What Factors are Causing the Decrease in Compression Ratio of Diesel Generator

Aug. 14, 2023

What is the compression ratio of a diesel engine? Regardless of whether the equipment is equipped with a gasoline or diesel engine, maintaining a stable and appropriate compression ratio is essential to ensure smooth and stable operation of the diesel engine. The compression ratio of a general diesel engine is immutable, as the combustion chamber volume and cylinder working volume are fixed parameters that have been determined in the design. So what will be the impact of a decrease in compression ratio for diesel generators?

 

The compression ratio is the ratio of the total cylinder volume of a diesel generator set to the combustion chamber volume. Its variation not only affects the power and economy of the generator set, but also affects its starting performance. In the design, each diesel generator set is specified with a compression ratio, but in use, due to various related factors, its compression ratio often decreases.


What Factors are Causing the Decrease in Compression Ratio of Diesel Generator

 

1.The position of the piston at the end of compression is low.

(1) The clearance between relevant parts is too large. When the clearance between the crankshaft main bearing and the main journal, the connecting rod bearing and the connecting rod journal, the connecting rod bushing and the piston pin, or the piston pin and the pin seat hole is too large, during the compression process, it often causes the actual position of the top dead center of the piston to move downwards, resulting in a decrease in the compression ratio. Therefore, during repairs, these fit gaps should be controlled within the allowable range.

 

⑵ Relevant parts are deformed or have extremely poor main dimensions. For example, when grinding the crankshaft connecting rod journal, the eccentricity is not adjusted properly, resulting in a smaller turning radius of the crankshaft after grinding; The bending of the connecting rod shortens the center distance between the large and small end holes of the connecting rod; The piston pin seat hole is misaligned, which shortens the distance from the centerline of the piston pin seat hole to the piston top plane. These factors can cause the piston to move down at the top dead center of compression, resulting in a decrease in compression ratio. Therefore, in the repair process, operating standards should be followed to ensure the quality of the repair; At the same time, do not forget to check when replacing parts, and do not replace or install unqualified parts by mistake. The contents to be checked during replacement include: the turning radius of the crankshaft, the center distance between the large and small end holes of the connecting rod, the distance from the center line of the piston pin seat hole to the piston top plane, and the distance between the upper plane of the engine body and the center line of the main bearing seat hole.

 

2. The combustion chamber volume is too large.

(1) The valve and valve seat are severely worn, and the valve sinking is too large (even exceeding the limit value). At this point, the valve and seat ring should be replaced.

 

(2) The thickness of the cylinder gasket exceeds the design requirements, or the thickness of the cylinder gasket is artificially increased. At this point, replace the cylinder gasket that meets the requirements.

(3)The concave pit at the top of the piston (a component of the combustion chamber) is burned or damaged, or the wrong part is replaced, resulting in an excessive volume of the concave pit (which can be checked by water injection comparison method). At this point, qualified pistons should be replaced.

 

The swirl chamber on the cylinder head is burnt, or the quality is unqualified, and the volume is too large (it can be checked by water injection comparison method). At this point, a qualified cylinder head should be replaced.

 

The above is the reason for the decrease in compression ratio of diesel generating sets, hoping to be helpful to everyone. If you would like to learn more about diesel generators, please feel free to contact us via email at: dingbo@dieselgeneratortech.com .


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