Answer EKM Question 38

Q38. A set of indicator diagrams cards has been taken for a main diesel engine. Analyze with reference to the following conditions and suggest corrective action in each case: 

a. Higher peak pressure with normal compression pressure. 

b. Normal peak pressure with lower compression pressure. 

c. Higher peak pressure with higher compression pressure. 

d. Normal compression pressure with fluctuating pressure line during expansion stroke after ignition.

Answer: a. Higher peak pressure with normal compression pressure:

Early ignition 

 

Ignition point starts earlier resulting in a higher Pmax, but  Pcom is the same. Exhaust temperatures decrease and it may cause knocking. It is corrected by adjusting the FQS setting for bad quality fuel or injection timings.

b. Normal peak pressure with lower compression pressure.

With the reduction of compression pressure, the peak pressure usually reduces.

But the above observation is a result of combine defects which caused Pcom to reduce but Pmax to kept normal.

A lower pcom is a result of leaking exhaust valve or warn piston rings. While with a lower Pcom getting a normal Pmax is a result of early ignition. 

Corrective actions required are check the exhaust valve leakage, piston rings and liner condition and adjust FQS.

c. Higher peak pressure with higher compression pressure

Observe that the Pcom is high, resulting in a higher Pmax. Ignition point is higher although there is late ignition.

 

d. Normal compression pressure with fluctuating pressure line during expansion stroke after ignition. 

 

Leaky injector or a worn fuel pump. Observe Pcom is same while there is a fluctuating pressure in the expansion stroke after the ignition point. Pmax and power decrease. Injection is done later and smoke increases.