If the goal is anything-but-diesel-or-gasoline/petrol, the use of propane (a fossil fuel that is a byproduct of oil and gas refining) is a well-understood, well-implemented practice. I am not advocating for propane as a primary solution, but rather as part of the journey towards truly clean vehicle emissions and the ramp-down of heavily polluting fossil fuel refining. Propane and the equipment to operate engines with it are available today, and we have the knowledge going back over a century to implement it successfully.
BTW, I wish I could find the article from the 1970s discussing how Ford Motor Company engineers had converted a brand-new 1960s Lincoln to propane and ran it with 100% synthetic motor oil, never changing the oil or filter. After 500,000 miles of daily use, they stripped the engine down to its parts and found it to be shiny and not exhibiting the expected amount of wear seen in usual engines of those years with much lower mileage. I'd have to pour through old magazines for that story, but life gets in the way, so let's treat my recollection as apocryphal.
There isn't any point to propane now. Electric busses got good enough to do the job. Propane reduces pollution, but the goal is to reduce CO2 emissions. Buying propane means buying electric in decade or two.
A local airport shuttle service converted some of their vans to propane. They told me the benefit is that they go about 3-4x longer between oil changes. (I suspect they aren't brave enough to go 500,000 miles.)
LPG had its chance here in Australia in the 2000's, but it didn't work out [1]. Subsidised conversions were offered back then, which many people took up on their 80's+90's model cars, but it probably led to the early demise of many of those cars. By the late 2000's there were factory cars selling with LPG "gas" systems, but they weren't as good as the petrol variants [2]. By 2011 you could get "liquid injection" models, which were as good [3]. But like the first article states, people with "large" cars were shifting to SUV's and dual cabs by that stage, and a lot of them were 4cyl petrol/petrol-turbo/hybrid/turbo-diesel, so their fuel efficiency was comparatively decent.
Also in 2011, the government introduced fuel-tax on to LPG, which it had been exempt/discounted on previously. So the price went up, and all of a sudden it wasn't as economical. So that put it in to a death-spiral, especially when many servo's started getting rid of it due to low demand. Now people with LPG cars have "range anxiety" [4]. Where I live (Perth, Western Australia), you are basically stuck in the metro area if you are LPG only. It also means there's a ton of ~2008-2012 LPG Falcons for sale second-hand at good price, but no one wants to buy them.
Out of curiosity, I just went and looked up some data for where I live - the Perth metro (source [5]);
If the goal is anything-but-diesel-or-gasoline/petrol, the use of propane (a fossil fuel that is a byproduct of oil and gas refining) is a well-understood, well-implemented practice. I am not advocating for propane as a primary solution, but rather as part of the journey towards truly clean vehicle emissions and the ramp-down of heavily polluting fossil fuel refining. Propane and the equipment to operate engines with it are available today, and we have the knowledge going back over a century to implement it successfully.
BTW, I wish I could find the article from the 1970s discussing how Ford Motor Company engineers had converted a brand-new 1960s Lincoln to propane and ran it with 100% synthetic motor oil, never changing the oil or filter. After 500,000 miles of daily use, they stripped the engine down to its parts and found it to be shiny and not exhibiting the expected amount of wear seen in usual engines of those years with much lower mileage. I'd have to pour through old magazines for that story, but life gets in the way, so let's treat my recollection as apocryphal.