Glenn Curtiss and his contemporaries made gasoline engines practical for motor vehicles and aircraft. Source: Glenn H. Curtiss Museum
With all the hoopla about electric vehicles and "carbon neutral" fuels lately, it brings up the question of why gasoline and diesel became the dominant fuel choices for mobile power plants in the first place. There, of course, have always been alternatives. Everything from coal to spermacetti oil have been tried in the past.
Two canards are worth disposing of right away: the inertia and conspiracy arguments.
The inertia argument goes something like this: "We use gasoline and diesel fuel for light trucks and passenger vehicles because that's what we've always used." This idea has appeal only to those who know nothing about early automobile development. From roughly 1890 through as late as 1920, enthusiastic inventors tried to use essentially every kind of engine and every available fuel to produce a commercially viable horseless carriage. The only ones that proved technically and commercially viable were powered by gasoline or diesel fuel. Everything else flopped for one reason or another, and most alternative fuel vehicles flopped for technical reasons related to their engines.
The conspiracy argument (Isn't there always a conspiracy theory?) holds that big oil companies, like Standard Oil, persued nefarious means to sabotage development of any vehicles that ran on anything but the gasoline and diesel fuel they supplied. While corporate leaders in the early 20th Century would gleefully have engaged in such behavior, they just weren't up to it. First, their companies didn't carry that much clout until the boom in automobile transportation - powered by gasoline and diesel engines - grew them into the giants we recall. Second, no amount of chicanery can make a winner out of a clearly technically inferior solution.
That's an important point to keep in mind.
The reasons gasoline and diesel became dominant fuels are simple and technical: power, weight, and storage/handling.
As students of aviation development know quite well, the Otto-cycle piston engine powered by gasoline has an enormous power-to-weight advantage over every other engine type in the sub-500 HP range, with diesel engines running a close second. The only engine type that beats them today is the Brayton-cycle turbine engine. (No, not the "turbocharged" or "turbo" engine, which is really a hotted up piston engine!) Technical issues involving manufacturing make turbine engines smaller than about 500 HP hard to justify, and 500 HP is rediculous overkill for a passenger car or light truck.
Airplanes proved impossible until Glenn Curtiss and his contemporaries made gasoline engines practical. The same power/weight advantages make these engines technically superior for passenger cars and light trucks as well. (Note that Curtiss started out making engines for racing motorcycles and only later adapted them to aircraft.)
Storage and handling make gasoline and diesel fuels technically superior as well. They are both non-volatile liquids, meaning that if you pour them out into an open container, they'll hang around for a useful length of time. Though gasoline will evaporate on the time scale of minutes to hours (depending on the container's geometry), that's long enough to run it through an engine and extract the energy locked inside. Diesel will hang around even longer.
Methane, propane, butane, and the mixture commonly known as natural gas must be kept pressurized or they'll have an instant escape. The same, by the way, goes for hydrogen, which has a host of additional issues. Gasoline and diesel fuel's low volatility makes designing, building, and maintaining in-vehicle fuel storage systems relatively cheap and easy. The skills involved are those of any Medieval Gypsy tinker, not those of a modern refrigeration specialist.
Another storage advantage gasoline and diesel fuel have is the amount of energy packed into every gram of mass and liter of volume. Ten gallons of gasoline, which weighs a mere 60 lb, is enough to push a four-passenger car weighing over a ton a couple of hundred miles without stopping.
This, of course, is the Achilles' heel of electric vehicles. While electricity, being pure energy, takes up no space and has no weight, the equipment needed to safely contain the stuff in quantities practical for motor transportation very definitely takes up large quantities of space and has enormous weight.
"But," you say, "those arguments hold quite well for that darling of the alternative fuels community, alcohol."
What messed up the works for alcohol at the dawn of the 20th Century, and haunts it still today, is the fact that the stuff doesn't occur naturally. Until humans figured out how to harness the sugar-munching-and-alcohol-pooping potential of microbes, alcohol simply did not exist in useful quantities. Fossil oil, on the other hand, occurs in oceanic quantities just below the surface of the Earth's crust. Not only is it laying around practically everywhere, but it's just dying to get out. One of the biggest technical problems for those whose life's work is to get the stuff out of the ground and into your tank is keeping it from spraying out all over the place before they have a chance to capture it in a pipe.
True, the stuff that comes out of the ground won't burn in your engine without some refining. That process, however, mainly involves heating it until the oversize molecules jiggle apart into smaller units, which are easy to separate and grade into various useful fractions - which include gasoline and fuel oil.
Alcohol, on the other hand, is a whole lot more expensive to produce. It is so expensive that nobody has found a way make it economically feasible for motor fuel. The same goes for other alternative fuels. The folks who advocate hydrogen for use as a fuel, for example, have to deal with this disadvantage as well.
Basically, we've disposed of pretty much all alternatives to gasoline and diesel fuel for motor vehicles. What makes the alternatives unable to compete with them are the same things that made our ancestors choose them in the first place. They're simply the best choice by far among many alternatives.
No matter how committed the Obama Administration is, and how politically charged the debate about climate change becomes, alternative fuels just won't displace gasoline and diesel as motor fuels as long as the latter is readily available. It's like King Canute commanding the tide to stay out. All he accomplished was getting his feet wet.
Yes, alternatives will win out eventually, but not until we use up the available fossil fuels. And that will take many decades, yet.
