172
Alternative Fuels for Transportation
where dp is a change in pressure, dv is a change in volume, and ρ is the
density of the fluid.
The bulk modulus can be calculated by,
K A
= (T) B
+ (T) p
⋅ ,
where A = −6.9167T + 628.33 and B = −0.0048T 1
+ .2278, for T in °C, p in bar,
and bulk modulus in N/mm 2 . A high value of the bulk modulus means that
the fluid is less compressible.
A final aspect of compressibility is that it is related to liquid sonic velocity
and hence the rate of propagation of pressure pulsations in fuel systems. The
sonic velocity in a fuel is given by
K
V s = −
,
ρ
where V s is the sonic velocity of the fuel (Obert 1972). For petroleum oil with
a bulk modulus of 1448 MPa (N/mm 2 ) and a density of 840 kg/m 3 , the sonic
velocity is 1313 m/s, while for DME with a bulk modulus of 400 MPa and a
density of 668 kg/m 3 , the sonic velocity is 774 m/s. This can be important
in the design of fuel injection systems in high speed diesel engines, where
pressure pulsations affect injection pressures and thereby the combustion
process.
Another important property of DME that is of interest in fuel applications is its high activity as a solvent. For many conventional polymer sealing compounds, DME can extract the plasticizer compounds, resulting
swelling, cracking, or embrittlement, and thus a loss in sealing capacity.
Two materials have been shown to be effective seals: Kalrez ® and Xflour ® ,
polymers containing Fluorine, the former being quite expensive. In some
applications, the polymer EPDM has been found effective, though this
apparently varies with production method. For static sealing, Teflon ® is
inert to DME. DME is not known to interact with metal components in
fuel systems.
With regard to health and environmental characteristics, DME is currently
used as a solvent/propellant in aerosol containers, including cosmetics. As
such, considerable effort was expended to examine the health aspects of
DME, and it was found not to exhibit any properties that are detrimental to
human health. DME in the atmosphere is not prone to form ozone in urban
environments, and is less active that most fuel hydrocarbons and organic
fuel additives in atmospheric reactions in urban areas (Bowman and Seinfeld
1995). Additional information on properties and calculation methods can be
found in the DME handbook (JDF, 2007).
Alternative Fuels for Transportation
where dp is a change in pressure, dv is a change in volume, and ρ is the
density of the fluid.
The bulk modulus can be calculated by,
K A
= (T) B
+ (T) p
⋅ ,
where A = −6.9167T + 628.33 and B = −0.0048T 1
+ .2278, for T in °C, p in bar,
and bulk modulus in N/mm 2 . A high value of the bulk modulus means that
the fluid is less compressible.
A final aspect of compressibility is that it is related to liquid sonic velocity
and hence the rate of propagation of pressure pulsations in fuel systems. The
sonic velocity in a fuel is given by
K
V s = −
,
ρ
where V s is the sonic velocity of the fuel (Obert 1972). For petroleum oil with
a bulk modulus of 1448 MPa (N/mm 2 ) and a density of 840 kg/m 3 , the sonic
velocity is 1313 m/s, while for DME with a bulk modulus of 400 MPa and a
density of 668 kg/m 3 , the sonic velocity is 774 m/s. This can be important
in the design of fuel injection systems in high speed diesel engines, where
pressure pulsations affect injection pressures and thereby the combustion
process.
Another important property of DME that is of interest in fuel applications is its high activity as a solvent. For many conventional polymer sealing compounds, DME can extract the plasticizer compounds, resulting
swelling, cracking, or embrittlement, and thus a loss in sealing capacity.
Two materials have been shown to be effective seals: Kalrez ® and Xflour ® ,
polymers containing Fluorine, the former being quite expensive. In some
applications, the polymer EPDM has been found effective, though this
apparently varies with production method. For static sealing, Teflon ® is
inert to DME. DME is not known to interact with metal components in
fuel systems.
With regard to health and environmental characteristics, DME is currently
used as a solvent/propellant in aerosol containers, including cosmetics. As
such, considerable effort was expended to examine the health aspects of
DME, and it was found not to exhibit any properties that are detrimental to
human health. DME in the atmosphere is not prone to form ozone in urban
environments, and is less active that most fuel hydrocarbons and organic
fuel additives in atmospheric reactions in urban areas (Bowman and Seinfeld
1995). Additional information on properties and calculation methods can be
found in the DME handbook (JDF, 2007).