Solid particulate mass and number from ducted fuel injection in an optically accessible diesel engine in skip-fired operation

Abstract

Ducted fuel injection (DFI) is a novel combustion strategy that has been shown to significantly attenuate soot formation in diesel engines. While previous studies have used optical diagnostics and optical filter smoke number methods to show that DFI reduces in-cylinder soot formation and engine-out soot emissions, respectively, this is the first study to measure solid particle number (PN) emissions in addition to particle mass (PM). Furthermore, this study quantitatively evaluates the use of transient particle instruments for measuring particles from skip-fired operation in an optical single cylinder research engine (SCRE). Engine-out PN was measured using an engine exhaust particle sizer following a catalytic stripper, and PM was measured using a photoacoustic analyzer. The study improves on earlier preliminary emissions studies by clearly showing that DFI reduces overall PM by 76%–79% and PN for particles larger than 23 nm by 77% relative to conventional diesel combustion at a 1200-rpm, 13.3-bar gross indicated mean effective pressure operating condition. The degree of engine-out PM reduction with DFI was similar across both particulate measurement instruments used in the work. Through the use of bimodal distribution fitting, DFI was also shown to reduce the geometric mean diameter of accumulation mode particles by 26%, similar to the effects of increased injection pressure in conventional diesel combustion systems. This work clearly shows the significant solid particulate matter reductions enabled by DFI while also demonstrating that engine-out PN can be accurately measured from an optical SCRE operating in a skip-fired mode. Based on these results, it is believed that DFI has the potential to enable fuel savings when implemented in multi-cylinder engines, both by lowering the required frequency of active diesel particulate filter regeneration, and by reducing the backpressure imposed by exhaust filtration systems.

Review of morphological and chemical characteristics of particulates from compression ignition engines

“…Novel catalysts control the soluble and non-soluble organic fractions in the engine exhaust. 127,128 DPF 129 efficiency depends on the soot concentration in the incoming exhaust gas stream. 130 Various DPF regeneration strategies oxidize the soot particles collected in the filter at high-temperature conditions.…”

Parametric evaluation of ducted fuel injection in an optically accessible mixing-controlled compression-ignition engine with two- and four-duct assemblies

“…This longer mixing length prior to ignition improves the diesel spray's potential to achieve LLFC. Based on early successes, multiple research groups have begun to investigate DFI both experimentally 1,[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] and computationally. 7,19,[22][23][24][25][26][27] A number of studies have investigated the impact of duct geometry on DFI combustion in pressure vessels [7][8][9][10][11][12][13]18,26 and engines.…”

“…They attributed these flare-ups to spray-spray interactions and/or entrainment of product gases upstream of the established LOL, 2 which likely decrease entrainment and increase soot production. 16,29 Wilmer et al 20 examined soot particle mass and number density from an optical heavy-duty single cylinder research engine for both CDC and DFI conditions at one operating condition using a 4-orifice/4-duct set up. They confirmed that DFI can significantly reduce engine-out soot and showed that DFI both reduces the total number of soot particles as well as their average size.…”

“…This longer mixing length prior to ignition improves the diesel spray’s potential to achieve LLFC. Based on early successes, multiple research groups have begun to investigate DFI both experimentally 1,6–21 and computationally. 7,19,22–27…”

“…A number of studies have investigated the impact of duct geometry on DFI combustion in pressure vessels 7–13,18,26 and engines. 14–17,19,20,28 Figure 1 shows important geometric parameters in DFI, including the duct inlet and exit shape, the duct inner diameter ( D ), the duct length ( L ), and the gap distance between the injector orifice and the duct inlet ( G ). Gehmlich et al 8 compared different inlet and exit geometries, finding that the best geometry (among those tested) was an inlet with a rounded inner surface and an exit with a tapered outer surface (compared to chamfered inlets or no exit taper); this so-called “delta” geometry is shown in Figure 1.…”