Analytical assessment of the difference in air flow rates as a diagnostic parameter of the cylinder-piston group of diesel engines

Introduction. Diesel engines remain the primary powertrain for trucks and special-purpose vehicles and their widespread replacement by electric traction is unlikely in the near future. Under these conditions, monitoring the technical condition of the engine, particularly the cylinder-piston group, whose service life determines the longevity of the powertrain, is a pressing issue. The cylinder-piston group wear during operation leads to a deterioration in the engine key performance indicators. Despite the availability of various diagnostic methods, most are labor-intensive or of limited practical value. The most reliable methods require the use of external diagnostic tools, while onboard self-diagnostic systems provide only indirect assessment of engine condition. Therefore, it is advisable to develop methods for estimating engine wear using parameters available for onboard monitoring, such as crankcase gas flow rate.

Materials and Methods. The study of the dependance of crankcase gas flow with increase of the clearance in the piston ring on cylinder diameter has been conducted by mathematical method. Various diesel engine models for passenger cars and commercial vehicles have been used in the research. Diesel engines with various characteristics have been selected for examination, including cylinder diameters ranging from 83 to 144 mm and engine capacity from 2 to 16.0 liters. Regression analysis methods in the MATLAB software environment have been applied to process the data, resulting in the determination of patterns of crankcase gas flow rate changes due to cylinder leaks and a proportional value – the difference in airflow rates with a closed crankcase ventilation system and with the crankcase breather isolated from the intake tract. The validation of the model has additionally been conducted by comparing the calculated data with experimental measurements in laboratory and in field conditions.

Discussion and Conclusion. The pattern obtained through the study allows us to determine the wear degree of the cylinder-piston group based on the air flow rate measured by standard on-board diagnostics. Measurements have been conducted with the forced crankcase ventilation hose connected and with this hose isolated from the measurement tract under identical conditions. The scientific contribution of this study lies in the experimental substantiation of a quantitative relationship between the difference in air flow in two measurement modes (with the crankcase ventilation hose connected and isolated) and the degree of cylinder-piston group wear. This relationship has not previously been presented in the literature as a clear diagnostic pattern suitable for use with standard sensors. It has been established that measuring the difference in air flow is a reliable indicator of cylinder-piston group wear, allowing to predict the engine condition without the use of invasive diagnostic methods. In conclusion, the study highlights the importance of regular monitoring the cylinder-piston group condition to maintain optimal performance and extend engine service life. Further work is recommended to focus on integrating the proposed methodology into on-board diagnostic systems.

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