A numerical investigation of isobaric combustion strategy in a compression ignition engine

Liu, Xinlei; Aljabri, Hammam; Mohan, Balaji; Babayev, Rafig; Badra, Jihad; Johansson, Bengt

doi:10.1177/1468087420970376

Cited by 13 publications

(5 citation statements)

References 45 publications

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“…However, one challenging concern is that soot emissions increased with isobaric combustion [20]. While several studies demonstrated the performance analysis and emission characteristics of isobaric combustion using multiple injections [11,12,21,22], the following research questions need better understanding from optical diagnostics perspective:…”

Section: Introductionmentioning

confidence: 99%

Optical Diagnostics of Isobaric and Conventional Diesel Combustion in a Heavy-Duty Diesel Engine

Panthi¹,

Goyal²,

AlRamadan³

et al. 2022

SAE Technical Paper Series

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Compared to conventional diesel combustion (CDC), isobaric combustion can achieve higher thermal efficiency while lowering heat transfer losses and nitrogen oxides (NOx). However, isobaric combustion suffers from higher soot emissions. While the aforementioned trends are well established, there is limited literature about the high-temperature reaction zones, the liquid-phase penetration distance, and the flame tip propagation velocity of isobaric combustion. In the present study, the line-of-sight integrated imaging of Mie-scattering, combustion luminosity, and CH* chemiluminescence were conducted in an optically accessible singlecylinder heavy-duty diesel engine. The engine was equipped with a flat-bowl-shaped optical piston to allow bottom-view imaging of the combustion chamber. The experiments were conducted using nheptane fuel for CDC and isobaric combustion modes. The peak cylinder pressure (PCP) and the fuel mean effective pressure (Fuel MEP) for both combustion modes are kept as 70 bar and 19 bar, respectively. For a given combustion mode, flame image velocimetry (FIV) analysis was performed on the consecutive combustion luminosity image pairs to obtain in-flame flow-field details, and the liquid-phase penetration distance and flame tip propagation velocity were also estimated. The combustion luminosity and FIV analysis show that compared to CDC, isobaric combustion has resulted in less prominent flame-flame interactions, which explained the lower heat release rate. Double-injection-based CDC has resulted in a shorter spray penetration distance compared to triple-injection-based isobaric combustion; however, shorter than the boundary of piston-bowl wall. In addition, it was found that CDC has a sudden increase in flame tip propagation velocity preceded by flame propagation due to flame-piston bowl impingement from the second injection and successive movement towards the squish region. However, isobaric combustion showed a trend of constant or slightly decreased flame tip propagation velocity for which the second injection flames remain within the piston bowl wall.

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Section: Introductionmentioning

confidence: 99%

Optical Diagnostics of Isobaric and Conventional Diesel Combustion in a Heavy-Duty Diesel Engine

Panthi¹,

Goyal²,

AlRamadan³

et al. 2022

SAE Technical Paper Series

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“…Due to lower peak cylinder temperature, the NOx emissions can be reduced with a limitation of soot emissions. While several previous studies [18][19][20][21][22] addressed the engine performance and emissions of isobaric combustion using multiple injections from a single injector, in-cylinder visualization remains limited. It was reported in previous studies [23,24] that successive fuel injection events in the high-temperature reaction zones enhanced the localized fuel-air rich mixtures which led to increased soot emissions.…”

Section: Introductionmentioning

confidence: 99%

Performance Analysis and In-Cylinder Visualization of Conventional Diesel and Isobaric Combustion in an Optical Diesel Engine

Goyal¹,

Panthi²,

Houidi³

et al. 2021

SAE Technical Paper Series

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Compared to conventional diesel combustion (CDC), isobaric combustion can achieve a similar or higher indicated efficiency, lower heat transfer losses, reduced nitrogen oxides (NOx) emissions; however, with a penalty of soot emissions. While the engine performance and exhaust emissions of isobaric combustion are well known, the overall flame development, in particular, the flow-field details within the flames are unclear. In this study, the performance analysis of CDC and two isobaric combustion cases was conducted, followed by high-speed imaging of Mie-scattering and soot luminosity in an optically accessible, single-cylinder heavy-duty diesel engine. From the soot luminosity imaging, qualitative flow-fields were obtained using flame image velocimetry (FIV). The peak motoring pressure (PMP) and peak cylinder pressure (PCP) of CDC are kept fixed at 50 and 70 bar, respectively. The two isobaric combustion cases, achieved using multiple injections, are maintained at the CDC PMP level of 50 bar for the low-pressure case (IsoL) and CDC PCP level of 70 bar for the high-pressure case (IsoH). For each operating condition, soot luminosity signals are captured at a frame rate of 20 kHz, and a semi-quantitative velocity flow-field is obtained from FIV postprocessing. Consistent with previous metal engine experiments, isobaric combustionin particular IsoH, resulted in similar gross indicated efficiency, lower heat losses but higher exhaust losses, compared to CDC. The soot luminosity images of CDC show initial signals originated close to the bowl-wall for certain jets while for the isobaric combustion, the flames corresponding to each jet are clearly distinguished during the earlier flame development process. The vector field distribution within the flames shows the transition of flame-wall impingement to flame-flame interaction regions between the neighboring jets for each combustion mode. Furthermore, higher flame-flame interaction regions and uniform distribution of signals around the combustion chamber for isobaric combustion, justifying higher soot formation and lower heat transfer losses, respectively, compared to CDC.

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“…Lam et al [14,20,22] reported that for the DCEE concept the isobaric combustion mode performed better compared to the CDC mode since it could generate higher exhaust energy that could be recovered at the expansion stage. However, studies on the isobaric combustion mode are still very limited and most of them [27,28,49] adopted a peak combustion pressure no higher than 150 bar. With the help of CFD tools, this work focuses on exploring the isobaric combustion mode with a significantly high peak pressure of about 300 bar.…”

Section: Resultsmentioning

confidence: 99%

“…However, such a high peak combustion pressure is still a challenge in practical experiments due to the mechanical limit of the metal engine body. To guide the practical engine design, it is better to conduct 3D simulations beforehand, which helps to expedite the optimization of engine parts and control parameters [27,28]. Additionally, due to the excessive pressure rise rate under the CDC mode, it is desirable to adopt an isobaric combustion strategy [21]; however, this brings about more complexity of injection control strategy since multiple injection events are needed to achieve isobaric combustion [29].…”

Section: Fig 1 Schematic Of the Dcee Concept With A 4-4 Stroke Setupmentioning

confidence: 99%

“…To guide the practical engine design, it is better to conduct 3D simulations beforehand, which helps to expedite the optimization of engine parts and control parameters. 27,28 Additionally, due to the excessive pressure rise rate under the CDC mode, it is desirable to adopt an isobaric combustion strategy 21 ; however, this brings about more complexity of injection control strategy since multiple injection events are needed to achieve isobaric combustion. 29 This work intends to numerically investigate the effects of various injection strategies on a high-pressure isobaric combustion engine.…”

Section: Introductionmentioning

confidence: 99%

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Numerical investigation of the effect of injection strategy on a high-pressure isobaric combustion engine

Liu

Aljabri

Al-lehaibi

et al. 2021

International Journal of Engine Research

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High-pressure isobaric combustion adopted in the double compression expansion engine (DCEE) has the prospect to achieve higher thermal efficiency compared to conventional diesel combustion. This work numerically explored the effects of various injection strategies on the combustion and emission characteristics of isobaric combustion. The study developed a mathematical model to predict the injection rate profile. After validations, extensive simulations were conducted with a peak pressure of up to 300 bar – mimicking the high-pressure unit of DCEE. Several major engine design parameters such as the exhaust recirculation gas (EGR) rate, engine speed, injection strategy, and intake pressure were varied and evaluated. The results demonstrated that a higher EGR rate resulted in a higher exhaust loss but a lower heat transfer loss owing to the lower combustion temperature, so the thermal efficiency exhibited a firstly growing and then declining trend. Besides, a higher engine speed generated a higher thermal efficiency due to the shorter combustion duration and thus lower heat transfer loss. Consequently, a peak thermal efficiency of 47.5% was achieved at EGR = 50% and 1800 rpm. The high-pressure cylinder performance can also be improved with an appropriate introduction of the isochoric combustion, but its impact on the whole DCEE setup needs further investigation.

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A numerical investigation of isobaric combustion strategy in a compression ignition engine

Cited by 13 publications

References 45 publications

Optical Diagnostics of Isobaric and Conventional Diesel Combustion in a Heavy-Duty Diesel Engine

Optical Diagnostics of Isobaric and Conventional Diesel Combustion in a Heavy-Duty Diesel Engine

Performance Analysis and In-Cylinder Visualization of Conventional Diesel and Isobaric Combustion in an Optical Diesel Engine

Numerical investigation of the effect of injection strategy on a high-pressure isobaric combustion engine

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