Bosch created the Diesel fuel injector in 1920 as a response to rising fuel demands and prices. Since the introduction of fuel injection in vehicles, the speed and acceleration of many have exaggerated making improvements in technology have made engines more fuel efficient, effective, and-created higher horsepower. This technology, although updated, is used in both diesel and gasoline engines today.
What is a Fuel Injector?
A fuel injector is a device for atomizing and injecting fuel into an internal combustion engine. The injector atomizes the fuel and forces it directly into the combustion chamber at the precise point in the combustion cycle. Newer injectors can also meter the amount of fuel as dictated and controlled by the electronic control module (ECM). Gasoline fuel injectors now act as an alternative to a carburetor, in which an air-fuel mixture is drawn in by the vacuum created by the downward stroke of the piston.
Typically, Diesel fuel injectors are mounted in the engine head with a tip inside the combustion chamber, hole size, number of holes, and spray angles can vary from engine to engine.
Gasoline injectors may be mounted in the intake manifold (multi-port injection, throttle body, or more recently directly into the combustion chamber (GDI).
Why do we Need Fuel Injectors?
Fuel injectors are necessary engine components because:
· The working principle of internal combustion engines dictates that the better the quality of fuel-air mixture will result in better combustion which, provides higher engine efficiency and lower emissions.
· The inefficient air-fuel mixing provided by carburetors leaves various un-burned particles inside the combustion chamber of an internal combustion engine. This leads to improper propagation of combustion flame due to a malfunction known as "knocking", as well as higher emissions.
· The unburned fuel in the form of carbon or un-burned gases and particles inside the combustion chamber negatively affects the efficiency (mileage), and emissions of the vehicle. To avoid this, upgraded fuel injection technology has become essential.
Types of Fuel Injectors
The advancement in fuel injection technologies gave rise to various fuel injection arrangements such as throttle body fuel injection, multi-point fuel injection, sequential fuel injection and direct injection that is varied according to the application.
On the Basics of Fuel Injection
There are 2 types of fuel injectors:
1. Diesel Fuel Injectors
Modern diesel fuel injectors are used to atomize and inject or spray diesel (which is heavier fuel than gasoline) directly into the combustion chamber of the diesel engine for compression ignition (no spark plugs).
Diesel fuel injectors require much higher injection pressure (up to 30,000 psi) than gasoline injectors as diesel is heavier than gasoline, and it takes much higher pressure to atomize the fuel.
2. Gasoline Fuel Injectors
Gasoline fuel injectors are used to inject or spray gasoline directly (GDI) or through intake manifold (multi-port) or throttle body into the combustion chamber for combustion which is ignited by spark.
The design of gasoline injectors varies by type… the newer GDI injectors use a multi holed nozzle, the multi-port and throttle body use a pointless style nozzle. Gasoline injection pressures are much lower than Diesel…3000 psi for GDI and 35 psi for Pinter style.
Basics of Fuel Metering - Injectors
There are 2 types of fuel metering (controlling duration of injection quantity, pressure, and timing of the fuel) fuel injectors. Modern engines have up to 5 injection events in every combustion cycle… to capitalize on efficiency and emissions reduction.
1. Mechanically Controlled Fuel Injectors
Mechanical fuel injectors in which the control of the fuel speed, quantity, timing, and pressure is done mechanically with the use of springs and plungers. These parts take the input from the cam or fuel injection pump.
2. Electronically Controlled Fuel Injectors
These fuel injectors are electronically controlled when it comes to fuel quantity, pressure, and timing. The electronic solenoid takes the input from electronic control module (ECM) of the vehicle.
Construction of Fuel Injectors
The simplified design of a fuel injector resembles a garden hose nozzle which is used to spray water over the ground grass. The same purpose is fulfilled by a fuel injector, but the difference is instead of water, fuel is atomized and "sprayed" inside the engine, making its way to the combustion chamber.
Let us understand the construction and operation of a fuel injector by looking at both mechanically controlled and electronically controlled fuel injectors.
Mechanically Controlled Fuel Injector
Mechanically controlled fuel injectors are comprised of the following parts:
· Injector body-The outer body or "shell" inside which all the other parts of an injector are arranged. The inside of the injector body is to hold a precisely designed capillary or passage through which the highly pressurized fuel from the fuel pump can flow for atomization and injection.
· Plunger - A plunger may be used in the fuel injector which is used to open or close the nozzle under the action of fuel pressure. It is governed by the combination of springs and shims.
· Springs - One or Two springs are used inside the mechanically controlled fuel injectors. They are:
1. Plunger spring- The to-and-fro movement of the plunger is controlled by the plunger spring which compresses due to increased fuel pressure. When the fuel pressure inside the fuel injector increases to a point that is higher than the preset spring/shim combination, the needle in the nozzle lifts, fuel is atomized and injected, as the pressure decreases, the nozzle closes.
2. Main spring- The main spring is used to control the injection opening pressure. The main spring operates against the action of fuel pressure provided by the fuel pump.
Electronically Controlled Fuel Injector
This is a "smart" type of fuel injector which is controlled electronically by the electronic control module (ECM)of the engine which is also known as brain of modern engines.
Electronically controlled fuel injectors consist of the following parts:
· Injector body- Same as the mechanically controlled fuel injector the body of this type of injector is a precisely designed hollow shell inside which all the other components are arranged.
· Plunger- Same as the mechanically controlled fuel injector a plunger may be used for the opening and closing of the nozzle but in electronically controlled fuel injectors the opening of the nozzle is controlled electronically with the help of electromagnets or solenoids.
· Spring - Same as the mechanically controlled fuel injector a plunger spring is used to hold the plunger in its position until injection pressure is obtained, then to close the nozzle of the fuel injector when required.
· Electromagnets - Unlike mechanically controlled fuel injectors, this type of injector is equipped with electromagnets or solenoids around the plunger which control the opening of the nozzle. This is done by taking the electronic signal from the electronic control module of the engine through the electronic connection connecting the fuel injector with the electronic control module of the engine.
· Electronic plug/connection- An electronically controlled fuel injector has a connector through which the electronic signal from the ECM of the engine is transferred to the injectors. This opens the nozzle to spray the fuel.