biogas, decentralization, and the car of the future

Hello Internet. It's been a while. I want to get back to writing again and feel like I might as well start with something light - I'm on my way back from the factory via Hong Kong (like I said, it's been a while - I'll explain later) and I'm currently pondering yet again whether I'll ever get a chance to own a classic Toyota Crown Comfort - aka the iconic Hong Kong taxicab.

There is so much to love about these cars - I think they have incredibly cool proportions and a hard-boiled pragmatism that reflects everything I love about technology. I was obsessed by the silhouette at first, but the last time I was in Hong Kong, I took a taxicab driven by a skilled older cabbie and realized that Hong Kong taxis can move. The torque curve of the Crown Comfort is gorgeous - it peaks at 2400 rpm, so it pulls like a bat outta hell in the city, despite its low nominal 108 HP. As I was going down the rabbit hole, I realized that the Crown Comforts I've been in all run on LPG (liquefied petroleum gas, a mix of propane and butane - very similar to the propane tanks you buy at the hardware store) - I'd seen the LPG tag under the badgeplate but never thought much of it.

In actuality, the LPG fueling of these cars is a bit of genius urban policy by the HK government. Apparently, in the late 90s, Hong Kong was in an air quality crisis that was exacerbated by the diesel engines of the ubiquitous Crown Comfort, so they instituted a policy of zero taxation for LPG and started running government LPG fuel depots. This meant that cab drivers switched right away - because LPG is much cleaner burning than gas, air quality in HK meaningfully improved!

One of my objections to owning a new internal combustion vehicle, no matter how cool, was the fact that I believe that gasoline-powered technology takes us further and further from the world I want - the complex and fragile process of efficient gasoline extraction¹ from crude oil makes us dependent on centralized, subsidized systems of production that exert implicit control over every aspect of our lives. As a freedom-loving american, I hate the idea that my iconic 1989 Honda Hawk GT could be rendered unusable by OPEC, BP, the American government, or anyone else's management or mismanagement of their crude oil reserves, refineries, pipelines, or anything else. Late-stage capitalism frequently results in market absurdities that we have to pretend are normal (cf. ....) and I don't want to keep investing in a world of dependence.

LPG, however, was totally unfamilar to me - I had no idea how it was refined or processed, and it turns out that it's a simpler refining process than gasoline, though still completely infeasible for decentralized production. Importing a Crown Comfort is blessedly straightforward, but I had no idea how I'd fuel it - a cursory search revealed no LPG fueling stations in the five boroughs. Converting it to gas would be very doable, but there are aspects of LPG (clean-burning, good for longevity) that feel like they define the character of the car. The LPG system itself is not so different from gas - changing ECU programming for ignition timing and updating the fueling system and tank are very straightforward to me. I was curious whether there were any other fuels that could be made on a small scale, by decentralized networks.

It turns out there is an obvious next step from LPG - biogas. Biogas is produced by fermentation, specifically the conversion of organic matter to methane and carbon dioxide by anaerobic bacteria (methanogens) under anaerobic conditions. It's totally doable at home with food scraps, and reminds me in nature of the efficiency of rocket mass heaters - twigs and odds and ends, burned with complete combustion², delivering reliable heat year round. Conveniently, one of the main factors in biogas production consistency is temperature - keeping a biogas reactor at an even 37 degrees celsius is key to yield from the reaction. I'm imagining a rocket mass heater with a programmable heat exchanger attached to it - when the reactor needs thermal energy, the heat exchanger allows heat to flow towards it from the thermal mass attached to the rocket mass heater. Biogas gives something like 18-19 MPGe - my gut says 60 miles/day of range would be amazing, and you can easily get that quantity with a 20 liter bioreactor setup. That might actually be setting our sights too low - I can imagine a society where the handful of internal combustion engines around run off of biofuel / electric hybrids³.

A biogas conversion for an internal combustion car is dependent on the fueling system the same way an LPG conversion is. New ECU programming, new fueling system, and you've got a very different relationship to fuel and the environment with the same inherent watchmaker's beauty that all internal combustion engines have. It would be amazing to make my Crown Comfort into a biogas / electric hybrid art project - the car of the past can be the car of the future.

To be clear about my framing, this is a thought exercise and a potential art project, not an idea borne of pragmatism or need. Writing this has been a delightful 15 minutes - I'm sure it's riddled with errors but I'll quit while I'm still having fun and get back to work. If you want to tell me all the reasons my biogas/hybrid Crown Comfort is a great / terrible / baffling idea, please email me or @ me on Twitter, Bluesky, or Mastodon. Sending love, the future doesn't have to be bleak!

-- Bert