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Liquid e-fuels such as methanol represent a possible solution to emission-neutral drivetrains. Reduced emissions from the combustion process increase the influence of cylinder wall interaction of the fuel spray and the influence of the fuel ingress into the lubricating oil. Combining emission analysis methods and optical measurements allows a deeper understanding of the processes around the piston assembly group and cylinder wall. This paper aims to increase the understanding of the processes resulting from fuel spray and cylinder wall interaction. Emission measurements from a single-cylinder SI research engine were gathered across multiple operating parameters. Optical measurements were taken at similar operating points using an optically accessible engine. A laser-induced fluorescence (LIF) setup with dyed fuel was used for the optical measurements. This paper focuses on thermodynamic steady state measurements at 2000 rpm, varying loads between 3 and 11 bar IMEP, and corresponding optical measurements at 11 bar IMEP. The measurements of both engines were correlated, and a more profound understanding of the processes involved and their influence on emission behavior was derived. Measurements showed a lower particle emission behavior with a tendency of a higher PN10 to PN23 ratio and higher formic acid emissions using methanol fuel compared to gasoline. A higher wall film interaction with methanol could be visualized, and possible effects were correlated to the exhaust emission measurements. Tests with two start of injection timings (SOI) of 430° crank angle (CA) after fired top dead center, as used for gasoline operation, and 550°CA as an optimized SOI for methanol operation were compared. A correlation between the results from the thermodynamic engine and the optically accessible engine was demonstrated. The optical measurements showed lower penetration depths for the optimized SOI and lower fuel spray-to-piston interaction. The thermodynamic measurements have shown higher efficiencies and fewer emissions for the optimized SOI.
Liquid e-fuels such as methanol represent a possible solution to emission-neutral drivetrains. Reduced emissions from the combustion process increase the influence of cylinder wall interaction of the fuel spray and the influence of the fuel ingress into the lubricating oil. Combining emission analysis methods and optical measurements allows a deeper understanding of the processes around the piston assembly group and cylinder wall. This paper aims to increase the understanding of the processes resulting from fuel spray and cylinder wall interaction. Emission measurements from a single-cylinder SI research engine were gathered across multiple operating parameters. Optical measurements were taken at similar operating points using an optically accessible engine. A laser-induced fluorescence (LIF) setup with dyed fuel was used for the optical measurements. This paper focuses on thermodynamic steady state measurements at 2000 rpm, varying loads between 3 and 11 bar IMEP, and corresponding optical measurements at 11 bar IMEP. The measurements of both engines were correlated, and a more profound understanding of the processes involved and their influence on emission behavior was derived. Measurements showed a lower particle emission behavior with a tendency of a higher PN10 to PN23 ratio and higher formic acid emissions using methanol fuel compared to gasoline. A higher wall film interaction with methanol could be visualized, and possible effects were correlated to the exhaust emission measurements. Tests with two start of injection timings (SOI) of 430° crank angle (CA) after fired top dead center, as used for gasoline operation, and 550°CA as an optimized SOI for methanol operation were compared. A correlation between the results from the thermodynamic engine and the optically accessible engine was demonstrated. The optical measurements showed lower penetration depths for the optimized SOI and lower fuel spray-to-piston interaction. The thermodynamic measurements have shown higher efficiencies and fewer emissions for the optimized SOI.
<div class="section abstract"><div class="htmlview paragraph">This study provides an overview of injector design adaptations and fuel pressure variations for oxygenated synthetic fuels, benchmarked against gasoline. The promising oxygenated fuels exhibited reduced emissions, especially with respect to particles. In gasoline engines, high fuel pressures are needed to keep the particle emissions below the permitted level. In oxygenated fuels, high fuel pressures are required to compensate for the lower volumetric energy density when used with non-adapted injectors. This study demonstrates that an adapted injector design enables engine operation with a fuel pressure reduction from 35 MPa to 10 MPa, without emission drawbacks.</div><div class="htmlview paragraph">The fuel investigated contained dimethyl carbonate (DMC) and methyl formate (MeFo). The fuel mass contained around 50% oxygen. A relatively high percentage of 35 vol.% MeFo was chosen because of its high vapor pressure, thus providing fast mixture formation and enabling very late compression stroke injections. The basic design adaptations are expected to be transferable to other oxygenated synthetic fuels, e.g., containing methanol (MeOH) and MeFo.</div><div class="htmlview paragraph">The main tests were conducted on a single cylinder research engine, based on a four-cylinder automotive engine. The exhaust gas composition was measured using an FTIR equipped with a fuel-tailored evaluation method, several standard exhaust gas analyzers, and a solid particle counting system with 10 and 23 nm cut-off sizes. The spray from both the two synthetic fuel injectors and the standard injector was further investigated at a spray chamber by means of a high-speed camera. Given a standard injector the spray pattern of 65vol% DMC+ 35vol%MeFo, and 85vol%MeOH+15 vol% MeFo were compared to the pattern of G100. All of the injectors were further investigated at an injection rate analyzer in order to provide necessary information about the injected fuel mass.</div></div>
<div class="section abstract"><div class="htmlview paragraph">A novel algorithm-based approach is employed in this publication to calculate multiple direct injection patterns for spark ignition engines. The algorithm is verified by investigating the combustion and emission behavior of a single-cylinder research engine. State-of-the-art standard exhaust gas analyzers, a particle counter and an additional FTIR analyzer enable in-depth investigation of engine exhaust gas composition.</div><div class="htmlview paragraph">With the upcoming worldwide pollutant emission targets, the emission limits will be reduced while the test procedures’ requirements to the engine increase. Special attention to the engine-out emissions must be paid during cold-start, during which the aftertreatment system lacks sufficient pollutant emission conversion efficiency.</div><div class="htmlview paragraph">With advanced injection control, the engine-out emissions can be reduced and exhaust aftertreatment heat-up can be accelerated. Such injection strategies separate the injected fuel quantity over several injection events for different purposes, respectively. However, increasing effort for engine calibration prevents the full employment of the advantages of complex, multiple injection strategies.</div><div class="htmlview paragraph">The algorithm-based approach used in this publication facilitates automatic injection pattern generation, instead of calibrating the multiple injections based on conventional Design of Experiment methods that are associated with extensive engine testing. To adapt to different operation conditions, a reduced number of calibration parameters are introduced to efficiently identify beneficial injection patterns. Special focus is placed on optimizing the engine cold-start behavior in view on engine-out emissions and rapid exhaust heating. Consequently, investigations have been undertaken with the research engine cooled down to -7°C. Combustion imaging using an endoscopic optical access complement to the thermodynamic measurement data and visualize the influence of injection strategy on combustion. The presented results proof that the automatically calculated injection patterns facilitate combustion optimization.</div></div>
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