Requirements of Fuel Injection System | Full Details.

T(caps)o run an engine, the fuel from the tank must reach by some means the engine cylinder. der. In a diesel engine, the fuel is Injected into the engine cylinder by an injector. The fuel burns in the cylinder and during the exhaust stroke, the burned gases leave the cylinder passing through the exhaust pipe and silencer.

Requirements of Fuel Injection System 

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In this article, I will discuss the requirements of the fuel injection system. 

Requirements of fuel injection system-

A fuel injection system is an essential component of an internal combustion engine that delivers fuel to the engine's cylinders. However, in the 1980s, the carburetor began to lose popularity, and it was eventually replaced by fuel injection systems. The carburetor was a critical component of gasoline-powered internal combustion engines for most of the 20th century. It mixed air and fuel in the right proportions and delivered the fuel to the engine's cylinders for combustion. Here are some examples of the requirements of the fuel injection system. 

Fuel injection system Requirements- 

The fuel injection system must be able to deliver the correct amount of fuel to the engine based on its operating conditions, including engine speed and load. The fuel injection system is a precise system over the traditional carburetor system. If the engine is to develop full power and operates efficiently, its fuel system must do the following :

1. Mete(Measure)- 

The fuel injection system must measure the fuel supplied to the engine very accurately since fuel requirements vary greatly from low to high engine speed. Fuel is measured within the injection pump or injector by ensuring it as it fills the pumping chamber (inlet metering) or as it leaves the pumping element (outlet metering). Although many variations of these two concepts exist, the basic principles have changed very little.

2. Time- 

The timing of fuel injected into the cylinder is very important during engine starting, full load, and high-speed operation. Diesel engines start best when fuel is injected at or very close to the top dead center (TDC) since it is at this point that air in the chamber is the hottest. After the engine is started and running at high speed, the injection timing may have to be advanced to compensate for injection lag, ignition lag, and other factors that influence combustion within the engine cylinder.

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Many modem injection pumps have an automatic timing device built into them that automatically changes the timing as the engine speed changes. These devices have been given names by their manufacturers, such as automatic advance, speed advance, intravance, and many others. Their major purpose is the varying fuel injection timing to produce a powerful yet efficient engine.

3. Pressurize- 

The fuel system must pressurize the fuel to open the injection nozzle (a spring-loaded valve) or the pressure required to open the nozzle. Some pressure is required to inject fuel into the combustion chamber to offset the pressure of compression, which may be 250 to 320 N/cm. 

The pressure setting of the injection nozzle or injector tip is directly related to the degree of atomization required. As the fuel is pumped through the holes in the tip (multihole type nozzle) or around the pintle (pintle type nozzle) at high pressure, 1050 to 2800 N/cm, atomization occurs. This atomization can be compared to the atomization that occurs when you attach a spray nozzle to the end of a garden hose.

4. Atomize(Breaking-up of fuel into small particles)-

The fuel must be atomized when it is injected into the combustion chamber since anatomized fuel will not bum easily. The degree of atomization required will vary from engine to engine depending on the combustion chamber design. Consider the following examples:

Fuel atomize process.

1. A pre-combustion engine will require very little atomization since the fuel is injected into the pre­ chamber first and then into the main combustion chamber. In most pre-chamber engines, the fuel is heated in the pre-chamber to start burning; as it burns, the resulting expansion forces it through a passageway into the main chamber. The turbulence created by the rapidly burning and expanding fuel help mix and fuel for complete combustion. Therefore, a high degree of atomization is not required during the initial injection. 
2. A direct injection engine relies solely on the atomization of fuel during injection and piston crown design to mix air and fuel for combustion. This engine design will obviously require a higher degree of atomization if complete combustion is to occur. A multihole-type nozzle tip is generally used with this combustion chamber design.

5. Distribute- 

Closely related to timing, the distribution of fuel must be accurate and according to the firing order. Distributor pumps deliver fuel to each pump outlet in succession and the lines are hooked to the cylinders in the correct firing order, much like a distributor used on a gas engine. In-line pumps have the camshaft designed to permit the pump outlets to fire in the required firing order. Along with distributing the fuel to the various cylinders, the fuel system must distribute the fuel within the combustion chamber during the initial injection.

Read more- Differences between four-stroke and two-stroke. 

The fuel must be injected throughout the chamber so that all of the air within the chamber is utilized. The requirement is fulfilled by the injection nozzle or injector, its hole size, and its angle.

6. Control, start and stop injection- 

Injection of fuel must start quickly and end quickly. Any delay, in the beginning, will alter the pump-to-engine timing, causing hard starting and poor running engines.

Any delay in injection ending can cause a smoky exhaust and irregular exhaust sound. The end of the injection should be instantaneous with no dribbling or secondary injections. In many systems, this is accomplished by a valve called a delivery valve or retraction valve. Other pumps have a camshaft designed with a sharp drop on the cam lobe that stops injection very rapidly.

Conclusion- 

In conclusion, fuel injection systems offer significant advantages over carburetors, including improved fuel economy, better engine performance, reduced emissions, easy starting, better control, reduced maintenance, and compatibility with modern engines. While the carburetor played a crucial role in the development of the gasoline-powered engine, fuel injection systems have become the standard in modern engines, providing better overall performance and efficiency.