The compression ratio is the ratio of the total cylinder volume and the combustion chamber volume of the diesel engine, and its change not only affects the power and economy of the diesel engine, but also affects its starting performance. In the design of each diesel engine has stipulated a good compression ratio, but in use, due to the influence of various related factors, its compression ratio is often reduced. The main reasons for the reduction of compression ratio and some problems that should be paid attention to in the maintenance process are summarized as follows:
First, the position of the piston at the end of compression is low
1, the deformation of the relevant parts or the main size is very poor. For example, when grinding the crankshaft connecting rod journal, the eccentricity is not adjusted properly, so that the crankshaft turning radius after grinding becomes smaller; The connecting rod is bent, so that the center distance between the big and small end holes of the connecting rod is shortened; The distance between the center line of the piston pin seat hole and the top plane of the piston is shortened. These factors will cause the position of the piston to move down at the top dead center of compression and the compression ratio to decrease. Therefore, the operation specification should be observed in the repair to ensure the repair quality; At the same time, do not forget to check when changing parts, and do not change or install unqualified parts by mistake. When replacing parts, the contents should be checked are: crankshaft rotation radius, the center distance of the connecting rod large and small end holes, the distance between the center line of the piston pin seat hole and the top plane of the piston, the distance between the plane of the body and the center line of the main bearing seat hole.
2. The gap between relevant parts is too large. When the clearance between crankshaft main bearing and spindle neck, connecting rod bearing and connecting rod journal, connecting rod bushing and piston pin or piston pin and pin seat hole is too large, the actual position of top dead center of the piston will often be moved down in the compression process, so that the compression ratio will decrease. Therefore, these matching gaps should be controlled within the allowable value range during repair.
Second, the combustion chamber volume is too large
1, the thickness of the cylinder gasket exceeds the design requirements, or artificially increases the thickness of the cylinder gasket. At this time, replace the cylinder gasket that meets the requirements.
2, the valve and valve seat are seriously worn, and the valve subsidence is too large (even exceeding the limit value). The valve and seat ring should be replaced at this time.
3, the top pit of the piston (part of the combustion chamber) ablation defect, or replace the wrong parts, so that the pit volume is too large (can be checked by water injection comparison). At this time, a qualified piston should be replaced.
4. The vortex chamber on the cylinder head is burned, or the quality is unqualified, and the volume is too large (can be checked by water injection comparison). At this time, the qualified cylinder head should be replaced.
It is worth mentioning that among the above factors that lead to the reduction of the compression ratio, often the influence of a single factor is not large, but the influence of multiple factors on the compression ratio is large when they accumulate. As mentioned above, in order to make the compression ratio of the diesel engine can be controlled within the specified range, the key is to improve the repair quality, do a good job of parts repair, measurement and matching work, and choose a small assembly gap as far as possible within the scope of technical requirements. When the diesel engine has difficulty starting, power decline, fuel consumption rise and the cylinder sealing, gas distribution and oil supply are normal, it seems that the cause of the failure can not be found, do not ignore the compression ratio check.
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Post time: Dec-09-2024