Optical investigation and thermodynamic analysis of premixed ammonia dual-fuel combustion initiated by dodecane pilot fuel

Ammonia (NH3) combustion has been investigated as a carbon-free fuel for internal combustion engines. The marine sector attempts to use NH3 as fuel for diesel engines. However, NH3 combustion in diesel engines can emit unburned NH3 and nitrous oxide (N2O) via the greenhouse effect, and the mechanisms of emission production remain unclear. In this study, the combustion of a premixed NH3–diesel dual-fuel initiated by a pilot fuel is investigated experimentally and numerically. The experiments reveal a change in combustion phasing and emission characteristics for up to 80% of the energy fraction of NH3. As the energy fraction of NH3 increases, the onset of combustion is delayed, the center of combustion is slightly advanced and then retracted, and the end of combustion is slightly advanced. NO and unburned NH3 emissions increased, whereas CO emission decreased as the energy fraction of NH3 increased; by contrast, N2O emissions increased. However, the increase in N2O diminished when the energy fraction of NH3 increased by 40% or more. Computation fluid dynamics simulations based on n-heptane and ammonia reaction kinetics qualitatively reproduced the experimental results. The numerical analysis facilitates the understanding of the underlying phenomena of emission via ammonia–diesel dual-fuel combustion. N2O formation can be categorized into two stages: a steep formation of N2O with main heat release and CO2 production, followed by a relatively low formation rate of N2O with a decreasing rate of NH3 decomposition and reduction in CO2 production. The early injection of pilot fuel allowed the pilot fuel to distribute to the wide area of the combustion chamber and NH3 to rapidly combust without remaining N2O. The rapid combustion eliminates the second stage of relatively slow combustion, which generated N2O. The low NH3 and N2O emissions observed experimentally with the early pilot fuel injection may be due to this mechanism

Section: Resultsmentioning

confidence: 96%

Section: Resultsmentioning

confidence: 99%

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Experimental and numerical analysis of unburned ammonia and nitrous oxide emission characteristics in ammonia/diesel dual-fuel engine

Niki

2023

“…27 The automated optical ignition delay detection proved to be reliable, also compared to the corresponding ignition delay detection from the heat release analysis. 28…”

Section: Optical Setup Methodology and Post-processingmentioning

confidence: 99%

Experimental study of lube oil pre-ignition in an optical gas engine test rig

Vera-Tudela,

Süess,

Albrecht

et al. 2024

Lean-premixed gas combustion is an attractive option for meeting future emission standards toward considerably lower particulate matter and emissions while obtaining an efficiency comparable to diesel combustion. However, ignition processes still pose considerable challenges, with pre-ignition being a major issue. The pre-ignition phenomenon might result from the self-ignition of lube oil in hot zones, making it challenging to observe in real engines. To study single or sparsely separated lube oil droplets under engine-like conditions, the “Flex-OeCoS” experimental test facility was used. To be able to induce such pre-ignitions artificially a novel piezo droplet injector was developed and manufactured, which enabled the metering of minor amounts of lubricating oil or even the injection of single droplets. High-speed cameras and specially developed and partially automatable and adaptive evaluation algorithms were used to record and track the behavior of the injected droplet using overlaid schlieren and OH* chemiluminescence. During the measurement campaigns, relevant operating parameters were varied, and optical investigations were carried out with an ignitable mixture on the Flex-OeCoS test facility under engine-relevant operating conditions. Spontaneous ignition of the vaporized lubricating oil was observed, which subsequently led to ignition of the whole air-fuel mixture in the optical combustion chamber. This was especially evident for lean methane-air mixtures up to an air-fuel ratio of 2.0. With this approach, information could be gathered about the necessary internal engine conditions that lead to pre-ignition in lean mixtures and where their limits lie.

“…Some studies NO x emissions. 37,38 Similar to other low-cetane LLCFs, NH 3 combustion in a compression-ignition engine involves a secondary high-cetane number fuel injection. Some ship engines are retrofitted to run on diesel-NG, in which diesel serves as the source of ignition.…”

Section: Ammonia As a Fuel For Marine Applicationsmentioning

confidence: 99%

The future of ship engines: Renewable fuels and enabling technologies for decarbonization

Curran,

Onorati,

Payri

et al. 2023

Shipping is one of the most efficient transportation modes for moving freight globally. International regulations concerning decarbonization and emission reduction goals drive rapid innovations to meet the 2030 and 2050 greenhouse gas reduction targets. The internal combustion engines used for marine vessels are among the most efficient energy conversion systems. Internal combustion engines dominate the propulsion system architectures for marine shipping, and current marine engines will continue to serve for several decades. However, to meet the aggressive goals of low-carbon-intensity shipping, there is an impetus for further efficiency improvement and achieving net zero greenhouse gas emissions. These factors drive the advancements in engine technologies, low-carbon fuels and fueling infrastructure, and emissions control systems. This editorial presents a perspective on the future of ship engines and the role of low-life cycle-carbon-fuels in decarbonizing the marine shipping sector. A selection of zero-carbon, net-zero carbon, and low-lifecycle-carbon-fuels are reviewed. This work focuses on the opportunities and challenges of displacing distillate fossil fuels for decarbonizing marine shipping. Enabling technologies such as next-generation air handling, fuel injection systems, and advanced combustion modes are discussed in the context of their role in the future of low-CO2 intensity shipping.