Cylinder Pressure Data Acquisition and Heat Release Analysis on a Personal Computer 860029

The availability and low price of personal computers with suitable interface equipment has made it practical to use such a system for cylinder pressure data acquisition. With this objective, procedures have been developed to measure and record cylinder pressure on an individual crank angle basis and obtain an average cylinder pressure trace using an Apple II Plus personal computer. These procedures as well as methods for checking the quality of cylinder pressure data are described. A simplified heat release analysis technique for an approximate first look at the data quality is presented. Comparisons are made between the result of this analysis, the Krieger-Borman heat release analysis which uses complete chemical equilibrium. The comparison is made to show the suitability of the simplified analysis in judging the quality of the pressure data.

One of the most useful tools in engine combustion research is the analysis of pressure time histories for determination of the apparent rate of heat release. Some initial efforts in this line were those by Schwietzer (1*) and Austen and Lyn (2). The most significant work was that by Krieger and Borman (3), which coupled the heat release analysis concept to detailed chemical equilibrium properties using a high-speed digital computer. Their work forms the basis for a large portion of the heat release analysis performed with engines today.

Average pressure traces of 100 to 300 consecutive engine cycles have traditionally been used as an input to heat release programs. This has often been performed using FM tape recorders and digitizers which operated at reduced speeds. Developments in data acquisition technology has made it possible to eliminate the tape recorder from the process and acquire data directly into a computer.

The personal computer or any computer which can be solely dedicated for acquiring data, is a useful instrument for internal combustion engine research. The output of the personal computer dedicated to the test cell, can be transferred to a multi-user mainframe computer for detailed engine analysis. This is attractive from an educational viewpoint since it makes it possible to perform data acquisition and graphical presentation of data in a location near the test cell on a single, inexpensive machine.

It is the purpose of this paper to describe the application of a personal computer to the acquisition of instantaneous cylinder pressure data and a simplified heat release calculation used to diagnose the quality of the pressure data. The results of this simplified analysis are compared to the results obtained from the comprehensive analysis made using the Krieger-Borman method with complete chemical equilibrium. This was done to judge the suitability of the simple heat release analysis.