Direct use of biomass powder in internal combustion engines

Abstract

Production of energy from lignocellulosic biomass using internal combustion engines (ICE) is desirable, provided that costs can be reduced. The recalcitrance of lignocellulosic biomass requires additional treatments for second-generation biofuel conversion processes, falling short of sustainability goals and profit margins. Rather than transforming solid biomass to liquid or gaseous fuels through multistep processes, this paper explores the direct use of biomass powder below 200 μm in an engine. Reducing biofuel production to a single milling process offers the chance to downscale biofuel production for implementation at the local level, through standalone or hybrid installations with other renewable energies. In scenarios using intermittent energies such as solar or wind, production of biomass powder can be operated during low demand periods to store surplus energy which can be later used for generating power on demand. To test the feasibility of this concept, four biomasses (rice husk, chestnut wood, pine bark, and wheat straw) were micronised to an average particle size of 20 μm and fuelled in an instrumented ICE. Our results confirm that an ICE can start and run with various biomass types at a wide range of operating regimes without any assistance. During these tests, efficiencies up to 17.5% were observed with powdered rice husk, using an intake temperature of 40 °C. Emissions (CO, NO_x, and SO₂) were found to be within acceptable operating limits of available aftertreatment technologies. This first assessment of the compared combustion behaviour of different biomass powders in ICE highlights the fact that the challenges associated with this alternative biofuel demand a cross-disciplinary approach from research domains such as dust explosion prevention, biomass combustion and engine technology.