Funcionamiento de la inyección de combustible DIESEL


The Injection Pump is a major component of the diesel engine fuel system and there are many components on diesel engine fuel system A device that pumps fuel (diesel) and injects it into the engine combustion chamber, with very high-pressure and truly precise timing also quantity. The performance of diesel engine is heavily influenced by the injection system. Traditionally, an injection pump is driven indirectly from crankshaft by gears, chains or toothed belts (often referred to as a timing belt) that also drives the camshaft of injection pump.It rotates at half crankshaft speed in a convensional four stroke diesel engine. its timing is such that the fuel is injected only very slightly before top dead point (top dead centre) of the cylinder compression stroke.

Convensional Injection Pump has two kinds of type such as In Line type and Distributor type. No matter what kind of product it is, the most important part is the pump. In line injection pump use an in line construction on plunggers arrangement which mean each cylinder of the engine is served by one plunger, that’s why this type is widely used large-powered engines or heavy vehicles such as buses and trucks. Distrubutor type uses rotary works system, one plunger works to injects fuel into all cylinders of engine. This type is commonly used in light and medium engines / vehicles.

1. In Line Type Injection Pump

A. Pumping Fuel

There is Camshaft in a pictuure above, it driven by the engine via timer gear that connected to the crankshaft. The Camshaft rotates at the same speed as the engine camshaft speed, speed of camshaft is half of the crankshaft speed.

Then there is tappets with rollers sit over the cam lobes. The number of tappets equals the number of engine cylinders. It push the plunger in charge of pumping the fuel into the combustion chamber. Above each tappet, plunger return springs are placed to the plungers in returning to the bottom dead centre (bottom dead point) after each stroke.

Plunger asssmbly consists of Plunger, Barrel, Driving Face, Feed Hole and Control Groove (Helix). The plunger is guided inside the barrel where the fuel is pressurized, plunger has vertical groove and helical groove that assist in varying the fuel quantity, The driving face is driven by control sleeve in regulating the amount of fuel delivered to the injector unit.

Before the fuel that’s pumped at high pressure by the plunger entering the injector (nozzle), it passes the delivery valve first. The Delivery Valve serves to keep the fuel pressure in fuel injection hose fixed. Thit can happen because the valve spring in the delivery valve holder pushed the relief when the plunger stops pumping.

B. Adjusting the amount of fuel

It has been explained that the plunger can adjust the injected fuel by the works of control sleeve. How can the control sleeve move?

At the front end of the Injection pump camshaft, there is a timer gear as the initial driver of the components in the injection pump. At the other end there is a device called as Governor, serves to adjust the engine speed according to the load on the mchine.

Governor works following the rotation that occurs on the machine (via the camshaft),if the rotation of engine is too slow the govrnor will automatically push the control rack forward, this makes the plunger delivers more fuel to the combustion chamber. And if the engine speed is too fast the governor will automatically push the control rack backwards so that the fuel distribution becomes reduced.

The governor pushes the control rack and finally the control rack moves the plunger by the control sleeve that connects both.

2. Distributor type Injection Pump

A. Pumping Fuel

The camshaft (drive shaft) rotates The Camplate (Camdisk) which has special groove/shape on the bottom The camplate sits on the timer roller so it can move back and forth while rotating. The rotating camplate moves the plunger to pump and distribute the fuel to all cylinders in turn.

Inside the plunger barrel (into a set with the plunger, this set is called the rotor head) there are several holes with the same number of cylinders of the machine. These holes serve as the fuel distribution lines, at the end of the holes are the delivery valves attached in the holders.

B. Adjusting the Amount of Fuel

The fuel quantity that’s injected by the plunger, is governed by a control sleeve (control spool) which is driven by a governor lever sub assy. To avoid overrunning on the machine, the sliding sleeve on the flyweight sub assy will push the governor to reduce fuel distribution when the engine spins at high speed.

There are several parts on governor working system :
* Flyweight sub assy
* Sliding sleeve
* Tension lever
* Starting lever
* Control sleeve (control spool)
* Starting spring
* Governor spring
* Idle spring
* Retaining pin

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