Cylinder pressure graph recorded from the engine in a good condition:
The yellow graph is the control current of the fuel injector of the tested cylinder.
The blue graph is the pressure graph in this cylinder.
The white dotted line shows what the pressure graph would look like if no fuel was supplied to the cylinder.
The peak pressure in the cylinder reached 48 Bar. The pressure in the cylinder gradually increased as the fuel burned.
- Section 1. First pre-injection of fuel
- Section 2. Second pre-injection of fuel
- Section 3. Third main fuel injection
This section of the graph is the main one. It determines the completeness of fuel combustion and the energy released.
The influence of washer thickness (Seating areas) under the injector on the diesel fuel combustion process
- The sealing washer under the injector is either absent or the seating area has been excessively machined
The flame of sprayed fuel is outside the mixture formation zone, fuel particles fall on the walls of the combustion chamber in the piston, not the entire mixture ignites, but the evaporated fuel residues from the walls of the combustion chamber ignite when the piston goes down and, accordingly, the pressure created in the cylinder is less, the efficiency of the working cycle is less with the same amount of fuel.
- One sealing washer under the injector (Normal)
According to the waveform, we observe the peak of ignition of the air-fuel mixture after TDC. This is the correct signal.
- Two sealing washers under the injector
When using thicker washers in the cylinder, very late ignition occurs of a small part of the injected fuel.
When two washers are installed, the fuel flame does not enter the combustion chamber.
Some of the fuel gets into the above-piston space, exactly where there is no oxygen, and the efficiency of the diesel engine decreases several times.
The pressure graph in the cylinder at the moment of ignition of the fuel mixture depends on many factors:
- Engine temperature
- Compression ratio
- Compression
- Valve timing
- Conformity of the spray flame to the original (in case of using non-original injectors or installed sprayers)
- Fuel spray quality
- Correct positioning of the spray nozzle in the combustion chamber both along the injector axis (correct thickness of the washers under the injectors and correct geometry of the seat) and along the radius (in case of inclined injectors relative to the cylinder axis and no positioning of the injector in the cylinder head)
- Conformity of the ECU control pulses, which depend on the correct coding of the injectors in conjunction with the ECU and, in some engines, adaptations of the injectors with the ECU
- Condition of the electrical part (wiring, connector)
