Abstract: Particulate emission experiments were conducted on two gasoline direct injection (GDI) engines to
study the influence of engine load, excess air ratio, and ignition advanced angel on the emission characteristics
such as particulate mass (PM), particulate number (PN), and size distribution after three way catalyst (TWC). The
component of soluble organic fractions (SOF) was analyzed using gas chromatograph-mass spectrometer (GCMS).
The results show that the PM and PN increase with the engine load, and the magnitudes of the increase
are significant at high load. The PM and PN both decrease with the increase of excess air ratio and the delay of
ignition timing. The catalyst reduces the SOF in the particulate matter and the concentration of the nucleation mode
particles. The peak diameter of the nucleation mode particles is between 10 and 20 nm; and the peak diameter of
the accumulation mode particles is between 50 and 70 nm. The engine load, TWC, excess air ratio and ignition
timing have small influences on the particle diameter range.

Key words: gasoline engines, gasoline direct injection (GDI), particulate mass, particulate number, size distribution, experiments