Quantitative, time-resolved detection of CH<sub>4</sub> concentrations in flows for injection analysis in CNG engines using IR absorption

Abstract

Abstract. The reduction of CO 2 and other greenhouse gas emissions is an important driving force for the development of modern engines. Especially in the transport sector, the use of alternative fuels like methane, the main component of compressed natural gas (CNG), is an applied measure to achieve this goal. This work describes the development of an optical measurement system for accurate quantification of CH 4 densities in gas flows based on broadband absorption of infrared light, i.e. non-dispersive IR absorption spectroscopy (NDIR). We demonstrate the capability of the system to achieve high time resolution as well as high measurement accuracy and precision. The optical set-up of the system is designed for usage at the inlet manifold of CNG-fuelled spark ignition engines. It allows for detailed analysis of the mixture formation during single engine cycles. CH 4 densities can be determined by monitoring the infrared light attenuation around 3.3 µm caused by the ν 3 antisymmetric C-H-stretch vibration. We calculate the nonlinear relation between transmittance and CH 4 density from absorption cross sections calculated from the HITRAN database. The theoretical transmittance signals are corrected for spectral influences of the bandpass filter, the detector sensitivity, the fibre transmittance and the emission spectrum of the light source in order to calculate CH 4 densities directly from the measured transmittance. A calibration function corrects remaining differences between experimental and simulated values and improves the accuracy. We show that the sensor system is capable for determination of air-fuel ratios (λ-values) and demonstrate the dynamic quantification of a CH 4 injection into a flow channel under various flow conditions. Furthermore, we present the first measurements with a prototype probe capable of measurements inside the inlet manifold of a four-stroke spark ignition engine. We validate the detection strategy in experiments with premixed gases using a modified inlet geometry and demonstrate its application under standard engine operation with port fuel injection while varying the injection parameters.

Quantitative measurement of combustion gases in harsh environments using NDIR spectroscopy

“…(4)). This procedure has been recently described in more detail in ; Bauke et al (2018)) for methane and might be applied for CO 2 and H 2 O accordingly.…”

“…Schematic overview of the data analysis procedure for determination of CO2 concentrations in IC engines by NDIR. Bauke et al (2018)). In case of CO 2 /H 2 O, this would however require the use of third filter, which would further raise the complexity of the system and the data analysis procedure.…”

“…The sensor system used in this work is a modification of the Internal Combustion Optical Sensor (ICOS) for LaVision GmbH and has been described extensively elsewhere (Grosch et al (2014);; Bauke et al (2018)). The schematic layout of the system is shown in Fig.…”

“…Both are usually achieved by controlling and optimizing the combustion process, i.e. mixture formation prior to ignition (Grosch et al (2014), Bauke et al (2018), ). A typical approach to reduce NO x emissions is the use of exhaust gas recirculation to lower combustion temperature.…”

“…In contrast to sensors for civil applications requiring lowcost solutions, systems for engine development application are less price-sensitive but have, on the other hand, more demanding requirements. For example, they need to offer µs time resolution to enable crank-angle resolution and resolve single engine cycles (Grosch et al (2014), Bauke et al (2018)).…”