Effects of the Combustion Enhancer Containing Alkyl Nitrate (CEN) to Dodecane and HVO as Pilot Fuels on a Compression Ignition Engine Operating in Dual-Fuel with Ammonia

Ammonia is a widely used and known chemical. Today it is seen as a carbon free solution to fuel thermal engines especially in applications where other solutions would not be realistic. For marine applications, electrical or fuel cells solutions for example would not allow spans long enough to sustain big cargo ships ranges. Engine manufacturer such as MAN, Wartsila or Win-GD have already announced the development of marine engine running on ammonia. But while ammonia is a non-CO₂ emitting fuel, it has some caveats such as being gaseous in standard conditions and hard to ignite. As it is now, ammonia is usually used in compression ignition engines with the help of highly reactive carbonated pilot fuels. Many forms of dual-fuel combustion are conceivable, although all the simple ones use a carbon-based fuel and quite often originated from fossil oil. The addition of High Reactivity Fuel to Ammonia is an interesting combustion mode that can be used to calibrate different fuel parameters and explore the mechanisms surrounding ammonia ignition and combustion. In this study Dodecane or HVO are used as the pilot fuel with a combustion enhancer containing alkyl nitrates (CEN). The pilot fuels injections were maintained to stay at 2% of the total energy provided by the fuel & the pilot fuel. The effects of the combustion additive were observed and measured. Adding 1% of volume fraction of the additive the Dodecane/HVO pilot fuel allows for better cycle to cycle stability (Coefficient of Variation – CoV_IMEP) and higher Indicated Mean Effective Pressure (IMEP). 10% of volume fraction additive in the pilot fuel further increases engine power output and smoothens the combustive event by lengthening it. It was difficult to truly investigate the emissions due to ammonia FTIR spectrum, but in this study IMEP, with the IMEP, CoV_IMEP, noticeable crank angle degrees (CA₁₀, CA₅₀, CA₉₀) and Indicated Thermal Efficiency (ITE) were measured with ammonia preheated (80°C) while kept at ambient pressure at intake. Three IMEP values (12 – 8 – 4 bar) were targeted for a one-cylinder engine with a displacement of 0.499L and a compression ratio of 16.4. The strategy of this study allowed to conclude that the combustive additive and the pilot fuel used in relatively low ratios vs. ammonia (2% energetic ratio) have a synergetic activity allowing for better ignition (than the pilot fuel alone), better cycle to cycle stabilization, better power output, and displacing the combustive event toward ammonia combustion in conditions (richness and engine loads) where it’s been otherwise repeatedly observed impossible.