The method of examining carburetted mixtures by chemical analysis of the exhaust gases, using the equipment developed by Mr. Claude BONNIER, is commonly used during the tests carried out by S.N.C.M. in the various study facilities of engines on the bench or in flight.

The method consists of looking for the carbon dioxide (CO²), oxygen (O²) and carbon monoxide (CO) content of the exhaust gas. Experience has shown that, as a result of incomplete combustion, the exhaust gases at one and the same time almost always contain these three elements; the calculation then completes the combustion so that only one of these two other gases remains with the carbon monoxide; the result obtained, called reduced analysis, is then plotted on the GREBEL combustion theoretical diagram based on the fuel weight combustion. Although the exhaust gases still contain hydrogen and methane, the representation on the combustion diagram of the result of the reduced analysis is practically unaffected by the presence of these two elements.

Finally it is useful to be able to appreciate the quality of the fuel mixture, starting from the proportions in air and fuel necessary for the complete theoretical combustion. This quality of the fuel is expressed by the term <<richness>> and is thus defined: it is the quotient of the weight of gasoline consumed during the unit of time by the weight of gas necessary for a theoretical comubustion which would have been consumed under these conditions during the same time. For both poor and rich mixtures, richness is a linear function of the percentages of (O²) and CO, resulting from the reduced analysis.

These analyses make it possible to make a certain number of deductions in particular: