Nanosecond Pulse Transient Plasma-Based Combustion of Ammonia and Hydrogen Fuels for Reduced CO2 Emissions

As a society, we must find a pathway towards sustainable/clean energy and combustion. Among all zero-carbon fuels, ammonia
$(\text{NH}_{3})$
and hydrogen
$(\mathrm{H}_{2})$
are the most promising candidates. With as much as 55% less
$\text{CO}_{2}$
released per Joule in comparison with petroleum and diesel, natural gas (mainly
$\text{CH}_{4}$
) is considered as a feasible “bridge” fuel. However,
$\mathrm{H}_{2}$
and
$\text{NH}_{3}$
combustion are challenging due to the high
$\text{NO}_{\mathrm{x}}$
(mainly NO and
$\text{NO}_{2}$
) emissions produced from combustion of both
$\mathrm{H}_{2}$
and
$\text{NH}_{3}$
and the low burning rates associated with
$\text{NH}_{3}$
. In the work presented here, we used nanosecond pulse transient plasma (NPTP) in a natural gas
$(\text{NG})$
engine to enhance the combustion of
$\mathrm{H}_{2}$
and
$\text{NH}_{3}$
, and reduce the emissions of
$\text{NO}_{\mathrm{x}}$
and greenhouse gases (GHG). To lower
$\text{CO}_{2}$
emissions,
$\mathrm{H}_{2}$
and
$\text{NH}_{3}$
are currently being mixed with natural gas (NG), but in relatively small ratios. With the ability to initiate a series of plasma discharges, our plasma-enhanced ignition system enables stable combustion of higher percentages of
$\mathrm{H}_{2}$
and
$\text{NH}_{3}$
. Using this approach, we find that transient plasma enables stable combustion of higher
$\text{NH}_{3}:\mathrm{H}_{2}$
ratios (up to 55%
$\text{NH}_2$
) than with conventional spark ignition, which is significant considering the difficulties in
$\mathrm{H}_{2}$
liquification, transport, and storage. Also, transient plasma enables stable combustion of higher
$\mathrm{H}_{2}:\text{CH}_{4}$
and
$\text{NH}_{3}:\text{CH}_{4}$
ratios than with conventional spark ignition. In addition, it enables further
$\text{CO}_{2}$
reduction (up to 58%) with
$\text{NH}_{3}$
under lean
$\text{CH}_{4}$
conditions than conventional spark ignition. Optical spectroscopy demonstrates the formation of atomic oxygen (0) and nitrogen monohydride (NH) radicals, which are considered as highly reactive intermediates accelerating the combustion kinetics.