Carbonyl Compounds and Toxicity Assessments of Emissions from a Diesel Engine Running on Biodiesels

This study elucidates the effect of biodiesel on the emission of carbonyl compounds generated from a diesel engine (generator), and the related biotoxicity characteristics. The Microtox test and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay were conducted to evaluate the acute toxicity and cytotoxicity, respectively, of gaseous extracts from diesel engine exhaust. The engine was tested using diesel fuel and biodiesel blends (10, 30, 50, 75, and 100% of biodiesel by volume). The operating conditions of the diesel engine were set as idling, 10, 33, and 55% loads. The regulated emissions of carbon monoxide (CO), nitrogen oxides (NO_x), and carbon dioxide (CO₂) were monitored. The carbonyl compounds in the exhaust were collected in 2,4-dinitrophenylhydrazine (2,4-DNPH) solution in an impinger and converted to corresponding hydrazone derivatives, which were then analyzed using high performance liquid chromatography (HPLC) with an ultraviolet (UV) detector. Analysis results indicate that the carbonyl compound emissions increased when the engine was run on biodiesels at all of the loadings; however, the total concentration of emitted carbonyls did not increase with the biodiesel content. The dominant carbonyls (formalde-hyde, acetaldehyde, acrolein, and acetone) accounted for 70 to 90% of all carbonyl emissions in the engine exhaust. The concentrations of CO₂ and NO_x from B10 were quite similar to those from diesel. Finally, in the toxicity assessments, B10 had a higher acute toxicity and cytotoxicity than diesel, indicating that blending with biodiesel may have adverse health effects because of toxic gas emissions. At various engine loads, higher toxicities were associated with greater carbonyl emissions in diesel exhaust, but not in B10, indicating that the carbonyls may not be the major pollutants that induce the toxicity of emissions from biodiesel.