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TECHNICAL PAPERS: Internal Combustion Engines

# Soot Formation Study in a Rapid Compression Machine

[+] Author and Article Information
I. Kitsopanidis, W. K. Cheng

Sloan Automotive Laboratory, Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139

At a charge density of $∼200mol∕m3$, the mean free path is $∼10nm$. The large particles may approach the continuum limit. Then the growth rate is proportional to $t3∕2$, which is even slower.

J. Eng. Gas Turbines Power 128(4), 942-949 (Oct 24, 2005) (8 pages) doi:10.1115/1.2180279 History: Received July 11, 2005; Revised October 24, 2005

## Abstract

A rapid compression machine was used to study the soot formation process under diesel enginelike conditions. The apparatus creates accurately controlled conditions at the end of compression (uniform mixture, temperature, and well-defined mixture composition) and, by decoupling chemistry with mixing, provides an unambiguous data interpretation for kinetics study. The soot evolution was studied by the line-of-sight absorption method (at $632.8nm$), which measured the soot volume concentration evolution in the initial stage of soot growth before the optical path became opaque. For a rich butane mixture at fuel equivalence ratio of 3, the ignition delay showed a negative temperature dependence at intermediate temperatures. The soot volume fraction showed an initial exponential growth, with a growth rate depending on the compressed charge fuel concentration. A substantial amount of soot was formed after the soot cloud became opaque. By weighing the total soot particles after the experiment, only $∼10–15%$ of the soot mass was formed when the beam transmission was reduced to 5%. The final soot mass was $∼15–18%$ of the total carbon mass for compressed charge density of $250mol∕m3$ and temperature from $740to930K$.

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## Figures

Figure 1

Schematic of a diesel fuel spray illustrating the combustion processes (4)

Figure 2

Conditions for soot formation in diesel engines and in various experimental studies

Figure 3

Schematic of the rapid compression machine

Figure 4

Calculated piston velocity and comparison of calculated and observed pressure traces. N-butane/oxygen/argon mixture; Ar∕O2=3.773, Φ=3; precompression pressure and temperature: 0.4bar, 49°C.

Figure 5

Schematics of optical setup

Figure 6

Effect of soot luminosity on apparent transmission: (a) signal with optical arrangement of Fig. 5 and (b) with detector and filter at 5cm from combustion chamber window

Figure 7

Soot luminosity and light transmission

Figure 8

Repeatability of data; five repeats. N-butane/oxygen/argon mixture; Ar∕O2=3.773, Φ=3; compressed conditions: 750K, 14bar, 250mol∕m3.

Figure 9

Ignition delay and combustion times. N-butane/oxygen/argon mixture; Ar∕O2=3.773, Φ=3; compressed conditions: 765K, 14bar, 250mol∕m3.

Figure 10

Ignition delay as function of compression temperature. N-butane/oxygen/argon mixture; Ar∕O2=3.773, Φ=3; compressed molar density: 250mol∕m3.

Figure 11

Combustion time as a function of compression temperature: (a) 5–20 % burn time and (b) 20–80 % burn time. N-butane/oxygen/argon mixture; Ar∕O2=3.773, Φ=3; compressed molar density: 250mol∕m3.

Figure 12

Soot formation history at two different gas densities. N-butane/oxygen/argon mixture; Ar∕O2=3.773, Φ=3; compressed temperature: 765K. Time zero corresponded to point of 90% light transmission.

Figure 13

Soot formation time constant as a function of compression temperature. N-butane/oxygen/argon mixture; Ar∕O2=3.773, Φ=3; compressed molar density: 250mol∕m3.

Figure 14

Final soot yield as a function of temperature. N-butane/oxygen/argon mixture; Ar∕O2=3.773, Φ=3; compressed molar density: 250mol∕m3.

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