Comparison of Primary and Secondary Emissions from an Internal Combustion Engine - Novel Combustion Concepts for Sustainable Energy Development - page 418

Fig. 8 Variation of total
particle-bound PAHs versus
engine load for primary and
secondary exhaust fuelled
with diesel and B20 (adapted
from Agarwal et al. 2013 )
emissions were higher as compared with primary emissions, at all engine loads.
High in-cylinder temperature facilitates cyclization of unburned fuel and lubricating
oil, leading to formation of PAHs at higher engine loads (Ravindra et al. 2008 ).
A large amount of gaseous PAHs undergo phase transition and condense as par-
ticles as a result of cooling and aging. PAHs adsorb on particles and persist during
incomplete combustion inside the engine (Atal et al. 1997 ). Even though there was
a major reduction in PM mass for B20 as compared to diesel, however the particle
bound PAHs were nearly comparable for both the fuels. This suggests that the
emitted particles from B20 were relatively heavily laden with PAHs.
6.3 Toxic Equivalent Potential Evaluation
To fully understand the overall toxicity of PAHs, toxic potential of individual PAHs
can be evaluated and a summation can be carried out. Integration of the individual
toxicity of PAHs can be carried out by multiplying the toxic equivalent factors
(TEFs) of the individual PAH species with their respective concentrations. TEFs for
PAHs were obtained from Nisbet and Lagoy 1992 and CAEPA 1993 . A total of 8
PAHs and 2 Nitro-PAHs were considered. Pan et al. 2000 showed the nitro-PAHs
and PAHs emissions from diesel and B100 (soy methyl ester), and B20. They
utilized a Cummins B5.9 engine. PAHs and nitro-PAHs concentrations were
obtained by using gas chromatography and mass spectrometry. For our calculations,
percentage distribution of PAHs species from the study of Pan et al. ( 2000 ) have
been employed. Overall PAHs concentration in our study is attributed to individual
PAHs based on the Pan et al. 2000 study.
The trend of total toxic equivalent potential (Fig. 9 ) was similar to particle-
bound PAHs emissions (Fig. 8 ). Diesel showed slightly higher toxic potential