Multi-parameter imaging of in-cylinder processes during transient engine operation for the investigation of soot formation

Abstract

Transient engine operation of direct-injection spark ignition engines can result in high particulate number emissions. To investigate the causes of soot formation, an engine test rig was developed to perform detailed measurements of real transient operation. For this purpose, a single-cylinder full-metal engine with a real combustion chamber geometry was equipped with minimally invasive optical accesses. Simultaneous high-speed endoscopic PIV, spray visualization, and combustion imaging were applied to investigate the in-cylinder processes in detail. Endoscopic PIV was first compared in the central symmetry plane with classical PIV performed at the equivalent optical engine at steady-state operation for verification. Then the engine parameters of a tip-in performed by the corresponding four-cylinder engine, which led to high particle number emissions, were applied to the single-cylinder engine. The engine parameters were in a good agreement and particle number emissions due to the maneuver were within the same range of several 106 #/cm3. In total, 19 repetitions of the tip-in maneuver were analyzed with respect to the in-cylinder processes and repeatability of engine parameters. Furthermore, the in-cylinder flow field during the late compression stroke, flame propagation, and soot luminosity of single cycles during the tip-in indicated cause-and-effect chains for the formation of pool fire and soot at the injector tip. The direction of the flow below the spark plug influenced the direction of flame propagation. An early arrival of the flame enhanced the formation of soot from fuel films formed on the piston surface or at the injector. In engine applications, counter measures can be applied to reduce the particle number emissions when accounting for these indicated cause-and-effect chains.

Investigation of in-cylinder soot formation in a DISI engine during transient operation by simultaneous endoscopic PIV and flame imaging

“…Since the engine parameters were in good agreement with those of the four-cylinder engine, the feasibility of the endoscopic test rig for realistic transient operation was demonstrated. 24 Furthermore, the low cycle-based standard deviation of the engine parameters (gray area in Figure 4) prove the good reproducibility of the maneuver. The higher standard deviations of the MFB50 were due to cycle-to-cycle variations in mixture preparation caused by the Miller cycle.…”

“…The measurements were performed in a single-cylinder DISI engine introduced in Fach et al 24 The engine was equipped with a four-valve cylinder head. The spark plug was placed between the exhaust valves and the multi-hole injector (Bosch HDEV 6) was located in the central symmetry plane.…”

“…[20][21][22][23] In a previous study, a multi-parameter imaging approach was introduced for the investigation of the in-cylinder flow, flame propagation and soot formation during transient engine operation. 24 Simultaneous endoscopic particle image velocimetry (PIV) and imaging of flame propagation and soot luminosity were applied to a single-cylinder DISI engine with combustion chamber geometry as in preproduction-type engines. The endoscopic PIV was verified by a comparison measurement at both the endoscopic engine and the equivalent optical engine.…”

Imaging of flame propagation and temperature distribution in an all-metal gasoline engine with endoscopic access via anisole fluorescence

“…Therefore, the application of such endoscopes is limited to relatively bright events in the visible range only. Few examples are visualization of broadband combustion in gasoline (Drake et al 2003;Fach et al 2022) and in diesel engines (Eismark et al 2009;Miers et al 2005), temporally resolved soot pyrometry (Bakenhus and R. D. Reitz 1999;Shiozaki et al 1996), visualization of the spray via Mie scattering (Sczomak et al 2010;Sementa et al 2012;Fach et al 2021), and particle image velocimetry (PIV) (Fach et al 2021(Fach et al , 2022Dierksheide et al 2002). Soot formation has also been investigated using endoscopic imaging in directinjection spark-ignition (DISI) engines by Burkardt et al (2021) and Etikyala et al (2022).…”

Numerical Analysis of GDI Flash Boiling Sprays Using Different Fuels

“…Significant advantages, such as increased efficiency, lower knocking tendency, volumetric efficiency enhancement, and improved transient response have diverted the research focus from the well-known port fuel injection (PFI) towards GDI systems [1][2][3]. With these benefits, new challenges manifest themselves requiring further optimization strategies in order to reduce soot and particulate matter emissions that may result from phenomena such as tip wetting and wall-impingement [4,5]. Thus, spray air interaction and mixture formation in GDI engines require great care as the effect on the subsequent combustion phase significantly impacts the engine's thermal efficiency [6].…”