Second generation biomass is an attractive renewable feedstock for transport fuels. Its sulfur content is generally negligible and the carbon cycle is reduced from millions to tens of years. One hitherto non-valorized feedstock are so-called humins, a residual product formed in the conversion of sugars to platform chemicals, such as hydroxymethylfurfural and methoxymethylfurfural, intermediates in the production of FDCA, a building block used to produce the polyethylene furanoate (PEF) bottle by Avantium.
The focus of this study is to investigate the spray combustion behavior of humins as a renewable alternative for heavy fuel oil (HFO) under large two-stroke engine-like conditions in an optically accessible constant volume chamber. To reduce the viscosity to HFO levels of the otherwise crystalline humins, methyl levulinate (ML), another side-stream from the same sugar dehydration process, is blended to the former compound at 25 wt.-%; a ratio comparable to that actually produced in many dehydration processes.
Various fuel properties of interest, including elemental composition, heating value, density, ignition quality, acid number, flash point, pour point, carbon residue, sediment, water and ash content are measured for the resulting humins-ML blend.
The blend is injected into an optically accessible constant volume chamber, the dimensions, injector characteristics and prevailing ambient conditions of which are representative of those found in large two-stroke marine engines. Commercial HFO is used as a benchmark.
The combustion process is evaluated by means of shadow imaging and OH*-chemiluminescence. The former and latter optical techniques are used to determine the phasing and overall magnitude of the heat release event, and ignition delay/location and flame lift off length, respectively.
From the results becomes clear that the average ignition delay is comparable to that of HFO, albeit at a higher cycle-to-cycle variation. Notwithstanding a longer lift off length and more downstream ignition kernels, the overall results suggest that the proposed bio-blend is a feasible renewable alternative for HFO in terms of technical feasibility.