From: "Gerald L. Hurst" <GHURST@austin.rr.com>
Newsgroups: alt.engr.explosives
Subject: Detonation velocity and pressure
Date: Wed, 06 Oct 1999 08:50:48 GMT

Detonation velocity and pressure are both functions of the density,
heat of reaction, moles of gas produced and the average molecular
weight of the products.  For CHNO explosives in the density range of
about 1-2 g/cc, there exist empirical equations which can predict both
velocity and pressure to within about 1% despite ignoring some of
the other, more subtle variables that play a role in complex computer
programs.

In applying the equations, arbitrary standard assumptions
are made about the order of consumption of oxygen:

    First all the hydrogen reacts to form water
    Then the carbon reacts to form CO2 (assume no CO is formed)

The constants in the equations were selected to give approximately
the correct values of velocity and pressure despite the reality that
reactions will not actually follow the idealized chemical reaction scheme.

A glance at the equations reveals the notable fact that detonation
pressure varies directly as the square of the density and (hold your
breath) the square root of the energy -- for constant composition.
Think about it.

Jerry (Ico)

From: "Gerald L. Hurst" <GHURST@austin.rr.com>
Newsgroups: alt.engr.explosives
Subject: Re: Detonation velocity and pressure
Date: Fri, 08 Oct 1999 02:06:31 GMT

Let:

A = 1.01
B = 1.30
K = 15.58
N= (number of moles of gaseous detonation products per gram
M= average molecular Wt. of product gases ( g/mole)
Q = chemical energy/g (-deltaH per gram)
C = NM^(1/2)Q^(1/2)
D = initial density g/cc

Then:

Velocity = AC^(1/2)(1+BD)
Pressure = KCD^(2)

These empirical equations are valid for C-N-H-O explosives
where D > 1.

Assume H2 burns first followed by C burning to CO2.

Although I used these equations often in days of yore, I
am not sure I remember what units of energy (cal or kcal),
pressure, and velocity the particular constants were set
for.  Over the years, conventions for these units have
changed.  Anyway, try kcal/g and look for the pressure
to pop out in kilobars.  A few runs through the computer
with the known parameters of some standard explosive
such as TNT or RDX will soon tell you what the proper units
are.  When you finish, Let me know and I will jot the correct
units in the notebook from which the equations came  -- for
the next guy who asks.

You (somebody) might also like to convert the equations to
The units more commonly used by students today in order to
make it easier for kids who think calories are only for
weight-watchers.

Jerry (Ico)

H. Beijeman <arcticus@dds.nl> wrote in message
news:37FC9B97.40581EED@dds.nl...
>
>
> Gerald L. Hurst wrote:
>
> > Detonation velocity and pressure are both functions of the density,
> > heat of reaction, moles of gas produced and the average molecular
> > weight of the products.  For CHNO explosives in the density range of
> > about 1-2 g/cc, there exist empirical equations which can predict both
> > velocity and pressure to within about 1% despite ignoring some of
> > the other, more subtle variables that play a role in complex computer
> > programs.
> >
> > In applying the equations, arbitrary standard assumptions
> > are made about the order of consumption of oxygen:
> >
> >     First all the hydrogen reacts to form water
> >     Then the carbon reacts to form CO2 (assume no CO is formed)
> >
> > The constants in the equations were selected to give approximately
> > the correct values of velocity and pressure despite the reality that
> > reactions will not actually follow the idealized chemical reaction scheme.
> >
> > A glance at the equations reveals the notable fact that detonation
> > pressure varies directly as the square of the density and (hold your
> > breath) the square root of the energy -- for constant composition.
> > Think about it.
>
> Intreguing... I was doing some calculations with some quantummechanical
> models, regarding molecular dynamics, and some computer simulations, and, I
> found it's not too hard to predict when a (potentially) explosive compound
> will detonate, but to calculate it's velocity is a bit harder the way I
> tried... I'll look up some literature on the info you provided... thanks
> anyway! by the way, can you give me the equation(s)??