Developing Surrogates for Liquid Transportation Fuels: The Role of Spherically Symmetric Droplet Combustion - Novel Combustion Concepts for Sustainable Energy Development - page 373

of combustion engines stands to have an immediate impact on petroleum fuel
supplies and their clean combustion.
Considering the design process for bringing new engine technologies to the
marketplace, experimental testing and prototype evaluation have been the standard
approach of the transportation sector. The emergence of powerful computational
capabilities is beginning to change this paradigm. For example, the Cummins ISB
6.7 l diesel was developed entirely by computer simulation (PRECISE 2011 ), with
the only testing coming from performance evaluation after prototype fabrication
and operation. The new engine also achieved mileage targets and emission con-
straints of the design.
The prediction of in-cylinder processes is a challenging task owing to the dif-

rst-
principles solver. The presence of liquid droplets associated with spray injection
and the combustion chemistry that provides the chemical pathways for oxidation of
the fuel are particularly problematic. Sub-model inputs and approximations are
typically needed to enable predictions of performance. For example, the often used
KIVA code (Amsden 1999 ; Lee and Reitz 2013 ) requires sub-models for soot and
the real fuel combustion chemistry, the phase equilibrium (distillation) character-
istics of the fuel, adjustable parameters to make the spray liquid and vapor pene-
trations match experimental data and values of the crank angle where 10 % of the
fuel is burned (Wang et al. 2013 ), thermofluid properties, turbulence, droplet col-
lision dynamics, and evaporation for multicomponent droplets.
The context of the challenges involved with predicting the performance of
engines powered by real transportation fuels is illustrated by considering their
compositions. Real petroleum-based fuels

ficulty of incorporating all of the relevant physics for engine processes in a

consist of hun-
dreds of miscible constituents with a wide range of volatilities, sooting propensities,
and thermo-physical properties. Table 1 lists broad chemical classes present in a
typical jet fuel (i.e., Jet A is basically JP8 minus additives for lubricity, de-icing,
and antistatic effects (Edwards and Maurice 2001 ), and Table 2 lists the major
components for diesel.
Figure 2 illustrates the mole percents of the broad chemical classes

— gasoline, jet, diesel —

hydrocar-
bons in a typical gasoline blend (Tsang 2003 ). The highly multicomponent nature
of real fuels is further complicated by the variability of manufacturing, with

'

Table 1 Constituents of a
typical Jet A fuel (Colket
et al. 2007 )

Component (v %)

Paraf ns 55.2

Monoclycloparaf ns 17.2

Dicycloparaffins 7.8

Tricycloparaf ns 0.6

Alkyl benzenes 12.7

Indans + tetralins 4.9

Naphthalene <0.2

Substituted naphthalenes 1.3