Medchill Caleb, Hauck Curtis, Perezselsky Armando A, Cortopassi Andrew C, DeSain John D, Briseno Alejandro L, Wang Yu Yun, Cronin Stephen B
Ming Hsieh Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, United States.
The Aerospace Corporation, El Segundo, California 90245, United States.
ACS Omega. 2025 Aug 21;10(34):38780-38787. doi: 10.1021/acsomega.5c04062. eCollection 2025 Sep 2.
A nanosecond pulse transient plasma is employed to initiate and control the exothermic decomposition of ionic liquids, namely, a mixture of hydroxylammonium nitrate (HAN) and 1-ethyl-3-methylimidazolium ethyl sulfate [EMIM]/[EtSO], as well as some noncombustible ionic liquids. Here, the plasma is discharged in a cylindrical geometry with a coaxial center wire electrode. High voltage (20 kV) nanosecond pulses (20 ns) at various frequencies up to 10 kHz produce a plasma discharge in the ionic liquid that initiates its nonthermal decomposition. Realtime imaging was used to observe and characterize electrically driven bubble formation (i.e., electrostriction), plasma initiation, and the evolution of ignition and extinguishing processes. This high-speed imaging shows that the flame can be toggled on and off within 66 ms. We hypothesize that the plasma-driven decomposition mechanism proceeds as follows: (1) bubble formation due to the high voltage-induced electric fields, (2) plasma initiation in the bubble regions where dielectric breakdown occurs, (3) the plasma then generates highly energetic electrons that, in turn, form highly reactive atomic and diatomic species, and (4) these radical species serve as short-lived reaction intermediates that drive nonthermal chemical reaction pathways when interacting with the ionic liquid, resulting in decomposition and ignition. Using in situ plasma emission spectroscopy, we have identified the following reaction intermediates: H, O, S, NO, and CO, which accelerate the conventional decomposition reaction pathways. Using FTIR emission spectroscopy of the flame plume, we have identified CO and HO as products, verifying the combustion of the HAN-EtSO mixture. These plasma-driven reaction intermediates deviate from the available chemical mechanisms of conventional thermal catalysis and thermal decomposition chemical pathways. As a control, we repeated the experiment with a DC voltage, which led to no decomposition or combustion up to 500 V, above which decomposition occurred. Here, the DC voltage provides Joule heating, which evaporates off water, destabilizing the HAN and causing ignition.
采用纳秒脉冲瞬态等离子体来引发和控制离子液体的放热分解，即硝酸羟铵（HAN）与1-乙基-3-甲基咪唑硫酸乙酯[EMIM]/[EtSO]的混合物，以及一些不可燃离子液体。在此，等离子体在具有同轴中心丝电极的圆柱形几何结构中放电。高达10 kHz的各种频率下的高压（20 kV）纳秒脉冲（20 ns）在离子液体中产生等离子体放电，引发其非热分解。利用实时成像来观察和表征电驱动气泡形成（即电致伸缩）、等离子体引发以及点火和熄灭过程的演变。这种高速成像表明火焰能够在66毫秒内开启和关闭。我们假设等离子体驱动的分解机制如下：（1）由于高压感应电场导致气泡形成；（2）在发生介电击穿的气泡区域引发等离子体；（3）等离子体随后产生高能电子，进而形成高活性的原子和双原子物种；（4）这些自由基物种作为短寿命的反应中间体，在与离子液体相互作用时驱动非热化学反应途径，导致分解和点火。使用原位等离子体发射光谱，我们确定了以下反应中间体：H、O、S、NO和CO，它们加速了传统的分解反应途径。利用火焰羽流的傅里叶变换红外发射光谱，我们确定了CO和HO为产物，验证了HAN-EtSO混合物的燃烧。这些等离子体驱动的反应中间体偏离了传统热催化和热分解化学途径的现有化学机制。作为对照，我们用直流电压重复了实验，在高达500 V时未发生分解或燃烧，高于此电压则发生分解。在此，直流电压提供焦耳热，使水蒸发，使HAN不稳定并导致点火。
