Combustion-Engine Wear Studies by a Radioactive Tracer Technique

In the Motor Car Research Institute (ÚVMV) the radiotracer technique is used to study the wear of Škoda combustion engines for passenger cars. In 1960 a laboratory was built for tests with radioisotopes. For five years examinations have been carried out under laboratory conditions on the test bench and on the road. Special attention was given to the most strained engine parts - top piston rings and crank bearings. The parts to be traced were irradiated in the reactor and the following gamma emitters were used: cast-iron piston rings contained the radioisotopes 59Fe and 54Mn, lead bearings with tin and antimony addition contained the radioisotope 124Sb. The tests were made in four-cylinder spark ignition engines Škoda 990 and 993, of standard production. The measuring method consists in detecting the amount of radioactive wear debris in the crank-case oil. The measuring equipment comprises a scintillation counter with a Nal(Tl) crystal for detecting gamma radiation and electronic counting instruments complemented by special accessories. In laboratory tests the activity of the oil is measured continuously during engine operation. In long duration performance tests periodical oil samples are drawn from the crank-case; samples and radioactive standards are measured in the same arrangement. When evaluating the rate of wear, a wide range of results may be found (due to the statistical errors depending on counting rate level, relative wear increases, measuring time, etc.). Because of the error theory it is necessary to reach a suitable compromise between test conditions and the demanded accuracy of the obtained results. Road and laboratory tests carried out in UVMV show how various parameters influence engine wear rate. The effect of different factors was studied (different oils, oil filtration, frequent oil changes, cooling water temperature, etc.) and it is concluded that piston ring wear and especially bearing wear is caused mainly by rising engine-speed and load. The sensitivity of the radiotracer technique allows the detection of 0.001 mg of wear debris per cubic centimeter of oil filling; this is one of the main advantages of the method. The accuracy and reliability of results, however, is limited to a certain extent by the statistical nature of the traced phenomenon. For good measurement reproducibility, strict observance of all operating parameters is inevitable. Care must be taken to measure and compare the wear rate during the same period of engine life for each test. (author)