The determination of aldehydes in the exhaust gases of LPG fuelled engines

Summary The exhaust gas of a LPG fuelled engine is drawn through two bubblers in series in an ice bath, and filled with saturated 2,4-dinitrophenylhydrazine in 2M HCl. After heating the derivatives are extracted with toluene-cyclohexane and 1l samples injected on-column on a OV1 capillary column. Using an FID the lower limit of detection is 15–18 pg for formaldehyde (about 8–10 ppbv for a 16l exhaust sample). Taking the blank into account, the limit is about 40 ppbv.The exhaust gases of a LPG-fuelled engine contain formaldehyde, acetaldehyde, propionaldehyde, acrolein and acetone. Carbonyl compounds of more than 3 C-atoms were not found in detectable amounts. The engine was rund under stoichiometric, lean and rich air/fuel conditions. Under rich conditions the concentrations of the aldehydes were: formaldehyde 2.8 ppm, acetaldehyde 1.3 ppm, propionaldehyde 0.06 ppm, acrolein 0.03 ppm, acetone 0.17 ppm; under stoichiometric conditions: 4.5, 1.6, 0.10, 0.03 and 0.18 ppm respectively; under lean conditions 17.0, 2.9, 0.13, 0.07 and 0.27 ppm respectively. These figures demonstrate the necessity of measuring aldehydes in exhaust gases of LPG-fuelled engines.