38th International Symposium on Combustion

tl;dr >1300 combustion scientists logged into the first virtual combustion conference. I was involved in the workshops leading up to the conference and presented our group's work on soot formation. Some main themes included; low T combustion for clean combustion, biofuels for easy fossil fuel replacement, ammonia as a clean fuel and soot formation remaining a mystery.

The combustion symposium happens every two years since 1928 and was planned for 2020 in Adelaide Australia. Due to the pandemic, the conference had to move online and was delayed until January. The talks were all prerecorded and played during the session and then the speaker was live afterward for taking questions. One advantage of this format is that you can access the recorded talks for up to a few months after the conference. A disadvantage was that you are unable to have casual conversations, though they did have a chat feature so you could talk with conference attendees. Below is the interface showing the video box that you play the video within the website.

The lead-up

Before the combustion symposium, there are a variety of workshops that were organised. This year I attended and presented at the 5th International Workshop on Flame Chemistry and the 5th International Sooting Flame Workshop (ISF-5) both done virtually via zoom. I was asked to provide an overview of soot formation at the Flame Chemistry Workshop the slides can be found here. For ISF-5 I worked with Matteo Pelucchi to prepare some summary slides. Below is a nice summary of the talk I gave in a single slide. Credit to Matteo for doing most of the consolidation. 

I also presented a poster as a video at ISF-5, which can be viewed online here. 

Some of the discussions centred around what is the molecular unit of clustering towards soot formation. Currently, there are two main views that small molecules around the size of pyrene form soot and the other view that molecules around the size of circumpyrene form soot. 

It is challenging to know in soot whether the larger molecules seen are formed in the gas phase before they cluster to form soot or if they form after being condensed in soot. We currently think it is the former.

Our work

At the symposium I was involved in three papers and a poster that were accepted and the group contributed in total six talks. Here is a summary slide that we prepared. 

The work I was closely involved in focused on localised pi-radicals this was published last year and there is a blog post written on it already. We were able to demonstrate some pi-radicals form from hydrogen addition to pentagonal rings that lead to localised pi-radicals with considerable reactivity. The spin density plotted below shows this localisation. 

Another paper Laura Pascazio presented extended this idea to crosslinked molecules. These can form from small PAH crosslinking reactions and lead to a flat molecule due to a double bond.

Laura explored how they physically condense and found they were similar to pericondensed species indicating they are not going to cluster together at flame temperatures. However, in a link with our previous work hydrogen addition to the pentagonal ring gives localised pi-radicals (species 1d in the figure above). Here is the spin density showing localisation for the penta-linked species.

These reactive sites can recombine and form strong bonds that are thermally stable in a flame. We also presented reactive molecular dynamics simulations of the dimer bound at flame temperatures. 

An interesting paper that was presented by KAUST showed that the m/z 154 ion that is usually ascribed to biphenyl is more likely to be acenapthene from fragmentation studies, which is what we predicted!

This raises the question, what is the concentration of the partially saturated species C12H9 that we expect to be a reactive localised pi-radical. 

Questions we received concerned what is the concentration of the partially saturated localised pi-radicals in the flame. This requires more complete reaction mechanisms to be simulated and new experiments that are able to measure the concentration of these partially saturated species. Optical approaches could also be applied and we are looking into these.

Another interesting paper looked at carbonaceous nanoparticle formation in pyrolysis experiments. It showed firstly that as pyrene is heated in a furnace it breaks up and forms species around the size of 600 Da in size before forming the nanoparticles. It was also shown an increase in nanoparticles with temperature indicating a chemical process and not a purely physical condensation leads to these small particles. 

The molecules thought to be involved in premixed flames are a little bit lighter with a peak concentration around 450 Da as was shown in another paper presented at the symposium. There appears to be a convergence in thinking around the size of aromatic molecules that cluster to produce nanoparticles in combustion and pyrolysis systems.

Some insights into what makes these aromatic molecules cluster was made in two papers. The first, already mentioned, showed that there are a reasonable number of aromatic molecules with more hydrogen than would be expected for pericondensed unsaturated aromatic such as pyrene. Second, the concentration of radicals in the flame was shown to be proportional to the amount of hydrogen in the soot. This indicates that hydrogen addition to aromatic can lead to more radicals. These results are all consistent with the aromatic rim-linked hydrogen mechanism we have proposed.

Low temperature combustion

There was a real focus on what role combustion has in a low carbon world. The most interesting technology was the development of low-temperature combustion engines by Mazda. In 2019 they released the first commercial engine that operates in the so-called homogeneous charge compression ignition (HCCI) mode. This practically operates a petrol engine like a diesel engine but at much lower temperatures. The high compression allows the engine to have 20-30% higher efficiency than a normal petrol engine and dramatically reduces the concentration of soot and nitrous oxide (NOx that causes acid rain). 

HCCI engines had been notoriously difficult to build requiring recirculation of the exhaust gas into the intake and superchargers to allow for the high compression of the fuel without autoigniting. The trick that Mazda developed was to make use of the spark plug to start things off. The video from Mazda shows the details of how this works. 

What is not discussed in the video is how Mazda developed a swirling fuel mixture that provides a slightly higher fuel mixture right where the spark plug is to allow it to ignite and push the charge above the critical pressure to auto-ignite in a homogeneous way. It can switch dynamically from spark ignition to the low-temperature HCCI combustion mode completely dynamically - some truly remarkable engineering.

So how does it reduce the soot and NOx pollutants? It comes down to the unique combustion mode that is able to operate in a sweet spot. The most helpful way to explain this is by using the equivalence vs temperature plot below.

Reference

The equivalence ratio is the ratio of fuel to air where a ratio of 1 is the exact amount of oxygen to completely burn the fuel and >1 is fuel-rich and prone to form soot. The blue line is showing the rough flame temperature and equivalence ratios in air during a cycle (adiabatic flame temperature in Kelvin so subtract ~273 to get Celsius). 

Diesel engines work by injecting fuel into a high-pressure chamber upon which it autoignites. A diesel engine will therefore have an equivalence ratio almost always >1 leading to soot, carbon monoxide and nitrous oxide. 

In a spark-ignition engine (like most petrol engines), the equivalence ratio is always close to one but because the flame front is quite concentrated and high temperature you get nitrous oxide formation. 

The clever thing about HCCI engines is they can operate in the 1400-2000 K by spreading out the flame so it homogenously burns and does not form NOx and by keeping the equivalence ratio <1 soot is not formed. 

Prof. Yiguang Ju gave a very nice talk on the chemistry of this low-temperature combustion and how multiple oxygen molecules attacking fuel molecules allowing for different types of flames if you are interested in the details.

Ammonia

There was a lot of work on ammonia combustion because it is being seriously considered as a low carbon fuel for ship and energy storage. Combustion of ammonia leads to water and nitrogen - so no greenhouse gases that accumulate. 

4 NH₃ + 3 O₂ → 2 N₂ + 6 H₂O (g)

Ammonia is also considered an chemical storage method for hydrogen. Hydrogen can be made from solar or wind powered splitting of water. Combining hydrogen with nitrogen in the air gives ammonia. Here is the usual sales pitch.

The reason you would want to convert hydrogen into ammonia is that the latter is much easier to store and transport. Many of the challenges of using this fuel were addressed at the combustion symposium including, the low flame speed and the formation of pollutants nitrous oxides (NOx) or worse cyanides were all discussed. 

The first issue the low flame speed means that ammonia by itself makes for a very poor fuel it can easily be blown off a burner and be extinguished. Here is what blow off looks like from a burner. This is a significant industrial problem for turbines i.e. you don't want the flame to blow off in your planes engine...

To maintain stability you must run ammonia in a fuel rich condition that leads to slip of the toxic gas ammonia through the combustor which is not ideal (called ammonia slip).

There are a couple of solutions to the low flame speed problem. The most widely studied at the symposium was the addition of hydrogen gives a much nicer fuel with flame speeds approaching hydrocarbons. The other option is to add some methane to improve the burning conditions. This could potentially form soot so a nice study was conducted to look into the production of soot in an ammonia/methane flame. With low mixing of ammonia into a methane flame much of the soot was removed which is a good sign. Mixtures of ammonia, methane and hydrogen were also considered. As was the addition of biofuels. However, this mixed fuel with a hydrocarbon still produces CO2 and therefore the hydrogen addition is preferable. 

The second issue is the pollutants produced. Basically at the high temperatures in the flame oxygen combines with nitrogen in the air (N2) or in with ammonia related species producing nitrous oxide (NOx). This is a toxic gas that can turn into acid rain in the environment or react with hydrocarbons in the air forming smog. It was clear that ammonia combustion produces a lot of nitrous oxide more than a hydrocarbon flame. One study demonstrated the highly toxic compound hydrogen cyanide could also be formed in parts per million concentration, which needs to be avoided at all cost. 

There was quite a lot of work on the chemistry of ammonia combustion highlighting in particular the importance of the OH chemistry. As well as considering the impact of pressure and flame structure.

The most interesting idea was the use of MILD combustion methods to reduce the emission of NOx. MILD combustion is a highly efficient flame-less form of combustion that preheats the inlet air and fuel so they they homogeneously combust in the reactor. It can increase efficiencies of furnaces by up to 30%. It is a form of low-temperature combustion that was mentioned in the previous section. A video of a furnace switch to the MILD combustion mode can be seen here.

For a real in-depth look at how MILD combustion works here is a section from a very informative lecture.

At the symposium a cyclonic reactor running in a MILD combustion mode was demonstrated allowing for significant reductions of NOx with water addition.

The conference was excellently put together, however, the online format did not capture the buzz that you have with an international conference with everyone in the same place and timezone. I also missed catching up with friends after the conference. Hopefully, the conference in two years will be in person.

Information overload in research

In academia, knowledge is stored in a variety of locations. These traditionally include, books, journal articles, lectures, conference talks and abstracts. There are now a huge number of other locations to find knowledge including websites, YouTube videos, preprint servers, blogs, audiobooks, massive open online courses, lecture notes online, online repositories, GitHub and many more.

All of these sources can lead to information overload for academics. It can seem like a never-ending stream of new information. Another issue is that we are bombarded by so much other non-academic information that it's easy to get information fatigue and the thought of reading papers on top becomes challenging. 

This blog post is about how I process the information I receive as an academic and how I reduce the amount of unnecessary information I'm exposed to so that I don't get overloaded. I will try to explain how I developed my own methods so that instead of trying to emulate them you can see the sort of decisions I made and decide for yourself how best to streamline your information channels. This is intended for those who are in research but I am sure some of the insights will be applicable for those in other information-heavy jobs.

Why do I prioritise reading the literature?

Although it can be a lot of work, I do prioritise reading the literature from my field. I personally enjoy this, which helps me stay motivated to keep up to date with new publications. Do you get a buzz out of finding out new information? While it can be difficult to dedicate time to this, the feeling of learning something important can motivate us to prioritise the literature. 

Another significant reason I prioritise reading literature is that I am lazy and the thought of starting a project, writing it into a paper and then realising that someone else has done the exact same thing drives a lot of my reading. There is too much reinvention of the wheel in research. In some ways, it is helpful to be able to demonstrate reproducibility and rarely will two people do exactly the same work. However, more often than not we repeat experiments to death and waste our time and others' resources.

There is a trap that if we see something attempted in literature and it does not yield the result we were expecting, we can think that it is not worth trying ourselves. Basically, we get stuck in ways of thinking that we never challenge. The antidote for this, I think, is reading more widely, especially looking just outside the boundaries of your field. I find if I do this instead of limiting my views they are broadened. Another antidote is not taking any one piece of information too seriously but waiting to see whether data is reproduced in different configurations. This is important for both positive and negative hypotheses. So a healthy bit of skepticism is needed and willingness to try something out you think might work.

Finally, reading the literature gives me lots of ideas. You may be familiar with the post-academic conference feeling of having so many ideas. A good conference exposes you to a wide range of interesting insights that broaden your view of the field and other topics. If you are constantly reading the literature then you will do better research and be able to understand how it fits more broadly into the literature, which will help to get your insights seen by a wider audience. 

Where to start?

When you approach a new topic it is often hard to know where to start with the literature. Here are some tips I have found useful: 

• Textbooks are a good place to start. Head to the library and pick up some books. Find an approach to the topic that fits with your background and carefully read that book, make notes, do some of the examples. I quite like trying to plot some of the figures in the book in python to really prove to myself that I have understood the concepts.
• Talk to people from that field. Look online - are there any free conferences/courses you can attend. Are there any workshops with recorded lectures. Can you attend a course in the department? You can usually sit at the back and audit the course. Attending a conference in person is very helpful for getting to know the cutting-edge research.
• Find out who are the leading groups in the field. Look at their website. See if they have any YouTube lectures. Which conferences do they attend? What have they published recently? How do they talk about other groups' work? 
• Theses are often very good places to start. Read theses written in your group or department. Most theses are available electronically on university library websites.
• Can you find a review paper on the topic or related topics? Review papers can be a bit hit-and-miss. There are roughly two types of review papers: those written by junior academics with minimal input from a senior academic and those that are written with input from someone who has spent their whole career in the field. It is pretty easy to tell. Another good sign is if many senior academics have come together to author a review. I will only read the really good reviews in full. As with the textbooks make notes and try to reproduce the information. Review articles are very good for finding the big questions in the field and setting future research directions.
• Don't just stop with Google Scholar. Microsoft has a search engine, CORE is for open source papers, US federal science has lots of reports and presentations that you will not find on google, PubMed is good for biology and medicine, Semantic Scholar is designed to get the most important papers in a field, JSTOR is also good for older sources. 
• Your library will have a nice search engine that you should look at also. Libraries have great resources like interlibrary loans that let you get some of the most recent books into your library to read for a small fee. Libraries will also have courses on research, referencing and software to use and I thoroughly recommend getting this training. 
• The internetarchive is a great resource with many older books available online for free. They also host the waybackmachine which can show you websites from a previous time. This can be very helpful for tracking down academics that have since retired or moved to other institutes.
• Look at the references in the introduction of journal papers. In many fields, there will be a set of papers that are always cited. These are usually quite a good place to start. What are the big questions in this field at the moment and what are the seminal papers? 
• Some education journals are very helpful at explaining complex topics with simple examples that have been developed with students in mind. Sometimes I find helpful insights from these education journals like Journal of Chemical Education.
• I usually consider whether the journal has a good community reviewing the content. Often an unrelated journal will let a paper be published that a more domain-specific journal would have allowed. I take this into account when I read a paper. You can also look at how people cite and talk about a paper to see how it is viewed in the community. Conferences are also good at seeing how results and values are interpreted. It is important to remember that the peer review process is not foolproof yet the scientific community goes to a lot of effort to make sure rigorous work is done. I recommend following some of the scandals around paper mills and lack of replication as a warning of what not to do.

Here is a funny article on how to read scientific papers and this article in The Conversation is quite good as well. 

Information pipelines

One helpful approach is thinking about your information flows. This will help with the consolidation and archiving of information into searchable content. Below is a drawing of my information flows. 

I make use of an RSS feed server called feedly.com to get the titles and abstracts of papers and blogs that I can then decide whether I want to read. I also get Google Scholar alerts for specific keywords and authors that I am following. 

For all of the papers I want to read I will download their PDF into a folder on Dropbox. From there Mendeley automatically searches through the document and extracts the bibliography information. I also hand prepare a bibtex file when I am writing papers, in the typesetting software LaTeX. For LaTeX I use Overleaf, an online LaTeXserver that lets you collaborate on papers together with others. I used to have a folder system to sort papers but I found this unhelpful. 

There is lots of information that does not fit into the category of easily downloadable, for example websites and YouTube lectures. For these examples I have a Google document written like a journal entry. I always start the new day at the top of the Google document and then add in the URL and perhaps a picture into the document with some notes. This acts as my online lab book. 

For more intense activities such as the writing of a review paper, I will make use of a Google slide. This allows me to include references to papers through a URL to the paper online. This allows for a better aggregation of figures and charts that are difficult in a normal document. I also find the slides easier to move around when trying to sort out the order of the review narrative. 

Another information pipeline that I find very helpful is following the papers that are referenced in a paper I enjoyed reading. What papers do they cite and value? I often like to check whether the referenced paper really says what the authors are claiming. Are they overstepping its claims to support their hypothesis? I find it helpful to talk to others about what they thought about a paper and what shortcomings they could see.

I have tried many different software packages and options such as Evernote, Word documents, hand writing out notes and Microsoft OneNote. The important thing is to find a set of tools that you want to use and avoid overcomplicating things. The use of online software like Google docs and Dropbox greatly simplified my information flows as I could access them from anywhere.

It is important to regularly reassess this information flow. How resilient is it? I recently had my iPad stolen at an airport. All of my notes were saved automatically to Dropbox, however, my handwritten notes on my iPad were lost. After this, I set up automatic archiving of my handwritten notes through the Notability app. Another question to ask is how many times do you deal with the same piece of information without actually reading it? Can you reduce this by automating or simplifying your process? 

Reducing distractions and removing barriers

Reading and processing information is hard. I find myself getting distracted or not being able to start because it is hard to start. Here are some tips I use: 

• Get a website blocker on your computer. I use the Chrome plugin BlockSite. Add your social media and news sites. Without blocking software I get nothing done. To keep social media separate I recommend software that can aggregate all of your social media channels such as Rambox. This keeps your emails and family Whatsapp group out of your work and also helps you not to miss anything. I have do not disturb enabled on my phone during the day so that I am not distracted by emails, messages, etc. I have also culled most social media apps from my phone. 
• Use a timekeeping approach to focus and take regular breaks. The approach I use is the Pomodoro technique with 25 minutes of focused work with a 5 minute break to follow. This helps to avoid decision paralysis where you have too many things to read/do. I find that writing down a task and doing it for 25 minutes without distractions helps me to get started. I use the website Pomodoro. I also only check my emails and news during my break. 
• Use the text-to-speech add-ons in Chrome or on the iPad to read out the paper for you. I find this helps me when I am feeling lazy. Often after having it read out to me for a few minutes I can concentrate enough to finish reading it without highlighting a paragraph and having it read out.
• Read things on a tablet or a e-reader. Reading in a comfortable chair with a tablet is more attractive than reading on my laptop screen. Using the iPad with the pen input also allows quick annotation. 
• Get together with friends to read things e.g. journal clubs. This forces you to read the paper and process it by explaining it to others. 
• If you have an idea during reading a paper write it down and then carry on reading. 
• See if your university allows you to use a VPN. This can sometimes avoid having to log in to download the paper for every single paper. This speeds up the process with academic papers.
• If I cannot access a paper, I usually head to ResearchGate and see if they have uploaded a preprint. Sometimes the university library will require the authors to archive their paper preprint. If all else fails I will email the corresponding author. I have yet to have someone reject my request. 
• I regularly trim the RSS feeds that are not useful and unneeded.

Particular insights for the chemical sciences

As this is my area of expertise I thought I would explain some tips for reviewing the literature within the physical chemistry subfield of chemical sciences.

• Don't know the name of a molecule? Use the chemspider structure search. Alternatively, you can build the molecule in MarvinSketch or Avogadro and view molecule properties or search for IUPAC name. 
• There are often many names for the same molecule so try them all in search engines. Often different fields will use different naming e.g. nanographenes, pericondensed aromatics, carbon flakes etc. Also try reaction classes or general naming strategies for the structures you are interested in e.g. aromatic, aliphatic, arynes etc.
• There are a number of databases of chemical information that are worth checking out (see the review of these from my colleague Angiras Menon). Some of my favourites are PubChem, https://cccbdb.nist.gov/, protein database and Cambridge Crystallography Database.
• Search for software on GitHub; there are lots of very helpful packages. Academic websites also include code that is free to use. 
• Many journals and governments require data associated with journal articles to be archived in open repositories. It is worth looking for input files or data before measuring/calculating it yourself. 

What about news and social media?

I am undecided about the role of social media. I have found ResearchGate and LinkedIn most helpful for connecting me with researchers and research. However Twitter, Facebook and Instagram I have found more distracting. I know quite a few academics who share their new papers on Twitter and journals as well but I find the mix of work and personal uncomfortable.

The news media is a little easier. I like catching up on the news. Often it can be helpful in understanding trends in government spending that will directly impact me as a researcher and it is important to be well rounded in my knowledge. I have tried to balance my news so as not to become polarised by it. I find media bias charts to be helpful in getting multiple perspectives on an issue. However, I have made it difficult to access news on my desktop computer as it is more distracting than helpful. 

For specific science news sites e.g. PhysOrg, ScienceDaily I will pull the RSS feed into Feedly to get articles that might be interesting. I also find Scientific American, National Geographic, Chemistry World, The Conversation, Education in Chemistry and C&EN to be good sources of general knowledge about science topics.

Information flow as a publisher of research

As an academic, we are not just readers of information but we are also publishers and therefore there is another important aspect of considering how your research can be most effectively communicated. This means putting yourself in the shoes of a researcher interested in your topic and thinking about how to make your insights accessible. Journal articles are still considered the highest quality output that has been vetted by your academic community but after this, it is important to consider how you communicate that research through your groups website, talks, conferences, press releases etc. However, this is a conversation for another blog post.