Abstract
Natural gas is an attracting alternative for diesel in
piston engines due to smaller carbon dioxide and
particulate mass emissions. However, also natural gas
engines need techniques that reduce their emissions.
Particle mass emissions of natural gas engines are small
in comparison with diesel engines (Jayaratne et al.,
2009). Yet, particle number emissions can be of the same
order of magnitude as those of diesel engines without
particulate filters (Holmén et al., 2002). Knowing the
generation process and origin of the emissions helps in
reducing them.
Measurements (Alanen et al. 2014) were steady-state tests
performed at an engine dynamometer with a passenger car
petrol engine. Test engine was retrofitted to run with
natural gas without exhaust after-treatment and with a
selective catalytic reactor (SCR). The engine was not
equipped with a turbocharger.
Particle measurements were made using EEPS, Nano-SMPS and
PSM with CPC. A thermodenuder (TD, maximum temperature
265 °C) was used to study particle volatility
characteristics and Nano-SMPS without the neutralizer was
used to study the electric charge state of particles.
Particle emission sampling system consisted of a porous
tube diluter, a residence time tunnel and an ejector
diluter (Dekati Ltd). Residence time in the dilution
system was 3 s. The dilution ratio over the porous tube
diluter (PDR) during the measurements was six but also
larger dilutions ratios were tested.
Results indicate that natural gas engine exhaust
particles are initially formed in engine cylinders and
they increase in size during sample dilution and cooling
process. The growth occurs by condensation of gaseous
compounds in exhaust gas if the conditions during primary
dilution process are favourable.
A small fraction of the particles carry an electric
charge. Particles carrying electric charge have been
charged most probably in the high temperatures of the
engine cylinders. Thermodenuder volatility measurements
suggest that the particles have a non-volatile core but a
notable part of their volume consists of volatile matter.
SCR influences particles by reducing their number
concentration. This can result from oxidative reactions
of hydrocarbons taking place inside the SCR or from
diffusion of particles on its walls.
Particles emitted from the natural gas engine were
extremely small with the particle size distribution peak
at about 4 nm. Number of particles with a diameter larger
than 50 nm was very low (Figure 1).
This was the first time the electrical charge of the
particle emission of a natural gas engine power plant was
investigated or particles under 4 nm in the particle
emission of a natural gas engine were measured. Also the
observation of particle size reduction at 265 °C rather
than complete evaporation was made for the first time in
this work.
Figure 1. Natural gas engine exhaust nanoparticle size
distribution measured by PSM, Nano-SMPS and EEPS
This work was supported by the The Finnish Funding
Agency for Technology and Innovation (TEKES), Neste Oil
Corporation, Wärtsilä Finland Oy, Dinex Ecocat Oy, AGCO
Power, Dekati Ltd, Viking Line, Suomi Analytics Oy and
Gasum Gas Fund.
Alanen, J. et al. Formation and characteristics of
natural gas engine exhaust nanoparticles. Manuscript in
prep.
Holmén, B. A, & Ayala, A. (2002). Environ. Sci. Technol.,
36, 5041-5050
Jayaratne, E. R.., Ristovski, Z. D. Meyer, N. and
Morawska, L. (2009). Science of the Total Environment,
407, 2845-2852.
Original language | English |
---|---|
Title of host publication | Aerosol Technology 2015, AT2015 |
Publisher | Tampere University of Technology |
Publication status | Published - 2015 |
Event | Aerosol Technology 2015, AT2015 - Tampere, Finland Duration: 15 Jun 2015 → 17 Jun 2015 |
Conference
Conference | Aerosol Technology 2015, AT2015 |
---|---|
Abbreviated title | AT2015 |
Country/Territory | Finland |
City | Tampere |
Period | 15/06/15 → 17/06/15 |
Keywords
- natural gas engine
- particle formation