Ignition Quality Parameters of Slow Speed Diesel Engine
Ignition quality parameters:
- Maximum firing pressure.
4. Injection delay
5. Ignition delay .
1. Energy comparison
• The injection pump is a volumetric pump
• The higher the density the more energy it contains per volume unit
• The density difference between HFO and MDO is larger than the difference in net calorific value
2. Viscosity comparison
- The viscosity of MDO is lower than the viscosity of HFO (even HFO is heated)
• Lower viscosity fuels result in more internal leakage in the injection pump from the high pressure side to low pressure side.
• Internal leakage has to be compensated by giving more fuel rack
3. Maximum firing pressure
- Dependent on the charge air pressure
• To achieve proper combustion, the firing pressure has to be high and thus also the charge air pressure
• Timing of the fuel pump
4. Injection delay
- Injection delay is the time it takes to build up a pressure higher than the opening pressure of the nozzle.
• Normally 4…5 ° of crank angle
• The delay is comparable to the condition of injection equipment
5. Ignition delay
- is the time gap between the commencement of injection and the commencement of ignition.
- Dependent on the fuel quality
- Compression temperature has a big influence on the ignition delay
- Compression temperature is not high enough for the fuel to ignite longer ignition delay
Besides consider the following for better ignition quality of slow speed diesel engine:
Higher peak pressures and higher exhaust gas temperatures:
• Normally 1…2 ° of crank angle.
• Too early timing of injection
• Higher peak pressure
Exhaust gas temperature after cylinder:
- Measured individually after each cylinder
- Each cylinder has two measuring
- The average temperature of all exhaust temperature sensors is approximately 100 °C lower than the exhaust gas temperature before the turbine.
- Maximum allowed difference between valves in one
- Maximum allowed difference of one cylinders average from the average of the all cylinders ,
- In normal operation the average temperature Cylinder temperature deviation can be up to 30 – 40 °
- Engine is (depending of installation) provided with a safety slow down arrangement if the temperature difference is too big
- A 10 °C increase in ambient temperature will result approximately 15 °C increase in exhaust gas temperature
Exhaust gas temperature after turbocharger:
- Indicates the kinetic energy of the exhaust gases that are running the turbine
- Indicates the condition of the turbo, e. scavenging of the engine
- If a de-Nox catalysator is installed the temperature has to exceed certain level to ensure the function of the catalysator.
Pressure difference over the cylinders:
- Measuring the pressure difference between charge air manifold and exhaust gas
- gives an indication of how well the scavenging works.
- Depends on the turbocharger, therefore values below should be considered as allusive
- The bigger the Dp is the better
- Is normal value with 100% load varies depending of installation once the value has been dropped down, it is an indication that something is wrong with the engine -e.g. dirty nozzle ring & turbine
Written from the news letter of Wartsila.