Numerical analysis of heat transfer characteristics of spray flames impinging on a wall under CI engine-like conditions

Simultaneous measurements of global engine heat transfer and subsurface piston temperatures were utilized to evaluate the potential of an extended duration combustion event to minimize heat rejection in a diesel engine. The combustion duration was parametrically varied by changing the injector orifice diameter (0.167, 0.196, and 0.230 mm) and fuel injection pressure (110–200 MPa) while exploring three high-output operating conditions. This investigation was limited to a single-pulse injection strategy while holding engine load constant to represent operating points at rated power and peak torque. For a constant combustion phasing, the results suggest the duration of the spray and combustion processes did not greatly influence gross indicated thermal efficiency (ITEg) or global heat transfer from the engine, except for extremely long combustion durations of approximately 50 crank-angle degrees or longer. At the longest combustion durations, there was a negative impact on ITEg and global heat transfer. Analysis of the steady-state piston temperature measurements at constant CA50 revealed two interesting, and opposite, trends: as the combustion duration was increased through a smaller orifice diameter injector, the piston temperatures increased by up to 60°C locally on the bowl rim; in contrast, as the combustion duration was increased through lower injection pressures, the piston temperatures decreased by up to 80°C locally on the bowl rim. CFD simulations coupled with a conjugate heat transfer model of the piston predicted the piston heat flux at the highest load operating condition. The CFD results qualitatively agreed with the piston temperature measurements in supporting the conclusion that orifice diameter had a stronger effect on piston heat flux than injection pressure. Overall, this research provides directional trends to engine designers and calibrators for optimizing the injection parameters for decreased engine heat transfer and managing piston temperatures.

Section: Conjugate Heat Transfer Resultsmentioning

confidence: 99%

Influence of spray and combustion processes on piston temperatures and engine heat transfer in a high-output diesel engine

Tess

Korivi

Gingrich

et al. 2022

“…Such second order derivatives would signify the rate of change of the heat transfer rate to the solid wall and would assist in the qualitative identification of the flame-wall interaction events. During spray flame impingement on the wall, the total wall heat flux reaches the largest, 18 hence second order derivative of wall heat flux as a function of crank angle, would provide the instances of the such spray flame impingement. The injection profiles used in the simulations were obtained from injection rate measurements and are illustrated in Figure 4.…”

Section: Evaluation Approachmentioning

confidence: 99%

Experimental and numerical investigation of an innovative complex piston with enhanced free spray length for the heavy-duty engine applications

Betgeri

Pischinger

Schönfeld

2023

The combustion and emission formation process in heavy-duty compression ignition engines are strongly influenced by the design of the piston bowl, the cylinder charge motion and the performance of the injection system. This paper proposes an innovative complex piston bowl design approach called as ’flower piston’ to improve the combustion process. It can be manufactured using the conventional machining approaches without use of still expensive additive manufacturing techniques. The flower piston features a scooped cavity with an intention of increasing the free fuel spray penetration. The potential of this innovative flower piston is evaluated using a validated 3D CFD model and compared with the results of single cylinder engine experiments at operating points with minimum fuel consumption. The results of the experimental investigations with the flower piston show an improvement in thermal efficiency in comparison to the conventional piston by up to 0.5%. This is due to a faster initial heat release and increased high pressure cycle work. However, the smoke emissions increased threefold due to fuel entrapment into the flower cavities, leading to formation of fuel-rich pockets. Also, the wall heat losses increased twofold with an increase in NOx raw emissions. With increased spray targeting angle, there was a drastic reduction in smoke emissions and an additional improvement in the thermal efficiency.

“…Moreover, some studies have clarified the flow near the wall and heat flux using numerical calculations. Phillai et al 13 conducted a numerical study on the effect of the fuel injection velocity on the wall heat flux. The research showed that the wall heat flux was largest near the stagnation point and decreased with increasing radial distance from the stagnation point.…”

Section: Introductionmentioning

confidence: 99%

Analysis of the relationship between near-wall velocity distribution and wall heat flux under diesel spray flame impingement in an RCEM

Jo,

Kawai,

Horibe

et al. 2024

To clarify the relationship between the near-wall flow and the heat flux through the wall, the velocity distribution of the diesel spray flame and the heat flux at the combustion chamber wall were measured in a rapid compression and expansion machine (RCEM), which has a twodimensional combustion chamber. The velocity distribution of the diesel spray flame near the wall was measured by the particle image velocimetry (PIV), and the heat flux through the wall where the diesel spray flame impinges was measured using a newly developed multi-point heat flux sensor. Furthermore, the velocity gradient tensor was calculated based on the measured velocity distribution results, and the effect of the shear flow characteristics on wall heat transfer was analyzed. As a result, the higher the injection pressure leads the higher the peak value of the heat flux. A fluctuation of the heat flux exhibits the same trend as the fluctuations of the velocity, and a high heat flux appeared in the high-velocity gradient tensor region, which suggests that the characteristics of shear flow near the wall can affect the heat flux.