Researchers at RWTH Aachen University in Germany report on their evaluation of two possible future biofuels—tailor-made from biomass—in a paper in the journal Fuel. The team investigated the use of 2-butanone (also referred to as methyl ethyl ketone, MEK) and 2-methylfuran, both of which had been identified within the Cluster of Excellence “Tailor-Made Fuels from Biomass” (TMFB) (earlier post).
Investigations of the fuels’ autoignition tendency were carried out on a rapid compression machine (RCM); thermodynamic investigations were conducted on a direct injection spark ignition single cylinder research engine.
In its search for optimal fuels for spark-ignited engines, the TMFB project first carried out an exhaustive analysis of all mathematically feasible CxHyOz molecules carrying one to eight carbon atoms. The initial set of ~168.8 million structures was reduced by eliminating infeasible substructures abd structures difficult to obtain by chemo-catalytic transformations of biomass monomers.
This process yielded abut ~12.4 million molecular structures. These in turn were screened for oxygenates comprising a set of engine-relevant fuel properties.
In a paper (Dahmen et al.) presented at the 2014 TMFB conference, TMFB researchers noted that the final 279 fuel candidates could be classified into acyclic ethers, ketones, aldehydes, alcohols, cyclic ethers and furans.
Because of the favorable boiling characteristics ketones were chosen for further investigation despite the limited experience on ignition quality. … Initial rapid screening in an Ignition Quality Tester (IQT) revealed remarkably low auto-ignition capabilities for 2-butanone (DCN <5), methyl isobutyl keetone (DCN 12.6), diisopropyl ketone (DCN 16.6), and methyl isopropyl ketone (DCN <5). Subsequent experimental testing yielded exceptionally high research and motor octane numbers in the case of 2-butanone.—Dahmen et al.
Other TMFB research showed that 2-Methylfuran has the best mixture formation of all investigated biofuels.
In the new Fuel paper, the researchers compared 2-Methylfuran and 2-butanone against ethanol—the present benchmark biofuel for spark ignition engines—and conventional RON95 gasoline.
They found that 2-methylfuran has an autoignition tendency similar to that of ethanol. 2-butanone exhibited very high ignition delay times—higher than those of ethanol and 2-methylfuran.
For 2-butanone and 2-methylfuran, the lower heat of vaporization in combination with higher vapor pressure and better primary breakup compared to ethanol are beneficial for mixture formation.
2-methylfuran showed an increased combustion stability, especially at low engine load and cold boundary conditions, resulting in a higher knock resistance than conventional gasoline. Combined with an increased compression ratio, this could enable an efficiency increase of up to 19%, they researchers said. Ethanol could deliver an even further increase of up to 21%.
2-Butanone shows increased combustion stability at low engine load and cold boundary conditions compared to ethanol and also conventional gasoline as well as a high knock resistance equal to ethanol.
However, both 2-butanone and 2-methylfuran showed increased emissions of NOx compared to ethanol. Both possible future biofuels and ethanol, show a significant reduction of particle emissions compared to conventional gasoline.
Fabian Hoppe, Ultan Burke, Matthias Thewes, Alexander Heufer, Florian Kremer, Stefan Pischinger (2015) “Tailor-Made Fuels from Biomass: Potentials of 2-butanone and 2-methylfuran in direct injection spark ignition engines,” Fuel, Volume 167, Pages 106-117,doi: 10.1016/j.fuel.2015.11.039
Dahmen, Manuel ; Marquardt, Wolfgang ; Hechinger, Manuel ; Weinebeck, Alexander ; Hoppe, Fabian ; Mottweiler, Jakob ; Kremer, Florian ; Murrenhoff, Hubertus ; Bolm, Carsten ; Pischinger, Stefan (2014) “Biomass-based Ketones as Successful Example for the Fuel Design Process” Konferenz: TMFB 2nd International Conference , Aachen , Germany
Matthias Thewes, Martin Muether, Stefan Pischinger, Matthias Budde, André Brunn, Andreas Sehr, Philipp Adomeit, and Juergen Klankermayer (2011) “Analysis of the Impact of 2-Methylfuran on Mixture Formation and Combustion in a Direct-Injection Spark-Ignition Engine” Energy & Fuels (12), 5549-5561 doi: 10.1021/ef201021a