A new study on ignition and combustion characteristics of fast pyrolysis bio-oil (FPBO) has been published. The study “Ignition and Combustion Characteristics of N-Butanol and FPBO/N-Butanol Blends With Addition of Ignition Improver” was conducted by the Department of Mechanical Engineering, University of Technology, Eindhoven (The Netherlands), in the framework of the SmartCHP Horizon 2020 project.
Using biomass-derived fuels such as FPBO to replace fossil fuels is a promising way to contribute to the energy transition and lower energy-related CO2 emissions. The FPBO is obtained through fast pyrolysis from feedstock such as forestry residues, sawdust, agricultural byproducts, corn stover as well as organic waste from the paper industry. It is studied to be used in stationary diesel engines for cogeneration, however its physical and chemical properties limit direct application in conventional diesel engines. Blending FPBO with a higher-quality base fuel is a common solution to use it in an unmodified diesel engine. As such, it is common practice to blend FPBO with polar solvents such as ethanol or butanol due to its polar properties. Nevertheless, the ignition characteristics of FPBO and alcohols are inferior than those of diesel. Thus, an additional ignition improver is to be added into the blend to achieve timely autoignition and appropriate combustion properties.
In this study, the ignition and combustion characteristics of fast pyrolysis bio-oil (FPBO) are investigated in a combustion research unit (CRU), which mainly consists of a constant-volume combustion chamber. To fuel the CRU with FPBO, n-butanol and 2- ethylhexyl nitrate (EHN) are used to improve the atomization and ignition properties of the fuel blends, respectively.
In the first part of this study, an appropriate proportion of EHN additive into n-butanol is determined based on the balance between the ignition improvement and the amount of EHN addition. Then, the effects of FPBO content (up to 30%) in FPBO/n-butanol blends with the same EHN addition are investigated. The effects of chamber wall temperature on the combustion are also studied. Finally, the different definitions of indicators are determined from the chamber pressure traces to quantitatively depict fuel ignition and combustion characteristics including ignition delay, combustion phasing, end of combustion and burn duration. Experimental results show that a distinct two-stage ignition process can be observed for all cases. For n-butanol with added EHN, the increase of EHN proportion could effectively advance both the low- and high-temperature reaction phases. However, this gain is obviously reduced when the percentage of EHN becomes higher than 8%. For FPBO/n-butanol blends with an addition of EHN, higher FPBO proportions have little effect on the low-temperature reaction phase, while they delay the high temperature reaction phase. Chamber wall temperature have a significant influence on the ignition and combustion processes of the tested FPBO/n-butanol blends. With these blends, negative temperature coefficient behavior was observed in a chamber wall temperature range of 535–565°C.
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