A study of soot formation in a rapid compression machine at conditions representative of cold-fast-idle in spark ignition engines

Abstract

The soot yield, defined as the ratio of the soot mass to the carbon mass in the fuel, for the homogeneous combustion of a rich fuel-air mixture has been measured in a rapid compression machine using the laser light extinction method. The temperature and pressure conditions are representative of those in spark-ignition direct-injection engines at cold-fast-idle. The fuels used are a certification gasoline (with 28% aromatic content) and a blend of the gasoline with toluene (the blend had 40% aromatic content by volume) so that the sensitivity of soot formation to the fuel aromatic content could be assessed. Beyond a threshold fuel equivalence ratio (ϕ) value, the soot yield increases exponentially with ϕ. The soot yield of the gasoline–toluene blend is four to six times higher than that of the gasoline. The soot yield decreases exponentially with temperature, by a factor of 0.58 for every 10 K increase in temperature. In the 657–695 K temperature range, the threshold ϕ value increases linearly from approximately 2.4 to 2.7, at a rate of 0.1 point per 10 K rise in temperature. This temperature dependence is insensitive to the charge density.

Experimental measurements of soot formation in fuel-rich homogeneous mixtures using an optical rapid compression machine

“…Their RCM trials also ensured a homogenous air-fuel mixture by vaporizing the fuel prior to mixing with air. Similarly, Ketterer and Cheng 15 found, through use of an RCM and laser extinction diagnostic, that the introduction of additional aromatics such as toluene, commonly found in gasoline, increased the sooting tendency of iso -octane and gasoline. This further highlights the need for oxygenated fuels and blends with these fuels, such as ethanol, in mixing-controlled combustion applications, as market gasoline can have high aromatic content.…”

“…RCM data is often used to validate detailed kinetic mechanisms in the prediction of autoignition behavior due to the simplicity and repeatability of each RCM trial. 15…”

“…RCM data is often used to validate detailed kinetic mechanisms in the prediction of autoignition behavior due to the simplicity and repeatability of each RCM trial. 15 The RCM is an ideal experimental platform for analyzing the sooting tendency for a wide-range of fuel types, including the low-cetane fuels. The work of Tanaka et al 16 used a He-Ne laser extinction diagnostics to determine particulate concentration of n-heptane in an RCM.…”

“…An optical rapid compression machine has an advantage over an all-metal single cylinder engine in that quantitative soot volume fraction data can be directly measured in the cylinder, rather than taking aggregate data from exhaust measurements. 15 This is due to the homogenous nature of the charge in RCM experiments, developing a single, well-controlled, set of reference conditions for the experiment. The analysis of ethanol and gasoline (or gasoline surrogates) at rich equivalence ratios in an RCM enables broader global understanding of soot formation characteristics and sooting tendencies of these fuels without the effects of sprays, turbulence, and soot oxidation present in globally lean diesel-style combustion engines.…”

Consequence of Blowby Flow and Idling Time on Oil Consumption and Particulate Emissions in Gasoline Engine

“…A particle arises from the collision between two PAH of pyrene (C 16 H 10 ). This is called nucleation [3][4][5][6][7][8]. For internal combustion engines, the main factor generating particulate matter is the high-temperature combustion or pyrolysis of unburnt fuel [9].…”