Impact of biodiesel and propanol blends on engine performance, regulated emissions and <scp>PAH</scp> formation
Nadir Yılmaz, Moses Ukaoma
Abstract
Central to the discussion on sustainable alternative fuels for diesel engines is a growing interest in oxygenated fuels such as blends of biodiesel and alcohols with high carbon content (high alcohols). Available literature is incomplete in assessment of this kind of fuel blend and its influence on quantity and type of polycyclic aromatic hydrocarbons (PAHs) content. PAH is a health hazard and is detrimental to engine components (wetstacking); effort should focus on its reduction. Impact assessment of fuels usually focuses on the engine's regulated emissions profiles. However, additional emphasis should be given to levels and characteristics of PAH produced (during combustion). In this current work, regulated and unregulated emissions of a diesel engine operating with a biodiesel-propanol-blend fuel (5%, 20% and 35% by volume of propanol) are presented and compared. Sample fuels were examined using gas chromatography-mass spectrometry (GC-MS). Results indicate a reduction in nitrogen oxides (NOx) and PAH levels including PAH-equivalent toxicity, and an increase in hydrocarbon (HC), carbon monoxide(CO), break specific fuel consumption (BSFC) and exhaust gases temperature (EGT), for the fuel blend compared to baseline diesel. While the results showed that adding up to 20% propanol to biodiesel further reduced PAHs, more than 20% propanol addition to biodiesel appeared to show a recurrence of increasing levels of PAHs and toxicity. With the addition of propanol to biodiesel, a significant reduction of 30.60%, 90.24% and 56.68% in total PAH emissions was obtained for 5%, 20% and 35% blends, and PAH-equivalent toxicity significantly decreased by 64.65%, 92.77% and 79.37%, respectively. This indicates the significant effect of combustion performance due to blended fuel properties on the formation of PAHs. In addition, it was evident that a link exists between PAH-formation and aromatic-content of the base fuel, as diesel generated more PAHs than biodiesel blends. Overall, biodiesel-propanol blends show potential in significantly cutting-down levels of carcinogenic pollutants including wetstacking effects in diesel engines running at low load or cold temperature operating conditions.