KAUST researchers show blending ammonia with DME yields low-carbon fuel with combustion properties similar to gasoline
Blending ammonia with a small amount of dimethyl ether (DME) gives a liquid fuel with low-temperature combustion properties very similar to gasoline, researchers at KAUST have shown. The development of such fuels could provide an option—in addition to electric cars—for “clean” power for the transportation sector. A paper on their work is published in the journal Renewable Energy.
Ammonia as a fuel provides a promising outlook to reach zero-carbon emissions, but its certain characteristics hinder its direct application in combustion devices.—Binod Raj Giri, corresponding author
Pure ammonia has a high autoignition temperature and narrow flammability limits, but these combustion properties can be modified by blending it with a secondary fuel.
The objective is to find the optimal promoter, which provides the best performance in terms of efficiency improvement and emission reduction while being added in as small of a fraction as possible.— Professor Aamir Farooq
The team showed that DME could be one such promoter. It burns cleanly, with a much lower autoignition temperature than ammonia, and can be produced in a sustainable net-zero carbon cycle.
The team found that an 18% molar blend of DME in ammonia mimicked the low-temperature combustion behavior of representative gasoline fuel. The blend could be suitable for ammonia-fed compression ignition engines at higher DME concentrations, although flame instabilities could be an issue for higher DME content at elevated pressures.
We showed that DME can strongly promote the combustion behavior of ammonia and that a proper blend can be a promising fuel to achieve a net-zero carbon emission. This particular blend can be very suitable for ammonia-fed spark ignition engines.—Binod Raj Giri
The researchers also developed a chemical kinetic model of ammonia-DME fuel-blend combustion based on their experimental findings. Such models could be used to optimize fuel-engine interactions to design high-efficiency future ICEs and achieve net-zero CO2 emissions, Farooq said.
Overall, our kinetic model offered reasonable predictive capabilities capturing the experimental trends over a wide range of conditions. In the worst-case scenario, our model underpredicted IDTs by a factor of ∼2.5 while overpredicting laminar flame speed by ∼20%.—Issayev et al.
The team is also investigating blends of ammonia with other additives such as hydrogen, methane, propene, dimethyl ether, diethyl ether and dimethoxy methane.
Issayev, G., Giri, B.R., Elbaz, A.M., Shrestha, K.P., Mauss, F., Roberts, W.L., Farooq, A. (2022) “Ignition delay time and laminar flame speed measurements of ammonia blended with dimethyl ether: A promising low carbon fuel blend.” Renewable Energy 181, 1353 -1370 doi: 10.1016/j.renene.2021.09.117