Identification of the piston machine combustion chamber tightness

The lack of integrity of the piston machine combustion chamber manifests itself in leakages of the working fluid between the piston and the cylinder liner, at valves mounted in the cylinder head and between the head and the liner. An untight combustion chamber leads to decreased power output or efficiency of the engine, while leaks of a fluid may cause damage to many components of the chamber. The actual value of working chamber leak is a desired and essential piece of information for planning operations of a given machine.

This research paper describes causes and mechanisms of leakage from the working chamber of internal combustion engines. Besides, the paper outlines presently used methods and means of leak identification and states that their further development and improvements are needed. New methods and their applicability are presented.

The methods of leak identification have been divided into diagnostic and non-working machine leak identification methods. The need has been justified for the identification of leakage from the combustion chamber of a non-working machine and for using the leakage measure as the value of the cross-sectional area of the equivalent leak, defined as the sum of cross-section areas of all leaking paths. The analysis of possible developments of tightness assessment methods referring to the combustion chamber of a non-working machine consisted in modelling subsequent combustion chamber leaks as gas-filled tank leak, leak from another element of gas-filled tank and as a regulator of gas flow through a nozzle.

A measurement system was built allowing the measurement of pressure drop in a tank with the connected engine combustion chamber, which indicated the usefulness of the system for leakage measurement in units as defined in applicable standards. A pneumatic sensor was built for measuring the cross-sectional area of the equivalent leak of the combustion chamber connected to the sensor where the chamber functioned as a regulator of gas flow through the sensor nozzle. It has been shown that the sensor can be calibrated by means of reference leaks implemented as nozzles of specific diameters and lengths. The schematic diagram of a system for measuring the combustion chamber leakage and a diagram of a sensor for measuring the cross-sectional area of the equivalent leak of the combustion chamber leakage are presented. The results are given of tightness tests of a small one-cylinder combustion engine conducted by means of the set up measurement system and a pre-prototype pneumatic sensor. The two solutions proved to be practically useful.