Performance characteristics of ammonia engines using direct injection strategies

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Zacharakis-Jutz, George
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Song-Charng Kong
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Mechanical Engineering
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In this study performance characteristics of ammonia engines using direct injection strategies are investigated. Ammonia is a carbon-free fuel, and thus its combustion does not produce carbon dioxide, a critical greenhouse gas. Ammonia can be produced by using renewable energy sources (e.g., wind and solar) and used as an energy carrier. Recent research also has shown that the efficiency of solar thermochemical production of ammonia can be increased by combining the ammonia solid-state synthesis cycle with hydrogen production. Ammonia is under consideration for a potential storage method for wind energy. Ammonia's nature as carbon-free and its ability to be renewably produced make it an alternative to fossil fuels.

In this study two direct injection strategies are tested and performance data, and exhaust emissions are recorded and analyzed.

The first strategy tested liquid direct injection in a compression-ignition (diesel) engine utilizing highly advanced injection timings. Ammonia was used with dimethyl ether (DME) in a duel fuel combustion strategy. Ammonia was mixed with DME prior to injection. DME was chosen as a diesel substitute for its close fuel properties to ammonia. Three ammonia-DME ratios were tested: 100%DME, 60%DME-40%NH3, and 40%DME-60%NH3. Engine speeds of 1900 rpm and 2500 rpm were used based on the operational capability of 40%DME-60%NH3.

Operation at 40%DME-60%NH3 required injection timing ranging from 90-340. Highly advanced injection timings resulted in homogeneous charge compression ignition combustion (HCCI). Cycle-to-cycle variations were reduced with increased load. NOx, NH3, CO, CO2, and HC were reduced with increased load for 40%DME-60%NH3. Low temperature combustion from low in-cylinder temperature from ammonia vaporization resulted in low NOx emissions meeting EPA emissions standards for small engine operation.

The second strategy tested gaseous direct injection of ammonia in a spark-ignition (gasoline) engine. A CFR engine was operated at idle using the existing gasoline port injection system. Ammonia was directly injected using a solenoid injector. A ruthenium catalyst was implementing to partially decompose ammonia into hydrogen. Testing was performed over a range of seven performance modes using gasoline, gasoline-ammonia, and gasoline-ammonia with ruthenium catalyst. Injection timings of 270, 320, and 370 BTDC were used.

Gasoline-ammonia showed little improvement in break specific energy consumption and CO2, and exhibited increased levels of NOx and HC over performance modes using gasoline only. Due to ammonia's low flammability limits and slow flame speed combustion efficiency was reduced. With the ruthenium catalyst Improvements in flywheel power were seen over performance modes without catalyst. The peak in-cylinder pressure was increased, and the start of ignition was advanced over both gasoline-ammonia and gasoline only performance modes. There was a significant reduction in NOx and NH3 present in the exhaust. Hydrogen present in the fuel increased combustion efficiency due to high flammability limits and high flame speed. Improvements in combustion efficiency resulted in reduced CO and HC over both gasoline-ammonia and gasoline only performance modes.

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Tue Jan 01 00:00:00 UTC 2013