Abstract
To mitigate the increasing concentration of carbon dioxide in the atmosphere, energy production processes must change from fossil to renewable resources. Bioenergy utilization from agricultural residues can be a step towards achieving this goal. Syngas (fuel obtained from biomass gasification) has been proved to have the potential of replacing fossil fuels in stationary internal combustion engines (ICEs). The processes associated with switching from traditional fuels to alternatives have always led to intense research efforts in order to have a broad understanding of the behavior of the engine in all operating conditions. In particular, attention needs to be focused on fuels containing relatively high concentrations of hydrogen, due to its faster propagation speed with respect to traditional fossil energy sources. Therefore, a combustion study was performed in a research optical SI engine, for a comparison between a well-established fuel such as methane (the main component of natural gas) and syngas. The main goal of this work is to study the effect of inert gases in the fuel mixture and that of air dilution during lean fuelling. Thus, two pure syngas blends (mixtures of CO and H2) and their respective diluted mixtures (CO and H2 with 50vol% of inert gases, CO2 and N2) were tested in several air-fuel ratios (stoichiometric to lean burn conditions). Initially, the combustion process was studied in detail by traditional thermodynamic analysis and then optical diagnostics were applied thanks to the optical access through the piston crown. Specifically, images were taken in the UV-visible spectrum of the entire cycle to follow the propagation of the flame front. The results show that hydrogen promotes flame propagation and reduces its distortion, as well as resulting in flames evolving closer to the spark plug. All syngas blends show a stable combustion process, even in conditions of high air and fuel dilution. In the leanest case, real syngas mixtures present a decrease in terms of performance due to significant reduction in volumetric efficiency. However, this condition strongly decreases pollutant emissions, with nitrogen oxide (NOx) concentrations almost negligible.
Highlights
The provision of an extended electricity distribution network in rural areas of developing countries is an objective which has been recognized by the governments of these countries as well as international institutions [1,2]
In-cylinder pressure was analyzed as the average value of 200 consecutive acquisitions for five
The motored pressure signal before the combustion process is depicted with dash-double-dot lines
Summary
The provision of an extended electricity distribution network in rural areas of developing countries is an objective which has been recognized by the governments of these countries as well as international institutions [1,2]. One potential option is to create small isolated grids, powered by small-scale generators with a low-cost fuel. Residues of biomass are discarded or directly burned in low-efficiency systems which implies high rates of waste. An improved process for obtaining fuel from biomass waste is gasification, a process in which syngas is obtained [3,4]. This alternative fuel is generally considered in the literature as a mixture of hydrogen and carbon monoxide [5].
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