Combustion Engines are the first area of exploration for most DIY minds. There are lots of fuels to be used out there, and some of them can even be produced in your backyard, garden, or compost heap. The Internal Combustion Engine or ICE is what currently powers the world from cars to planes to trains. Steam and Stirling engines are External Combustion engines, which are an alternative engine type to the ICE.

The Internal Combustion Engine has an interesting history with human transportation. Most often these engines are powered by fossil fuels, but this was not always the case, and most certainly, it is not the only option in todays modern ICE. Many renewable fuels abound including biomass derived methane, ethanol or butanol, biodeisel, wood or producer gas, and of course, hydrogen. Theses fuels can power an ICE and all of them can be produced at home, but the real question in using an ICE-powered vehicle is “what are you using the vehicle for?”.

Converting an ICE to a renewable fuel can be easy or difficult, depending on the new fuel, the old fuel, the system components and the eventual use of the vehicles. Different fuels contain different amounts of energy and storage can pose problems, especially with gaseous fuels.

The main trade offs with home-produced biofuels are vehicle conversion vs fuel conversion. Ethanol is easy to make, but require extensive conversions to your vehicle, including replacing fuel lines, modifying your ignition timing, and possibly compression ratios to get the most power out of the fuel. Butanol, on the other hand, is a direct replacement for gasoline, and requires very little modification to the vehicle, however, it is difficult to produce, and requires intensive distillation and water separation methods. Wood gas is a viable option, but requires a heavy gas producer on board the vehicle, although your engine does not require much modification. Biodeseil requires a small refinery, including handling questionable substances, like methanol. Hydrogen requires extensive engine system modification plus producing and storing the gas in significant quantities is difficult.

The main thing about ICE conversions to remember is that there is no silver bullet. If there was, we would all be driving renewable-fueled vehicles. The best approach is to figure out what sort of vehicle you need for a specific task and find the fuel that best matches that task. A work tractor on a farm rarely goes beyond the farms property line, so a vehicle conversion system is then viable. Wood gas or methane would be a good application. A vehicle to take long trips needs to be able to run on gasoline as well, so butanol might be the better option here.

Some vehicles produced today are “flex-fuel” vehicles, meaning they can run on many types of fuels, including biofuels. These systems are really beyond the DIYer at this point, however, as they become widespread, more information will become available.

Replacing fossil fuels can be tricky, but it can also be done. Focusing on the vehicle's operation requirements will solve most issues upfront and eliminate unsuitable candidates.