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Item type:Publication, Access status: with files , Investigation of oil emission mechanisms in a marine medium-speed dual-fuel engine(Sage Publications, 2024-05); ; ; ; Pilot-ignition Otto marine engines are known for greatly reduced emissions of air pollutants (sulphur oxides, nitrogen oxide, particulates) compared to marine diesel engines. However, lubricating oil emissions still are about one order of magnitude higher than in land-based systems. To identify reduction potentials, a better understanding of oil emission mechanisms has to be gained. For this purpose, mass spectrometric oil emission measurements and fluorescence lubricating film thickness measurements were performed on a medium-speed marine engine. With the fluorescence measuring system, the varying lubricating oil film on the cylinder wall can be visualised and analysed in sub-crank-angle resolution. By applying the developed calibration method to the measurement data, the oil film thickness can be determined in µm. It is shown that the oil film left by the piston rings on the liner as it moves down is almost halved after ignition compared to during intake stroke. The authors have further been able to detect and time operating point dependent ring rotation and investigations show a connection between ring rotation and cylinder liner temperature distribution. Aligning ring gaps allow blow-by to happen. This and other high intensity events such as engine knock, load shedding or the transition from diesel-mode to gas-mode, heavily disturb the oil layer and cause peaking oil emissions.Publicationtype: Journal Article84 24 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , LED-induced-fluorescence measurements at an LNG dual-fuel marine engine test bed : the test bed, the measurement technology, findings from the measurement results(2022-05-06)LNG operation in so-called dual-fuel engines is viewed as an environmentally friendly alternative in shipping. In these engines a natural-gas/air mixture is ignited via Diesel fuel pilot injection. This is a combination of the Diesel and the Otto processes. Classic Diesel operation is generally still possible. The current limits for nitrogen oxide emissions and sulfur can be met with these systems without exhaust gas purification even in Emission Control Areas. Dual-fuel engines also have an advantage over classic Diesel engines in terms of particulate-matter emissions, but so far they have not reached the values of Otto engines. Since almost no soot occurs in dual-fuel operation, the majority of particulate-matter emissions originate from lubricating oil. This oil is intended to minimize mechanical wear as well as chemical wear in the cylinder. Due to the sulfur content in many Diesel fuels, sulfuric acids are formed during combustion, which are neutralized by alcalic additives in the lubricating oil. With the 2020 sulphur-cap of the IMO the necessity of acid neutralization is reduced considerably. This allows adjustments of the lubrication system and thus a reduction of particulate-matter emissions. A positive side effect is the associated economic benefit of reduced lube oil consumption. The Department of Marine Engineering at TUHH operates a medium-speed LNG dual-fuel marine engine test bed. With LED-induced fluorescence, a technology is used in the cylinder liner that has not yet been applied in the marine engine sector. A fluorescent agent added to the lubricating oil is excited via an LED and the intensity of the resulting radiation is measured. This allows conclusions to be drawn about the amount of lubricating oil present at the measuring points. In addition, emitted aerosols and oil masses are recorded immediately after ejection from the cylinder and analyzed in terms of size, number and mass of particles. The particular challenge is to combine these two very different measuring methods in order to be able to draw conclusions about the underlying physical and chemical mechanisms. The goal is a deeper understanding of these operating point-dependent mechanisms of particulate-matter emission generation in order to be able to find measures to control these emissions.Publicationtype: Conference Presentation71 46