This is in relatively good condition — at least from the outside. Nozzle from a BMC engine. Note the smaller pilot hole to squirt fuel onto glowplug and the radial crack through both holes. Nozzle from a BMC engine — other end. The smallest hole bottom right is the fuel feed, the other pair being for dowel pins in the injector body to ensure the pilot jet points in the correct direction.
This valve, as can be seen when compared to those on the right, has worn badly with the end having a much smaller diameter and is tapered. When the injector was tested it squirted a solid jet of fuel — not atomised as it should have been.
When rotated, the tip of the valve was also seen to be bent, a sign of mishandling of the injector outside the engine at some time.
These are a pair of old top and new valves from equivalent nozzles. There are minor differences in design including the new one showing a slight concave curve, possibly to generate a wider spray pattern. The top valve shows little wear.
The injection pump feeds fuel into the injection pressure area in the above diagrams. More wear between valve and nozzle results in higher leakdown. Once the valve starts to lift from its seat there is a rapid drop in pressure in this area leading to more valve lift. The valve shown here is a pintle type which has an end which projects beyond the nozzle body when closed.
This end is of smaller diameter than the higher length and, as it lifts into the nozzle hole when it opens, fuel passes between the pintle and hole. The shape of this end section accelerates the fuel venturi effect and lowers its pressure — working correctly it leads to a very fine atomised spray. A fine atomised spray will ignite much more easily than a jet of liquid and burn more uniformly, producing more power.
The valve stem moves in the nozzle body using fuel as a lubricant. When the nozzle, valve and injector pump are working correctly together, the valve should seal without dribbling then make a rapid transition from closed to open again influenced by the valve shape with a fine mist-like spray. So, to get correct operation, the nozzle and valve must move smoothly, have its correct shape to atomise fuel, be free from carbon and other deposits. Wear will also lead to an increase in leakdown.
Hopefully this can be found from the workshop manual or other documentation but if not, taking the average from the removed injectors before disassembly is better than nothing. Injector holder homemade. Some injectors can be held in the vice by their mounts without damage but sometimes a length of steel with 3 holes injector body and two fixing bolts may be needed to hold the injector while undoing or tightening parts. Testing pump. Ultrasonic cleaner and carburettor cleaner. Some nozzles are the two-piece type, and have a removable center section.
These pieces should be kept together as a set any time the nozzles are removed. The nozzle is also where the fuel is mixed with air to atomize the fuel to make it combustible. See photos 03 and 04 on page On both normally-aspirated and turbocharged configurations, the intake manifold pressure is slightly lower than the pressure in the air bleed chamber of the nozzle, so air is continually drawn through the air bleed into the manifold.
See photo 05, page Most of the time, fuel injection systems operate trouble-free. When a problem occurs in the fuel injection system, it is often intermittent and sometimes can be difficult to pinpoint at first. Rough-running engines are usually fairly straightforward to diagnose. Usually a defect in the ignition system, such as a fouled spark plug or incorrect magneto timing is to blame, but occasionally trouble in the fuel system is the culprit.
Most mechanics start at the nozzles and work their way backward until the source of the trouble is found. Clogged fuel nozzles. When a problem occurs in a fuel injection system, it usually is caused by small pieces of dirt or debris that partially clog a line or injector. If one or more of the nozzles becomes restricted, fuel pressure will increase because the servo keeps sending out the same amount of fuel.
The fuel flow meter in the cockpit displays fuel flow in gallons per hour; but this number is derived from a fuel pressure reading at the flow divider. An increase in fuel flow may be seen on the gage if one or more nozzles are clogged, even though throttle settings remain unchanged. Higher pressure at the divider caused by a clogged nozzle shows up as higher flow rates on the fuel flow meter. An increased fuel flow indication along with a rough-running engine is an indication that one or more nozzles may be partially or fully plugged.
The reason for the roughness is simple; the cylinder with a clogged injector is only getting enough fuel to run intermittently. This can be verified if the aircraft has EGT probes on each cylinder. On the cylinder s with partially clogged nozzles, the exhaust gases will be hotter than other cylinders; evidence that the cylinder is running too lean.
A simple way to check for restrictions flow test each nozzle and line is to remove all the nozzles from the cylinders. After removing the nozzles, reconnect each of them to the correct fuel supply line. Place each nozzle in a small clear cup or jar that is labeled for the corresponding cylinder.
Have someone in the cockpit turn on the master switch and fuel boost pump, with the mixture rich. Slowly advance the throttle from idle to full and back again while someone else observes the output of the nozzles. Each one should have roughly the same flow. Next, remove the jars without spilling any of the fuel. Compare the fuel level of the cups. A partially clogged line or nozzle should have a cup with a lower fuel level than the others. See photos 06, 07 and 08 on page Lycoming Service Instruction C gives instructions on nozzle cleaning.
The nozzle should be cleaned with acetone or MEK and blown out with compressed air. No picks or sharp tools can be used in the discharge hole or it will be deformed. If a particular nozzle or line has a chronic clogging issue and becomes clogged quickly even after cleaning, it may be best to replace both the line and nozzle.
Even though a line or nozzle has been cleaned, microscopic particles or debris often remain and become dislodged with subsequent use, clogging the nozzle once again.
Caution should be used when removing or installing fuel nozzles. The nozzle is screwed into the intake plenum of each cylinder. The plenum is located outside of the cylinder combustion chamber, in the intake manifold preceding the intake valve. The end of the nozzle that threads into the cylinder has fine-tapered pipe threads.
The intake plenum is aluminum and the receiving threads in it are also aluminum. It is very easy to accidentally cross thread or overtighten a nozzle. The aluminum threads in the cylinder are easily damaged if this happens. See photo 09, page Generally, nozzles should be threaded in finger tight, then torqued to 40 to 60 inch-pounds maximum. These features not only affect the combustion characteristics of the diesel engine, they can also affect the stability of the emissions and performance over the lifetime of the engine and the mechanical durability of the injector.
All nozzles must produce a fuel spray that meets the requirements of the performance and emissions goals of the market for which the engine is produced regardless of details of the fuel system design i. Additionally, specific requirements for injection nozzles can also depend on the fuel system type [] :. Then, what is the definition of the injector? In the petrol fuel injection system, the injector acts as a door to spray fuel from fuel lines into the intake manifold.
The injector function is not only a sprayer, but the injector also atomizes the fuel in the intake manifold.
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