CFD Analysis of the Fuel–Air Mixture Formation Process in Passive Prechambers for Use in a High-Pressure Direct Injection (HPDI) Two-Stroke Engine

Ciampolini, Marco; Bigalli, Simone; Balduzzi, Francesco; Bianchini, Alessandro; Romani, Luca; Ferrara, Giovanni

doi:10.3390/en13112846

Cited by 19 publications

(7 citation statements)

References 45 publications

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“…The same design criteria presented in [23,24] were adopted for the prechamber layout. Direction of orifices was chosen to avoid the direct impingement of jets on the cylinder head walls; in particular, a higher slope was set toward the exhaust port due to the asymmetric shape of the cylinder head (Figure 2b).…”

Section: Pc-#a Pc-#b Pc-#c Pc-#dmentioning

confidence: 99%

“…However, passive prechambers were found to be unstable in PFI fuel-lean engines [13]. For this reason, direct injection technologies have been investigated in the Literature [18][19][20][21][22][23]. The fuel stratification that can be achieved by means of dedicated injection strategies [21,23] or unconventional piston bowls [18][19][20] allowed to reduce further the equivalence ratio in the cylinder without worsening cycle-to-cycle variation, thus lowering the fuel consumption [19,20,22].…”

Section: Introductionmentioning

confidence: 99%

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Jet ignition in small two-stroke engines: an experimental survey on benefits and challenges

et al. 2021

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Increasingly stringent policy on carbon dioxide have proved to be a severe constraint on the design of light two-stroke (2S) engines. The enhancement of efficiency is claimed to be the main target to make these devices compliant with future regulations. Low-Pressure Direct Injection (LPDI) was found to be effective in the reduction of fuel short circuit, thus improving efficiency and mitigating pollution. Innovative combustion technologies are required to exploit further the fuel potential. Jet Ignition (JI), i.e., ignition provided by means of hot turbulent jets, was found to improve the fuel ignition process, leading to a faster and more uniform combustion. Several benefits are shown in over forty years of Literature, from the higher performance to wider flammability limits. However, few studies have been performed on small 2S engines, for which only full-load data are available. This paper aims at experimentally evaluating benefits and challenges of adopting the JI technology on light 2S LPDI engines at both full- and low- load operation. Different configurations of passive prechambers have been investigated in terms of indicated cycle, brake efficiency and cycle-to-cycle variation. A sensitivity analysis on the spark timing was performed to fine-tune the combustion process. Results show the adequacy of the JI for use in devices operating close to full torque, like garden tools; however, issues related to the excessive amount of residual gas or to the rapid pressure decrease during the expansion phase were highlighted. Different solutions for solving these challenges are proposed.

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Section: Pc-#a Pc-#b Pc-#c Pc-#dmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Jet ignition in small two-stroke engines: an experimental survey on benefits and challenges

et al. 2021

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“…For the spray-guided stratified direct injection system, the fuel injector and the spark plug were close-spaced, and the fuel injector confined the spray fuel reducing contact with the piston, so it was easier to form a proper ignitable mixture near the spark plug to improve combustion and emissions. Clearly, the combustion process depends more on the spray characteristics of the injection system than on the in-cylinder air flow [21].…”

Section: Central Combustor Of the Enginementioning

confidence: 99%

Effects of Injector Spray Angle on Performance of an Opposed-Piston Free-Piston Engine

Zhang¹,

Xu²,

Liu³

et al. 2020

Energies

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A free-piston engine is a novel internal combustion engine which has the advantages of a variable compression ratio and multi-fuel adaptability. This paper focuses on numerical simulation for combustion process and spray angle optimization of an opposed-piston free-piston engine. The working principle and spray-guided central combustor structure of the engine are discussed. A three-dimensional computational fluid dynamic model with moving mesh is presented based on the tested piston motion of the prototype. Calculation conditions, spray models, and combustion models were set-up according to the same prototype. The effects of spray angle on fuel evaporation rate, mixture distribution, heat release rate, in-cylinder pressure, in-cylinder temperature, and emissions were simulated and analyzed in detail. The research results indicate that the performance of the engine was very sensitive to the spray angle. The combustion efficiency and the indicated thermal efficiencies of 97.5% and 39.7% were obtained as the spray angle reached 40°.

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“…The usage of a passive pre-chamber extends the knock limit significantly when compared to a conventional SI engine, which can be even further extended with an active pre-chamber [12]. A 3D CFD analysis of a passive PC design for a two-stroke engine was published in [13]. Two variants of pre-chambers, which have the same volume but different numbers of nozzles (6 or 8 nozzles), were analyzed.…”

Section: Introductionmentioning

confidence: 99%

Optimization of Pre-Chamber Geometry and Operating Parameters in a Turbulent Jet Ignition Engine

et al. 2022

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A turbulent jet ignition engine enables operation with lean mixtures, decreasing nitrogen oxide (NOX) emissions up to 92%, while the engine efficiency can be increased compared to conventional spark-ignition engines. The geometry of the pre-chamber and engine operating parameters play the most important role in the performance of turbulent jet ignition engines and, therefore, must be optimized. The initial experimental and 3D CFD results of a single-cylinder engine fueled by gasoline were used for the calibration of a 0D/1D simulation model. The 0D/1D simulation model was upgraded to capture the effects of multiple flame propagations, and the evolution of the turbulence level was described by the new K-k-ε turbulence model, which considers the strong turbulent jets occurring in the main chamber. The optimization of the pre-chamber volume, the orifice diameter, the injected fuel mass in the pre-chamber and the spark timing was made over 9 different operating points covering the variation in engine speed and load with the objective of minimizing the fuel consumption while avoiding knock. Two optimization methods using 0D/1D simulations were presented: an individual optimization method for each operating point and a simultaneous optimization method over 9 operating points. It was found that the optimal pre-chamber volume at each operating point was around 5% of the clearance volume, while the favorable orifice diameters depended on engine load, with optimal values around 2.5 mm and 1.2 mm at stoichiometric mixtures and lean mixtures, respectively. Simultaneous optimization of the pre-chamber geometry for all considered operating points resulted in a pre-chamber volume equal to 5.14% of the clearance volume and an orifice diameter of 1.1 mm.

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CFD Analysis of the Fuel–Air Mixture Formation Process in Passive Prechambers for Use in a High-Pressure Direct Injection (HPDI) Two-Stroke Engine

Cited by 19 publications

References 45 publications

Jet ignition in small two-stroke engines: an experimental survey on benefits and challenges

Jet ignition in small two-stroke engines: an experimental survey on benefits and challenges

Effects of Injector Spray Angle on Performance of an Opposed-Piston Free-Piston Engine

Optimization of Pre-Chamber Geometry and Operating Parameters in a Turbulent Jet Ignition Engine

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