Maximum combustion pressure and exhaust temperature are a very important indicator for knowing the engine combustion conditions and the changes with elapse of time
A decrease in engine performance will be indicated by the following
- Reduction in maximum combustion pressure
- Abnormal Increase in exhaust Temperatur
Maximum combustion pressure(Pmax)
- Pmax of an engine is determined by the load fuel quality, fuel temperature, and viscosity, air intake temperature, fuel pump timing.
- Measurement of Pmax should be carried out at least ones for every 250 running hrs or within the recommended time interval on the manufacturer's instruction.
Precaution
- Pmax should be measured after warming up of the engine and when the load is stable
- The measured value can change due to the fluctuation of load, in that case, perform the measurements again
- Wear proper PPE as handling very hot objects
Measuring Pmax
- Open indicator valve and close after releasing after 1 or 2 times this confirms that indicator valve is not chocked
- Install the Pmax indicator on the valve and secure it by turning the lock valve
- Close the exhaust valve of the Pmax indicator.
- Open the indicator valve.
- Check the reading of the Pmax indicator.
- Close the indicator valve.
- Open the exhaust valve and then confirm the Pmax pressure to be zero.
- Remove the indicator after loosening the lock nut.
Ideal limits
Ideal Pmax difference between cylinder should be within 0.6mpa or less or whatever is specified in the manual
Reason for lower Pmax
- Leaky exhaust valve (due to wear down, incorrect lapping, etc).
- Exhaust valve opening too early, incorrect tappet clearance.
- Leak through piston ring (Broken, worn out, wrong piston ring clearances, etc).
- Worn cylinder liner.
- Worn piston crown.
- Low boost air pressure or temperature.
- Poor fuel quality or wrong fuel pump timing.
Reason for higher Pmax
- Exhaust valve opening too late due to incorrect tappet clearance.
- Overload of the engine.
- Wrong fuel pump timing.
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