WEBVTT 1 00:00:00.260 --> 00:00:01.270 Mark Kushner: There's a way. 2 00:00:01.990 --> 00:00:30.239 Mark Kushner: Welcome to the 1st seminar the winter 2025 semester. We've arranged appropriate winter weather for you. Sorry for those people who had to walk between buildings to get here. 3 00:00:30.500 --> 00:00:55.180 Mark Kushner: It's my pleasure to introduce Professor Carmen Garrett Garcia, the Charles Starr, Dr. Associate, Professor of Aeronautics and Astronautics at the Massachusetts Institute of Technology. Professor Garrett Garcia received her Bachelor's degree in aeronautical engineering at Polytechnic University in Madrid, after which she is with the Damo Space Group in Spain. 4 00:00:55.260 --> 00:01:02.600 Mark Kushner: She then went to Mit to earn her master's and Phd. Degrees in Aeronautics and Astronautics. 5 00:01:02.980 --> 00:01:15.830 Mark Kushner: He was in with the Boeing Research and Technology Group in Europe, and a visiting professor at Princeton before moving to Mit in 2017, as assistant professor. 6 00:01:15.940 --> 00:01:38.480 Mark Kushner: a Professor Derek Garcia leads the interdisciplinary aerospace plasma group that crosses over aerospace engineering, low temperature plasma technologies and gas discharge visits. The research topics span from interaction of lightning with spacecraft and wind turbines to plasma technologies for ignition, combustion, and chemical conversion. 7 00:01:38.780 --> 00:01:52.370 Mark Kushner: Professor Garrett Garcia has been widely recognized by her work by an Nsf. Career award. The office of Naval Research Young Investigator Award and the International Floor, Bryant Science and Technology Award. 8 00:01:52.650 --> 00:02:01.860 Mark Kushner: The title, Professor Garrett Garcia's Seminar is understanding, controlling the interactions of plasmas with flames and fluid gases. 9 00:02:01.900 --> 00:02:15.719 Mark Kushner: But before the seminar we would like to add to that recognition by loading Garrett Garcia down with a little bit of hardware, and the 1st is a plaque to recognize 10 00:02:15.720 --> 00:02:35.180 Mark Kushner: that Professor Gare Garcia is this year's Mipsi early career lecturer. This is a distinction that we make to the excellence of young early career researchers who have a wonderful trajectory and will do even greater things in the future. 11 00:02:35.490 --> 00:02:40.569 Mark Kushner: Now we need to memorialize this in a picture. Thank you so much, Mike. 12 00:02:44.570 --> 00:02:45.370 Mark Kushner: Thank you. 13 00:02:45.899 --> 00:02:49.630 Mark Kushner: Congratulations, and we have a little house for it over here. 14 00:02:50.110 --> 00:02:59.390 Mark Kushner: But the even more prized possession. Oh, yeah, that will fight over throughout the world is our nipsy monk. Thank you so much. 15 00:03:03.577 --> 00:03:05.070 Mark Kushner: Thank you, Mike. 16 00:03:05.620 --> 00:03:35.570 Mark Kushner: so thank you so much for that wonderful introduction. I'm humbled to be here just a correction, mark. I've never was a visiting professor at Princeton. I was only a visiting student researcher, but thank you so much for your kind words, and I'm humbled to get that award and be here with all of you, presenting some of our group's research. So the title of my talk, like Professor Mark Kushner already announced, is understanding and controlling the interactions of plasmas with flames. 17 00:03:35.570 --> 00:03:43.720 Mark Kushner: in with flames and flowing gases. And I highlighted 2 words there, understanding and controlling, which I think bring together sort of 18 00:03:43.760 --> 00:03:51.779 Mark Kushner: the the how to do of nipsi understanding, related more to this, is not working properly 19 00:03:52.510 --> 00:04:10.959 Mark Kushner: to plasma, science and controlling related more to plasma engineering of this plasmas. And in order to control, we need to understand, although maybe we don't need to understand. But it's nice to do so. And this sort of infuses all of the work that my group has been doing. 20 00:04:11.390 --> 00:04:33.850 Mark Kushner: So let's start a little bit by the mission of my group, which is the aerospace plasma group at Mit. We work at the intersection of aerospace engineering and plasma science, and we deal with fundamentals of electrical breakdown in this aerospace environments that often have to deal with fast flowing gases, reactive flow environments. And we focus on applications for aerospace 21 00:04:33.850 --> 00:04:52.179 Mark Kushner: one of the big applications we're looking at is plasma assisted aerospace technologies on plasma. Assisted combustion is the topic that I'll touch upon today. But we're also looking at technologies for Mars and City to resource utilization, converting the Martian Co 2 atmosphere into useful products and whatnot. And we're also dealing with 22 00:04:52.360 --> 00:05:12.000 Mark Kushner: the plasma environments that aircraft have to deal with in particular lightning safety, and that comprises a completely different regime of plasmas. But some of the challenges and environments that we face are pretty similar. And hopefully, through this presentation, I'll be able to sort of convince you of the similarities of those 2 problems. 23 00:05:12.240 --> 00:05:35.989 Mark Kushner: So I'll start. Give a couple of examples of the presence of plasmas in this reactive and flowing gas environments. And I'll start with plasma. Assisted combustion start from a motivation perspective sort of the engineering perspective. Why are we studying these problems? And through that engineering framework, postulate some fundamental questions for which we need plasma science to help us with. 24 00:05:36.430 --> 00:05:37.260 Mark Kushner: So 25 00:05:37.380 --> 00:05:53.819 Mark Kushner: why are we studying plasma? Assisted combustion? Well, plasma assisted combustion gives us an extra knob to control combustion processes. Some of the earlier work has been on supersonic combustion processes and whatnot. But in the last decade or so we've been focusing on sustainability applications. 26 00:05:54.240 --> 00:06:02.579 Mark Kushner: So the future of aviation is going to rely on combustion for years to come, and also other hard to decarbonize sectors. 27 00:06:02.810 --> 00:06:08.309 Mark Kushner: So we need to understand how to be able to get rid of emissions in this processes 28 00:06:08.480 --> 00:06:33.899 Mark Kushner: one of the emissions that is hard to get rid of because we get it, even if we have 0 carbon fuels is nox, and at least for hydrocarbon fuels. We know that the thermal root of Nox formation is highly correlated to the temperature of the process. So we want to reduce Nox emissions. We need to burn either rich or lean, but of course lean combustion with less fuel is preferred, because then we don't have other emissions like carbon and particulate. 29 00:06:34.020 --> 00:06:43.139 Mark Kushner: So the problem with lean combustion is that it's quite unstable. It's very hard to stabilize those flames. And we need some extra technology to be able to do that 30 00:06:43.800 --> 00:07:06.790 Mark Kushner: traditionally. What we've been doing is sort of having advanced combustion combustor geometries where we start off with with a rich flame that is acting as a pilot, and helps with the stability of the problem, and then we rapidly quench to transition very fast through the high temperature regime and go to the lean zone, where we have low Nox emissions, but that can be at odds with efficiency and whatnot. 31 00:07:06.910 --> 00:07:20.329 Mark Kushner: So it is preferred to burn directly lean. But again, this flames are prone to combustion dynamics, other instabilities that need some technology for stabilization. And that's where plasmas can play a role 32 00:07:20.600 --> 00:07:35.190 Mark Kushner: going beyond hydrocarbon fuels. There's other fuels like ammonia that is being contemplated for combustion processes that are lazy and hard to burn. Plasmas can help us facilitate the burning of these fuels, and possibly deal with the emissions, challenges 33 00:07:35.410 --> 00:07:48.569 Mark Kushner: so just some demonstrations from the literature. This is not work by my group, but sort of showcasing how plasmas and in particular pools Nanosecond discharges, can help with this combustion challenges in lean limit operation. 34 00:07:48.710 --> 00:07:54.330 Mark Kushner: So this is a swirl stabilized burner that is representative of gas, turbine combustion. 35 00:07:54.360 --> 00:08:19.240 Mark Kushner: So in this case these researchers at centralize a flame with an equivalence ratio, the fuel air ratio compared to stoichiometric mixture that was much lower by utilizing plasma. So that was one of the 1st demonstrations that you can extend the lean limit and burn with less fuel. Using pulse. Nanosecond discharges at low power. 36 00:08:19.690 --> 00:08:29.489 Mark Kushner: The next example is that plasmas can be used to suppress combustion dynamics, and that deals with the dynamic stability of flames. In a similar combustor. 37 00:08:29.880 --> 00:08:43.349 Mark Kushner: You can get this pressure oscillations that can be damaging to the structure that oscillate at a certain frequency with both Nanosecond discharger. The group was able to greatly reduce those pressure, amplitude oscillations. 38 00:08:43.350 --> 00:09:02.900 Mark Kushner: but by utilizing a slightly different strategy they actually made things worse. So that sort of shows that you can control the dynamic combustion environment, using full standard second discharges, but achieving the desired outcome which would be completely suppressing the instability is hard to do. And we need to really understand the interaction between both. 39 00:09:02.940 --> 00:09:12.129 Mark Kushner: to determine what is the energy pathways? What are the energy pathways that lead to a favorable outcome, and the maximum benefit we can achieve with this practice. 40 00:09:12.210 --> 00:09:16.320 Mark Kushner: So those sort of of questions is what we're trying to answer with her work. 41 00:09:16.700 --> 00:09:21.140 Mark Kushner: But the 1st thing that I want to motivate is why we're using pools. Nanosecondition. 42 00:09:21.690 --> 00:09:32.569 Mark Kushner: So the strategy, the plasma strategy we're utilizing is called the nanosecond repetitive full discharge strategy. We use high voltage, pulses of very short duration repeated at Kilohertz. Frequencies! 43 00:09:33.020 --> 00:09:55.620 Mark Kushner: Why this type of discharge? Well, first, st we want to maintain a non-thermal plasma. We don't want to heat up the gas significantly, because then we will be just heating up the gas, which is efficient for combustion processes. But it's not introducing anything new. We want to excite other degrees of freedom by heating up the electrons that then undergo electron impact processes to create new chemistries. 44 00:09:56.030 --> 00:10:01.109 Mark Kushner: And we want to keep low ionization fractions. So basically, most collisions are electron neutral. 45 00:10:03.260 --> 00:10:15.040 Mark Kushner: We want to access high reduced electric fields like, you know, plasma. Chemistry is largely controlled by that parameter. But we cannot sustain high reduced electric fields for long amounts of times because of plasma shielding effects. 46 00:10:15.140 --> 00:10:36.809 Mark Kushner: So basically, if we look at the fraction of energy that goes into each collisional process is a strong function of the reduced electric field. In this sort of plasmas we can use the local field approximation where all of the energy gained by the electrons is locally expended in collision. So there's a 1-to-one coupling between electron temperature and reduced electric field. 47 00:10:37.030 --> 00:11:05.130 Mark Kushner: So controlling the reduced electric field controls the electron temperature and therefore the kind of chemical activity that we can access in particular for combustion processes. It turns out that a range between 200 500,000 is particularly efficient because we're exciting a lot of electronic excitation of the mixture that I will go into later, and we're keeping a low ionization fraction. So we want to be in this regime where we're coupling little power from the plasma compared to the combustion power. It's about 1%. 48 00:11:06.000 --> 00:11:10.180 Mark Kushner: And we are accessing this high reduced electric field conditions. 49 00:11:11.400 --> 00:11:37.359 Mark Kushner: So how does this affect the combustion process? Well, if you've attended any lecture in combustion. The kind of chemistry that you have to deal with is Arrhenius type reaction rates that are strongly dependent on the temperature. So the 1st way to modify those combustion reactions is by introducing thermal effects. If you increase the temperature, you naturally increase the temperature, the reaction rates of combustion. 50 00:11:37.490 --> 00:11:49.069 Mark Kushner: but that is sort of trivial. We can also do that with an electric heater. The benefit of plasma is that we can also add radicals into the mixture in reactions that do not depend on temperature. 51 00:11:49.310 --> 00:12:07.990 Mark Kushner: And to explain that this example from Professor Yuan Yu in Princeton, it's quite good. It's a hydrogen oxygen mixture. You see the reactions that take place in the combustion process. The rates of those reactions are strongly dependent on temperature. You need to start by creating some radicals. 52 00:12:08.350 --> 00:12:21.959 Mark Kushner: and those rates are particularly slow at low temperature. So you need to split the hydrogen oxygen bonds and produce some hydrogen radicals that then need to propagate and branch out, producing more radicals. 53 00:12:21.980 --> 00:12:46.740 Mark Kushner: and those reactions are again quite slow at low temperature. How can we bypass that process and accelerate the whole chemistry? Well, if we have some reactions that are independent on temperature, electron impact collision reactions that depend on the reduced electric field. This can accelerate our combustion process by introducing some radicals into the mixture, and that's what we call the kinetic effects of plasma assisted combustion. 54 00:12:47.790 --> 00:13:06.100 Mark Kushner: So we can go through the cascade of energy transmission all the way from the electrical energy into those effects that influence the combustion process. So we couple the electrical energy to the electrons. They undergo collisions that lead to vibrational and electronic excitation, direct dissociation and ionization reactions. 55 00:13:06.970 --> 00:13:18.810 Mark Kushner: And that's what I've labeled here. The 1st level of energy transfer just electrons colliding mostly with nitrogen molecules and oxygen molecules because they're in larger concentration in the fuel air mixture 56 00:13:19.030 --> 00:13:22.860 Mark Kushner: and depending on the reduced electric field profile. Here in black. 57 00:13:23.060 --> 00:13:38.270 Mark Kushner: you have that some part of the energy goes into vibrationally exciting the molecular nitrogen. Some share of the energy goes into electronically exciting the molecular nitrogen, and some goes into electronically exciting the oxygen molecule and some share to other processes 58 00:13:38.470 --> 00:13:56.970 Mark Kushner: that oxygen can directly dissociate into a radical production so that can directly participate in the combustion reactions. But all of this process happened at nanosecond time scales and they're strongly correlated to the reduced electric field profile that we like here. I think the simulation was run for 180,000 piga. 59 00:13:57.760 --> 00:14:25.349 Mark Kushner: Now, what happens after this is too fast for the combustion chemistry to keep up with. Well, those plasma. Activated species react with each other and with other neutrals in the gas to produce some more kinetic effects than some thermal effects. So that's the second level of energy transfer. Now, electrons have already done their job, and now it's the heavier molecules that collide with each other to produce some amount of heating in nanosecond timescales through the relaxation of those electronically excited states. 60 00:14:25.510 --> 00:14:32.360 Mark Kushner: and also some dissociation of the molecules producing O radicals, hydrogen, radicals, and whatnot. 61 00:14:32.740 --> 00:14:57.489 Mark Kushner: And then the vibrationally excited states also plant and release heat in microsecond time scales. So we can sort of track the energy all the way from the electrical energy delivery in the nanosecond time scale into electronic excitation, vibrational excitation, dissociation, reactions, and then at slower time scales. If we look at a train of pulses rather than a single pulse. All of the energy ends up. 62 00:14:57.650 --> 00:15:00.070 Mark Kushner: occurring in 4 different modes. 63 00:15:00.210 --> 00:15:11.010 Mark Kushner: slow heating, which is the relaxation of the vibrational states, fast gas heating, which is the relaxation of the electronically excited states and radical production. O atoms, hydrogen fuel fragments. 64 00:15:11.330 --> 00:15:27.750 Mark Kushner: So that's what impacts combustion. The accelerated Arrhenius rates the heating effects at different timescales that cannot really be accessed through the regular combustion reactions, as well as the bypassing of those chain initiation and branching steps through the production of radicals that are not dependent on temperature. 65 00:15:27.950 --> 00:15:37.500 Mark Kushner: So this part of the problem we sort of understand quite well as a community. The challenge is that it's strongly dependent on all of the conditions in our mixture. 66 00:15:37.620 --> 00:15:46.379 Mark Kushner: So one of the work that we've tried to do with with my student Rafael de Jou is. Look at how this energy breakdown changes with the composition of the mixture. 67 00:15:46.880 --> 00:16:01.889 Mark Kushner: So we know that reduced electric field and energy deposition is what controls the chemistry. Reduced electric field is a metric of the electron temperature. Energy deposition is a metric of the number density of electrons that we have. So the amount of reactions that can take place in the plasma. 68 00:16:02.080 --> 00:16:30.949 Mark Kushner: But it's strongly correlated to whatever mixture we're looking at. So through numerical modeling, we can sort of sample large parameter spaces of different environments that are of interest to different industries. So in this plot, I'm not sure if it's very well seen here. But what we're doing is we're sampling different methane oxygen nitrogen mixtures at one atmosphere, and we're plotting the Townsend ionization coefficient as a function of the nitrogen oxygen ratio and the equivalence ratio, how much fuel we have. 69 00:16:31.140 --> 00:16:58.529 Mark Kushner: So this line here is stoichiometric fuel, air concentration. This line here is air. If we're enough per segment, we're talking about fuel, rich conditions that could be interested for pilot flames for stability purposes. If we're looking at this segment here, this quadrant, we're talking about fuel, lean mixtures that are interesting for emissions, reductions, low Nox production of combustion. If we're looking at this fragment here, we're talking about 70 00:17:00.510 --> 00:17:25.040 Mark Kushner: oxy rich environments that are used in the welding industry. If we're looking at this region here, we're talking about oxygen, vitiated flows that appear in afterburners for military aircraft, so depending on the composition. The Townsend ionization coefficient is very different, and we have that for oxygen, rich fuel, rich environments. The Townsend ionization coefficient is higher than for oxygen, lean fuel, lean mixtures. 71 00:17:25.099 --> 00:17:41.919 Mark Kushner: Why does that matter? It means that we're producing electrons more quickly for the oxygen, rich environments, fuel, rich environments than in this other quadrant. So the energy coupling is going to happen faster. And we're also modulating the energy transfer by the temperature of the gas. If the gas is hot. 72 00:17:42.250 --> 00:17:43.085 Mark Kushner: then. 73 00:17:44.210 --> 00:18:07.550 Mark Kushner: this temperature is high, and we couple less energy than in a cold mixture. So we need to account for all of these things and the energy coupling, indeed, is correlated very heavily with the mixtures we're considering. This plot show the average energy deposited for each pulse for different compositions. When we have Low Townsend ionization coefficient. We deposit less energy than if we have High Townsend ionization coefficient. 74 00:18:07.790 --> 00:18:18.589 Mark Kushner: So that is one metric that we don't really have that much control over. It depends with the Median that we have. So all of these things make the problem a little bit more complicated than we originally thought about. 75 00:18:19.150 --> 00:18:43.039 Mark Kushner: Now, this is the amount of energy we deposit. If we have a cooler gas, then the energy deposition is higher, and we know that it must be limited by some external means. So we have energy limitations by the power supply. We have energy limitations, by plasma, shielding effects. So if we produce too many electrons, the voltage pulse will shut off, and we basically will have a truncated voltage pulse. 76 00:18:43.250 --> 00:18:55.840 Mark Kushner: So what that means is that if we set some limitations to the energy at low temperatures we might saturate how much energy we can deposit, whereas at high temperatures we will get less energy deposition. 77 00:18:56.220 --> 00:19:04.810 Mark Kushner: That's the total amount of energy. And what about the energy pathways? Does this have any implication on that? Well, it actually does. 78 00:19:05.410 --> 00:19:18.199 Mark Kushner: And here I'm plotting the amount of energy that goes to vibrational translational relaxation. And we can see that for an oxygen, lean fueling mixture we have more energy going to that process than for an oxy, rich fuel, rich environment. 79 00:19:18.330 --> 00:19:41.809 Mark Kushner: The reason for that is that for this oxygen, lean fuel, lean environment, we don't have any energy cutoff. So we are able to sample the whole pulse reduced electric field. So we are able to access electron impact reactions for electronic excitation at high reduced electric field values and for vibrational excitation at low, reduced electric field values. If we have some external energy cutoff. 80 00:19:42.020 --> 00:20:02.900 Mark Kushner: what happens is that the pulse gets truncated and we're only able to sample the high reduced electric field region. So most of our energy goes to electronic excitation and very little of the energy goes to vibrational excitation. So we're changing the energy transfer modes just by simply changing the composition of the gas, which makes the problem more harder to control. 81 00:20:03.870 --> 00:20:18.420 Mark Kushner: Now, to make things a little bit more complicated. Things not only depend on the gas state, they also depend on the electrical external circuit, and that's 1 of the challenges with pulse. Nanosecond discharges. Because we have this very fast propagating signals. 82 00:20:18.480 --> 00:20:38.529 Mark Kushner: We have to account for transmission line theory of the voltage and current wavelength going from the power supply to the plasma and everything from the voltage level that the load sees. Your plasma reactor sees to the energy that you can deliver depends on the load conditions. So all of this needs to come at play so recently. 83 00:20:38.600 --> 00:20:42.999 Mark Kushner: we've been working on this tutorial. If you're interested in pools, Nanosecond discharges, I really 84 00:20:43.110 --> 00:21:03.359 Mark Kushner: encourage you to take a look. We're looking at how to accurately make electrical measurements in this reactors and how to basically interpret your measurements depending on the probe location, the types of probes you have looking at the mathematical background to interpret these signals. So as an example, basically, here you have the voltage. 85 00:21:04.260 --> 00:21:12.040 Mark Kushner: the voltage at the load and the energy deposition at the load depending on the load conditions. So if we have a high resistant. 86 00:21:12.280 --> 00:21:36.570 Mark Kushner: the high resistance of the load, this ab waveforms, the voltage is doubled compared to the power supply value, and we have low energy deposition. Once the plasma channel is formed, the resistance drops and the voltage seen by the load drops, the energy increases, so the energy delivery is fully coupled to the electrical circuit. If you have intermediate circuit elements and and whatnot. 87 00:21:37.020 --> 00:22:05.539 Mark Kushner: Now, this is not really related to the understanding, but it is to some extent we have different ways of measuring the electrical signals. If you put your probe at the load. Compared to the mid cable, the voltage waveforms and the energy waveforms look very different. But if you're doing things correctly, you should be able to measure the same energy deposition in your plasma discharge. So these are things that sort of are built into the complexity of pulse. Nanosecond discharges by the fast nature of the signals. 88 00:22:06.630 --> 00:22:19.109 Mark Kushner: So all of this sort of relates to a 0 d problem. We can understand the effects of fuel, composition, temperature, pressure, chemical kinetic model and electrical parameters in a 0 d platform. 89 00:22:19.370 --> 00:22:27.010 Mark Kushner: If we're interested in flames, we need to account for transport. So 0 D is not good enough. At the very least we need to go to one dimensions. 90 00:22:27.180 --> 00:22:49.559 Mark Kushner: One of the simplest flames to study is what we call a premixed laminar flame. So you premix their fuel air mixture, and then it leads to a self-propagating front, which is your Laminar flame and a fundamental flame parameter. That is very interesting to study is the laminar flame speed, which depends on the composition, the temperature of your gas. 91 00:22:49.920 --> 00:22:56.359 Mark Kushner: Now, what happens if we put a plasma? Can we manipulate this laminar flame speed, using a plasma discharge? 92 00:22:56.670 --> 00:23:14.420 Mark Kushner: And what is the effect of actuating the plasma in the reactants on top of the flame and other locations in the outcome that we observe. We've seen that there's different outcomes depending on the strategy on those dynamic combustion experiments. What happens if we work with a smaller scale platform, simpler fradiment. 93 00:23:14.610 --> 00:23:21.330 Mark Kushner: Can we basically map out the envelope of performance of plasma systems in this plane speed measurement? 94 00:23:21.600 --> 00:23:42.940 Mark Kushner: So my student and Colin Pavan put together this parallel, almost parallel plate reactor. It's a dielectric bar discharge configuration with post nanosecond discharge. We ignite a flame at one of the ends of the reactor, and this flame enters the discharge region to understand and look at how the flame speed is modified by the plasma systems. 95 00:23:43.920 --> 00:24:02.179 Mark Kushner: So I think it will be easier to look at one of the experiments. One of the novel features we've been exploring is utilizing transparent electrodes so that we can visualize the plasma flame interaction along a line of sight that is parallel to the main electric field in the dielectric bar discharge, which is a completely new view. 96 00:24:02.430 --> 00:24:21.260 Mark Kushner: So in this video you'll see the flame entering from one end of the channel this crescent shaped fashion. Then we have micro discharge forming here, and when the flame enters the dielectric bar discharge, it gets accelerated, the curvature is modified, and whatnot. So there's a strong influence on that plasma in the flame properties. 97 00:24:21.510 --> 00:24:26.389 Mark Kushner: And there's a lot of things we've been looking at in this platform. But what I want to highlight today 98 00:24:26.650 --> 00:24:30.689 Mark Kushner: is the one dimensional property. The fling speed is sort of constant 99 00:24:30.840 --> 00:24:42.589 Mark Kushner: before it reaches the plasma, and then it gets accelerated. Can we quantify it? And can we explore what effect, what effect different activation strategies have on that prompt. 100 00:24:43.380 --> 00:24:52.069 Mark Kushner: So to that end, we've been looking at the laminar flame speed in the presence of plasma, and we can measure that experimentally, thanks to these transparent electrodes. 101 00:24:52.380 --> 00:24:54.559 Mark Kushner: So I'll play again the video. 102 00:24:54.870 --> 00:25:14.830 Mark Kushner: Now, if you focus on the flame contour, we can draw the flame contours every 5 ms. If they're equally spaced, that means that the flame speed is constant. If they become closely packed, it means we are decelerating the flame. If they become spread out. It means we're accelerating the flame. And we can plot also this in a height versus time plot. 103 00:25:14.930 --> 00:25:27.370 Mark Kushner: where we can plot the flame speed in this map and look at the, at the coloring, to see whether we are accelerating or or decelerating the flame or having no impact. 104 00:25:28.330 --> 00:25:42.469 Mark Kushner: Looking at things experimentally, we can get some metrics, but we are also looking at things from a numerical perspective that can help us isolate different mechanisms of interaction and determine which ones have a stronger influence in the plasma assisted problem. 105 00:25:42.790 --> 00:26:03.290 Mark Kushner: So we have a narrow channel Laminar flame propagating inside a DVD reactor. This is a 1 d model where we solve the reactive flow equations in the presence of plasma. So some terms in the energy and species equations. And we solve it using an operator splitting scheme because there's very different time scales involved in the problem. 106 00:26:03.620 --> 00:26:09.609 Mark Kushner: And then we look at the metric of Laminar flame, speed, enhancement with and without plasma and depending on the location of the plasma. 107 00:26:11.050 --> 00:26:20.530 Mark Kushner: So what different strategies can we think about? Well, the 1st sort of naive approach would be to put the plasma in the reactants, but very far away from the reaction front. 108 00:26:20.800 --> 00:26:37.739 Mark Kushner: If we do that, one possible solution is we have no interaction but what we actually observed, both from the numerical perspective. And then the experimental perspective is that we actually slow down the flame when we have the plasma on. So we have the plasma here activating in this region. 109 00:26:37.960 --> 00:26:57.530 Mark Kushner: From the video we have a flame propagating when we turn on the plasma, those contours become closely packed, meaning that we decelerate the flame. We turn off the plasma and the plasma sorry, and the flame continues to propagate at the constant initial speed. So we're decelerating the flame because of a plasma that we're applying far ahead of it. 110 00:26:58.010 --> 00:27:04.210 Mark Kushner: The numerical model sort of tells us the story of why? That is because we have this plasma produced 111 00:27:04.580 --> 00:27:11.280 Mark Kushner: ahead of the flame. We're inserting this pressure disturbances that are locally reducing the flame speed. So we have some 112 00:27:11.400 --> 00:27:18.680 Mark Kushner: flame deceleration by about 30% measured both with the numerical model and the experiments because of those pressure disturbances. 113 00:27:19.650 --> 00:27:22.820 Mark Kushner: So not good. Now, if we put the 114 00:27:23.020 --> 00:27:30.069 Mark Kushner: plasma closer, we're still treating the reactants. And then we turn off the plasma. Once the flame front reaches the 115 00:27:30.290 --> 00:27:33.549 Mark Kushner: the plasma treated region. What happens? 116 00:27:34.110 --> 00:27:40.880 Mark Kushner: We can look at the video. Again, we have the flame traveling towards the dielectric wire discharge. We turn on the plasma. 117 00:27:41.150 --> 00:27:55.619 Mark Kushner: and we have some deceleration. We turn off the plasma. The flame propagates underneath the electrodes and is able to consume the plasma produced. Species benefit from that plasma heating, and the plasma and the flame actually gets accelerated in that location. 118 00:27:55.890 --> 00:28:08.860 Mark Kushner: So you can see here, turn on the plasma some deceleration. The flame controls become closely packed, turn off the plasma, the flame goes underneath the electrodes, they become more spaced out, the flame is accelerating. 119 00:28:08.920 --> 00:28:31.429 Mark Kushner: and the numerical model sort of tells the same story. We have some plasma produced species under the electrode. The flame is reaching the electrode. And once we start interacting with this plasma produced species, the pressure disturbances sort of become less important, and we start having some acceleration, and the net effect in this case is about 30% increase in the flame speed because of the plasma systems. 120 00:28:31.980 --> 00:28:38.730 Mark Kushner: Even better is if we put the plasma overlaid with the flame. So now we have 121 00:28:39.550 --> 00:28:43.549 Mark Kushner: the flame propagating towards the DVD. We turn on the DVD. 122 00:28:43.970 --> 00:29:03.720 Mark Kushner: And then we continue pulsating the plasma until the flame fully progresses underneath the electrodes, and then we have much greater acceleration also observed in the numerical model. So in this case we have flame speed increase of up to 50%. In some of the experiments we reach up to 75% flame speed acceleration by the post nasecond discharge. 123 00:29:03.850 --> 00:29:28.649 Mark Kushner: So the bottom line here is that plasmas can have both beneficial and adverse effects on the flame controlling the strategy, the positioning, the timing of the plasma can have a strong influence in the outcome that you can have, and this sort of one dimensional models and one dimensional experimental platforms allow you to sort of explore that systematically and sort of map out the best performance that you can achieve. 124 00:29:29.800 --> 00:29:43.220 Mark Kushner: Now, this is sort of half of the story. The reduced electric field in all of the models has been prescribed as a constant. In reality, this reduced electric field depends on the combustion background that you have. So if you go to any 125 00:29:43.460 --> 00:29:56.649 Mark Kushner: classic textbook on gas discharge physics, you typically look at parallel electrodes. One dimensional conditions, uniform gases. Possibly helium argan inert gases, combustion is totally different. So we have 126 00:29:56.700 --> 00:30:14.970 Mark Kushner: environment where you have multiple phases, temperatures, compositions, and the gas discharge physics just is a little bit of a mess. So even if we look at the simple platform of the laminar flame propagating in a narrow channel, we have a situation like this one where we have burned gas, high temperature gases. 127 00:30:15.060 --> 00:30:23.529 Mark Kushner: cold reactants, low temperature gases, and the flame is sorry. And the plasma is actually going to be driven by this environment. 128 00:30:23.920 --> 00:30:51.620 Mark Kushner: We can take a look at the same video and see how the electrical discharge behaves very differently. We have it in the cold reactants we have micro discharges forming or in the hot products, uniform discharge forming, and then the channel is cooling from the sides inward, and we get recovery of the micro discharges as that channel cools down. So, looking at this backward problem, how does the combustion environment influence? The plasma has been one of the areas of research of microbe for the past few years. 129 00:30:54.350 --> 00:31:15.910 Mark Kushner: So what implications does this have on industry? Relevant claims that we started talking about initially so many of the small scale learnings can translate into larger scale setups. This is work we're doing in collaboration with Ahmed Gonim and Santosham pock at Mit in the combustion lab. And as local startup spectre aerospace, Felipe. 130 00:31:16.000 --> 00:31:35.380 Mark Kushner: And what we're doing here is utilizing the plasmas for control of combustion dynamics. So the experimental setup looks very different. It looks similar to what I showed in the motivation. It's a swirl, stabilized burner. We have a swirler here that locally produces a region of lower velocity flow so that we can have a flame. And this flame, unfortunately. 131 00:31:35.700 --> 00:31:52.209 Mark Kushner: when we use lean equivalence, ratios for control of Nox emissions, we have some unstable modes that make the flame oscillate back and forth pressure oscillations that are pretty significant. And the question is, can we use a post, nanosecond, discharge here to anchor the flame and suppress those pressure oscillations. 132 00:31:54.660 --> 00:32:15.159 Mark Kushner: So the plasma discharge is very hard to characterize in such an environment, because we have swirling flow that actually leads to swirling filamentary discharges to form. So it's hard to probe with lasers or optical diagnostics. Our diagnostics here is going to be limited to electrical energy measurements, and that sort of goes back to some of the work we did 133 00:32:15.600 --> 00:32:45.569 Mark Kushner: in that tutorial. So we're able to sort of look at different plasma regimes that happen in that combustor based on the electrical waveforms and direct imaging, and we were able to see 2 different types of discharges appearing, one a streamer corona, which is sort of a branching out filamentary discharge from the tip central electrode to the rim that has low energy deposition, and then a nanosecond spark that is a single bright filament that is basically shorting the electrode space with higher energy deposition. 134 00:32:45.640 --> 00:33:00.410 Mark Kushner: And in between we see some transitional redeems streamer to spark and spark to streamers with some hysteresis to the phenomena they don't look exactly the same. They look morphologically different, and they have energy values in between the other 2 modes. 135 00:33:01.400 --> 00:33:07.340 Mark Kushner: Now, what is more interesting for combustion, dynamic suppression. And that's sort of one question that we wanted to ask. 136 00:33:07.460 --> 00:33:22.499 Mark Kushner: So first, st look at what we can do with this plasma. We had some pressure oscillations with a post nanosecond discharge. We're able to reduce those oscillations, but not suppress them entirely. And that's a problem, because that's sort of what we had set off to do. 137 00:33:22.760 --> 00:33:27.920 Mark Kushner: and it's sort of what triggered some of the other work that I'll be presenting. 138 00:33:28.260 --> 00:33:56.539 Mark Kushner: So the 1st thing we looked at is sort of a backward problem. What is? What regime is the plasma operating in? And is that a good regime to be at? To be able to have this degree of control. So what you see here is correlation of the pressure oscillations in the combustion chamber with the energy delivery in red, deposited by the plasma. And you see that we're oscillating during the combustion oscillation cycle between the 2 streamer Corona and Nanosecond spark modes. 139 00:33:56.640 --> 00:34:12.280 Mark Kushner: and that those 2 modes are appearing complete synchronization with the oscillatory flame behavior which makes sense. We have different combustion environment when the flame is lifted off compared to when it's anchored, and we might have a more favorable or less favorable environment for electrical breakdown. 140 00:34:12.489 --> 00:34:14.290 Mark Kushner: But now, if we correlate 141 00:34:14.610 --> 00:34:36.139 Mark Kushner: the fraction of time that the discharge is operating in the nanosecond spark mode to the instability reduction that we achieve, we see that the greater the amount of time we spend in Nanosecond spark mode, the greater instability reduction we get. So what we did is go back to the system, redesign it to favor the nanosecond spark mode in the reactor and see what that does. 142 00:34:36.570 --> 00:34:48.499 Mark Kushner: So this is the results with a new injector where we reduced the discharge gap, spectre aerospace came up with a new design from 4 from 12 to 4.5 143 00:34:48.760 --> 00:35:03.340 Mark Kushner: and that had a strong effect on the discharge characteristics. The discharge regimes we were able to encounter and the energy deposition. And here I'm plotting again the pressure oscillations in the combustion chamber, compared to the energy deposited by the discharge. 144 00:35:03.870 --> 00:35:25.270 Mark Kushner: When we actually achieved complete suppression of the combustion dynamics. We were entering a plasma discharge that was fairly constant in energy, deposition, meaning that we no longer had that bimodal operation mode of the discharge we were able to consistently get the Nanosecond spark regime, and that was sufficient to actually get us to the complete suppression of the combustion dynamics. 145 00:35:25.590 --> 00:35:28.439 Mark Kushner: So our flames basically look something like this. 146 00:35:28.600 --> 00:35:34.390 Mark Kushner: we have a compact lifted flame. And then when we apply the plasma, we have this Y-shaped flame. 147 00:35:34.550 --> 00:35:48.349 Mark Kushner: This combustor still presents the pressure oscillations with half limit cycle pressure oscillations, meaning that they're pretty large compared to the atmospheric pressure we have with plasma. We're completely able to suppress the combustion dynamics. 148 00:35:48.620 --> 00:36:00.709 Mark Kushner: This is for an equivalence ratio of one. The interesting thing is, we were able to do this across equivalence ratios all the way from stoicometric to lean mixtures. In all conditions, the combustion dynamics are fully suppressed by the strategy. 149 00:36:02.700 --> 00:36:25.759 Mark Kushner: So in summary basically, plasma flame interactions are a multi-physics problem. We need to considerations for gas discharge physics combustion, but also electrical engineering. There's a two-way coupled problem here that we cannot bypass. We're interested and motivated by the influence of plasma and combustion processes. But equally important is the consideration of the influence that the combustion environment has on the plasma and gas discharge physics. 150 00:36:26.320 --> 00:36:42.180 Mark Kushner: Naively, we can think about reduced electric field and energy deposition as the key elements controlling the chemistry, but in reality everything else influences the composition of your gas, the temperature, the environment, and even the electrical circuit that you have. So it's not so easy to control. 151 00:36:42.620 --> 00:36:53.029 Mark Kushner: And I think, very importantly, plasmas can have both beneficial and adverse effects on flames. So we really need to control the interaction, to be able to exploit the maximum benefit that we can have. 152 00:36:54.120 --> 00:37:16.299 Mark Kushner: So that example basically shows one type of plasma pulls nanosecond discharge in reactive flow environments. But in aerospace we encounter different types of plasmas in different flowing gas conditions. And one example that we've been working on a lot is lightning safety, and in particular the behavior of a long lightning arc. Once it adheres or attaches to an aircraft fuselage. 153 00:37:16.300 --> 00:37:26.849 Mark Kushner: and how it is swept back by the flowing gas. So in this case we have, we go from pools. Nanosecond discharge to DC long arcs and from reactive flow environments to fast flowing gases. 154 00:37:27.920 --> 00:37:48.899 Mark Kushner: This is basically how it looks like this is what we call the swept stroke phase. This is simulations by one of my master's students, Nathaniel Jenkins. We have a lightning arc incepted at the nose of the aircraft, and flashing back towards the tail. This is sort of real time observation of what happens. This is a numerical simulation. 155 00:37:49.080 --> 00:38:01.510 Mark Kushner: If we run it in slow motion to just take a little bit of of the metrics. Here we have the arc attaching to different surfaces and different current levels flowing through the arc as it moves down. The aircraft 156 00:38:01.820 --> 00:38:23.549 Mark Kushner: like having this sort of predictive simulation is very hard. The physics of lightning are not really well understood, and one of the things or the problems that has captured little attention is the behavior of these long arcs in cross flows. So we would want to investigate that in far more detail, so we can have better numerical models of the interaction that we can use for engineering purposes. 157 00:38:24.610 --> 00:38:30.120 Mark Kushner: How can we study the swept stroke phase experimentally? That's a good question. 158 00:38:30.210 --> 00:38:41.049 Mark Kushner: So the 1st thing to do is literally fly aircraft and thunderstorms, and luckily for us, there were very good flight programs. Back in the 19 eighties. The NASA Storm Hazards program 159 00:38:41.050 --> 00:39:02.069 Mark Kushner: is one of them. This military aircraft was flown in thunderstorms and struck by lightning about 700 times, and it's a pilot aircraft. It's not an autonomous vehicle, and they recorded a lot of information. They have these diagrams where they record the pattern of lightning attachment for a particular discharge starting at the canopy and then going towards the tail plane. 160 00:39:02.330 --> 00:39:12.659 Mark Kushner: So we have that information available to us. And this is where most of our knowledge of aircraft, aircraft, and aircraft lining interaction comes from 161 00:39:13.120 --> 00:39:22.440 Mark Kushner: now repeating this sort of experiment in a lightning. Sorry in a laboratory. Academic laboratory is not really easy to do so. We have other options. 162 00:39:22.640 --> 00:39:43.289 Mark Kushner: and the community is very adventurous. So you see different moving surface experiments. If you think about it, it's a lightning arc attaching to a moving electrode. So if we can recreate a moving electrode scenario, we have a similar situation. So these 2 works are recorded in a review article of different testing 163 00:39:43.500 --> 00:39:59.959 Mark Kushner: experiments for for lightning attachment physics. Here you have a moving track moving underneath. A Marx generator looks quite dangerous. Here you see an elastic propelled sample. There's also experiments with rockets, triggering samples underneath 164 00:40:00.020 --> 00:40:23.429 Mark Kushner: different generators and whatnot, and this one here is quite recent. This was done at Onera by Vincent and Broad and Rafael Sosa Martins. They're using an electromagnetic launcher to launch a projectile at velocities that are comparable to aircraft in flight across 2 electrodes that are triggering a lightning arc of about 400 amps, so pretty close to the real conditions. 165 00:40:23.580 --> 00:40:33.479 Mark Kushner: Now, from my perspective, the complexity of this platforms is that you have little degree of control about the flow conditions, and it's hard to to study systematically. 166 00:40:33.720 --> 00:40:47.459 Mark Kushner: So the last option we have is a wind tunnel test. There are certain differences with the real environment that we have, but it gives us very nice flow fields that we can measure. We can control. We can modify and study things parametrically. And this is sort of the approach we've been following 167 00:40:47.880 --> 00:41:13.200 Mark Kushner: since last spring. We've started wind tunnel experiments of long arcs in cross flow, and it's been quite a trip we've been working with. Anera Raphael, Sosa. Martins is in this picture, Vincent and Broad, and also with my colleagues at the Polytechnic University of Catalonia, led by Juan Montana. Here. That's myself, and these are my students. Sankars Rao, Nicolas Gomezbega and Fabian Lin are in the picture. 168 00:41:13.350 --> 00:41:32.050 Mark Kushner: So we have this open section wind tunnel, where we're studying the influence of flowing gases on long arcs. We generate arcs using a retractable electrode. So we short circuit a DC. Power supply. We open it up, generate an arc about 20 cm length, and then with a cross flow, it gets elongated, pushed back. 169 00:41:32.380 --> 00:41:35.560 Mark Kushner: interacting with this earth web. These are DC arts. 170 00:41:35.690 --> 00:41:52.719 Mark Kushner: and we measure the electrical characteristics of the arc. This current voltage waveforms look totally different to what we saw before. Now we have current flows of about 3 amps in this red line. The voltage is here. We have 4 kilovolts of voltage. We short circuit the power supply, and we start open it up. 171 00:41:53.570 --> 00:42:11.790 Mark Kushner: We have some arc elongation here in yellow, and then, once we have the fully, the electrodes fully retracted, we start seeing the interaction of the airflow with the arc, the arc gets elongated and the voltage increases to keep approximately the same electric field inside the arc. 172 00:42:12.550 --> 00:42:33.139 Mark Kushner: So this is sort of the experiment at play. We have a lightning arc forming in this retractable electrode system and flown back along the airfoil. The total length of the arc at its maximum point is over a meter in length. So this is a pretty big arc created here. The green light is because we're shining a laser sheet there. 173 00:42:34.390 --> 00:42:50.380 Mark Kushner: So what do we want to learn from this experiment? One of the things that we want to understand is the interaction of different flow profiles on the arc, dynamics and arc root dynamics. So to that end we need to be able to quantify both the arc dynamics and the flow physics. 174 00:42:50.560 --> 00:43:11.290 Mark Kushner: So to quantify the arc, we do high speed video. The interesting thing here is we're doing a lot of post-processing to determine the position of the arc, the arc route motion, all of those magenta points there are the different locations of the arc route in time, so we have in this picture an arc route that is skipping along the airfoil. 175 00:43:11.420 --> 00:43:26.150 Mark Kushner: We're able to measure the arc length at least in 2 dimensions and other metrics. So we're able to generate a lot of data. I think we did more than 300 tests in that experiment and then analyze that statistically to get good information about the interaction. 176 00:43:26.870 --> 00:43:55.629 Mark Kushner: The other thing we want to quantify is the flow, and I think I haven't seen much of this work done before we're using particle image velocimetry. We're seeding the flow with oil droplets, and we shine 2 laser sheets in close proximity in time to eliminate those particles and from there get the velocity vectors in the whole two-dimensional space. So here you see the airfoil as 0 angle of attack, 2 meters per second velocity flow. So we have. 177 00:43:55.710 --> 00:44:07.330 Mark Kushner: The streamlines are all parallel to the airfoil, and pretty pretty nice there, and we have the arc there that it's locally evaporating the particles. That's why we are not able to measure the velocity in that location. 178 00:44:08.470 --> 00:44:33.530 Mark Kushner: So what sort of questions are we able to look at in this platform first, st what is the influence of the boundary layer on the arc and arc route motion? So we start with 0 angle of attack. Very nice streamlines adhere to the flow, and we look at the position of the arc. In this environment the arc gets moved or affected by the flow, and the arc root moves from the leading edge towards the trailing edge. 179 00:44:33.840 --> 00:44:53.909 Mark Kushner: This is for a number. This is a picture. I apologize. You cannot see very well, but we see the arc here before extinction, and all of the locations of the root in magenta. There we can see that the arc root is skipping by about 6 every 7 ms. And the arc column is a vector 180 00:44:54.290 --> 00:45:00.549 Mark Kushner: now, what happens if we have flow separation? So if we change the angle of attack to 20 degrees. 181 00:45:01.560 --> 00:45:12.280 Mark Kushner: We basically separate the flow. So we have the flow here, basically separated. So we have a low velocity, high, turbulent region in this location. 182 00:45:12.720 --> 00:45:34.840 Mark Kushner: And what does that do to the arc root and arc column motion? Actually, the root gets stagnant in the separation point of the boundary layer, and the arc column follows that separation region very nicely, so our arc is not able to penetrate that low velocity region as you would expect. But I hadn't seen an experiment like this done before. 183 00:45:35.170 --> 00:45:38.030 Mark Kushner: So this is the high speed video. 184 00:45:38.140 --> 00:45:47.499 Mark Kushner: just the location of the ark at the point of extinction. And you can see that the arc root stays in place, and it follows very nicely the separation reach. 185 00:45:48.010 --> 00:45:49.330 Mark Kushner: So in this case 186 00:45:49.600 --> 00:46:02.879 Mark Kushner: this flow, separation plays a very important role in the arc root, motion, and the arc column dynamics. So the bottom line here is that the arc column is indeed affected by the flow. Even at this low velocity. Fields 187 00:46:03.100 --> 00:46:11.049 Mark Kushner: and flow, features like separation, can constrain the motion of the arc route and completely change the dynamics along the aircraft. Fusella. 188 00:46:11.250 --> 00:46:35.770 Mark Kushner: Now the situation is different for anodes and cathodes. So for the anodic route we have the arc root jumping and moving along the aircraft fuselage. This is the picture of the arc right before extinction for a cathode. The root tries to stay in place. It's very hard for it to move, even for the 0 angle of attack. So there's anodic cathodic processes there that play an important role. 189 00:46:37.260 --> 00:46:54.390 Mark Kushner: How are we using all of this information? Well, we want to incorporate this local scale physics into large scale models of lightning attachment that we can use for engineering purposes, but inducing some physical knowledge there. So our modeling that I showed in the 1st slide that introduced the lightning physics is just 190 00:46:54.570 --> 00:47:08.370 Mark Kushner: and an arc, that it's a line of points that are freely affected by the flow. We have an imposed internal electric field on the arc. That is a function of the current that's known from experiments. 191 00:47:08.540 --> 00:47:12.009 Mark Kushner: and we're able to calculate the voltage. Drop along the arc 192 00:47:12.160 --> 00:47:31.490 Mark Kushner: with regards to the aircraft surface to determine whether there's going to be reattachment events or reconnection events. So we determine that an arc reconnects to a new location. If there's electrical breakdown of the gap between both, or if there's a geometrical intersection, and we use that 193 00:47:31.780 --> 00:47:43.489 Mark Kushner: for a large scale. Cfd model in an aircraft in flight. So this is the same aircraft that was used for the NASA Storm hazards program, comparing the inception of a lightning arc 194 00:47:43.620 --> 00:48:05.170 Mark Kushner: at the canopy like in the experiment, and combining with Cfd. To see where the arc gets swept to it, reattaches to the vertical stabilizer in green. You see the results from the storm hazards program, and I think you cannot see them very well here. But there they are. The green points are the results from the experiment, and how it compares to our simulation. 195 00:48:05.870 --> 00:48:34.680 Mark Kushner: Of course, simulating a single arc. There's a lot of error in a single simulation. What we're striving to do is, look at things statistically. What happens if we simulate thousands of arcs? Are the statistics of lightning attachment more or less accurate or not. So we're producing heat, maps of lightning attachment like this one here, where the high probability of lightning attachment is in red, very low probability or no probability seeing Gray, and we compare with the experimental data points in green. 196 00:48:35.400 --> 00:48:51.700 Mark Kushner: Now that we have some confidence that such an approach is robust, we can apply it for certification process. Well, not for certification. We can envision new ways of certifying aircraft, and determining which zones of the aircraft are going to be struck by lightning and compared to engineering standards. 197 00:48:51.700 --> 00:49:06.870 Mark Kushner: So what I presented is what we refer to as the zone, 2 region that refers to points of the arc that are going to be swept around, and then we have zone 2 a. Which is regular swept stroke, and if the arc stays there for a long time, that's what we call zone 2 B. 198 00:49:07.730 --> 00:49:26.379 Mark Kushner: We can compare that to the metrics of how long the arc stays in place for different pitch angles. So we need to account for different flight envelopes, and we can look at the probability of lightning attachment also for a wide range of conditions that would be relevant to a flight envelope. 199 00:49:26.560 --> 00:49:36.360 Mark Kushner: and we can compare the results of our model to engineering standards, and they actually match quite well to determine which areas of the aircraft are going to be struck by lightning. 200 00:49:36.660 --> 00:49:49.509 Mark Kushner: and it's not extremely relevant to do this for a conventional transport for which we already have information. What we want to do is be able to utilize. This approaches to look at aircraft for which we don't have zoning maps 201 00:49:49.730 --> 00:50:00.590 Mark Kushner: available to us. And this physics-based approach. We believe it's a good robust way of dealing with new geometries and vehicles for which we don't really know how they're going to interact with with lightning. 202 00:50:01.300 --> 00:50:23.119 Mark Kushner: so sort of to wrap up instead of going through the same points again just taken from the decadal assessment of plasma science, lightning research. There's not too much going on in academia for lightning protection standards. But there's a lot of fundamental questions about lightning attachment that can really improve the practices of of dealing with with this threat 203 00:50:23.730 --> 00:50:42.789 Mark Kushner: and to wrap up the presentation. Basically, I started by science and engineering. But in plasma science, really, they go hand in hand. We cannot decouple them both. We use engineering as our motivation and sort of the framework in which we pursue our science-based questions. But there's always new questions that arise. 204 00:50:43.050 --> 00:50:59.179 Mark Kushner: and in aerospace. In particular, we have the discharges occurring in fast flowing gases, reactive flow environments, and many of those environments are uncharted. So we really need to answer some fundamental questions before being able to control and develop the technologies. 205 00:50:59.300 --> 00:51:27.279 Mark Kushner: So just acknowledgement to all of my team. I presented work by Colin Poban, Raphael de Joon Jenkins, Sankars, Rao and Feli Lynn. But I also have other students that are equally brilliant and are doing other other work listed here. My collaborators in plasma assisted Combustion, Lightning, safety, and the sources of funding from Onr. Nsf. Department of Energy and Boeing and Lockheed Martin and the Misty Office for International collaboration. 206 00:51:27.470 --> 00:51:32.990 Mark Kushner: So thank you so much for for listening in the talk, and I'm looking forward to your questions. 207 00:51:39.550 --> 00:51:42.249 Mark Kushner: Thank you so much, Arthur Page. 208 00:51:44.490 --> 00:51:46.329 Mark Kushner: Question about the 209 00:51:46.580 --> 00:52:09.310 Mark Kushner: the when you have separation in the boundary layer, then the attachment point stays like the front of that separation. Does that decrease the amount of time that the arc is in existence like overall, since it can't like travel along it, or does it like, are they around for the same? That's a great question. So basically the extinction of the arc is related to the length. 210 00:52:09.360 --> 00:52:37.349 Mark Kushner: because we have approximately constant current about 3 amps. The internal electric field of the arc is set. So we're limited by the voltage supply. We have 4 kilovolts supply. Basically, the arc will be as long as extinction, but it will look different because what is anchored at 1 point it will be just as long as stretched as much, but the other one, the one that is not anchored, will move along the airfoil, and therefore therefore 211 00:52:37.730 --> 00:52:41.890 Mark Kushner: be be stretched or in that direction if that makes sense. Thank you. 212 00:52:43.590 --> 00:53:10.990 Mark Kushner: Yeah. I was interested in the sort of kinking of the arc during some of those videos. And it looks like when you show, like the flow velocity field that, like it's associated with a flow perturbation. I was curious, though, is that kind of kinking to do with the flowing of the air, or does it sort of self generate and change? That's a great question. So this 213 00:53:10.990 --> 00:53:32.840 Mark Kushner: long arcs are highly tortuous at high currents. You also have magnetic effects that contribute to that tortuosity. What we've seen is that the fluid dynamics also contributes to the tortuosity pretty significantly in this experiment. We're only able to measure 2D profiles. So we haven't really explored that into much detail, but eventually it would be great if we have. 214 00:53:32.840 --> 00:53:47.589 Mark Kushner: like 3 dimensional view of the arc, and be able to look at how much of the tortuosity is driven by the flow physics, and how much of it is driven by magnetic effects and others, and it will depend a lot on on the current levels that that we operate at 215 00:53:50.070 --> 00:54:06.138 Mark Kushner: question about the different observations in terms of the anode versus cathode changes in what you observe as a root attachment. Can you provide some insight? Yeah, these are all great questions. So let me see if I can go back. 216 00:54:07.750 --> 00:54:09.080 Mark Kushner: so basically 217 00:54:09.240 --> 00:54:38.900 Mark Kushner: full disclosure, we've just finished wrapping up all of the analysis. And we have to really think through all of these results. The Anode route basically skips and the Cathodic route stays in place, and we think that has to do with the mechanisms of sustaining the current in the anode and the cathode processes and field emission processes. Probably in the Cathodic group, playing a key role in being able to regenerate and move 218 00:54:39.180 --> 00:55:06.750 Mark Kushner: that route along the surface and not being able to supply enough electrons and just staying where it is, because it cannot move to a new location. But that is sort of hypothetical, and it's something we will need to investigate further. The good news is that the Cathodic route, because it stays in place, it will be much easier to probe with optical emission spectroscopy, for example, and make some more detailed diagnostics, whereas the anodic route is going to be more complicated because it tends to skip. 219 00:55:06.790 --> 00:55:10.680 Mark Kushner: and we will know exactly where the root is. At each point. 220 00:55:12.270 --> 00:55:13.990 Natalia Babaeva: Carmen, if you hear me. 221 00:55:14.170 --> 00:55:14.870 Natalia Babaeva: Hi! 222 00:55:14.870 --> 00:55:16.249 Mark Kushner: Are you well, not me? 223 00:55:16.250 --> 00:55:18.599 Natalia Babaeva: You very much for wave and for the nice. 224 00:55:18.600 --> 00:55:19.300 Mark Kushner: Secular trend. 225 00:55:19.300 --> 00:55:42.409 Natalia Babaeva: Very interesting and very informative. I have very simple question. If you use Nanosecond discharges. Probably I understand there is not much heating in such discharges. Still, I wonder what was typical gas temperature in your measurements and simulation? The question is because I saw rather large numbers of gas temperature in your figures? 226 00:55:42.990 --> 00:55:51.210 Natalia Babaeva: And can you comment on the so-called fast gas heating effect? And did you include this effect in your simulation? By the way. 227 00:55:51.210 --> 00:56:12.140 Mark Kushner: Yeah, those are great questions, Natalia, for those of you here, if you haven't heard. Basically, she's asking about the heating effects in the Nanosecond discharges and the typical gas temperatures and comment on the fast gas heating effects so full disclosure. Because I'm guessing you're talking about our setup with the micro discharges 228 00:56:12.440 --> 00:56:42.109 Mark Kushner: we weren't able. We haven't been able to do adequate probing of the discharge in this conditions. Our assumption through the modeling is that the heating effects. We're not heating the gas significantly. Maybe a few 100 Kelvin. What we're trying to do now is isolate. One of these micro discharges and probe it with optical emission spectroscopy to actually be able to measure the temperature in a single micro discharge channel. 229 00:56:42.110 --> 00:56:42.930 Natalia Babaeva: Simulation. 230 00:56:42.930 --> 00:56:59.860 Mark Kushner: To answer that question better so. The share of energy into gas heating and so forth, has only been done in my experiments from a numerical perspective. But there's other groups and people that have looked at this in much more detail. 231 00:57:00.440 --> 00:57:01.440 Mark Kushner: Yes. 232 00:57:02.060 --> 00:57:07.019 Natalia Babaeva: Yes, thank you, and in the future will you include it in your simulations? 233 00:57:10.874 --> 00:57:17.520 Mark Kushner: Could you please type in the chat for additional questions? 234 00:57:17.820 --> 00:57:23.140 Mark Kushner: Yeah, unfortunately, it's really hard to hear. Yeah, you should be able to turn it off on that. 235 00:57:23.430 --> 00:57:31.169 Natalia Babaeva: It's the same. It's the same questions about the fast heating effect. Did you include it in your simulation? 236 00:57:31.170 --> 00:57:31.880 Mark Kushner: Oh yes! 237 00:57:31.880 --> 00:57:32.670 Natalia Babaeva: I was going. 238 00:57:33.710 --> 00:57:50.789 Mark Kushner: Yes, yes, everything is included in the simulation. So we are tracking different, electronically excited states up to 8 vibrationally excited states of molecular nitrogen. So all of the fast gas heating effects, slow fast heating effects are accounted for in the simulations. Yes. 239 00:57:50.790 --> 00:57:51.990 Natalia Babaeva: Okay. Thank you. 240 00:57:52.240 --> 00:57:56.330 Mark Kushner: Thank you any last questions. 241 00:57:56.760 --> 00:58:21.870 Mark Kushner: So this is one of the things that I'm most proud of. I think from the work that my group has been doing. We didn't come up with the idea. There's a lot of people in the pattern formation community using Ito indium tinoxide electrodes for that particular process. The novelties that we applied it to plasma assisted combustion. But they're very easy to get hold of. 242 00:58:21.870 --> 00:58:43.000 Mark Kushner: You can buy them online. You can just type it in and get them very easily, and it just gives you a complete, different way of looking at the problem, and reveals features that you wouldn't be able to access with a side view that we had been using for several years before starting doing this experiments. So it's ideal in the obtainoxide. 243 00:58:43.300 --> 00:58:59.549 Mark Kushner: Yeah, I mean, it's just like a glass slide covered with this thin film. The way we operated the thin film is put at the dry end of the reactor, not the wet end, so we don't damage it. If you flip it over you will damage it with the discharge. 244 00:59:03.840 --> 00:59:05.680 Mark Kushner: Thank you very much. Thank you so much.