Impact of a Urea-Selective Catalytic Reduction System on Volatile Organic Compound Emissions from a Diesel Engine

The impact of a vanadium based urea-water selective catalytic reduction (SCR) system on volatile organic compounds emissions from the tailpipe of a diesel engine were studied. The engine was run on an AC electrical dynamometer in an 8-mode steady-state cycle and the gas-phase VOCs were collected in Tenax TA^® tubes from diluted exhaust. Collected samples were extracted by a thermal desorber and analyzed by gas chromatograph-mass spectrometry. It was found that VOCs were in abundance under a full engine load upstream and downstream of the SCR system and that the SCR positively abated these pollutants. Toluene exhibited the maximum relative contribution (RC) to total VOCs at about 43 and 48% upstream and downstream of the SCR, respectively. After toluene, benzene, ethyl benzene, and undecane were the next major contributors, with a similar order of magnitude. Styrene and butyl acetate were the lowest relative contributors. The RC of benzene was reduced but those of toluene and ethyl benzene were increased downstream of the SCR. The VOC conversion rate (CR) exceeded 17% over the catalyst temperature and space velocity ranges 321-435°C and 27. 63 × 10³-37. 94 × 10³ h^-1, respectively. The optimum catalyst temperature was 321°C, giving a maximum CR of 33%. The CR of benzene and styrene revealed maxima during the full-load modes and minima during the lowest-load modes of the cycle. The CR of benzene increased with increasing catalyst temperature.