Carburetor vs Fuel Injection

Most engines need gasoline. But did you know that engines can’t run on gasoline alone? In order for a gas-powered engine to run, air needs to be introduced with the fuel in order to combust when heat is added to the mixture. Fire requires three things: fuel, oxygen, and heat. Typically referred to as a fire triangle, these elements combine together in order to cause a fire. A fourth component, the chemical reaction, is what allows the fire to keep burning. When you remove an element from the fire, whether it’s oxygen or the fuel source, the fire will not be able to survive.

The same concept can be applied to car engines. Whether an engine is powered by a carburetor or fuel injection, the premise behind each is relatively similar as they are both found in internal combustion engines. For internal combustion engines to work, an explosion of sorts must take place within the engine in order to convert the energy and power the vehicle. A mixture of fuel and air is ignited by a spark plug in order to create a small explosion that moves the pistons up and down. The energy created from the pistons is what turns the crankshaft and powers the vehicle. When you’re talking about comparing a carburetor vs fuel injection, it’s important to know that they both serve the same function. Both carburetors and fuel injection have the same end goal, although they operate differently.

Fuel injection has replaced the role of the carburetor in modern vehicles. Although carburetors are more or less obsolete now, some people prefer the simplicity that a carburetor offers in comparison to the more complex electronic fuel injection. Because fuel injection has more moving parts and is more intricate than a carburetor, it’s more difficult to fix if something goes awry. Fixing a carburetor is much simpler than fixing a fuel-injected engine because there aren’t all those electrical components that can easily break. Carburetors in comparison to fuel injection systems are also less expensive to install and cheaper to fix as they are less complex.

What Is a Carburetor?

First developed by Mercedes founder Karl Benz, the carburetor is a tunnel-shaped device for internal combustion engines that disperses a mixture of air and fuel into the cylinders. Some carburetors operate differently, but the general process is the same for most carburetors. While carburetors can be labeled by how many barrels they have — one, two, or four — there are several different types of carburetors. Downdraft, natural or side draft, and updraft are the most common types. These classifications all refer to how the carburetor is positioned. Perhaps the most common style, the downdraft carburetor, consists of filtered air flowing down through the top of the tube. Downdraft carburetors are usually the most popular for American-made vehicles, but side draft carburetors replaced downdraft carbs in Europe as they sit on top of the engine and free up space. A side draft carburetor is located on the side of the engine so the air can flow horizontally in the intake manifold. The updraft design can be seen in older carburetors and consists of air flowing in from the bottom up.

How Does a Carburetor Work?

Carburetors operate using the Bernoulli principle. Daniel Bernoulli, a Dutch-born scientist, developed a principle that states that a rapidly flowing fluid exerts less pressure than a slow-flowing fluid. The Bernoulli effect is all around us. From airplane wings to baseball, this principle is evident in many different applications including carburetors. Carburetors draw in air and fuel into the cylinders using a vacuum created by the engine. Even though air is technically a gas, it can be considered a fluid because it can flow and form different shapes. For a carburetor to function, air is drawn in through a filter through the top of the tube, often referred to as a barrel. Some carburetors have a choke valve at the top of the tube in order to restrict air flow and increase the fuel content. Carburetor chokes can be either manual or electric. Carburetors equipped with manual chokes usually have a lever inside the vehicle that you pull in order to restrict air from flowing in the tube. Electric chokes are automatically controlled and choose the proper airflow without having to manually adjust anything or pull a lever.

Further down in the tube is a narrow section called a venturi. When air travels through the venturi, the lower pressure causes the air to flow faster. Within the venturi is a small hole, known as the jet. The low pressure from the venturi creates a vacuum that pulls in fuel from the jet, which then mixes with the air. The fuel is drawn in from an attached float chamber, which houses the fuel and determines the correct percentage to disperse into the venturi. In this visual depicting how a venturi works, you can see the high-pressure regions in dark blue, which are moving slower than the lower pressure regions illustrated in light blue.

The throttle plate is a butterfly valve at the bottom of the carburetor and controls how much of the air and fuel solution to send into the cylinders at a given time. Controlled by the accelerator pedal, the throttle opens when pressing down and closes when the pressure is released. As the throttle opens, more air and fuel reaches the engine, adding more power and increasing the speed of the vehicle. When the throttle closes, power is reduced as no fuel reaches the cylinder. Because the throttle has to stay open in order to send fuel into the cylinder, idling with a carburetor is a bit more complicated than with a fuel-injected engine. Since the throttle is closed while idling, no gas is able to reach the cylinder. In order to prevent stalling, idle jets send a tiny amount of fuel into the cylinder in order to keep the engine running.

What is Fuel Injection?

As the most common method of powering internal combustion engines, fuel injection has superseded the carburetor. Fuel injection requires higher fuel pressures in order to pump fuel through injector nozzles that atomize the fuel. Atomizing allows the fuel to disperse in a fine mist so it can combine with air in order to combust once a heat source is introduced to the mix. There are three types of fuel injection: direct, ported, and throttle body. Direct fuel injection sprays fuel directly into the combustion chamber, while ported fuel injection sprays the intake manifold outside the valve. When the valve opens, the fuel and air are then released into the combustion chamber. Throttle body fuel injection, while similar to a carburetor, has a separate throttle body with one fuel injector rather than fuel injectors located in each cylinder. The air and fuel mixture in the throttle body then travels through the intake valves and into the cylinders. Some fuel injection is mechanical, while more modern systems are electronic.

How Does Fuel Injection Work?

For electronic fuel injection engines, a fuel pump draws out fuel from the gas tank. The fuel then travels through the fuel lines and is filtered before dispersing to the fuel rail. A fuel pressure regulator maintains the correct pressure of the fuel in relation to the intake pressure. The engine control unit, or ECU, determines how much fuel to release into the cylinders. The ECU controls the pulse width, or the amount of time the fuel injector stays open. In a basic sense, the ECU grounds the injector and closes the circuit, sending current to the solenoid. The magnetic field generated by the solenoid controls the electromagnet attached to the plunger that opens and closes the valve, which is what allows the fuel to be dispersed and thus atomized. In order for the ECU to determine just how much fuel to release, it relies on sensors that relay information including voltage sensors, mass airflow sensors, oxygen sensors, and manifold absolute pressure sensors. For multi-port fuel injection systems, the injectors can either open individually, known as sequential multi-port fuel injection, or all at once. The ECU is also responsible for maintaining the vehicle’s idling speed, typically through electronic throttle control systems.

Diesel engines only use fuel injection to operate. However, instead of adding heat in the form of a spark plug, diesel engines use compression in order to heat up the air. Because the compressed air is so hot, once the atomized fuel is injected, the solution self-ignites. Most diesel engines use direct fuel injection, but some diesel engines are operated by indirect fuel injection.

Carburetor vs Fuel Injection: Which is Better?

If you’re a fan of the newest technology, then you’re definitely going to prefer fuel injection over a carburetor. Carburetors are old school, but that doesn’t mean they aren’t good. Carburetors offer simplicity whereas fuel injection is much more complex. If you’re looking at a classic Mustang or a vintage Chevy C10, chances are that it will have a carburetor installed. Perhaps you have fuel injection but you’d rather convert it back to the tried-and-true carburetor instead. Whatever your preference, find all the parts you need at CJ’s!

Sources:How Electronic Fuel Injection Works, Jalopnik | How a Carburetor Works, Jalopnik | Engine Fuel System, NASA | Beroulli's Principle and the Venturi Tube | Carburetor vs Fuel Injection-A Short History and Pros and Cons, NAPA Know How Blog | Carburetor vs Fuel Injection: Understanding the Pros and Cons, Cars Direct|Image Credit: Wikimedia Commons, General Motors, Porsche, Auto Blog, treehugger.com