In-Cylinder Measurements of Soot Production in a Direct-Injection Diesel Engine

In-cylinder and exhaust soot mass measurements have been made on a single-cylinder conversion of a 4-cylinder, 2.8 1, high-swirl, direct-injection diesel engine using a sampling system which allows dumping, diluting, quenching, and collecting the entire contents of the cylinder on a time scale o£ about 1 ms. Experiments have been performed at engine speeds of 1,000 and 1,500, and equivalence ratios, ϕ, of 0.4 and 0.7. Soot mass first appears shortly after top dead center and reaches a peak between 15 and 30 crankangle degrees after top dead center (CAD ATDC). After reaching its peak value, soot concentration decreases with increasing crankangle and approaches exhaust levels by 40-60 CAD ATDC. The time lag between the start of combustion and the first appearance of soot increases with ϕ and ranges from 0.2 to 1 ms. The initial rate of soot formation ranges from 0.26 to 0.30 mg ms⁻¹ and varies little with speed or ϕ. The peak in-cylinder soot concentration only increases slightly (less than 20%) with ϕ. On the other hand, at ϕ = 0.4, oxidation reduces the exhaust soot concentration to roughly 15% of the peak in-cylinder value, while at ϕ = 0.7, oxidation is much less effective and the exhaust soot concentration is 60–80% of the peak value. It appears that oxygen availability late in the cycle is a critical factor in determining exhaust soot concentrations of this engine.