The compression ratio of a diesel engine in a silent diesel generator set is the ratio of the total cylinder volume to the combustion chamber volume. Its change not only affects the power and economy of silent diesel generator set, but also affects its starting performance. Each diesel engine is designed with an optimal compression ratio, but in the process of use, due to the influence of various related factors, the compression ratio of silent diesel generator sets often decreases.
At the end of compression, the piston position is low, and the fit clearance of relevant parts is too large. When the fit clearance of the main bearing and main journal of the crankshaft of the silent diesel generator set, connecting rod bearing and connecting rod journal, connecting rod bushing and piston pin, or piston pin and pin hole is too large. In the compression process of the mute diesel generator set, the actual position of the top dead center of the piston of the mute diesel generator set often moves down, and the compression ratio will decrease. Therefore, during maintenance, these fit gaps should be controlled within the allowable range, and the deformation or main dimensions of the relevant parts are very poor.
When grinding the crankshaft connecting rod journal, the eccentricity is adjusted improperly, and the Radius of gyration of the crankshaft becomes smaller after grinding. The connecting rod of the mute diesel generator set is bent to shorten the Centre-to-centre distance between the connecting rod and the small end hole, and the piston pin hole of the mute diesel generator set is hinged together to shorten the distance between the center line of the piston pin hole and the top surface of the piston. All of these factors will cause the piston to move downwards at the top dead center, resulting in a decrease in compression ratio. During maintenance, the operating procedures shall be followed to ensure the maintenance quality of the silent diesel generator set. At the same time, when replacing parts, do not forget to check, and do not install or replace unqualified parts by mistake. The items to be checked during replacement include the turning radius of the crankshaft of the silent diesel generator set, the Centre-to-centre distance between the big end hole and the small end hole of the connecting rod, the distance between the center line of the piston pin seat hole and the top surface of the piston, and the distance between the plane of the engine body and the center line of the main bearing seat hole.
The swirl chamber of the cylinder head of the quiet diesel generator set is burnt out or unqualified, and the volume is too large. Replace the qualified cylinder head. It is worth mentioning that among the factors that lead to the reduction of compression ratio of low noise diesel generator sets, the influence of single factor is often small, but the influence is greater after the superposition of multiple factors. To control the compression ratio of the diesel engine of the silent diesel generator set within the specified range, the key is to improve the repair quality, do a good job in the repair, measurement and cooperation of parts, and try to select a smaller assembly clearance within the technically permissible range. When the diesel engine of the silent diesel generator set is difficult to start, the power decreases, the fuel consumption increases, and the cylinder seal, gas distribution and oil supply are normal, it seems that the cause of the failure cannot be found, so do not ignore the inspection of the compression ratio.
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