Title : Large-eddy simulations of ammonia spray combustion under direct injection engine-like conditions using a hybrid Stochastic Fields/Flamelet Progress Variable methods
Abstract:
For the first time, liquid ammonia spray combustion in engine-like conditions using Large-eddy simulations (LES) approach based on a hybrid Stochastic Fields (SF)/Flamelet Progress Variable (FPV) method is presented. Ammonia has been identified as “the low hanging fruit” for carbon-free hydrogen alternative energy carriers for the following reasons beacsue: (1) Compared to hydrogen, ammonia storage is easily achievable. It is liquefied at room temperature at 9.90 atm (similar to propane, a fuel with widespread domestic applications), whereas hydrogen storage essentially requires very low temperature (below -239.95 C) or very high pressure (e.g., 700 atm in fuel cell vehicles). (2) Liquid ammonia has a very high hydrogen density (kg H 2 per litter of liquid ammonia), even higher than liquid hydrogen. (3) Mass production and shipping technologies of ammonia have been long established due to its applications in the fertilizer industry. Despite great economic and technological advantages, ammonia cannot be directly used in conventional-based Internal Combustion Engines. The main problem is that these engines have been traditionally designed to operate with highly reactive fossil-based fuels which are not compatible with the fundamental combustion characteristics of ammonia. Nonetheless, a very long ignition delay time (IDT) of ammonia/air mixture compared to most hydrocarbon-based fuel counterparties makes is an ideal fuel for future engines that are operating with advanced modes of combustions, namely, the Homogeneous Charge Compression Ignition (HCCI) engines and its derivates. To date, there is very little known about the structure of ammonia spray combustion under practical ICEs conditions. For example, it is not very clear how IDT of ammonia can affect the structure of ammonia spray when it is injected into an engine-like environment. Whether the mixture reaches to a homogeneously mixed condition, as it is intended in an HCCI engine, or it involves some levels of stratification in mixture’ temperature or composition, is predominately affects the combustion progress and its efficiency. In this paper, first, we formulate a new spray combustion modeling approach based on our previous work in which a hybrid (ES/FPV) was developed and used for modeling non-premixed jet flames. The method is then used to simulate the so-called Sandia’ Spray A - a benchmark for diesel spray combustion in modern engine-like conditions. This follows by modeling ammonia spray in an advanced DI-engine like conditions. The results will be analyzed and the dominate combustion modes in each case are identified. We shall discuss the combustion performance of each case in terms of heat release modulations, combustion efficiency, and NOx emissions.
Audience Takeaway:
- LES for spray
- The concept of tabulated stochastic field method
- LES for LNH3 in engine conditions
- Awareness of LNH3 as a liquid fuel hydrogen alternative
- Challenges associated with LNH3 as a carbon-free engine fuel
- The potential of detailed three-dimensional and unsteady numerical simulation for the future engine design
