Cause of surge
Usually when the supercharger is selected, the compressor matching line is selected at the right side of surge line B according to the operating characteristics of different supercharger systems. At this time, the diesel engine can not only meet the predetermined turbocharging target and the turbocharger working in the high efficiency area, but also ensure that the turbocharger does not surge in the whole working range of the diesel engine.
Therefore, under normal circumstances, generally no surge occurs. But when the working conditions change, such as the blockage of the supercharged system passage, the overload or overload, the uneven load of the diesel engine and the sudden change of the load, the working line will enter the surge zone partially or completely, thus causing surge. Here are some reasons that may cause turbocharger surge. One of the direct consequences of channel blockage in turbocharger is to increase the resistance of air flow in the system. When a diesel engine is running, the gas flow path of the turbocharging system is: compressor inlet filter and muffler compressor impeller compressor diffuser air cooler scavenging box diesel inlet (valve) exhaust pipe exhaust turbine nozzle ring exhaust turbine impeller chimney. The circulation area of each component is fixed. If any part of the flow path is blocked, such as dirt, carbon deposition, deformation and so on, the compressor back pressure will be increased and the flow rate will be reduced, resulting in surge. Among them, the easily dirty parts are compressor inlet filter, compressor impeller and diffuser, air cooler, diesel engine inlet (sweep) and exhaust (valve), exhaust turbine nozzle ring, exhaust turbine impeller. Usually, the obstruction of the turbocharger airflow channel is the main reason for its surge. Management
Regular inspections should be carried out to see if the above-mentioned parts are stained and cleaned so that the resulting surge can be prevented or eliminated.
Diesel engine operating conditions (load, speed) change when the diesel engine runs at low speed and high load. When the diesel engine fails or the ship full load, headwind, dirt bottom makes the external load increase, the speed of the diesel engine decreases, at this time the governor automatically increases the fuel supply, so that the diesel engine runs at low speed and high load. The increase of fuel supply and exhaust gas energy will inevitably lead to the increase of turbocharger speed, compressor exhaust volume and exhaust pressure. At this time, the diesel engine speed is low, less gas consumption, so that the supply and demand balance between the supercharger and diesel engine gas consumption is broken. The compressor's back pressure is increased, and the flow rate is reduced.
When entering the low-temperature sea area, the air density becomes higher because of the lower ambient temperature, the air inlet of the compressor increases, the energy obtained by the turbine increases, the speed of the turbocharger increases, and the surge margin increases, while the surge margin decreases when entering the high-temperature sea area. For some supercharged diesel engines without air cooler matched in the low temperature navigational area, or those with air cooler matched in the high temperature navigational area, when navigating in the low temperature sea area, because of the matching relationship between the two, the operating point is easy to approach the surge area and cause surge.
Fuel injection failure
When the fuel injection system fails and the poor quality heavy oil is used, the post combustion is aggravated and the exhaust temperature is high. No matter the full load or part load, no matter how serious the afterburning, the matching operation point is on the normal matching operation line. With the delay of combustion end point, the exhaust temperature increases, the speed of turbocharger increases, the compressor flow rate increases, the pressure ratio increases, and the surge margin is less when the operating point moves to the height of the curve.
When the cooling capacity of the air cooler decreases, the exhaust temperature of the diesel engine increases, the speed of the compressor increases, and the surge margin decreases when the operating point moves to a higher level.
In a word, the influence factors of Non-Runner blockage will not affect the flow characteristics, will not change the position of turbocharger and diesel engine operating line, only change the position of turbocharger and diesel engine operating point in the line, is the secondary cause of diesel engine turbocharger surge.
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