Ducted Fuel Injection vs. Free-Spray Injection: A Study of Mixing and Entrainment Effects Using Numerical Modeling

Ducted fuel injection (DFI) is an innovative method that curtails or prevents soot formation in direct-injection compression-ignition engines. DFI uses a simple duct, positioned outside each injector hole, facilitating the fuel/charge gas mixing before ignition. This reduces the equivalence ratio below two, in the autoignition zone, which in turn decreases soot formation. But this method also reduces fuel-conversion efficiency. This study investigates the effects of DFI on in-cylinder heat transfer. Experiments with conventional diesel combustion (CDC) and DFI were performed at four different dilution levels. Computational fluid dynamics (CFD) simulations were carried out at conditions matching those of the experiments, and the simulations were validated by the experimental data. The CFD simulations enabled to examine of in-cylinder heat release and temperature distributions. The heat transfer to the piston, head, and cylinder was investigated. The results show that DFI increased the heat transfer to the walls compared to CDC under the same conditions. This could help explain why DFI has been observed to reduce fuel-conversion efficiency by approximately 1% (absolute) relative to CDC under certain conditions. The efficiency loss typically decreases with dilution, such that DFI can improve fuel-conversion efficiencies relative to CDC at higher dilution levels.

Section: Computational Setupmentioning

confidence: 99%

A Computational Investigation of Engine Heat Transfer with Ducted Fuel Injection

Şener

Nilsen

Biles

et al. 2023

“…In addition to mixing, another important and related physical behavior for DFI is the entrainment of charge gas into the fuel spray, which has been investigated in different studies. Studies by Millo et al, 13 Nilsen et al, 14 and Zhang et al 11 have shown enhanced levels of entrainment at the duct inlet compared to an unconfined free spray, which is attributed to the higher axial velocities and associated lower pressure within the duct interior. The low-pressure region within the duct then draws in fluid at the inlet to drive the increased entrainment; the phenomenon has been termed as a ''jet-pump'' effect.…”

Section: Introductionmentioning

confidence: 98%

Analysis of ducted fuel injection at high-pressure transcritical conditions using large-eddy simulations

Guo

Brouzet

Chung

et al. 2023

Ducted fuel injection (DFI) is a proposed fuel injection concept for achieving substantial reductions in emissions. In this concept, the fuel is injected through a coannular duct, resulting in increased fuel-air mixing and minimized formation of soot and other unwanted combustion products. Apart from comprehensive experimental investigations on DFI, so far computational studies have been limited to single-point Reynolds-averaged Navier Stokes simulations. Therefore, the objective of this work is to complement these studies by performing large-eddy simulations using a diffuse-interface method to examine the physical mechanisms and combustion processes of DFI, specifically focusing on the mixing process and the effect of fuel-ducting on combustion and pollutant emissions. To this end, finite-rate chemistry simulations are performed of the DFI configuration corresponding to the Engine Combustion Network Spray A injector at transcritical conditions (n-dodecane fuel, 60 bar pressure and 1000 K temperature chamber conditions). A two-equation soot model is employed for the qualitative analysis of soot emissions. Direct comparisons of averaged and instantaneous flow field results with the Spray A configuration are performed to assess the effect of DFI on the first- and second-stage ignition and soot formation. Compared to the free-spray condition, the results show that the DFI case exhibits a combination of (i) increased mass flow rate and entrained air, (ii) larger pressure drop magnitude and flow velocity, and (iii) a closer-to-stoichiometric mixture composition (both globally and locally), each of which is conjectured to contribute toward reduced soot production.

“…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. [14][15][16][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).…”

Section: Introductionmentioning

confidence: 99%

“…Some studies have found that there is limited effect on air entrainment into the spray upstream of the duct, 19 yet others have found that DFI significantly increases entrainment upstream of the duct. 13,24 This increase in potential entrainment is attributed to a low-pressure region at the entrance of the duct that drives flow into the duct. 24,26 Segatori 26 showed that the low-pressure region might be up to 10 bar below ambient pressures and that the annular region between the spray and the duct inner wall corresponds to the minimum pressure zone.…”

Section: Introductionmentioning

confidence: 99%

“…13,24 This increase in potential entrainment is attributed to a low-pressure region at the entrance of the duct that drives flow into the duct. 24,26 Segatori 26 showed that the low-pressure region might be up to 10 bar below ambient pressures and that the annular region between the spray and the duct inner wall corresponds to the minimum pressure zone. Thus, the duct diameter and gap distance play a role in optimizing the entrainment into the duct.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

Yraguen

Steinberg

Nilsen

et al. 2023

Ducted fuel injection (DFI) is a strategy to improve fuel/charge-gas mixing in direct-injection compression-ignition engines. DFI involves injecting fuel along the axis of a small tube in the combustion chamber, which promotes the formation of locally leaner mixtures in the autoignition zone relative to conventional diesel combustion. Previous work has demonstrated that DFI is effective at curtailing engine-out soot emissions across a wide range of operating conditions. This study extends previous investigations, presenting engine-out emissions and efficiency trends between ducted two-orifice and ducted four-orifice injector tip configurations. For each configuration, parameters investigated include injection pressure, injection duration, intake manifold pressure, intake manifold temperature, start of combustion timing, and intake-oxygen mole fraction. For both configurations and across all parameters, DFI reduced engine-out soot emissions compared to conventional diesel combustion, with little effect on other emissions and engine efficiency. Emissions trends for both configurations were qualitatively the same across the parameters investigated. The four-duct configuration had higher thermal efficiency and indicated-specific engine-out nitrogen oxide emissions but lower indicated-specific engine-out hydrocarbon and carbon monoxide emissions than the two-duct assembly. Both configurations achieved indicated-specific engine-out emissions for both soot and nitrogen oxides that comply with current on- and off-road heavy-duty regulations in the United States without exhaust-gas aftertreatment at an intake-oxygen mole fraction of 12%. High-speed in-cylinder imaging of natural soot luminosity shows that some conditions include a second soot-production phase late in the cycle. The probability of these late-cycle events is sensitive to both the number of ducted sprays and the operating conditions.