For advanced engine and heat-exchanger design, it is essential to know
the critical points of the fuel and fuel-product mixtures. Ultrasonic
velocity measurements provide critical-point information, and can als
o be used to obtain compressibilities. A novel system has been designe
d and constructed to measure the velocities of sound at temperatures u
p to 400 degrees C and pressures to 300 bar. A quartz crystal has been
used to generate and receive the ultrasonic waves. Methylcyclohexane
is used as a model for new endothermic fuels, and critical points have
been measured for methylcyclohexane and mixtures of methylcyclohexane
and benzene. Experimental velocities and critical points are compared
to values calculated from a Benedict-Webb-Rubin equation of state, th
e corresponding-states principle, and mixing rules. (C) 1997 Elsevier
Science B.V.