The influence of oxygenated fuels on emissions of aldehydes and ketones from a two-stroke spark ignition engine

A spark-ignited two-stroke chainsaw engine was used to study the influence of pure oxygenated fuels on exhaust emissions of carbonyls (aldehydes and ketones) and regulated emissions, i.e. hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). Three fuels-methanol, methyl tert-butylether (MTBE), and ethyl tert-butylether (ETBE)-were used in the tests, each at three air/fuel ratios (λ) and the generated emissions were compared to those observed in previous tests with ethanol, aliphatic gasoline, and regular gasoline. Use of all four oxygenated fuels (ETBE, ethanol, methanol and MTBE) resulted in substantially higher total carbonyl emissions (11, 11, 8.9 and 7.8 g/kWh, respectively) than use of both aliphatic and regular gasoline (2.1 and 2.6 g/kWh, respectively). Further, up to 44-fold higher levels of specific carbonyls were generated from the oxygenated fuels than from regular gasoline: significant amounts of formaldehyde were produced from all of the oxygenated fuels, but they were especially high from methanol and MTBE; acetaldehyde was formed in high amounts from ethanol and ETBE; while acetone and methacrolein were formed from both MTBE and ETBE. In addition, increases in λ increased exhaust emissions of formaldehyde, acetaldehyde, acetone, and methacrolein in cases where these were the main carbonyls formed. Increasing λ also variously increased, reduced or had no significant effect on emissions of other measured carbonyls. Lower amounts of CO and NOx emissions were formed from all oxygenates (especially methanol) than from regular gasoline.