Estimation of bulk modulus of DME on the basis of the sound speed measurement in a wide range of pressures and temperatures including the critical point

Abstract

Sound speed is one of the most important thermodynamic properties for developing a fuel injection system and it is often used to validate the equation of state. There are a few measurement data of sound speed in DME, however the measurement range of pressure and temperature was limited. The critical temperature of DME is lower than that of diesel fuel and close to the injection condition. At the critical point, the isothermal bulk modulus theoretically drops to 0. Thus, the isothermal bulk modulus and sound speed are expected to show a complex behavior around the critical point. In this study, sound speed in DME over a wide range of pressures and temperatures, from 1 MPa to 80 MPa, 298 K to 413 K including the critical point, was measured, and the isothermal bulk modulus of DME was estimated from the measured sound speed. The sound speed increased with increasing pressure or decreasing temperature. Around the critical point, the sound speed drastically dropped with approaching the critical point. Measurement results of the sound speed in this study were in good agreement with the estimated values from the equation of state proposed by Wu. The isothermal bulk modulus of DME was extremely low around the critical point. It is indicated that the performance of the injection pump of DME significantly decreases near the critical point.

Keywords

• dme
• sound speed
• isothermal bulk modulus
• critical point
• equation of state