Changes in Diesel Particulates with Engine Air/Fuel Ratio

Systematic changes have been observed in the character of diesel exhaust particulates as the engine air/fuel ratio is varied. For air/fuel ratios below 20 the particulates are primarily carbonaceous, cluster into chain-like agglomerates and exhibit high specific optical extinction. Increasing the air/fuel ratio leads to increases in the volatile organic content, to less clustering and to lower specific optical extinction. The specific optical extinction decreases from over 10 m2·g−1 at air/fuel ratios below 20 to less than 5 m2·g−1 for air/fuel ratios above 30.