Combustion control and sensors: a review

Recent advances in room-temperature, near-IR and visible diode laser sources for tele-communication, high-speed computer networks, and optical data storage applications are enabling a new generation of gas-dynamic and combustion-flow sensors based on laser absorption spectroscopy. In addition to conventional species concentration and density measurements, spectroscopic techniques for temperature, velocity, pressure and mass flux have been demonstrated in laboratory, industrial and technical flows. Combined with fibreoptic distribution networks and ultrasensitive detection strategies, compact and portable sensors are now appearing for a variety of applications. In many cases, the superior spectroscopic quality of the new laser sources compared with earlier cryogenic, mid-IR devices is allowing increased sensitivity of trace species measurements, high-precision spectroscopy of major gas constituents, and stable, autonomous measurement systems. The purpose of this article is to review recent progress in this field and suggest likely directions for future research and development. The various laser-source technologies are briefly reviewed as they relate to sensor applications. Basic theory for laser absorption measurements of gas-dynamic properties is reviewed and special detection strategies for the weak near-IR and visible absorption spectra are described. Typical sensor configurations are described and compared for various application scenarios, ranging from laboratory research to automated field and airborne packages. Recent applications of gas-dynamic sensors for air flows and fluxes of trace atmospheric species are presented. Applications of gas-dynamic and combustion sensors to research and development of high-speed flows aeropropulsion engines, and combustion emissions monitoring are presented in detail, along with emerging flow control systems based on these new sensors. Finally, technology in nonlinear frequency conversion, UV laser materials, room-temperature mid-IR materials and broadly tunable multisection devices is reviewed to suggest new sensor possibilities.

https://iopscience.iop.org/article/10.1088/0957-0233/9/4/001/pdf

Diode laser absorption sensors for gas-dynamic and combustion flows.

Motor vehicles are one of the largest sources of air pollutants worldwide. Despite their importance, motor vehicle emissions are inadequately understood and quantified. This is due in part to large variations in individual vehicle emissions with changing operating conditions, and to significant differences between vehicles. To better relate emissions with operating conditions, a new parameter termed "specific power" (SP) is presented. SP is the instantaneous tractive power per unit vehicle mass. This parameter has three main advantages: it can be calculated from roadside measurements, it captures most of the dependence of light-duty vehicle emissions on driving conditions, and it is directly specified in emissions certification cycles. The dependence of CO, HC, and NOx emissions on SP is better than on several other commonly used parameters, such as speed, acceleration, power, or fuel rate. Using SP as the basic metric allows meaningful comparisons to be made between data from different remote sensing sites, dynamometer driving cycles, and emission models. Modem U.S. vehicles are likely to operate under commanded enrichment when SP exceeds the maximum value on the Federal Test Procedure (-22 kW/Metric Ton). This may allow transient high emissions to be screened out during future remote sensing campaigns. Remote sensing can address the problem of inter-vehicle differences by quickly and cheaply measuring the emissions of large numbers of vehicles. Here, a tunable infrared laser differential absorption spectrometer (TILDAS) remote sensor was used to gather the first on-road measurements of N20 and N02, and the first high precision measurements of NO. NO was detected with a sensitivity of 5 ppm, which allowed even Ultra Low Emission Vehicles to be measured. On-road accuracy was demonstrated by comparing the TILDAS results with the on-board measurements of a heavy-duty diesel truck (HDDT). The remote sensor could operate with an optical path length of 88 meters, more than five times that of competing instruments. The NO and N20 emission distributions of passenger cars (PCs) and light-duty trucks (LDTs) were found to be highly skewed, while the NO emission distribution for HDDTs was not. N20 emissions from PCs and LDTs are estimated to contribute between 0.5% and 0.9% to U.S. greenhouse gas emissions. Thesis supervisor: Gregory J. McRae Title: Bayer Professor of Chemical Engineering

Understanding and quantifying motor vehicle emissions with vehicle specific power and TILDAS remote sensing

The availability of new lasers in the nearand mid infrared spectral region has led to the development of sensors for gas measurements that are now applied extensively in the process industries. Based on tunable diode laser absorption spectroscopy (TOLAS) molecules like O2, CH* H2O, CO, CO2, NH3, HC1 and HF can be detected in-situ with high selectivity and sensitivity in continuous, real time operation. Using sensitive detection techniques like wavelength modulation spectroscopy (WMS), often low ppb and ppm concentration measurements with Is integration time are feasible. Detection limits can be improved by using extractive sampling and a long multi-pass cell. TOLAS has become an accepted technique in the process industries for difficult measurement tasks, because it is compatible with high temperatures, pressures, dust levels and corrosive media. Gas concentrations, temperatures, velocities and pressures can be determined. TOLAS is used widely for continuous emission monitoring and process control with over 1,000 field instruments worldwide. In this article, after an introduction to the basics of TOLAS, several interesting applications and installations in various process industrial units with some examples from other industries are reviewed.

Tunable diode laser absorption spectroscopy (tdlas) in the process industries – a review

This paper reports the simultaneous measurements of multiple flow parameters in a scramjet facility operating at a nominal Mach number of 2.5 using a sensing system based on tunable diode-laser absorption spectroscopy (TDLAS). The TDLAS system measures velocity, temperature, and water vapor partial pressure at three different locations of the scramjet: the inlet, the combustion region near the flame stabilization cavity, and the exit of the combustor. These measurements enable the determination of the variation of the Mach number and the combustion mode in the scramjet engine, which are critical for evaluating the combustion efficiency and optimizing engine performance. The results obtained in this work clearly demonstrated the applicability of TDLAS sensors in harsh and high-speed environments. The TDLAS system, due to its unique virtues, is expected to play an important role in the development of scramjet engines.

/pdf/simultaneous-measurements-of-multiple-flow-parameters-for-4arj1b4mfb.pdf

Simultaneous measurements of multiple flow parameters for scramjet characterization using tunable diode-laser sensors

A tunable infrared diode laser was used in the F4 high-enthalpy hypersonic wind tunnel at ONERA to make line-of-sight measurements on nitric oxide (NO). The NO is generated in the arc chamber and remains frozen in the hypersonic flow. We report the results of a medium enthalpy run. The Ω (14.5), Ω = 3/2 doublet was recorded simultaneously in two views : one normal to the flow and the other biased at 63-deg to the flow axis. Spectra were recorded at 2 ms intervals during a tunnel run, and 30 sets of spectra were analyzed by a least-squares fitting procedure. The mean of the velocity measurements inferred from the Doppler shift of the doublet was 2740 m/s (±5%). The velocity decayed about 10% over 60 ms. The temperature and NO column density determined by the least-squares fits were subject to much larger uncertainties. The static temperature of the freestream is estimated to be 168 K (±35%). The median inferred NO column density of 4 X 10 17 molecule/cm 2 corresponds to an NO number density of order 5 x 10 15 molecules/cm 3 in the freestream.

D. Henry

Papers

Tunable diode laser measurements on nitric oxide in a hypersonic wind tunnel

Tunable diode laser measurements on nitric oxide in a hypersonic wind tunnel

Application of infrared diode laser absorption spectroscopy to the F4 high enthalpy wind tunnel