The performance and emission characteristics of C-1-C-5 alcohol-gasoline blends with matched oxygen content in a single-cylinder spark ignition engine

Alcohols with carbon numbers ranging from C-1 to C-5 were individually blen ded with unleaded test gasoline. All the alcohol-gasoline blends had the sa me oxygen mass content. The performance characteristics of the blends were quantified using a single-cylinder spark ignition engine. The knock-limitin g spark timing was determined by analysis of the third derivative of the me asured in-cylinder gas pressure versus crank angle. The engine operating co nditions were optimized for each (C-1-C-5) blend with two different values of matched oxygen mass content (2.5 and 5.0 per cent). Emission mass rates of carbon monoxide (CO), nitric oxides (NOx), total unburned hydrocarbons ( THCs), alcohols and aldehydes were quantified. The brake power specific rat e emissions were compared with that of neat gasoline. Adding lower alcohols (C-1,C-2 and C-3) to gasoline improved the knock resistance. Further impro vement was achieved by increasing the oxygen content of the fuel blend. Ble nds with higher alcohols (C-4 and C-5) showed degraded knock resistance whe n compared with neat gasoline. Generally, all alcohol-gasoline blends showe d reduction in CO emissions. Higher alcohol-gasoline blends with an oxygen mass content of 5.0 per cent showed a pronounced increase in NOx emission r ates when operating at high compression ratios and 5 degrees before top dea d centre timing. This is attributed to their lower enthalpy of vaporization and higher flame temperature. All blends tested at optimized operating con ditions showed reduction in THC emission rates. Unburned alcohol emission r ates were higher for blends with higher content of alcohol, and aldehyde em issions were higher for all blends with formaldehyde as the main constituen t.