Abstract
Current biofuels for diesel engines are largely derived from food crops and there is significant concern, recognised by legislation, that such fuels do not result in net reductions of greenhouse gas emissions when considering the entirety of the production to usage lifecycle. A potential alternative approach is to utilise the lipid content of organic waste streams arising from food crop cultivation for the manufacture of sustainable diesel fuels. This paper therefore presents experimental studies carried out on a modern direct injection diesel engine supplied with a biodiesel (fatty acid methyl esters) produced from waste date pits to determine the combustion and emissions characteristics of an alternative fuel produced from a food residue. Date pit methyl esters were tested relative to both rapeseed and soybean methyl esters, unblended and as blends with a reference fossil diesel, alongside reference fossil diesel and a commercially available fossil diesel from Oman, at constant injection timing and constant ignition timing at a constant engine speed of 1200 rpm. Gas chromatograph analysis of the methyl esters fatty acid composition found a significantly shorter mean alkyl moiety chain length and lower number of double bonds in the case of the date pit esters than either the rapeseed or soybean biodiesel. All of the methyl esters exhibited a similar duration of ignition delay less than that displayed by a reference fossil diesel, but with a higher premixed burn fraction and peak heat release rate in the case of date pit methyl esters relative to those of rapeseed and soybean. Exhaust emissions of NOx were found to be lowest for the unblended date pit methyl esters, suggesting a greater influence of adiabatic flame temperature on rates of thermal NOx production than global in-cylinder temperatures in the case of the unblended methyl esters. Relative to the reference fossil diesel and Oman diesel, all of the methyl esters tested resulted in low particulate matter emissions.
Highlights
Increasing acceptance as to the potentially catastrophic effects of anthropogenic climate change and the contribution of fossil fuel usage to global warming has continued to drive the identification and deployment of alternative energy sources [1,2,3]
This paper presents the first detailed results of combustion experiments with waste date pit methyl esters (DPME) in a single-cylinder direct injection compression ignition engine, undertaken so as to investigate the combustion and emissions characteristics of a biodiesel derived from a potentially low indirect land use change (ILUC) feedstock (DPME) relative to that produced from more commonly utilised feedstocks (RME and SME)
From tests of date pit methyl esters in a modern direct injection diesel engine, the following conclusions regarding the combustion and emissions performance of this biodiesel relative to those comprised of rapeseed methyl esters and soybean methyl esters can be drawn: Fig. 2
Summary
Increasing acceptance as to the potentially catastrophic effects of anthropogenic climate change and the contribution of fossil fuel usage to global warming has continued to drive the identification and deployment of alternative energy sources [1,2,3]. There is a need for renewable fuels potentially suitable for compression ignition combustion which are sustainable in both the context of production and the exhaust emissions arising from end-usage. While legislative targets for the percentage of transportation fuels from renewable sources have been in place for some years, for example in the EU [10], US [11] and China [12], there is realisation that for the use of alternative fuels to result in a sustainable reduction in greenhouse gas emissions (GHG), the production of these should not compete with the cultivation of food crops. In the EU this has resulted in the limiting of the level of biofuels from food crops allowable in road transport fuels at 7%, while promoting the uptake of advanced biofuels and those from waste feedstocks which result in reduced negative
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