Thermal Efficiency Comparison of Different Injector Constellations in a CI Engine

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High-pressure internal combustion engines promise high efficiency, but a proper injection strategy to minimize heat losses and pollutant emissions remain a challenge. Previous studies have concluded that two injectors, placed at the piston bowl's rim, simultaneously improve the mixing and reduce the heat losses. The two-injector configuration further improves air utilization while keeping hot zones away from the cylinder walls. This study investigates how the two-injector concept delivers even higher efficiency by providing additional control of spray -and injection angles. Three-dimensional Reynolds-averaged Navier-Stokes simulations examined several umbrella angles, sprayto-spray angles, and injection orientations by comparing the twoinjector cases with a reference one-injector case. The study focused on heat transfer reduction, where the two-injector approach reduces the heat transfer losses by up to 14.3 % compared to the reference case. Finally, this study connected the two-injector approach to a waste-heat recovery system through GT-Power 1-D simulations, increasing the importance of heat transfer reduction. The final two-injector system then delivered a 54.4% brake thermal efficiency compared to 53% of the one-injector reference case.

Section: Merit Functionsupporting

confidence: 92%

“…High heat losses further follow in other engine concepts due to the current trend towards higher compression ratios giving higher incylinder temperatures [7,8]. To tackle this challenge, studies have suggested that multiple injectors reduce heat losses while keeping emissions at decent levels [9,10].…”

Section: Introductionmentioning

confidence: 99%

Effects of Multiple Injectors on Spray Characteristics and Efficiency in Internal Combustion Engines

Jiménez

Nyrenstedt

Goyal

et al. 2021

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“…However, further efficiency increases are possible. Similarly, the enhanced mixing by an increased number of injector holes is reported to decrease soot and NOx levels in addition to reduced heat losses [11]. Thus, this concept diminishes the NOx-soot-efficiency trade-off.…”

Section: Introductionmentioning

confidence: 96%

Isobaric Combustion for High Efficiency in an Optical Diesel Engine

Nyrenstedt

Ramadan

Tang

et al. 2020

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Isobaric combustion has been proven a promising strategy for high efficiency as well as low nitrogen oxides emissions, particularly in heavy-duty Diesel engines. Previous single-cylinder research engine experiments have, however, shown high soot levels when operating isobaric combustion. The combustion itself and the emissions formation with this combustion mode are not well understood due to the complexity of multiple injections strategy. Therefore, experiments with an equivalent heavy-duty Diesel optical engine were performed in this study. Three different cases were compared, an isochoric heat release case and two isobaric heat release cases. One of the isobaric cases was boosted to reach the maximum in-cylinder pressure of the isochoric one. The second isobaric case kept the same boost levels as the isochoric case. Results showed that in the isobaric cases, liquid fuel was injected into burning gases. This resulted in shorter ignition delays and thus a poor mixing level. The lack of fuel/air mixing was clearly the main contributor to the high soot emissions observed in isobaric combustion. The lower heat losses of the isobaric strategy were further explained by tracking the chemiluminescence. Unlike a long single injection, multiple injections helped to contain the hot gases away from the walls. However, the opposite effects were also found from the high thermal radiation caused by the extensive soot formation. Highpressure fluctuations from the rapid heat release of the isochoric case were further seen. Finally, better mixing for improved air utilization was deemed needed when utilizing isobaric heat release.

“…The latter advantages make the isobaric combustion suitable for split-cycle concepts such as the double compression expansion engines (DCEE) concept [15][16][17], which has the potential to achieve BTE up to 56%. Numerical and experimental work has shown that the use of multiple injectors can reduce the soot emission, while still achieving the desired isobaric combustion [13,18,19]. The advantage of multiple injectors provides flexibility in the temporal and spatial control of fuel sprays avoiding the injection into the burnt zone and hence reducing the soot emissions along with enhanced mixing.…”

Section: Introductionmentioning

confidence: 99%

Flow-Field Analysis of Isobaric Combustion Using Multiple Injectors in an Optical Accessible Diesel Engine

Panthi¹,

Goyal²,

Houidi³

et al. 2021

Isobaric combustion has shown the potential of improving engine efficiency by lowering the heat transfer losses. Previous studies have achieved isobaric combustion through multiple injections from a single central injector, controlling injection timing and duration of the injection. In this study, we employed three injectors, i.e. one centrally mounted (C) on the cylinder head and two side-injectors (S), slantmounted on cylinder head protruding their nozzle tip near piston-bowl to achieve the isobaric combustion. This study visualized the flame development of isobaric combustion, linking flow-field details to the observed trends in engine efficiency and soot emissions. The experiments were conducted in an optically accessible single-cylinder heavy-duty diesel engine using n-heptane as fuel. Isobaric combustion, with a 50 bar peak pressure, was achieved with three different injection strategies, i.e. (C+S), (S+C), and (S+S). Bottom-view high-speed soot luminosity images were recorded at a frame rate of 20 kHz for all cases, together with pressure traces. Flame image velocimetry (FIV) analysis was performed on the high-speed soot luminosity images to obtain a qualitative description of the flow-field obtained for the three injection strategies. Distinctive vortex structures were evident from the FIV analysis and that can be attributed to strong flame-wall and flameflame interactions. For the C+S and S+S injection strategies, the distinct large vortex structures were found near the bowl-wall while for the S+C case, vortex structures are less prominent. The large vortex structures close to the cylinder walls contribute to lower gross indicated efficiency and higher soot level intensity of the C+S and S+S cases, compared to the S+C configuration.