the pyrometric method for weak signals and provide insight to the late-cycle KL and T, which are closely related to the exhaust stream emissions. 48 For PIDING combustion, shown in Figure 10, the KL factor is generally lower, relative to diesel combustion, as expected with NG as the primary fuel. The high methane content and low load lead to premixing of the NG before ignition and ultimately result in lower temperatures and less potential for soot formation.…”

“…after 20 CAD aTDC) where the refinements can increase robustness of the pyrometric method for weak signals and provide insight to the late-cycle KL and T , which are closely related to the exhaust stream emissions. 48…”

Development and validation of a virtual soot sensor: Part 1: steady-state engine operation

“…Furthermore, as previously mentioned, correlations from a characteristic kL end value to the exhaust soot emission can be performed engine specifically, as shown in Kirchen et al 22 and Barro et al 28 Modelling concept…”

“…After calibrating each channel (wavelength) from the amplifier voltage to the known uniformly emitted intensity by a tungsten lamp in combination with an integrating sphere (to cover the whole OLP view field), which has already been used in Kirchen, 21 Kirchen et al 22 and Schubiger, 23 the wavelength-specific black body temperature ( T BB ) can be derived for each wavelength (680, 790, 903 nm) according to Planck’s law. A pair of black body temperatures is used to calculate the real soot cloud temperature, assuming an optical diffuse surface of the soot cloud.…”

Development and validation of a virtual soot sensor: Part 2: Transient engine operation

“…7 Correlations from a characteristic kL end value to the exhaust soot emission can be done engine specifically, as shown in Barro et al 22 and Kirchen et al 28 For such a correlation, a characteristic kL end value is required to compare the soot level before and after passing the exhaust valve. For this particular case, the characteristic kL end value has been connected to a characteristic end value close to the end of combustion that is to a characteristic value of the heat release rate.…”