6
2 and Engine 3), the TNCs were lower than correspond-
ing TNCs in the exhaust of the “traditional” engine oper-
ated with the muffler or DOC (Figure 3). The lowest TNCs
were found in the exhaust of the DOC/DPF-fitted Engine
2. Those were between 155 and 1,679 times lower than
corresponding TNCs in the exhaust of Engine 4 fitted with
the muffler, and somewhat higher than those in the exhaust
of Engine 4 retrofitted with DPF. It is important to note
that in the case of Engine 2, unlike in the case of Engine
4 retrofitted with DPF, the average TNCs included those
intermittent spikes in concentrations coinciding with peri-
odic DPF regeneration events.
The average TNCs were 96 to 99 percent lower in the
exhaust of Engine 3 than in the exhaust of Engine 4 fitted
with the muffler for all test conditions. The engine operat-
ing conditions were found to have a profound effect on
TNCs of aerosols in the exhaust of the DOC-fitted Engine
1. The concentrations were substantially higher when that
engine was operated at rated speed (R100 and R50) condi-
tions than at intermediate speed (I100 and I50) conditions.
When operated at the R50 condition, the TNCs of aerosols
in the exhaust of Engine 1 exceeded those in the exhaust
of Engine 4 fitted with the muffler by 38 percent and in
the exhaust of Engine 4 retrofitted with the DOC by 76
percent. When operated at the R100 condition, the TNCs
were 38 percent higher in the exhaust of Engine 1 than in
the exhaust of Engine 4 fitted with DOC. For I100 and
I50 conditions, the TNCs were substantially lower in the
exhaust of Engine 1 than in the exhaust of Engine 4 fitted
with the muffler or retrofitted with the DOC.
The aerosols in the unfiltered exhaust of Engine 1 and
Engine 3 were lognormally distributed in single accumula-
tion mode or between accumulation and nucleation modes
(Figure 4 and Table 4). The nucleation mode aerosols with
count median diameters (CMDs) smaller than 14 nm were
found in the exhaust of almost all evaluated engines/config-
urations and for almost all operating conditions. The con-
centrations of those were found to be substantially lower
than the corresponding concentrations of accumulation
mode aerosols.
The CMDs of the accumulation mode aerosols emitted
by the non-DPF “clean” engines were noticeably smaller
than the corresponding CMDs of the aerosols emitted by
the “traditional” engine in non-DPF configurations. In
cases of the Engine 2, the aerosols in the filtered exhausts
were lognormally distributed between single accumulation
mode and single nucleation modes (Figure 4 and Table 4).
The TNCs in the filtered exhaust were found to be rather
low and quite variable. Generally, the concentrations of
Figure 4. Size distribution of aerosols captured 1,800s into
tests for: (a) R100, (b) R50, (c) I100, and (d) I50 engine
operating conditions. The results for Engine 3 and Engine 4
were adopted from a previous publication [39]
2 and Engine 3), the TNCs were lower than correspond-
ing TNCs in the exhaust of the “traditional” engine oper-
ated with the muffler or DOC (Figure 3). The lowest TNCs
were found in the exhaust of the DOC/DPF-fitted Engine
2. Those were between 155 and 1,679 times lower than
corresponding TNCs in the exhaust of Engine 4 fitted with
the muffler, and somewhat higher than those in the exhaust
of Engine 4 retrofitted with DPF. It is important to note
that in the case of Engine 2, unlike in the case of Engine
4 retrofitted with DPF, the average TNCs included those
intermittent spikes in concentrations coinciding with peri-
odic DPF regeneration events.
The average TNCs were 96 to 99 percent lower in the
exhaust of Engine 3 than in the exhaust of Engine 4 fitted
with the muffler for all test conditions. The engine operat-
ing conditions were found to have a profound effect on
TNCs of aerosols in the exhaust of the DOC-fitted Engine
1. The concentrations were substantially higher when that
engine was operated at rated speed (R100 and R50) condi-
tions than at intermediate speed (I100 and I50) conditions.
When operated at the R50 condition, the TNCs of aerosols
in the exhaust of Engine 1 exceeded those in the exhaust
of Engine 4 fitted with the muffler by 38 percent and in
the exhaust of Engine 4 retrofitted with the DOC by 76
percent. When operated at the R100 condition, the TNCs
were 38 percent higher in the exhaust of Engine 1 than in
the exhaust of Engine 4 fitted with DOC. For I100 and
I50 conditions, the TNCs were substantially lower in the
exhaust of Engine 1 than in the exhaust of Engine 4 fitted
with the muffler or retrofitted with the DOC.
The aerosols in the unfiltered exhaust of Engine 1 and
Engine 3 were lognormally distributed in single accumula-
tion mode or between accumulation and nucleation modes
(Figure 4 and Table 4). The nucleation mode aerosols with
count median diameters (CMDs) smaller than 14 nm were
found in the exhaust of almost all evaluated engines/config-
urations and for almost all operating conditions. The con-
centrations of those were found to be substantially lower
than the corresponding concentrations of accumulation
mode aerosols.
The CMDs of the accumulation mode aerosols emitted
by the non-DPF “clean” engines were noticeably smaller
than the corresponding CMDs of the aerosols emitted by
the “traditional” engine in non-DPF configurations. In
cases of the Engine 2, the aerosols in the filtered exhausts
were lognormally distributed between single accumulation
mode and single nucleation modes (Figure 4 and Table 4).
The TNCs in the filtered exhaust were found to be rather
low and quite variable. Generally, the concentrations of
Figure 4. Size distribution of aerosols captured 1,800s into
tests for: (a) R100, (b) R50, (c) I100, and (d) I50 engine
operating conditions. The results for Engine 3 and Engine 4
were adopted from a previous publication [39]