Comparison of Primary and Secondary Emissions from an Internal Combustion Engine - Novel Combustion Concepts for Sustainable Energy Development - page 407

lates) and unregulated emissions (aldehydes, benzene toulene xylene (BTX), PAHs,
etc.) (Di et al. 2009 ). Current emission norms look only at the mass concentration of
tail pipe exhaust. However, recent studies have linked the deleterious human health
effects to the overwhelmingly large number of tiny diesel exhaust particles (Diaz
et al. 2012 ). Efforts to reduce diesel emissions have traditionally focused on
advancements in combustion, engine technology, improved fuel injection systems,
and employment of after-treatment technologies (Khair et al. 2006 ). Although mass
emissions have lowered signi

cantly from the modern diesel engines, particle
number emissions continue to rise up (Kittelson 1998 ). Bergmann et al. ( 2009 )
showed that after-treatment devices namely diesel particulate -

cantly decrease the overall mass of tail-pipe emissions. Nevertheless, it leads to an
increase in the number concentration of nuclei mode particles downstream of DPF
and enhances the formation of secondary organic aerosol (SOA) as it provides
required surface area for condensation of gas phase organics as SOF (Bergmann
et al. 2009 ).
Formation of particles in the exhaust is a very complex process. Various
volatile organic species condensed over tiny particles emanate out of the Tailpipe.
It gets diluted and cools down when emitted in the atmosphere. Gas-to-particle
phase transition of low-volatility compounds is enhanced by the free-radicals
mediated photo-oxidation reactions as well as aqueous oxidation mechanisms
active during this period (Kaul et al. 2011 ). The tail-pipe emission dilutes and
cools down when it comes into the atmosphere and thus secondary emissions like
SOA are formed. Aerosol properties are signi

filters (DPF) signifi-

cantly affected by the level of
dilution and the temperature of the ambient environment (Robinson et al. 2007 ).
SOA has adverse effects on human health, climate, and environment (Balten-
sperger et al. 2008 ).
Inhalation exposure to diesel exhaust has shown to cause cough, bronchial
irritation, nausea, lightheadedness and phlegm. Nasal intake of diesel exhaust
aggravates the immune response to the antigens (Diaz-Sanchez et al. 1994 , 1997 ).
A study by Tsien et al. 1997 suggested that organic fraction of the diesel engine
emissions cause most harmful health effects. The in

ammatory potential of the
exhaust particles in the lungs of rats aggravates with ozone (Madden et al. 2000 ).
The current emission standards focus solely on the primary emissions. Therefore, it
is essential to investigate the secondary particles formed via atmospheric photo-
chemical aging of primary diesel emissions.
Biodiesel has emerged as an important alternative fuel for diesel engines. It is
important to study the toxicity of biodiesel exhaust particulates in primary and
secondary emissions which in turn largely depend upon the overall SOF content.

fl