α-Pinene - A High Energy Density Biofuel for SI Engine Applications

This study proposes a novel biofuel for spark ignition (SI) engine, α-pinene (C₁₀H₁₆), which is non-oxygenated and thus has a gravimetric energy density comparable to that of hydrocarbon fuels. The ignition characteristics of α-pinene were evaluated in an ignition quality tester (IQT) under standard temperature and pressure conditions. The measured ignition delay time (IDT) of α-pinene is 10.5 ms, which is lower than that of iso-octane, 17.9 ms. The estimated research octane number (RON) for pinene from IQT is 85. A temperature sweep in IQT showed that that α-pinene is less reactive at low temperatures, but more reactive at high temperatures when compared to isooctane. These results suggest that α-pinene has high octane sensitivity (OS) and is suitable for operation in turbocharged SI engines. With these considerations, α-pinene was operated in a single cylinder SI engine. The engine combustion characteristics of α-pinene are compared with FACE A gasoline (RON = 85), Euro V gasoline (RON = 97) and ethanol (RON = 109). The experimental investigation reveals that the spark timing and start of combustion for α-pinene is closer to Euro V gasoline under knock limited spark advance (KLSA) condition. Also, peak in-cylinder pressure for α-pinene is comparable to Euro V gasoline, suggesting that α-pinene is a viable gasoline fuel for SI engines. The brake specific fuel consumption (BSFC) for α-pinene is 18% lower than that of ethanol at an Indicated mean effective pressure (IMEP) of 14.5 bar. While there is volumtric fuel saving compared to ethanol, Brake thermal efficiency (BTE) is lower as the high reactivity of pinene hinders advancment in spark timing. In terms of engine emissions, Carbon monoxide (CO) emission for α-pinene is higher compared to ethanol, while it is similar to that of Euro V gasoline. Total hydrocarbon emission (THC) is 57.2% higher for α-pinene than Euro V gasoline at an IMEP of 14.5 bar. Nitrogen oxide (NO_X) emission for α-pinene is lower than ethanol and Euro V gasoline, while it is higher than that of FACE A gasoline. However, the soot concentration for α-pinene is higher than that of gasoline due to its unsaturated cyclic structure.