Biodiesel/alcohol blends as fuel for compression ignition engines – a review

Abstract

The replacement of petroleum-based fuels with alternative fuels derived from renewable resources remains a critical aspect of the development of combustion engines, both in the automotive sector and the energy industry. This study presents a review of the literature on the combustion, performance, and emissions of compression ignition (CI) engines using a blend-mode technology, where the co-combustion of various types of biodiesel with six alcohol-based fuels—methanol, ethanol, propanol, butanol, pentanol, and octanol was examined. The research focused on engines operating at a constant rotational speed and under maximum or near-maximum load conditions. The analysis explored the impact of alcohol additives, expressed as relative percentage changes in selected engine performance parameters compared to a reference fuel. The reference fuel varied in each case, depending on the studies referenced in the manuscript. This literature review is among the few that comprehensively presents the potential of using blends of various renewable fuels in diesel engines within a single study. The review covers several types of biodiesel, six types of alcohols, and a range of engine operational parameters, including ignition delay, combustion duration, maximum in-cylinder pressure, maximum heat release rate, thermal efficiency, specific fuel consumption, coefficient of variation of indicated mean effective pressure, and emissions of NO_x, HC, CO, and Soot. The research findings indicate that the addition of alcohol to biodiesel in the CI engine cylinder increases ignition delay, shortens combustion duration, raises the maximum heat release rate, and causes an increase in cycle-to-cycle variability of engine operation. The impact of alcohol on engine efficiency is inconclusive and depends on the specifics of the study and engine type. For alcohol content up to 30 %, the addition of alcohol increases NO_x emissions, while above 30 %, it leads to a reduction in NO_x emissions. Partial substitution of biodiesel with alcohol-based fuel in a CI engine results in higher HC emissions, while reducing CO and Soot emissions.