Measurement of Blowby in a Turbocharger
The purpose with this Masters Thesis was to design a measurement rig for measurement of the blowby flow that originates from the turbocharger in a passenger car engine. A leakage of com-bustion gases and fresh air from the turbine and the compressor into the bearing housing of the turbocharger is the source of the blowby flow. Principally the measurement rig consists of two parts: a flowmeter for measurement of the blowby flow and a separation unit for separation of the blowby gases from the engine oil that is used for the lubrication of the bearings in the turbo-charger. The rig will be connected between the return oil pipe from the turbocharger and the en-gines crankcase and should only be used in engine testcells.
First, an extensive study of different methods for measurement of gas flow and separation of gas and oil was carried out. Methods that best fulfill the set specifications of requirements are chosen to be used in the rig. From the results of the study a conclusion can be made that the best solu-tion is to use a flowmeter specifically made for engine blowby metering with another measure-ment pipe for more accurate measurements. A tank is used for the separation of oil and gas and it functions at the same time as a collecting vessel for the oil. A rack of baffle sheets inside the tank is used as the separation technique. The tank is also equipped with a pump and associated limit switches for controlling the oil level inside the tank. An oil heater is also applied to the tank for heating of the oil while kept in the tank.
Testing of the equipment was executed with an engine in testcells to verify the functionality of the equipment. A test cycle that extended over the engines whole load and speed range was used. Gained results show that the turbocharger blowby follows the same pattern as the total engine blowby. It increases with higher engine load rather than with higher engine speed. It is also pos-sible to confirm that the rig has an influence on the engines blowby system, but also that the size of it is not conclusive to the measurements. A conclusion that the turbocharger blowby should not be measured simultaneously with the engine blowby can be done from the test results.
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