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National Advisory Committee for Aeronautics, Technical Notes - Charts of Thermodynamic Properties of Fluids Encountered in Calculations of Internal Combustion Engine Cycles

Reference 1 presented thermodynamic property charts for
the products of combustion of octene and air in different ”
ratios. For the calculation of Various engine cycles, there
is necessary in addition a chart or set of charts giving the
thermodynamic properties of unburned air—fuel mixtures. Such
an unburned—fuel-air mixture chart has been calculated, and
so plotted that it applies to various airnfuel ratios and
various ratios of burned to unburned gases, and includes pure
air as the basic chart.

This investigation, conducted at the Massachusetts
Institute of Technology, was sponsored by and conducted with
the financial assistance of the National Advisory Committee
for Aeronautics.

The completion of this project would-not have been pos-
sible without the conscientious and efficient assistance of
Mrs. Edward Addelson, who made all the calculations and did
all the drafting and lettering on the final charts.

The charts in reference 1 were each on a basis of 1
pound of air plus the appropriate fuel. and the coordinates
were entropy S and internal energy E. A set of correspond;
ing "unburned“ charts on the same basis could be prepared,
one corresponding to each “burned" chart. If, however, the
basis for the preperties of unburned mixtures is not 1 pound
of air but 1 pound mol of mixture, the p—v—T relations for _
various mixture ratios are substantially the same - identical,
of course, if the various air~fuel mixtures were perfect
gases.

Furthermore. if the coordinates of the chart are entropy
S and temperature T rather than S and E as previously,
the representation of the properties of different mixtures on
a single chart is facilitated. It will be shown that the
small variations, with air—fuel mixture ratios, from a"common
pnv—T relation due to gas imperfections and from a common H—T
or E—T relation due to molal—specific—heat variations from
fuel to air, can be allowed for on a single chart. Such a
chart can then be used for all mixtures.