An attempt to make a step change improvement in the thermodynamic performance of Stirling engines.
As the year ends I want to lay out my motivations for one of two projects I’m now committing regular time and effort towards. If these motivations pique your interest then please reach out! The shortest pitch for this project is - If you had a shot at bringing a step change improvement in thermodynamic performance into the world, could you really turn it down? But maybe that’s not convincing enough, so let me further elaborate and hopefully by the end you’ll understand why I’m excited about this project and the the potential impact that’s at stake.
Some who and what before getting to why
A cold email back in February is how I first got involved with this project. While researching biochar - a sort of super-fertilizer and potential climate mitigation solution, I reached out to the author of an extremely well written piece on the subject. At the end of my call with Austin he asked if I wanted to hear about an invention he’d been working on that had even bigger climate implications. Now if you spend any time with Austin you’ll quickly realize just how smart he is. So the invitation to learn more was a no-brainer.
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Austin’s invention is a new version of a Stirling engine. These are external combustion engines that can convert a temperature difference into mechanical work or vice versa. Toy versions operate off just the difference between the warmth of your hand and your surroundings. In commercial applications they’ve found a home in cryogenic refrigeration (i.e. storing COVID vaccines). There aren’t many use cases between the hobbyist toy engines and the niche refrigeration solutions for various reasons that I’ll touch on below. What’s important however is that Austin’s version, if it works, should significantly increase the performance of this engine cycle bringing it much closer to its theoretical optimum. To learn more about what exactly that means as well as the history of these engines, I suggest going through some of these videos and articles I’ve curated as I’ve built up my own understanding over the past few months.
Useful Stirling engine explanations:
Video explanation from Phillips on their engine design - Part 1 and Part 2
At this point you might be thinking - You and a stranger you met online want to improve a technology that can at best said to be a small niche within refrigeration? And it’s a technology that's historically been left by the wayside? And neither of you have relevant degrees or experience in engine development? What could possibly be compelling about working on this? It’s compelling because the answer to all those questions is yes. If you’re trying to make a step change improvement as we are, these feel like the right conditions under which such a feat can take place. But to be less tongue in cheek, here’s the case for why this project is worth anyone’s time and energy.
Be a part of the fourth most impactful climate solution
The world is expected to have approximately 3 times as many air conditioning units in 2050 compared to today. That’s around 3.6 billion units that have yet to be made, not accounting for all those that will have to be replaced. Current air conditioning technology makes heavy use of low boiling point substances called refrigerants in what’s known as the vapor compression cycle. The most common refrigerants are all 1,500 to 4,000 times worse in terms of how much warming they cause when compared to CO2 (called global warming potential). That’s why Project Drawdown, the comprehensive source for climate solutions, lists refrigerant management and disposal as its fourth most impactful solution.
While our technology doesn’t help with management or disposal, it could replace vapor compression cycle based units with heat pumps based on the Stirling cycle. This would remove the need for refrigerants in all the air conditioning units that have yet to be made. In addition, there’s a very real likelihood that if our technology works that it would also be much cheaper due to the performance gains provided by more closely approximating the ideal Stirling cycle. So while today the application of Stirling engines is limited to cryogenic refrigeration, a much improved version could move “up temperature” towards the larger industries of air conditioning and commercial refrigeration. And that starts to make things quite interesting from both a climate mitigation and business value perspective.
Flipping unturned stones with new technology is all the rage
Technological development is path dependent which means there are always forks in the road that are never visited. Research into Stirling engines peaked in the 1960s when companies like Phillips were looking into using them for tube-type radios and as an alternative to internal combustion engines (ICEs) for transportation. But transistor based radios came into existence and ICEs always had the advantage of being able to shift power levels quickly so resources flowed towards those technologies. The other problem is that Stirling engines are quite difficult to create at both the design and assembly phases. Especially in the era before computer simulation and advanced manufacturing processes. So competing technologies which offered more immediately valuable trade-offs received support. By the time modern techniques were available the world had already moved on from further exploring Stirling engines. Until now.
Climate change changes the equation on what features we want or don’t want from technologies such as engines and heat pumps. Refrigerants are bad, and so are fossil fuel based ICEs. Equally important is that we now have modern tools and techniques that were unimaginable 60 years ago. Looking back at paths not taken armed with new constraints (no emissions) and new capabilities (CNC lasers) can lead to new opportunities. Consider the company Turntide - the idea for synchronous reluctance motors existed for decades but only recently have we made enough advances in computer controlled servos and software to bring the concept to life (with potential for great success). Times change and what was once impossible can very easily become quite feasible - it’s worth it to find out.
This Stirling engine project is a combination of revisiting a well known concept with modern methods along with also having new modifications to the design itself. It's exciting to revisit an old fork in the road to answer the question of what happens if we choose the other route? And that’s because the nature of path dependency implies we aren’t always on the “best” path today. When you combine that knowledge with the aforementioned new constraints and capabilities, the appeal of chasing down these unexplored paths only grows. Who knows what awaits us, but the journey itself it exhilarating.
There's a sense of identity in being the outsiders
The question of experience vs. new perspectives comes up in almost every field. Experts become entrenched in their ways while newcomers are oblivious to things that are obvious to the veterans. In the case of Stirling engines, the remaining experts have seemingly stopped pushing forwards (remaining is a loaded term as most of them are in their 70s and 80s). Back in 2016 Austin tried to present his ideas to Allan Organ, a preeminent professor in the field, only to be dismissed before he even got a chance to show his work. Organ said he had given up and that there was no point to trying anything new.
And maybe the experts are right. Maybe it’s a technology that has some promise yet is ultimately impractical. They do have the expertise after all. But what if they’re wrong? Or at least what if they’ve overlooked things that Austin and I won’t because we don’t have years of failed attempts rattling around our brains? Taking on the experts and looking to prove them wrong provides surprisingly strong motivation to forge ahead. You can build culture around going against the prevailing view - just look at SpaceX and reusable rockets. Persevering where others have given up is a powerful elixir. The probability that we succeed might be low. The path to finding out is surely going to be hard. But it’s in that struggle that real bonds are built and your identity is shaped. We’re coming to this problem knowing what obstacles we have to hurdle but unencumbered by the weight of previous disappointment. Good conditions for pouring in time and energy.
If it doesn’t work, oh well, but if it does, oh boy
Zooming out a little, the broader point worth emphasizing is that if we can deliver even 50% of our hypothesized performance gains, it’s still a step change improvement for heat engines. And heat engines are the workhorses of the modern world. Processes as varied as water desalination and thermal energy storage would all be possible applications for this technology. It’s all at stake but obviously depends on whether or not theory translates into reality. Friction, heat bleeding, and many other factors will all chip away at our idealized vision for performance. On the use case side while so many opportunities do exist, each market has its own nuances and we won’t have unlimited resources to explore each and every one. Working on this project feels equal parts unbelievable and equal parts unsurmountable. Which is what makes it so compelling. Even if the likelihood of success is less than 1%, the upside is staggering while the downside is just our time and some initial capital for building a prototype. It’s hard to decline such a seemingly imbalanced set of outcomes.
Where are we now and where are we going?
So hopefully the motivations and incentives to work on this project are a bit more clear. Those are the most important factors for me when committing to any project. Everything else is something to iterate upon while keeping the end objectives in sight. Given that motivations are set, our focus is now shifting towards taking this from a hypothesis in our heads to hardware in our hands.
The goal for the upcoming months is to create a detailed 3D model of the engine and start machining the component parts required for a small scale prototype. We need to answer for ourselves whether or not the working principles Austin has theorized will work in practice. Second to that is building up contacts in industries where even a rough version of the engine could still win market share. If we have a prototype that demonstrates a pathway towards our hypothesized performance gains within the next year, we’ll then be able to start turning those contacts into customers.
If you’ve made it all the way here and are curious to get involved or learn more, reach out to Austin or me! There are so many opportunities out there but for all the reasons above this one should deserve some attention. We’re pushing forwards with our plans and eager to work with new people who bring experience or enthusiasm for the goals I’ve laid out.
Berkana is the ancient Norse word for birch tree. It can be said to represent a fresh new perspective or rebirth. Appropriate for the spirit of this project.
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