Experimental assessment of renewable diesel fuels (HVO/Farnesane) and bioethanol on dual-fuel mode

Abstract

Currently, alkyl esters dominate the renewable share of the CI engine fuels market, but it can potentially be replaced by more modern diesel-like fuels such as HVO and farnesane. Aiming to integrate even more renewable alternatives, these second-generation fuels can be used alongside lower reactivity fuels such as ethanol, taking advantage of the so-called dual-fuel operation. In this study, the use of green diesel fuels operating with and without bioethanol in dual-fuel mode is assessed and compared to Brazilian commercial diesel for small scale power generation application. Experiments were carried out in a single-cylinder compression ignition engine with an electronic port-fuel injection system, and five different dual-fuel bioethanol energy fractions (EF) with both HVO and farnesane. The results show that using renewable diesel presented delayed start of injection, shorter ignition delay, lower heat release peak rate at premixed combustion phase, inferior combustion duration, reduced in-cylinder peak pressures (6.2% and 6.1% reduction for farnesane and HVO, respectively) and lower average in-cylinder temperatures when compared to diesel, decreasing NOx, CO, CO2, HC and particulate matter (PM) for nearly all tested conditions. Dual-fuel operation with bioethanol presented acceptable combustion stability up to 40% bioethanol energy fraction (COVIMEP < 5%), while decreasing NOx, PM and CO2. Considering EF = 40%, HVO-bioethanol dual-fuel operation reduced NOx up to 43% and PM up to 82% compared to diesel single-fuel condition. The addition of bioethanol reduced in-cylinder temperature, soot emissions and presented lower diffusive and total combustion durations. However, CO and HC emissions increased in dual-fuel mode, particularly for higher energy substitution rates (EF > 27%). Considering single-fuel condition, neat diesel presented the lowest brake thermal engine efficiency (23.59 %), followed by farnesane (24.37 %) and HVO (24.66%). Renewable diesel with bioethanol in dual-fuel mode showed an interesting option for a sustainable energy supply with reduced carbon footprint.