December 2, 2023

The Fall of the Carburetor

In the early days of the internal combustion engine, its carburetor was the component that supplied energy to an engine. For many other machines like lawnmowers or chainsaws, the carburetor is still used. As the automobile developed, the carburetor got more complex in its attempt to manage all demands of operation. For example, in order to manage certain tasks, the carburetors were equipped with five distinct circuits:

  • Main circuit – Offers the fuel needed for fuel-efficient cruises
  • An idle circuit provides only enough gas to allow the motor to run
  • Accelerator Pump – Gives an additional boost of gas when the accelerator first released, which reduces hesitation before the engine starts to accelerate.
  • The power enhancement circuit – Boosts the fuel when a car is climbing a hill and towing trailers
  • Choke – Boosts the amount of gas when an engine gets cold to ensure it can begin

To meet the higher standards for emissions, catalytic converters were developed to meet the stricter emission requirements. The control of the ratio of air to fuel was essential to ensure that the converter would be efficient. Oxygen sensors measure the amount of oxygen present in the exhaust. The Engine Control Unit (ECU) utilizes this information to alter the air-to-fuel ratio at a real-time rate. This is referred to as controlled by a closed loop, and it wasn’t feasible to accomplish this type of control using carburetors. It was only a short phase of electronically controlled carburetors prior to when fuel injection systems were introduced however, these electronic carbs were more complex than mechanical ones.

In the beginning the carburetors were replaced by the throttle body’s fuel-injection systems (also called single-point or central fuel injection systems) that integrated electronically controlled fuel injection valves inside the body of throttle. They were basically an alternative to bolt-in the carburetor. Therefore, automakers did not have to make major modifications to their engine designs.

In the course of time, as new engines were created and developed, the throttle body fuel injector was replaced with multi-port fuel injectors (also referred to as portmulti-point or sequential fuel injection). These systems feature one fuel injector per engine, typically located in a way that they can spray directly to an intake valve. These systems give more precise fuel metering as well as faster response.

When You Step on the Gas

The gas pedal of your vehicle connects with the throttle valve — it’s the valve that controls the amount of air that enters the engine. The gas pedal actually functions as an air pump.

A partially open throttle valve

When you get on the gas pedal, the throttle valve is opened and allows the air in. It is the engine’s control unit (ECU the computer that manages all the electronic components in your vehicle) “sees” the throttle valve as open and raises the rate of fuel consumption in anticipation of a greater flow of air into the engine. It is essential to boost the rate of fuel when the throttle valve opens; otherwise, as the throttle is initially hit, there could be a hesitation because some air gets into the cylinders, but not enough fuel.

Sensors track the amount of air that enters the engine and the amount of oxygen that is in the exhaust. The ECU makes use of this data to refine the flow of fuel so that the ratio of fuel to air is at the right level.

The Injector

An injector for fuel is an electronic controlled valve that is electronically controlled. It is fed with pressurized fuel from the fuel pump inside your vehicle. It can be opened and closed several times per second.

Inside a fuel injector

If the injector is powered it is activated. An electromagnet triggers a plunger, which opens the valve, allowing pressurized fuel to flow through a small nozzle. The nozzle is made to create atoms of the fuel to create the most fine mist possible, so that it will burn efficiently.

A fuel injector firing

Fuel quantity that is supplied into the motor is determined by length of time that the fuel injector is open. This is known as”the the pulse width and will be managed by the ECU.

Fuel injectors are mounted on the intake manifolds of the engine.

The injectors are placed inside the intake manifold so they can spray fuel directly into those intake valves. A pipe known as”the the fuel rail is used to supply fuel under pressure to all injectors.

In this image, you can see three injectors. This is the fuel rail, on the left.

To provide the appropriate amount of fuel to the engine, it has a number of sensors. Let’s look at the most important ones.

Engine Sensors

To ensure that you get the appropriate amount of fuel for each operating situation, the engine control unit (ECU) is required to keep track of the input of a multitude of sensors. Here are some examples:

  • The sensor for airflow mass informs the ECU the amount of air flowing into the engine
  • Oxygen sensor(s) – It monitors the amount oxygen in the exhaust so that the ECU will know the amount of lean or richness it is that the mix of gasoline, and adjust accordingly.
  • The throttle position sensor The sensor monitors the position of the throttle valve (which determines the amount of air that is injected through the motor) to ensure that the ECU will respond rapidly to changes in the situation, raising or decreasing the rate of fuel consumption as required.
  • Temperature sensor for the coolant This sensor allows the ECU to detect the time when the engine is at the proper operating temperature
  • Voltage sensor is used to monitor the system voltage inside the car, so that the ECU can increase the idle speed in case voltage drops (which indicates a large electrical load)
  • Manifold Absolute Pressure Sensor is used to monitor the pressure of air that is in the intake manifold
  • The quantity of air in the engine is an excellent indicator of how much power it produces; The more air flows through the intakes, the less manifold pressure. Therefore, this is a good way to measure the amount of power that is being produced.
  • Sensor for engine speed monitors engine speed and can be one of the elements that determine the pulse width

There are two types of controls used in multiple-port systems The fuel injectors could all be opened simultaneously, or they can each be opened just prior to the intake valve of the cylinder is opened (this is referred to as simultaneous multi-port fuel injector).

The benefit for sequential fuel injections is, if the driver is making a sudden modification, the system will respond faster since when you make the modification it will wait till the valve for intake opens instead of waiting for the next complete turn of the motor.


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