Optical Spray Investigations on OME3-5 in a Constant Volume High Pressure Chamber

Mitigation of the carbon footprint of internal combustion engines is mandatory to ensure a future for this technology. Within this scope, e-fuels are considered a potential solution to replace conventional fossil fuels. However, in some cases, their physical and chemical properties are so different that its application in conventional engines is complex. For this reason, this work focuses on the study of oxymethylene ethers (OMEX) as a potential low-carbon fuel alternative. The aim is to improve the understanding of the combustion process of these e-fuels when they replace fossil Diesel in internal combustion engines under equivalent operating conditions. To achieve this objective, a computational fluid dynamics model of an optical compression ignition engine has been developed. The operating conditions chosen are representative of a medium load point of the engine, which coincide with experimental work previously done on this platform. n-Heptane was used as surrogate of fossil Diesel while OMEX was simulated as a simpler mixture of oxymethylene ether molecules. Results show remarkable differences between Diesel and OMEX. This fuel provides lower equivalence ratio fields. Thus, oxidation reactions are promoted in wider areas within the combustion chamber, leading to a faster combustion process. Besides, the soot formation is also drastically decreased in comparison to the other fuel. These results have been corroborated with experimental information.

Section: Spray Cone Angle Calculationmentioning

confidence: 76%

Numerical analysis of the combustion process of oxymethylene ethers as low-carbon fuels for compression ignition engines

García-Oliver

Novella

Micó

et al. 2022

“…POMDME optical investigations. POMDME as a sole replacement for compression ignition is optically investigated in constant volume chambers, 46,50,54,[59][60][61][62][63][64] rapid compression expansion machines, optically accessible engines 42,51,65,66 and as blends. 45,51,67 Macroscopically, the spray of OME 3-5 offered a high lift-off length despite a short ignition delay in a constant volume high-pressure chamber, indicative of a favorable mixing behavior with relatively high air-fuelratio -positively affected by the inherent oxygen content -in the fuel-rich zone near the injector.…”

Section: Pilot-ignited Lean-premixed Natural Gas Enginesmentioning

confidence: 99%

Optical study on a heavy-duty natural gas dual-fuel engine applying POMDME as pilot fuel

Mühlthaler,

Prager,

Jaensch

2024

In this study, a fully optically accessible single-cylinder research engine is the basis for the visualization and generation of extensive knowledge about the in-cylinder processes of mixture formation, ignition, and combustion of alternative fuels for the dual-fuel combustion process. POMDME substitutes the fossil pilot fuel as a drop-in, non-sooting alternative to widely eliminate the NOx-PM tradeoff. Furthermore, an optimized ignition behavior, increased degrees of freedom in combustion phasing, and the pilot’s energy content are expected. The flame luminosity transmitted via an optical piston was split in the optical path to record the natural flame luminosity simultaneously with an RGB high-speed camera. The second channel consisted of OH chemiluminescence recording, isolated by a bandpass filter via an intensified monochrome high-speed camera. To investigate the combustion process spectrally, spatially, and temporally resolved in more detail, selected operating points were re-recorded via a high-speed imaging spectrograph. POMDME is benchmarked against regular diesel oil, according to EN590. Synthetic natural gas is applied as the primary gaseous fuel. Experimental sweeps along the overall pilot’s energy content (2%, 5%, 10%), injection pressure (500–1600 bar), and start of energizing (5–55 CAD bFTDC) are carried out. The given conditions result in decreased liquid-penetration length between 25% and 30% for the oxygenate, larger for earlier SOE and higher dilution. The lift-off length is nearer the liquid penetration length, increasing for higher rail pressures. The light-based ignition delay for EN590 is enlarged by 0.8 CAD after adding methane, while the oxygenate is not visibly retarded. Without methane, the oxygenate preceded EN590 by 0.6 CAD. The temporal and spatial position and extent of premixed, diffusive, and OH*, change significantly. RCCI operation at practically relevant 18.4 bar IMEP is demonstrated, highlighting the influence of the start of energizing variation with 51% decreased burn duration in the first half of combustion.

“…Further, the diesel combustion characteristics of OME have been investigated with numerical analysis, 17 and with experiments in constant volume vessels. 18,19 In diffusion spray combustion at high-load operation in diesel engines, the degree of constant volume heat release decreases with slower heat release and longer afterburning, resulting in lower thermal efficiencies. Here, the afterburning is defined as the heat release after the end of fuel injection.…”

Section: Introductionmentioning

confidence: 99%

“…Further, the diesel combustion characteristics of OME have been investigated with numerical analysis, 17 and with experiments in constant volume vessels. 18,19…”

Section: Introductionmentioning

confidence: 99%

Mechanism of the reduction in afterburning and thermal efficiency improvement with highly oxygenated fuels in diesel combustion

Kawabe,

Inoue,

Mori

et al. 2023

Highly oxygenated fuels can effectively reduce afterburning in diesel diffusion combustion and improve the degree of constant volume heat release in spite of increases in injection duration due to smaller heating values. The mechanism of afterburning reduction and the structural differences in the diesel fuel spray with changing the oxygen content in the fuel were investigated in a constant volume vessel and analyzed with 3D CFD simulation. The result showed that the equibalance ratio inside the spray decreased with increases in the oxygen content due to lower theoretical air-fuel ratios, promoting the spray combustion after the end of injection. Further, the combustion characteristics and the exhaust gas emissions of the oxygenated fuels were investigated in an experimental single cylinder diesel engine with modern specifications. With increasing oxygen contents, the degree of constant volume heat release increased with reductions in the afterburning, resulting in higher indicated thermal efficiencies. However, the indicated thermal efficiency showed a maximum at around 27 mass% of the oxygen in fuel and further increases in the oxygen contents resulted in lower indicated thermal efficiencies due to larger cooling losses.