Emissions - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 85

5.2.3 Remote Sensing Technology
There are several optical remote sensing methods to measure the composition of
exhaust gases, e.g., when flying over ships with airplanes. Laser analyzers,
installed on the test airplane, measure the composition of the exhaust gas emitted
from the smoke stack. These methods are very expensive and are used only in
protected areas to control the ship's real emissions. Similar methods have been
used at airports for analyzing the emissions of taxiing and taking-off airplanes.
The detection system measures the emissions using the absorption of laser signals
from the reflected optical path. The lowest concentrations, which can be detected,
are 0.5-1.0 ppm of CH 4 , 2.0-3.0 ppm of CO, 10.0-20.0 ppm of NO, and 0.5-
1.0 ppm of CO 2 . The resolution of laser operated remote sensing devices generally
presents a very high quality measurement technology with clustered, coherent laser
beams, not only at the test bench but under natural conditions too. Remote sensing
systems cost from 20,000 to several hundred thousand Euros or US Dollars [ 23 ].
Monitoring combustion in the engines of vehicles, ships, and airplanes can be
done in several phases. In the research and development phase, large, expensive,
and locally fixed systems in laboratories are usually used. These devices can detect
very small concentrations, provide large measuring ranges, and display extremely
short-term events. They can also measure a wide range of different gases at the
same time. However, the mobile application of these devices is very limited and
transport of them is, in most cases, not possible.
Emissions in Road Traffic
Emissions can be determined with large analyzers on-board, if the verified
equipment tested at the test bench is carried by a holding device with springs and
absorption devices in cars and in duty vehicles. Despite the general feasibility, the
use of certified large instruments in traffic is still very limited because of their
sensitivity to vibrations, high temperatures, pressures, and soot peaks in the
exhaust gas. However, certified gas analyzers produce precise results in driving for
short time intervals, if their mechanical construction is very stable and cushioned
and high capacity accumulators save the energy.
CO 2 and NO concentrations present similar tendencies because all of these
parameters are dependent on the load of the engine. In the most cases, unburned
substances have an inverse or a diverged course.
An oxygen sensor in road vehicles is the state of the art and uses a uniform
interface system. Others, mostly experimental systems, consist of sensors for the
common analysis of HC and CO, and individual temperatures or pressures. Further
systems measure engine speed, acceleration, angle of inclination, turbidity, and
NO concentration in the exhaust gas. The development of further sensors still
requires intensive research activity.