Nozzles
The injectors are the final stage of the diesel injection system. Their job is to inject fuel under high pressure into the swirl chamber. Only if the fuel pressure rises above 125-140 bar, the injector needle rises and lets fuel into the swirl chamber. The high compression force prevents a backlash into the fuel system from the combustion pressure. The cooling and lubrication of the injector needle is provided by the fuel. Since the entire amount of fuel can never be injected, excess fuel is drained back into the tank via the drain pipe mentioned earlier in this chapter.
The specified interval between the start of injection and ignition is only 0.002 s. The smallest inaccuracy leads to major malfunctions. A stuck nozzle needle, for example, results in irregular and excessive fuel supply, poor fuel-air mixing due to incorrect atomization, uncontrolled ignition (with a petrol engine they would talk about knocking). This can cause the engine to run rough and produce noises and knocks similar to those of a faulty bearing.
Knocks
Typical for diesel is a harsh noise during combustion, which can also be heard in trucks. Diesel only knocks loudly when the engine is not warmed up.
The fuel injection advance clutch, which operates for about 3 minutes after the engine is started, is partly to blame for this.
A warmed-up diesel engine sounds almost no different from a petrol engine.
Therefore, it is very unpleasant if knocks appear on a warm engine. The main reason is usually a delay in ignition, that is, too long an interval between the start of injection and the spontaneous ignition of the working mixture. This occurs for the following reasons:
- When the injection start time is shifted;
- If the injector needle is stuck;
- With thickened fuel, for example, summer fuel at low temperatures;
- When the load is too high at low speeds;
- When the compression pressure is too low.
- Sometimes it is useful to clean the engine, for which purpose it is added to the fuel "Autol Desolite" or another suitable additive. High-speed driving on the highway often helps.