Getting involved with the technical end of the automotive world means there are a lot of things to learn. You’re going to spend time studying engines, transmissions, suspension components, electrical systems, and so forth. But as you dive deeper and deeper, don’t forget to brush up on the basics as well. Something fundamental used in nearly every vehicle is fuel. And sure, you’re familiar with regular ol’ gasoline and diesel, but what about methanol, nitromethane, or ethanol? What are these different types of fuel and what are they used for?
Compression Ratio and Octane Rating
Before diving into the rabbit hole, we need to address another basic: compression and octane ratings. Every internal combustion engine uses compression to its advantage. Compressing fuel and air in the cylinder of an engine makes it react violently enough to push the piston down during the combustion stroke. Raising the compression makes for a more violent explosion and creates more power. And this is where octane ratings come into play.
Low octane fuel is subjected to detonation during compression. This means that if the fuel and air mixture is compressed too much, it can spontaneously combust well before the combustion is meant to take place. The higher the octane of a fuel, the more compression it can take before detonating. This means that the higher a compression ratio an engine has, the higher the octane rating of fuel it will require in order to prevent detonation. Got all that? Okay, good.
Gasoline vs Diesel
One common type of fuel that takes advantage of this concept is diesel. Engines intended to run on diesel don’t use an ignition source like spark plugs to burn the fuel. Instead, they use compression. If you were to compare the compression ratio of a diesel engine and a gasoline engine, you’ll find that diesels run on much tighter compression ratios. This is because they want to ensure they squeeze that fuel so tight that it ignites on its own.
Diesel engines are typically much more durable than gasoline engines and can be found in all types of vehicles. Yes, big trucks and industrial equipment is where you’ll encounter most of these engines dwelling, but they are also subjected to endurance race vehicles and even in some drag vehicles.
In any engine, the goal is to prevent the fuel from igniting before the piston reaches its peak during the compression cycle. With diesel engines, the fuel is ignited by the piston reaching this point. With gasoline powered engines, this piston comes all the way up, compressing the fuel, and then the spark plug ignites the mixture, sending the piston back down to turn the crankshaft.
Again, higher compression warrants higher octane. This is because as the fuel and air are compressed, the temperature will rise, and if the air is too hot, the fuel will ignite. If you own an engine with a compression ratio running 10:1 or less, you can get away with pump gas.
But the closer you get to that number, or even a little over, the better off you are using premium fuel from the pump. For race vehicles using gasoline and high compression, there are many of sources for high-octane gasoline which will be required.
Many race cars run on alternative fuel types. These different types of fuel include nitromethane, ethanol, and even methanol. Ethanol and Methanol may sound similar, but they are derived from two very different sources. Methanol, which is less commonly used, is wood alcohol and ethanol is grain alcohol.
The properties of alcohol allow it to act as extremely high-octane gasoline would. Though, technically speaking, the octane rating cannot be measured. Indy cars, champ cars, and even dirt cars like midgets and sprints have engines with properties that require it.
Nitromethane is a fuel that is used in some of the fastest and most powerful race cars in the world. This is because of the explosive properties of the substance. It’s interesting to note that the compression ratios of cars that use this fuel—like top fuel dragsters—don’t actually have high compression ratios. The engines in these classes are usually around 6:1-7:1. But, they do have massive amounts of boost running through the system, which has a major impact on this area. Often it is also the fuel of choice because it can produce 2.3 times more power than gasoline.
Now that you know a little bit more about the basics of some the different types of fuel out there, let’s address one of the myths about fuel types in engines. If you have a gasoline-powered engine, you may have heard that running higher-octane fuel can increase the amount of power that engine can produce. This isn’t always the case. In fact, running the wrong octanes can be extremely harmful to the internals of an engine. Sure, in some cases, engines run better with higher octanes but that’s really because of the fuel requirements. The best rule of thumb to making any engine run well is to use high-quality fuel that’s within its range.