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limited by the endurance of the user and the stability of its parts. Its compact size allows even critical
parts to be replaced comparatively at will, whether they were dirty, broken, or just misbehaving.
Despite its size, parSYNC® also has sensors for the standard reaction products NO, NO
, CO
and CO used
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by similar machines. Our measurements have shown similar behavior to more complex and expensive
devices under identical conditions. (EEPS, Dekati, etc.)
The inclusion of the opacity, scattering, and ionization sensors in parSYNC® requires a greater
explanation. There are no other iPEMS devices that track all of these measurements simultaneously.
Thus, an obvious question to ask would be why parSYNC® has all three.
One reason for their inclusion is that they have been used individually in comparable situations. Note
that although these functions are similar, each sensor reacts to different types of sizes of particles in
identical situations. Their inclusion in a multi-sensor view allows parSYNC® to perceive changes in the
distribution of the sizes of the particles.
This is important because, as documented in various papers, most PEMS devices compute particle
number from particle mass by assuming that the particles are approximately uniform in size. This would
be correct if we could assume that the engine's behavior is essentially uniform throughout its usage.
However, the engines run in varying gears for various speeds under a variety of conditions and particulate
filters. As parSYNC® evolves, we will continue to add functionality to draw greater inferences on the
distribution of particles sizes from their combined output using reference data from the literature and
laboratory dynamometer studies.
The parSYNC® device uses three different types of sensors to determine particle mass and particle
number. Each sensor is sensitive to different ranges of particle sizes and can measure the particle
throughput in real-time.
7.4.1
Opacity
Opacity, also known as extinction, is governed by the Lambert-Beer law. Measuring obstruction and
diffusion, the greater the number of particles per unit volume and/or the greater the average size of the
particles, the higher the opacity. More precisely,
Lambert-Beer opacity: O = 1 – exp (–n*a*q*l)
n = number of particles per unit volume
a = mean projected area (a.k.a. attenuation cross-section or effective cross-sectional area)
q = particle extinction coefficient
l = path length of beam through the sample (technically, the length of effluent path)
The particle extinction coefficient varies versus wavelength and particle size. These numbers have been
determined experimentally at different wavelengths for different particles. The standard wavelength of
typical opacity sensors is in the green range, and parSYNC® follows suit by using gel filters. Opacity is
measured by the change in the current within the circuit that the opacity meter resides.
There are known limitations with using green light, such as the cross-sensitivity to NO
. However, merely
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changing the color will require other trade-offs; for example, red light is less sensitive to smaller particles
and ultra-violet light is sensitive to methane.
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