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.
Abstract. Laser induced fluorescence is used to develop a 2D measurement technique for mixture formation analysis of fuel and air in a broad temperature regime from 398 K up to 548 K. The measurement principle is called FARLIF (fuel-air ratio by laser-induced fluorescence). Its application is tested on the tracer toluene in the non-fluorescent model fuel isooctane as well as on an auto-fluorescing nearstandard gasoline. A frequency quadrupled double-pulse Nd:YAG laser at 266 nm is used for excitation while the fluorescence is detected by an intensified doubleframe CCD camera. The double-frame images are used for analysis of the mixture motion. For elevated temperatures the FARLIF signal shows a temperature dependence. Therefore, a correction mechanism is suggested.
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