Equation of state and temperature measurements for shocked nitromethane

Abstract

A thermodynamically consistent equation of state (EOS) was developed for unreacted liquid nitromethane (NM). The specific heat cv, the coefficient of thermal pressure (∂P/∂T)v, and the isothermal bulk modulus BT, were modeled as functions of temperature and volume using existing experimental data. To test our EOS predictions, temperature measurements using time-resolved Raman spectroscopy were obtained from NM subjected to stepwise loading. In contrast to previous EOS developments, calculations using our EOS show good agreement with the measured temperatures. Comparison with previous EOS models shows that simplifying assumptions, such as holding (∂P/∂T)v or Γ/v constant, lead to significant inaccuracies in temperature predictions for shocked NM. The assumption that the Gruneisen parameter Γ is a function of volume only is not consistent with our EOS.

Shock-to-detonation transition of nitromethane: Time-resolved emission spectroscopy measurements

“…Besides, Yoo et al [22] pointed out that shocked NM remains transparent in the spectral range 0.35-0.75 µm. The radiant temperature after shock entrance, prior to the detonation transition, reaches 2500 K. Such a temperature is not in agreement with Chaiken model, which predicts a shock temperature of about 1000 K. It is also clearly greater than those predicted by Lysne and Hardesty [23] (1100-1200 K) or Winey and Gupta [24] (1000 K). Yet a similar high temperature has been also recorded by pyrometry technique in the visible range in the same single sustained shock experiments [15] and in multiple-shock experiments performed at the CEG [25,26].…”

Development of a Single-Stage Implosion-Driven Hypervelocity Launcher

“…The post shock pressure in this case lies between 400 and 560 MPa. This translates into a theoretical detonation velocity in the range of 6.4 to 6.5 km/s due to precompression [11,18]. A piston traveling at 6.57 km/s would generate an 8.88 km/s shock.…”

“…The expanding tube madel shows that the pump tube and tamper reach an equilibrium state where the nitromethane is at the post-shock pressure. According to [18], nitromethane compressed to 190 MPa reaches a density of about 1.2 gjcc. This translates in a detonation velocity of about 6.2 km/s according to [11].…”

Dynamic temperature measurements with embedded optical sensors.

“…This is unfortunate because temperature measurements more strongly constrain theoretical models than mechanical measurements, especially for off-Hugoniot states. 4 Furthermore, dynamic compression studies of phase transitions and chemical reactions are largely speculative without knowledge of the temperature states where these phenomena are observed. While temperature measurements are relatively simple under static conditions, they are extremely difficult in dynamic compression due to a host of diagnostic and physical limitations.…”

“…Temperatures can be inferred from Raman spectra containing Stokes and anti-Stokes peaks; the amplitude ratio of these feature is related to a Boltzman factor. 4 Such measurements are only feasible in transparent samples with a reasonable Raman cross section, so many materials (such as metals) cannot be studied with Raman thermometry. Neutron resonance thermometry (NRS) 10 relies on minute differences in neutron absorption to detect temperature change in a tracer isotope embedded into the sample.…”