Understanding Your Car’s Systems: The Fuel System

Vintage car at a country service station.
When I wrote about the powertrain I left a pretty big question unanswered. How does the fuel get into an internal combustion engine?  The answer is one of the most sequential automotive systems; the fuel system. 

The fuel system starts with the filler neck. In its simplest form is a pipe that runs from outside the vehicle, downward, into the top of the fuel tank. Typically it’s closed off at the top by a door attached to the car’s body, a screw-on cap, and a valve that opens by inserting a filler nozzle. It’s also common for the door or cap to lock in order to prevent theft by siphoning, a technique I intend to right about in the future. On my car the fuel door is locked as part of the power door locks. 

The fuel tank is the simplest part of all. It’s just a tank, made of steel or some other material that the fuel won’t corrode, that fills from the top and drains from the bottom. 

Gravity feeds the fuel into the fuel pump, which pressurises the fuel enough for it to reach the engine. Now, this is where things vary. 

Older cars used a device called a carburetor. Fluid dynamics means that by having fast moving air flow directly over the surface of a pool of fuel causes them to mix creating a viable fuel/air mixture. That fuel/air mixture is then sucked into the cylinder. Usually there’s an intake manifold after the carburetor to split the flow to all the cylinders, but multiple carburetors are far from unheard of. If you’re interested in the physics behind the carburetor, look up Bernoulli’s principle.

Most newer cars use a computer controlled system called fuel injection. In this system the fuel is fed into the airflow through atomising nozzles, which create a fine enough mist to produce the needed fuel/air mixture. 

All of these components are interconnected with the fuel lines, a system of corrosion resistant pipes and hoses. A fuel filter is also commonly included somewhere before the carburetor or fuel injectors to remove contaminants from the fuel supply.

If you’re wondering how gas and diesel fuel systems are different, they’re not. Both fuels are thin liquid at even frigid temperatures so their fuel systems work on exactly the same principles. 

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