Local fuel concentration measurement through spark-induced breakdown spectroscopy in a direct-injection hydrogen spark-ignition engine

Abstract

Quantitative measurements of local fuel concentrations were conducted in a directinjection hydrogen spark-ignition research engine using the spark-induced breakdown spectroscopy (SIBS) technique. For SIBS measurements, a new sensor was developed from a commercially available M12-type spark plug with no major modifications to the electrodes. The new plug sensor showed better durability and required less maintenance when used in a hydrogen research engine. Emission spectra from the plasma generated by the spark plug were collected through an optical fibre housed in the centre electrode of the plug and resolved spectrally for atomic emissions of H α , O(I), and N(I). The main focus of the present work was to characterise the effects of ambient pressure at ignition timing on spectral line emissions and to improve the accuracy of SIBS measurements by taking into account the pressure dependency of atomic emissions. A significant effect of the corresponding pressure at ignition timing was observed on spark-induced breakdown spectroscopic measurements and emission line characteristics. Retarded spark timing (i.e. higher ambient pressure at the ignition site) resulted in lower spectral line intensities as well as weaker background emissions. It is well established that with relatively higher pressure and density of atoms or molecules, the cooling of expanding plasma accelerates, and the collision probability increases, leading to both a weaker broadband [2] continuum and atomic emissions. A "calibration MAP" representing the correlation of air excess ratio (relative air/fuel ratio) with both intensity ratio and pressure at ignition timing was created and subsequently used for quantitative measurements of local fuel concentrations for both port injection and direct injection strategies to demonstrate and explore the effects of pressure dependency of atomic emission on the accuracy of the SIBS measurements. Local stratification of the fuel mixture in the vicinity of the spark gap location associated with direct injection strategies was confirmed; the coefficient of variation of the local air excess ratio was relatively small for measurements made using the calibration map. This demonstrated that the measurement accuracy of local fuel concentrations through a spark plug sensor can be improved significantly when the pressure dependency of atomic emissions is taken into account.

Flame Front Propagation in an Optical GDI Engine under Stoichiometric and Lean Burn Conditions

“…Results demonstrated a good linear relationship between lambda values and CN/OH ratios. In agreement with the literature [49,50], the change in the pressure near the spark plug determined a change in the linear tendency. CN emissions at 388 nm were observed until around 15 CAD ASOS, when the end of the glow phase occurred; this result is in agreement with the images of Figure 10 that showed evidence of the spark for about 15-20 CAD after ignition was initiated.…”

“…Results demonstrated a good linear relationship between lambda values and CN/OH ratios. In agreement with the literature [49,50], the change in the pressure near the spark plug determined a change in the linear tendency. Χ 2 Π electronic transition was also observed, but the intensity resulted too low for the retrieving procedure.…”

“…Results demonstrated a good linear relationship between lambda values and CN/OH ratios. In agreement with the literature [49,50], the change in the pressure near the spark plug determined a change in the linear tendency. As observed in previous works [25,39,40], flame kernel emission could be well distinguished at around 10 CADs after spark timing due to the luminosity of plasma induced between the spark plug's electrodes.…”

Spark-induced breakdown spectroscopy for fuel-air equivalence ratio measurements at internal combustion engine-relevant conditions

“…Spark-induced breakdown spectroscopy can be used as a diagnostic tool to characterize the local mix ture conditions around the spark plug during the ignition attempt [ 1 1 ,31 ]. From SIBS spectral response, it has been shown that the local fuel-air equiv alence ratio of different fuels such as methane [1 1 ,32], hy drogen [31 ], propane and iso -octane [33] can be deriv ed, or plasma temperatures [34] determined. Ando and Kuwahara [35] and Fansler et al [33] hav e reported measurements of the equiv alence ratio at the spark gap using the ratio of CN (388 nm) and OH (306 nm) emission intensity from the spark, using different fuels (propane, isooctane, and gasolin e).…”

Experimental and Numerical Analysis of Laser-ignition of Wet Ethanol with Elevated Water Content

“…Details of the calibration and background subtraction methods can be found in Ref. [40]. From Figure 7, it is evident that the intensity ratio of Hα to N(I) increases gradually with the addition of water in ethanol.…”