Bob McCormick: Chuck and I will talk about the results – or some of the results – from the U.S. Department of Energy's Co-Optimization of Fuels and Engines program and in particular will be trying to answer the question, "How can fuels and combustion reduce pollutants from future diesel engines?" And for those of you who didn't just hear the automated announcement, I'll remind you that this webinar is being recorded. Next slide, please.

So, just an overview of what we're gonna talk about. It's quite a challenge to introduce new diesel fuels – low net carbon diesel fuels – and also to reduce emissions from diesel engines and we'll talk a bit about that challenge. We'll talk about our goals in terms of achieving more sustainable diesel – or heavy-duty transportation – and then I'll preview the key takeaways from this presentation and then dive into a little more detail on our research approach, notable outcomes, and next steps. And with that, I'll turn it over to Chuck to begin to talk about the challenge.

Chuck Mueller: Thank-you, Bob. So, many heavy-duty vehicles and machines are powered by diesel engines due to their many advantageous characteristics. But diesel engines burning fossil fuels are a significant source of atmospheric carbon dioxide and their toxic emissions have been too high. So, our main challenge is to maintain the desirable attributes of diesel engines while achieving net-zero carbon, nitrogen oxides, and soot emissions.

Motivation for this work is that society needs cost-effective, clean, low-carbon powertrains for applications where long range, rapid re-energizing, lightweight, and compact size are critical. Most of these are freight-hauling applications like rail, long-haul trucking, and transoceanic shipping. So how can we meet this challenge? Obviously there has been a lot of discussion around electrification these days, but electrification faces significant hurdles in terms of the cost, mass, volume, and recycling of batteries – not to mention the tremendous infrastructure changes that will be required to enable widespread rapid re-energizing.

Fuel cells are another possibility, but they are expensive. They suffer from the inherently low-energy density of hydrogen, and there are high net-carbon-dioxide emissions from hydrogen production by steam reforming of methane. As a result, these freight-hauling applications have been dominated by diesel engines, but the engines have been powered by petroleum fuels with unacceptably high net-carbon-dioxide emissions. This, combined with high emissions of soot and nitrogen oxides, has led a number of governments around the world to seek other solutions and, in some cases, even to ban internal combustion engines entirely. Does this make sense? I would respectfully request that we keep in mind that, from a climate change perspective, the problem isn't internal combustion engines; it's the burning of petroleum-based fuels that is adding CO₂ to the atmosphere.

Diesel engines can actually be an important tool for fighting climate change if they can be powered by sustainable fuels. Fuels can be made from biomass like plants and algae, as well as from solar energy. These approaches can halt the increase of CO₂ emissions by capturing CO₂ from the atmosphere and recycling it back into fuels with ideal properties. If we can do this, then the only remaining big challenge for diesel engines is lowering their pollutant emissions. And overcoming this emissions barrier is the focus of our research.

So why diesel? As I mentioned earlier, diesel engines have many desirable attributes – including that they're very cost effective, they have inherently high efficiency, and it's easy to control ignition timing. In general, they're compatible with fuels with widely varying properties. They have high torque and power density. They have low cyclic variability. They're durable, reliable. They have low emissions of unburned hydrocarbons and carbon monoxide, but the main challenge has been with two emissions – high soot emissions and nitrogen oxides – or NO_x – emissions.

Now, if we want to better understand why these emissions have been problematic, it's helpful to learn a bit more about diesel combustion. On the right side here, you see a black and white movie of conventional diesel combustion that was acquired by looking through the window in the piston in the optical engine in my lab. In the center is the tip of the fuel injector, which has tiny orifices through which fuel is directly injected into the combustion chamber.  

For this engine, you can see that there are six orifices because there are six fuel sprays. We can see the six sprays of liquid fuel because they're illuminated by incandescence from hot sub-particles that are formed during the combustion process. These sub-particles give off light when they get hot, just like the filament in an incandescent light bulb; and in this movie, we'll be viewing that incandescence from hot soot. The time from the start of fuel injection is shown in the lower left corner, and the rotational angle of the engine's crank shaft is shown in the upper left corner. Now I'm going to play the movie and hopefully, this will work.

Ah, yep, there it goes. So, diesel engines don't have spark plugs. Their high compression ratios cause the in-cylinder gas mixture to be so hot that typically, within just a half a millisecond or so from the start of fuel injection, all of the fuel's sprays auto-ignite more or less simultaneously, and that's what you'll see here. The signal comes up more or less simultaneously from all of those little sprays. Then, a large amount of hot soot is created, as you can see from the white regions of signal, but it ideally all oxidizes before the exhaust valves open at a crank shaft angle of about 120 degrees after top dead center. The whole combustion process is over within about 1/200th of a second, so it's very fast. Now, this movie is nice because it let’s see where the soot is, but it doesn't really tell us how the soot is formed. And what about the nitrogen oxides (or NO_x) emissions?

For an even better understanding, let's look at the anatomy of just a single fuel spray. So now we're just going to focus in on this one spray here.

So why does diesel combustion produce soot and NO_x? Well, John Deck from Sandia created this conceptual model of diesel combustion, and basically, what you have is liquid fuel being injected into the combustion chamber. It pulls in hot charge gas and – at some distance downstream from the injection orifice – auto-ignition occurs, after which a stoichiometric diffusion flame is established around the periphery of the spray. The diffusion flame is indicated by the orange line around the outside of the spray. On the inside of the diffusion flame, the conditions are perfect for pyrolysis. There are high temperatures above about 1,400 kelvin and there is no free oxygen.

These mixtures tend to produce a lot of soot. On the outside of the diffusion flame, there are even higher temperatures – on the order of 2,700 kelvin – and there is plenty of excess oxygen. This environment tends to lead to NO_x formation by the thermal mechanism. So, you can see that conventional diesel combustion produces both soot and NO_x within the combustion chamber, and this leads to a problem called the soot/NO_x tradeoff.

So, what is the soot/ NO_x tradeoff? This slide shows a plot of engine-out soot emissions on the Y axis and NOx emissions on the X axis per unit work done by the engine in my lab. The black curve is a fit to the measured emissions. Now soot and NO_x are both toxic pollutant emissions that are regulated by the U.S. Environmental Protection Agency, and those regulations are continually tightening. So, engine manufacturers are always trying to get below the legislative thresholds, which in this figure are shown by the orange box.

You can see that our engine isn't meeting the current emissions regulations, and I would argue that once significant amounts of both soot and NO_x are present within the combustion chamber, we've lost a lot of ground in the emissions battle because we're effectively constrained to stay on this black curve. What do I mean by this? Well, let's start with soot. The previous movie showed that the vast majority of soot is oxidized before the exhaust valves open, but the current emission standards are sufficiently tight that extra measures must be taken to curtail even the tiny amounts of remaining soot. The way this is typically done is by taking measures to enhance soot oxidization.

This is effective for curtailing soot emissions, but perhaps it shouldn't be too surprising that creating an oxidizing environment facilitates the production of more oxides including nitrogen oxides. When one approaches the problem from the standpoint of curtailing NO_x emissions, approaches typically involve creating a chemically reducing environment, that is one that inhibits oxidation. And again, maybe we shouldn't be too surprised that inhibiting oxidation would lead to higher soot emissions. And this is really the essence of the soot/NO_x tradeoff, and it's why it's difficult to get into the box to meet emissions regulations without using catalytic aftertreatment systems to clean up the emissions after they leave the engine. The aftertreatment systems required to meet current regulations cost about the same amount as the engine itself, and the systems required to meet even tighter emissions regulations on the horizon are likely to be even more expensive.

So, the goal of the diesel-focused research within Co-Optima is to identify low-carbon fuel blendstocks and engine combustion strategies that are capable of reducing NO_x and soot emissions simultaneously.

In other words, we want to maintain all the desirable attributes of conventional diesel combustion to support a wide range of commercial applications while dramatically lowering soot and NO_x emissions, not just 10 or 20 or 30 percent, but something closer to 90 to 100 percent. And we want to do all this while achieving net-zero carbon using homegrown fuels. We believe this will give us a solution that is practical, clean, and secure, both in terms of mitigating climate change and also in terms of enhancing domestic energy production. So now I'm going to turn it back over to Bob to talk about some of our findings.

Bob McCormick: I think the key takeaway here is going to be that we're well on the path to achieving this goal – and if we can go to the next slide, please – we've screened a large number of potential fuels to identify those with critical diesel properties, and the outcome of that was we identified 14 diesel blendstocks with low net-carbon production pathways made from biomass and waste feedstocks.

And so, these include hydrocarbons, which can be drop-in fuels; esters, which are already on the market today as biodiesel; and ethers, which would be a new material in the diesel market, but that has some very advantageous properties although higher barriers to introduction. And in addition, we've developed, under Chuck's leadership, a new approach to diesel combustion called ducted fuel injection that breaks the NO_x tradeoff, leading to very low levels of engine-out emissions. Go ahead, Chuck. So, digging a little more deeply into our approach, really we've tried to connect engine performance to fuel properties and then to fuel chemistry or molecular structure. Next slide.

One of the major hypotheses used in Co-Optima is that equivalent fuel properties result in equivalent engine performance, regardless of the chemistry of the fuel. So, with that in mind, we took a fuel-properties-based composition-agnostic approach to fuel selection, and then, in addition, considered new engine designs to realize emission benefits. Next.

So, for diesel fuel, the critical properties include rapid fuel ignition, which is achieved with an adequately high cetane number; complete evaporation of the fuel, so it has to boil in the correct range for a diesel engine; cold temperature operability, so that means that the fuel cannot have components crystallizing out at cold temperatures where we want the vehicle to be able to operate. The fuel needs to be compatible with or enable fuel pump and injector operability and durability, so it needs to have the viscosity in the right range. Fuel also lubricates these components and so it needs to have adequately high lubricity, but that's typically achieved with fuel additives rather than being an intrinsic property of the fuel. And then for safe handling, the fuel has to have an adequately high flashpoint. And of course we don't want the fuel to degrade in storage and handling, so the fuel needs to have adequate oxidization stability, and this is also a property that can be impacted by fuel antioxidant additives. Next slide.

So, the fuel screening process followed a tiered approach, where at the top level, we're really just kind of asking the question, "Can it be a diesel fuel based on the criteria I outlined in the previous slide?" To do that, we don't necessarily need any of the fuel because we developed fuel molecular structure property relationships to predict fuel properties. Then, as we moved into the second level – tier two – we needed to validate those predictions with actual samples of the fuel and also to look at properties of the fuel blended into conventional diesel fuel, because Co-Optima is a program that focuses on blending up to 30 volume percent as a – perhaps viewed as a steppingstone toward ultimately achieving higher blend levels. Then for those fuels that we selected as having the best properties – both fuel properties and sustainability properties – in tier two, we moved on to tier three – candidate evaluation – which involved having enough fuel to do engine combustion studies as well as analysis, which I'll talk about on the next slide.

And so, to evaluate impacts, we did a wide range of analyses of impacts on the economy, impacts on jobs, but I think, critically, on analysis – technoeconomic analysis – to understand the fuel production process, what was driving costs in the fuel production process, and what those modeled costs were, and also using the GREET model to evaluate well-to-wheels or lifecycle greenhouse gas emissions from these fuels. Next slide.

And so, as a notable outcome of this work, we've identified many sustainable blendstock options. I suspect there are more. And then we've also identified a combustion strategy with a pathway to near-zero soot and very low NO_x emissions. And I am giving you a little bit more detail on that on the next slide.

Here we list the 14 mixing-controlled compression-ignition – or MCCI – blendstocks. All of these have acceptable – or even excellent – diesel fuel properties. They reduce greenhouse gas emissions by at least 50 percent and over 60 percent in most cases and well over that in some cases. And they have potential to be produced with reasonable production economics. And if we move to the next slide, the top group there are hydrocarbons, which can be drop-in fuels, so have the lowest barriers to introduction.

Some of these will look familiar, I think. In the bottom right of the hydrocarbon group is hydroprocessed esters and fatty acids, known as renewable diesel today – so this is a fuel on the market today. And also, Fischer–Tropsch's diesel fuel in the top center of the hydrocarbons, which today is produced commercially in some places in the world from natural gas, but which can also be produced from biomass via biomass gasification syngas, which has very low lifecycle greenhouse gas emissions. The next group is esters, which have some barriers to use, especially at high blend levels.

In the center, we have the biodiesel – that is a very important contributor to sustainable fuel use in the market today. So that's a fuel that's already on the market, but it's not used at 30 volume percent or higher blend levels, so there may be some barriers to that. The other esters we have are not hugely different from conventional biodiesel but may have barriers in terms of developing the feedstock for the short chain esters or for the fatty acid fusel esters. Now on the bottom, we have a group of ethers. It turns out that ethers are quite reasonable to make from biomass.

They can have really excellent diesel fuel properties, a high cetane number, very low soot formation tendency, but because they've never been used in the market before, have some significant barriers to introduction. You would probably need some sort of ASTM standard for them as a blendstock, for example. There's a couple of questions that always come up when you mention ethers, especially to people who know some things about chemistry and about fuel. One is about storage stability, and we have examined that for all of these ethers. Some of them will definitely require antioxidant additives to be handled and stored, but these are already used in the marketplace with biodiesel.

So while that is an issue that has to be addressed, it doesn't seem like an insurmountable one. The second issue is toxicity and biodegradation, which is related to issues that came up more than a decade ago with the use of ethers in the gasoline market, such as MTBE. And so we are assessing toxicity and biodegradation for these, and that assessment should be completed during the current fiscal year. And let's go on, Chuck.

So, this chart – I apologize for it being kind of an eye chart, but the bar links as the carbon intensity, as grams of CO₂ equivalent per megajoule of fuel energy. And there's a dashed vertical line that shows that the bars that are to the left of it achieve greater than 60 percent greenhouse gas emission reduction. I'd note that the black dots on the bars are the net greenhouse gas or CO₂ emission reduction and so we have quite a few that are better than 60 percent and some that are much better than 60 percent lifecycle greenhouse gas emission reduction. And these are the ones we focused on primarily in Co-Optima and that we would recommend for future research. Next slide please.

So this is essentially a modeled cost and these bars – where the black dot, again, is the net modeled cost – we're not using a number here, because there's a lot of factors that go into what a fuel product actually costs. But the neutral range means roughly the same as conventional petroleum fuels today. So, many of our fuels have higher costs than that and would require additional development to lower cost before they could be marketed, but some are within the range of conventional fuels and potentially even lower. So with that, we'll move on to the next slide.

So one thing that we do with these fuels is we use them in a conventional diesel engine – at least some of them. So on the right-hand side of this chart, you see the identity of the fuels. They're all 30 percent blends into a conventional diesel fuel that was EPA certification fuel. The chart shows soot on the Y axis and NO_x on the X axis. So, these are NO_x/soot tradeoff curves, much like what Chuck showed you before as a hypothetical example. These are actual NO_x/soot tradeoff curves measured in-engine by increasing the EGR rate.

So over on the right side of the chart, four to five grams NO_x, we're not really using EGR, and here you can see the black line, which is the conventional diesel fuel. Generally, the biofuel blends have lower soot – some of them, quite a bit lower soot than the conventional fuel. And as we increase exhaust gas recirculation to lower NO_x, at some point, for most of these fuels, soot emissions begin to rise quite strongly, but some of them can tolerate quite a bit of EGR without suffering high soot emissions. And the purple curve at the bottom for the polyoxymethylene ether is – and this is just a 30 percent blend of the polyoxymethylene ethers – makes it extremely low soot relative to the conventional diesel and we could not really get it to spike in soot at the EGR rates that we were using in this study, so the low soot emissions from that fuel are quite interesting and worthy of additional study.

And so with that, I'll turn it over to Chuck to talk about ducted fuel injection.

Chuck Mueller: Great. Thanks, Bob. So you may have noticed from the last slide that while oxygenated bio-blendstocks can help tremendously with soot and NO_x emissions, they didn't totally get as fully into the box in terms of emissions compliance. So we need to get even cleaner.

How do we propose to do this? Well, the solution that my group has been working on is called ducted fuel injection – or DFI. What is DFI? It's a simple mechanical approach for improving diesel combustion that is motivated by the Bunsen burner concept. I don't know if you've ever played around with a Bunsen burner without the tube on, but if you have, you know that you get a rather tall orange flame.

The flame is orange because it's producing hot soot, which incandescence is just like we saw earlier in the movie of diesel combustion that I showed. Robert Bunsen's breakthrough was realizing that if you attach a tube to the burner and let some air in upstream of the tube, that big orange flame becomes a shorter blue flame. The gas flow rate is the same, so the energy release rate is the same. But with the Bunsen burner, the energy release is happening over a much smaller area, and the flame is blue because there's no soot being produced. Both of these changes occur because the fuel and the air are more uniformly premixed before they ignite. So my idea was – why can't we do something similar in a diesel engine? That is – put a tube around each fuel spray to enhance the extent of premixing before ignition occurs.

So we tried this and lo and behold, it works. Again, we're looking up through a window in the piston toward the cylinder head. This time, the injector tip has just two orifices instead of six like in the previous movie. On the left side, there is no duct, so we have just conventional diesel combustion; and you can see from the whitish brassy-looking cloud there that we get a lot of incandescence from hot soot, as we would expect. On the right side, though, we added a duct, and now you can see that we get a blue flame because there is no soot being produced.

This is very important because it enables us to break the soot/NO_x tradeoff. So if we go back to our soot/NO_x tradeoff plot, we can see that we can use DFI combined with dilution to break the soot/NO_x tradeoff. And what do I mean by this? We first use DFI to prevent soot formation and the colored squares here are measured data points with DFI. And now that soot is no longer a problem, we can use other cost-effective measures – like dilution with inert gases – to control NO_x emissions.

So in practice, this dilution is typically obtained by recirculating some of the exhaust gas back around and feeding it into the intake of the engine. This enables NO_x reductions of an order of magnitude or more. Notice the X axis has a logarithmic scale here, so the difference in NO_x between the red square on the right and the dark blue square on the left is about a factor of 50. I also want to note here that these results were acquired with current conventional diesel fuel.

This backward compatibility of DFI with today's diesel fuel removes a major potential barrier to its introduction. It means that DFI could be introduced immediately to start lowering emissions, potentially even via retrofits. Now, if the results were this good with today's petroleum diesel fuel, it begs the question, "What if we now combine DFI with the beneficial effects of oxygenated low-net CO₂ fuels like Bob showed earlier?" As you might expect, we get additional benefits, and we see that DFI really is synergistic with oxygenated sustainable fuels.

Now, many sustainable fuels contain oxygen bonded into the fuel molecule because they're starting from carbon dioxide and it costs money and energy to remove each of those oxygen atoms from CO₂, hence we can leave a little bit of oxygen in the fuel molecule, and that's both easy to do and it's desirable from economic and energetic perspectives.

So, what I'm showing here is a plot of the amount of hot in-cylinder soot for different operating conditions. Note, again, the Y axis scale is logarithmic. The left-hand pair of bars is for conventional diesel combustion with petroleum diesel fuel. The middle pair of bars is for DFI with petroleum diesel fuel. And as we saw before, we get approximately an order of magnitude reduction in soot by switching from conventional diesel combustion to ducted fuel injection.

Now the pair of blue bars on the right side shows the hot in-cylinder soot when we add 25 percent by volume of an oxygenated compound to petroleum diesel fuel, and we see that this approach gives an additional order of magnitude reduction of in-cylinder hot soot. And that gives us, overall, about 100 times lower soot. This additional soot-reduction benefit provides substantial market incentive or the more widespread use of oxygenated sustainable fuels. Also note that the bar on the right in each pair shows the result at a moderate dilution level, indicating that exhaust gas recirculation – or EGR – can still be used to control NO_x emissions. Taken together, these results show that DFI with oxygenated sustainable fuels provides a promising path to practical, clean, and secure energy conversion for transportation applications, particularly those for which long range and rapid re-energizing are essential.

Now, I'll turn it back over to Bob.

Bob McCormick: Well, thanks, Chuck. Every time I hear about ducted fuel injection, I just think that is the coolest thing I've ever heard. So the next steps in this work are to continue development of these fuel production processes to achieve net-zero carbon and removing barriers to market entry for the fuels, and to continue research to achieve zero or near-zero criteria pollutants.

So, many of these ideas are listed here – working to reduce carbon intensity, increase blend-level scaling up for commercial production, learning to achieve net-zero criteria pollutants in terms of adoption barriers for the fuel. In some cases, there is a need for fuel quality standards, regulatory compliance. We need to address engine manufacturer concerns and get their, essentially, sign-off that these fuels are acceptable in the products they're selling. And then, a multimedia assessment, which is a requirement in California, but really matters everywhere, which is just understanding what happens if there is a fuel spill, what are the environmental impacts and various other aspects? And with that, I'll go to the next slide, which acknowledges our sponsors at the Department of Energy – the Bioenergy Technologies Office and the Vehicle Technologies Office – we're very grateful to have had their support over six years to work on Co-Optima.

The next slide is an advertisement – if we could go to the next; there we go – for future webinars in this series. The next one is May 27th where Avantika Singh will talk about environmental and economic benefits that might be realized by co-optimization of fuels in spark-ignition engines. And my final slide is thanking you for being here today and provides a link to some additional – if we could go to the next slide – links to information about Co-Optima as well as a Co-Optima publication's database. Our e-mail addresses are here. I think we have plenty of time for questions, so hopefully we can answer them all. But if some other questions come up, please don't hesitate to send either of us an e-mail.

I do see some questions in the chat. I'll read this one to you, Chuck, and let you take a stab at it. This is from Zia Abdullah at NREL. "How can we apply what we've learned about soot reduction in compression-ignition engines to gas-turbine engines?"

Chuck Mueller: Yeah, so that's a great question. I wonder – I'm certainly not an expert in gas turbine – current gas-turbine-engine combustor technology, but I guess it's possible that maybe we could use DFI or something like it in gas-turbine engines. Maybe if you have expertise in this area and you'd like to comment, I would be interested in hearing it. I don't know if Nick can un-mute you.

Zia Abdullah: Yeah, this is Zia Abdullah. So of course, soot formation and then contrail formation because of soot is a major source of global warming and order of magnitude of this effect is comparable to actually the CO₂ emitted by a gas-turbine engine. So this is a big opportunity for the labs to collaborate and work in this area and I found your results very interesting that you just presented. So I'm wondering if combustors in gas-turbine engines can be modified for this.

And I guess what you alluded to as a mechanism was mostly poor mixing, but in gas-turbine engines, much of the soot is formed because of aromatics in the fuel also. And for certain reasons, it's not practical to completely get rid of aromatics. So the question is that if techniques such as this can be used to reduce soot in fuel, which has a fraction of which is aromatics? So that's my question. Thank you.

Chuck Mueller: Yeah. So, I mean, based on – I don't know too much about jet fuel, but I know that diesel fuel has a lot of aromatics too. And if it works for diesel, it's probably going to work pretty well for jet. Thank you.

Zia Abdullah: Thank-you.

Bob McCormick: Jim McMillan, would you like read or say your own question?

Jim McMillan: Sure. I have some construction going on near my house though, so I hope this –

Bob McCormick: Oh, OK.

Jim McMillan: If it's too loud, you can take it. But I also share your sentiment there, Bob, that DFI sounds like a really positive development if it can be realized in industry. And so, I just wanted to know what the timeline or the path for industry adopting DFI for CI engines is. Thank you.

Chuck Mueller: Yeah, thanks for your question, Jim. I appreciate it. And it's definitely something that is on our minds and we are actually preparing a DFI consortium proposal. And the idea of that proposal would be to assemble a team of OEMs as well as national labs to move DFI from the current technology readiness level, which is about four, out to something that is much closer to where we can hand it off to production companies. And so the proposal that we're currently considering would be four years to get us to DFI being tested in a multi-cylinder engine over test cycles of interest. And I wouldn't imagine – that it's not going to make it into production in four years, but at least maybe by 2030 we could be there or around that, give or take a couple of years. That is kind of what I'm thinking.

Jim McMillan: Sound encouraging. Thank-you. Every success with that effort.

Chuck Mueller: Thanks.

Bob McCormick: Andre, do you want me to read your question, or would you like to ask it? I'll just read it for him then. "If you can reach low soot in NO_x with DFI using a hydrocarbon – including a drop-in, low greenhouse gas bio-hydrocarbon – why would you want to use an oxygenate with DFI to bend high load?"

Chuck Mueller: Yeah, OK, great question, Andre. The problem is, we can reach low soot and relatively low NO_x with DFI, but I think we're going to realize the biggest benefits when we can – what I would love to see is completely eliminating soot formation, because then we have a very strong lever with which to create conditions that lead to lower NO_x. And so I think, across the board, when you use an oxygenate with DFI, you're going to have lower soot emissions.

The results that I showed were for a two-hole injector tip you may have seen. You know, that is what I was showing. And so at those conditions, where your global in-cylinder equivalence ratio is very lean, the need for – the fuel bound oxygen is not such a big deal, but I expect at higher load conditions – and, as you said, tip in transient type conditions – the oxygenate is going to help a lot. I don't know if you're un-muted or if you want to discuss further, but –

Bob McCormick: He asked me to read his question, so...

Chuck Mueller: OK.

Bob McCormick: The next question I'll read from Ken Holeman – and Ken, if you want to elaborate on it, please un-mute and do so – "Has DFI been investigated in retrofit applications?"

Chuck Mueller: Yeah, so thank-you for the question and there have been no dedicated DFI engines built, as far as I know, up to this point. So everything that we've tested so far has been a retrofit. Toyota has published some work with a retrofit DFI head. Ours had been a retrofit and I would imagine that there are others out in industry.

I'm not at liberty to talk about things like that, nor do I have good knowledge in that area, but I would imagine there have been quite a few retrofits just for testing. Now, as far as retrofits for a long-term solution, I'm not sure that is a great idea, just given the history of retrofits and enhancing diesel – you know, we had some issues with DPF retrofits. And the alignment of the duct assembly with the in-cylinder sprays – it is a critical aspect of getting DFI to work properly. So yeah, I think it would be better if probably it was implemented in production, but I think if it's done right, a retrofit could work really well, and it could make a lot of sense, especially in very expensive engines like you find in ships or maybe locomotives. Engines with long lifetimes that are very costly – well, then, a retrofit, I think, makes a whole lot of sense.

But I haven't seen publications about that. DFI is still pretty new. Thank you for the question, though.

Bob McCormick: The next question is from Carol Hale. "What is the added potential for adding low levels of an iron-containing metallocene like ferrocene to oxygenated diesel fuel to improve soot oxidation and also adding something like an ammoxidation catalyst, which creates a reducing environment downstream in the combustion chamber?" I have noticed in my career an extreme unwillingness on the part of regulatory agencies to even consider metal-containing fuel additives. So it's certainly not something we've examined under Co-Optima. And while I know what ammoxidation catalyst is in the petrochemical sense, I'm not sure what you mean in this context, Carol.

Would you like to un-mute and elaborate? Well, I guess not. Well, do you have anything to add, Chuck?

Chuck Mueller: No. No. I'm grateful that you can field this one because there are a lot of words in here that – this is not my area.

[Laughter]

Thank-you.

Bob McCormick: It was an interesting question. John Martin – oh, Carol is elaborating in the chat. "Ammoxidation catalysts also have utility in terms of reducing oxides and exhaust emissions." OK. I guess I'll need to look into that. I need to learn more about that to answer your question. I'm really unfamiliar.

Jonathan Martin from NREL asks, "Any investigation on the effects of DFI on particle size distribution or just total mass and number?"

Chuck Mueller: Yeah, OK. Thank-you for the question, Jonathan. We actually do have a paper that just came out by a visitor that we had by the name of Brady Wilmer from the University of Minnesota.

He is working on his Ph.D., and so we just published a paper. He is the first author on it in International Journal of Engine Research. And we used an EEPS – an Exhaust Emissions Particle Sizer – to look at the particle size distributions from DFI as well, and I can send you that paper or folks can find it online. Brady's last name is spelled W-I-L-M-E-R. And what we found is that DFI dramatically reduces the number of larger particles – so, greater than 23 nanometers.

But the very small particles seemed to go up by some fraction. I can't remember exactly –so, sub-23 nanometers. So those particle sizes are not currently regulated, but they might be in the future. And he saw those numbers go up and a current hypothesis is not that DFI is producing more small particles, it's just that those small particles are ash particles coming from the combustion of lube oil. And because there are fewer large particles around with DFI, those large particles kind of scavenge the smaller ash particles and so, when you have fewer large particles, then you have the ability to see more and more of those small ash particles that are left in the aerosol. So anyway, we can talk more about it offline, but thank you for the question. There is a little bit of work done in that area but not a ton.

Bob McCormick: That appears to be all the questions in the chat. Would anyone like to un-mute and offer a question or a comment?

I see a new question in the chat from Scott Ian.

Chuck Mueller: Oh, yeah. Go ahead. I was going to read one to you because –

Bob McCormick: Go ahead, Chuck.

Chuck Mueller: OK. I think this one is probably better addressed by you, Bob. So, "Can you discuss any general conclusions of the Co-Optima program related to diesel efficiency? Have fuel type and engine operating strategy matching led to any breakthroughs?"

Bob McCormick: So, well, maybe you want to comment on this too, Chuck, but in general, diesel engines are really efficient. There are commercial engines – there is a strong market driver for them to be as efficient as possible. And so, while there certainly are some approaches out there to try to improve the efficiency of diesel engines, the ones that we were aware of were not really related to the fuel, unlike the situation, say, in spark-ignition engines where fuels with a lot higher NO_x resistance than today's fuel would allow you to increase compression ratio and do some other things to improve efficiency.

The things that we were aware of for improving the efficiency of diesel engines weren't fuel-related and so we didn't directly pursue efficiency improvements in Co-Optima. I think early on in the program, we had thought that we might, but as we looked into it, it just didn't seem like a fuel-related phenomenon. It's possible we were wrong about that, and if you have any ideas that you'd like to share on how we might have tried to leverage fuel properties to improve efficiency, we'd love to hear them. But it ended up not being a focus of the research.

Chuck Mueller: Yeah, I would echo Bob's comments. I mean, the combustion efficiency for even conventional diesel combustion is typically 99 to 99 and a half percent – so, very high. So, combustion efficiency is not an area where we need to really apply much effort. And thermal efficiency or fuel conversion efficiency – depending on how you think about it – it's hard to squeeze more out of that, because effectively what you have to do is limit the amount of heat rejection either to the exhaust gases or to the coolant.

And, as Bob said, that is not really a function of the fuel or even necessarily of the combustion strategy, although the combustion strategy can change things. So, I mean, at least speaking from the standpoint of DFI, our hope is that we will achieve these really dramatic emissions reductions without having any kind of an efficiency penalty. And that is what we've seen so far – is that the efficiency just kind of – it's either a little bit higher or a little bit lower, plus or minus one point but there's not a big change. Thanks for the question. I'm not seeing any more questions, Bob.

Bob McCormick: I'm just – you know, some people are like me and are slow to think up their question so I'm trying to give everybody time. But we do have a few minutes left if there are other questions and, again, as you can see on this slide, our e-mail addresses. If you feel the need to ask us a question via e-mail, don't hesitate. But, if there are no more questions or comments, I guess we can close it off. I'd like to thank you all again for attending the webinar today and I hope you can join us for future webinars in the Capstone series.