Engineering in Kenya

Mechanical Fuel Injection

Posted by on Feb 16, 2018 in Mechanical Engineering | 0 comments


Fuel injection is a system which involves mixing of fuel with air in the internal combustion engine; Mechanical Fuel Injection (MFI) refers to the metering functions of the fuel injection. The design of the system and the calibration has been made specifically for the types of the fuel the system handles. The most common fuel injection systems are those for gasoline and diesel. Recent technology has brought about electronic fuel injection; however, the two systems function in the similar manner. Engineering in Kenya has more articles. 

Mechanical Fuel Injection Mechanical Fuel Injection

Mechanical Fuel Injection

How Mechanical Fuel Injection System Operates

 There has been a variety of the injection systems that have existed since the introduction of the internal combustion engine. Fuel injection works by atomizing the fuel by pumping the fuel through a small nozzle under high pressure. Whatever the design it is, fuel injection systems have the same principle. This system is a precursor of the modern electronic fuel injection developed by Bosch. It one of the most complicated fuel delivery systems to be ever created.

The Mechanical Fuel Injection consist of two major parts namely the injection/distribution pump and the throttle bodies. The electric fuel pump is usually located on the front of the car. It supplies the injection pump with fuel at a high pressure. The distributor is said to function as a heart to the system. It is therefore responsible for metering and supplying fuel to each cylinder.

The fuel consists of two parts, fuel assembly and the compensating unit. The fuel assembly is responsible for the actual delivery of fuel to each of the cylinders. The compensating unit is responsible for adjusting the fuel delivery to the levels set by the accelerator and the speed of engine.

The Mechanical Fuel Injection system happens to be used mostly by diesel cars. Here, a time injection is absolutely paramount. The advantage of this system is that the fuel delivery is metered by the rpm of the engine. This implies that the system supplies the cylinders with fuel in a more precise and aggressive manner than the carburetors. The design of the system is closed with nonvented fuel supply.

The emissions are also better by far than the carburetors. The system has a very high injection pressure, greater than the recent electronic fuel injection system. Fuel is usually squirted out of the injectors at a remarkably high 220-250psi. The high pressure results from the atomization of the fuel. This in turn increases the surface area of the mixture. The results are a more efficient and complete burn of the fuel.

The Principle behind the Mechanical Fuel Injection

The main goal of all fuel injection system is to supply the proper mixture of air and fuel to the engine. The MFI system is not an exceptional. It uses the injection pump to coordinate the amount of delivery of the fuel. Airflow into the cylinder is regulated by the velocity stacks and the throttle bodies mounted on the top of the heads. In many ways, this system combines the principles of the modern fuel injection systems with those of the traditional carburetors.

For example, the Mechanical Fuel Injection uses the asset of throttle bodies to regulate the airflow intake into the system. The main goal of the fuel injection is to balance air fuel mixture. Therefore, they must be properly synchronized with the fuel pump. Also the linkage rods must be aligned properly. The length of the connecting rod must be set exactly at 114 +/- 0.2 millimeters from the ball center to make the system function appropriately. The rods usually connect the pump regulator lever and the cross shaft.

Identifying problems in the Mechanical Fuel Injection

When looking for the problems in any of the fuel injection system, one should check the air cleaner for any blockages and clogs. Appropriate and even compression for all cylinders should be checked. More so, the spark plugs should be examined to check for any deposits.

The dwell angle should also be checked of the points. Check and set ignition timing, fuel pressure and flow the injectors.  Regular inspection for dirt and any build up should be done. Also one should check the injection timing and synchronization with the engine crankshaft.

One should also measure and adjust the system linkage arms for their proper correlation to the pump. Lastly, Mechanical engineers should   also to perform an emission test to check carbon monoxide levels at idle and under load from the Mechanical Fuel Injection.

 

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