Ammonia Distribution Measurement on a Hot Gas Test Bench Applying Tomographical Optical Methods

Abstract

Measuring the distribution of gas concentration is a very common problem in a variety of technological fields. Depending on the detectability of the gas, as well as the technological progress of the sector, different methods are used. In this paper, we present a device and methods to detect the ammonia concentration distribution in the exhaust system of diesel engines in order to increase the performance of the exhaust aftertreatment system. The device has been designed for usage on a hot gas test bench simulating exhaust gas conditions. It consists of multiple optical beams measuring ammonia line concentrations by applying nondispersive absorption spectroscopy in the deep ultraviolet region. The detectors consist of photodiodes allowing high sampling rates up to 3 kHz while providing a high signal-to-noise ratio. A detection limit of only 1 ppm has been achieved despite the short path length of only eight centimeters. The obtained line concentrations form an inverse problem. The methodology of the tomographic techniques is described in detail in order to best solve the inverse problem and obtain the ammonia concentration distribution images for each time step.

Ammonia Gas Sensors: Comparison of Solid-State and Optical Methods

“…The cross-section (σ), defining the system sensitivity, is the highest in the UV region. It is about 10-times larger than at the 11 µm region (e.g.,~10 −18 cm 2 ) and even 10 5 -times larger than in other NIR ranges [44].…”

“…The cross-section (σ), defining the system sensitivity, is the highest in the UV region. It is about 10-times larger than at the 11 µ m region (e.g., ~10 −18 cm 2 ) and even 10 5 -times larger than in other NIR ranges [44]. Unfortunately, in the UV and NIR range, there is a problem with interferences by water vapor and N2O or NO2 molecules, which occur at high concentrations in air.…”